Distance measuring device and distance measuring method

Abstract

A distance measuring device includes a calculating section configured to calculate, based on phase information acquired by a first device and a second device, at least one of which is movable, a distance between the first device and the second device. The first device includes a first reference signal source and a first transceiver configured to transmit two or more first carrier signals and receives two or more second carrier signals using an output of the first reference signal source. The second device includes a second reference signal source configured to operate independently from the first reference signal source and a second transceiver configured to transmit the second carrier signals and receives the first carrier signals using an output of the second reference signal source. The calculating section calculates the distance based on a phase detection result obtained by reception of the first and second carrier signals.

Description

CROSS-REFERENCE TO RELATED APPLICATION

This application is based upon and claims the benefit of priority from the prior Japanese Patent Applications No. 2017-053379, filed on Mar. 17, 2017 and No. 2017-138306, filed on Jul. 14, 2017; the entire contents of which are incorporated herein by reference.

FIELD

Embodiments described herein relate generally to a distance measuring device and a distance measuring method.

BACKGROUND

In recent years, keyless entry for facilitating unlocking and locking of a car has been adopted in many cars. This technique performs unlocking and locking of a door using communication between a key of an automobile and the automobile. Further, in recent years, a smart entry system that makes it possible to perform, with a smart key, unlocking and locking of a door lock and start an engine without touching a key has been also adopted.

However, a lot of incidents occur in which an attacker intrudes into communication between a key and an automobile and steals the automobile. As measures against the attack (so-called relay attack), a measure for measuring the distance between the key and the automobile and, when determining that the distance is equal to or larger than a predetermined distance, it is being reviewed to prohibit control of the automobile by communication.

As a distance measuring technique, many techniques exist, such as a two-frequency CW (continuous wave) scheme, an FM (frequency modulated) CW scheme, a Doppler scheme, and a phase detection scheme. In general, in distance measurement, a distance from a measuring device to a target object is calculated by providing a transmitter and a receiver in the same housing of the measuring device, hitting a radio wave emitted from the transmitter against the target object, and detecting a reflected wave of the radio wave with the receiver.

However, when it is taking into account a relatively small reflection coefficient of the target object, limitation on output power due to the Radio Law, and the like, in the distance measuring technique for measuring a distance using the reflected wave, a measurable distance is relatively small and is insufficient for use in the measures against the relay attack.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing a distance measuring system in which a distance measuring device according to a first embodiment of the present invention is adopted;

FIG. 2A is an explanatory diagram for explaining the principle of distance measurement by a phase detection scheme for detecting a phase of a reflected wave and problems of the distance measurement;

FIG. 2B is an explanatory diagram for explaining the principle of the principle of distance measurement by a phase detection scheme for detecting a phase of a reflected wave and the problems of the distance measurement;

FIG. 3A is an explanatory diagram for explaining problems of the distance measurement by the phase detection scheme;

FIG. 3B is an explanatory diagram for explaining the problems of the distance measurement by the phase detection scheme;

FIG. 4 is a circuit diagram showing an example of specific configurations of a transmitting section 14 and a receiving section 15 shown in FIG. 1;

FIG. 5 is a circuit diagram showing an example of specific configuration of a transmitting section 24 and a receiving section 25 shown in FIG. 1;

FIG. 6 is a flowchart for explaining operation in the first embodiment;

FIG. 7 is an explanatory diagram for explaining a method of calculating a distance using a system of residue;

FIG. 8 is an explanatory diagram for explaining the method of calculating a distance using the system of residue;

FIG. 9 is an explanatory diagram showing an example in which a distance is plotted on the horizontal axis and a phase is plotted on the vertical axis, in which three wave signals having different angular frequencies each other are transmitted;

FIG. 10 is an explanatory diagram for explaining a method of selecting a correct distance through amplitude observation of a detected signal;

FIG. 11A is a flowchart for explaining a second embodiment;

FIG. 11B is an explanatory diagram for explaining the second embodiment;

FIG. 11C is an explanatory diagram for explaining the second embodiment;

FIG. 12A is an explanatory diagram for explaining the second embodiment;

FIG. 12B is an explanatory diagram for explaining the second embodiment;

FIG. 13 is an explanatory diagram for explaining the second embodiment;

FIG. 14 is an explanatory diagram for explaining the second embodiment;

FIG. 15 is an explanatory diagram for explaining the second embodiment;

FIG. 16 is a block diagram showing a third embodiment of the present invention;

FIG. 17 is an explanatory diagram showing a fourth embodiment of the present invention;

FIG. 18 is an explanatory diagram showing the fourth embodiment of the present invention;

FIG. 19 is an explanatory diagram showing one of various sequences;

FIG. 20 is an explanatory diagram showing one of the various sequences;

FIG. 21 is an explanatory diagram showing one of the various sequences;

FIG. 22 is an explanatory diagram showing one of the various sequences;

FIG. 23 is an explanatory diagram showing one of the various sequences;

FIG. 24 is an explanatory diagram showing one of the various sequences;

FIG. 25 is an explanatory diagram showing one of the various sequences;

FIG. 26 is an explanatory diagram showing one of the various sequences;

FIG. 27 is an explanatory diagram showing one of the various sequences;

FIG. 28 is an explanatory diagram showing one of the various sequences;

FIG. 29 is an explanatory diagram showing one of the various sequences;

FIG. 30 is an explanatory diagram showing one of the various sequences;

FIG. 31 is an explanatory diagram showing one of the various sequences;

FIG. 32 is an explanatory diagram showing one of the various sequences;

FIG. 33 is an explanatory diagram showing one of the various sequences;

FIG. 34 is an explanatory diagram showing one of the various sequences;

FIG. 35 is an explanatory diagram showing one of the various sequences;

FIG. 36 is an explanatory diagram showing one of the various sequences;

FIG. 37 is an explanatory diagram showing one of the various sequences;

FIG. 38 is an explanatory diagram showing one of the various sequences;

FIG. 39 is an explanatory diagram showing one of the various sequences;

FIG. 40 is an explanatory diagram showing one of the various sequences;

FIG. 41 is an explanatory diagram showing one of the various sequences;

FIG. 42 is an explanatory diagram showing one of the various sequences;

FIG. 43 is an explanatory diagram showing one of the various sequences;

FIG. 44 is an explanatory diagram showing one of the various sequences;

FIG. 45 is an explanatory diagram showing a relation between a transmission sequence and a period in which an initial phase is maintained;

FIG. 46 is an explanatory diagram showing a carrier frequency used for distance measurement;

FIG. 47 is a flowchart for explaining a modification;

FIG. 48A is an explanatory diagram showing, in a simplified manner, an example of the configurations of an oscillator 13, the transmitting section 14, and the receiving section 15 of a device 1;

FIG. 48B is an explanatory diagram showing, in a simplified manner, an example of the configurations of an oscillator 23, the transmitting section 24, and the receiving section 25 of a device 2;

FIG. 49A is an explanatory diagram showing, in a simplified manner, an example of the configurations of the oscillator 13, the transmitting section 14, and the receiving section 15 of the device 1;

FIG. 49B is an explanatory diagram showing, in a simplifier manner, an example of the configurations of the oscillator 23, the transmitting section 24, and the receiving section 25 of the device 2;

FIG. 50 is a circuit diagram more specifically showing an example of a circuit that generates signals given to multipliers TM11 and TM12 in FIG. 4;

FIG. 51 is a circuit diagram more specifically showing an example of a circuit that generates signals given to multipliers TM21 and TM22 in FIG. 5;

FIG. 52 is a circuit diagram showing an example of specific configurations of the transmitting section 14 and the receiving section 15 shown in FIG. 1;

FIG. 53 is a circuit diagram showing an example of specific configurations of the transmitting section 24 and the receiving section 25 shown in FIG. 1;

FIG. 54 is a circuit diagram showing an example of the specific configurations of the transmitting section 14 and the receiving section 15 shown in FIG. 1;

FIG. 55 is a circuit diagram showing an example of the specific configurations of the transmitting section 24 and the receiving section 25 shown in FIG. 1;

FIG. 56 is a flowchart for explaining an example corresponding to FIG. 11A in which a second device transmits phase information to a first device; and

FIG. 57 is a flowchart for explaining an example corresponding to FIG. 47.

DETAILED DESCRIPTION

A distance measuring device according to an embodiment is a distance measuring device that calculates a distance on a basis of carrier phase detection, the distance measuring device including a calculating section configured to calculate, on a basis of phase information acquired by a first device and a second device, at least one of which is movable, a distance between the first device and the second device. The first device includes: a first reference signal source; and a first transceiver configured to transmit two or more first carrier signals and receives two or more second carrier signals using an output of the first reference signal source. The second device includes: a second reference signal source configured to operate independently from the first reference signal source; and a second transceiver configured to transmit the two or more second carrier signals and receives the two or more first carrier signals using an output of the second reference signal source. The calculating section calculates the distance on a basis of a phase detection result obtained by reception of the first and second carrier signals.

Embodiments of the present invention are explained below in detail with reference to the drawings.

First Embodiment

FIG. 1 is a block diagram showing a distance measuring system in which a distance measuring device according to a first embodiment of the present invention is adopted.

In the present embodiment, an example is explained in which a phase detection scheme for detecting a phase of an unmodulated carrier is adopted and communication-type distance measurement for calculating a distance between respective devices through communication between the respective devices is adopted. In a general phase detection scheme for detecting a phase of a reflected wave, a measurable distance is relatively short as explained above. Therefore, in the present embodiment, the communication-type distance measurement for performing communication between devices is adopted. However, since respective transmitters of the respective devices independently operate from each other, initial phases of transmitted radio waves from the respective transmitters are different from each other. An accurate distance cannot be calculated by the phase detection scheme in the past for calculating a distance according to a phase difference. Therefore, in the present embodiment, as explained below, phase information calculated by reception of one device is transmitted to the other device to make it possible to calculate an accurate distance in the other device.

First, the principle of distance measurement by the phase detecting scheme for detecting a phase of a reflected wave and problems of the distance measurement are explained with reference to the explanatory diagrams of FIGS. 2A and 2B.

(Phase Detection Scheme)

In the phase detection scheme, for distance measurement, signals having two frequencies deviating from a center angular frequency ω_C1 by an angular frequency ±ω_B1 are transmitted. In a distance measuring device that measures a distance using a reflected wave, a transmitter and a receiver are provided in the same housing. A transmission signal (a radio wave) emitted from the transmitter is reflected on a target object and a reflected wave of the radio wave is received by the receiver.

FIGS. 2A and 2B show this state. A radio wave emitted from a transmitter T is reflected by a wall W and received by a receiver S.

As shown in FIG. 2A, an angular frequency of a radio wave emitted from the transmitter is represented as ω_C1+ω_B1 and an initial phase is represented as θ_1H. In this case, a transmission signal (a transmission wave) tx1(t) emitted from the transmitter is represented by the following Equation (1):tx1(t)=cos {(ω_C1+ω_B1)t+θ_1H}  (1)

The transmission signal reaches a target object (a wall W) apart from the transmitter by a distance R with a delay time τ₁ and is reflected and received by the receiver. Since the speed of the radio wave is equal to the speed of light c(=3×10⁸ m/s), τ₁=(R/c) (seconds). The signal received by the receiver delays by 2τ₁ with respect to the emitted signal. Therefore, a received signal (a received wave) rx1(t) of the receiver is represented by the following Equations (2) and (3):rx1(t)=cos {(ω_C1+ω_B1)t+θ_1H−θ_2×Hτ1}  (2)θ_2×Hτ1=(ω_C1+ω_B1)2_τ1  (3)

That is, the transmission signal is received by the receiver with a phase shift of a multiplication result (θ_2×Hτ1) of the delay time and the transmission angular frequency.

Similarly, as shown in FIG. 2B, the transmission signal tx1(t) and the received signal rx1 (t) in the case in which an angular frequency ω_C1-ω_B1 is used are represented by the following Equations (4) to (6) with an initial phase set to θ_1L:tx1(t)=cos {(ω_C1−ω_B1)t+θ_IL}  (4)rx1(t)=cos {(ω_C1−ω_B1)t+θ_1L−θ_2×Lτ1}  (5)θ_2×Lτ1=(ω_C1−ω_B1))2_τ1  (6)

When a phase shift amount that occurs until the transmission signal having the angular frequency ω_C1+ω_B1 is received is represented as θ_H1(t) and a phase shift amount that occurs until the transmission signal having the angular frequency ω_C1-ω_B1 is received is represented as θ_L1(t), a difference between phase shifts of the two received waves is represented by the following Equation (7) obtained by subtracting Equation (6) from Equation (3):θ_H1(t)−θ_L1(t)=(θ_2×Hτ1−θ_2×Lτ1)=2ω_B1×2τ₁  (7)where τ₁=R/c. Since the differential frequency ω_B1 is known, if the difference between the phase shift amounts of the two received waves is measured, the distance R can be calculated as follows from a measurement result:R=c×(θ_2×Hτ1−θ_2×Lτ1)/(4ω_B1)

Incidentally, in the above explanation, the distance R is calculated taking into account only the phase information. Amplitude is examined below concerning a case in which a transmission wave having the angular frequency ω_C1+ω_B1 is used. The transmission wave indicated by Equation (1) described above delays by a delay amount τ₁=R/c at a point in time when the transmission wave reaches a target object away from the transmitter by the distance R. Amplitude is attenuated by attenuation L1 corresponding to the distance R. The transmission wave changes to a wave rx2(t) represented by the following Equation (8):rx2(t)=L₁ cos {(ω_C1+ω_B1)t+θ_1H−(ω_C1+ω_B1)τ₁}  (8)

Further, the transmission wave is attenuated by attenuation L_RFL when the transmission wave is reflected from the target object. A reflected wave tx2(t) in the target object is represented by the following Equation (9):tx2(t)=L_RFLL₁ cos {(ω_C1+ω_B1)t+θ_1H−(ω_C1+ω_B1)τ₁}  (9)

The received signal rx1(t) received by the receiver is delayed by a delay amount τ₁=R/c(s) from the target object. Amplitude is attenuated by attenuation L1 corresponding to the distance R. Therefore, the received signal is represented by the following Equation (10):rx1(t)=L₁×L_RFL×L₁ cos {(ω_C1+ω_B1)t+θ_1H−2(ω_C1+ω_B1)τ₁}  (10)

In this way, the transmission signal from the transmitter is attenuated by L₁×L_RFL×L₁ until the transmission signal reaches the receiver. Signal amplitude that can be emitted from the transmitter in distance measurement needs to conform to the Radio Law according to an applied frequency. For example, a specific frequency in a 920 MHz band involves limitation to suppress transmission signal power to 1 mW or less. From the viewpoint of a signal-to-noise ratio of the received signal, it is necessary to suppress attenuation between transmission and reception in order to accurately measure a distance. However, as explained above, since attenuation is relatively large in the distance measurement for measuring a distance using a reflected wave, a distance that can be accurately measured is short.

Therefore, as explained above, in the present embodiment, by transmitting and receiving signals between the two devices without using a reflected wave, attenuation is reduced by L_RFL×L₁ to increase the distance that can be accurately measured.

However, the two devices are apart from each other by the distance R and cannot share the same reference signal. In general, it is difficult to synchronize the transmission signal with a local oscillation signal used for reception. That is, between the two devices, deviation occurs in a signal frequency and an initial phase is unknown. Problems in distance measurement performed using such an asynchronous transmission wave are explained.

(Problems in the Case of Asynchronization)

In the distance measuring system in the present embodiment, in distance measurement between two objects, two devices (a first device and a second device) that emit carrier signals (transmission signals) asynchronously from each other are disposed in the positions of the respective objects and the distance R between the two devices is calculated. In the present embodiment, carrier signals having two frequencies deviating from a center angular frequency act by the angular frequency ±ω_B1 are transmitted in the first device. Carrier signals having two frequencies deviating from the center angular frequency ω_C2 by an angular frequency ±ω_B2 are transmitted in the second device.

FIGS. 3A and 3B are explanatory diagrams for explaining problems in the case in which the phase detection scheme is simply applied between two devices A1 and A2. It is assumed that a transmission signal of the device A1 is received by the device A2. A local oscillator of the device A1 generates a signal having a frequency necessary for generating, in a heterodyne scheme, two transmission waves having carrier angular frequencies ω_C1+∫_B1 and ω_C1−ω_B1. The device A1 transmits two transmission waves having the angular frequencies. A local oscillator of the device A2 generates a signal having a frequency necessary for generating, in a heterodyne scheme, two transmission waves having carrier angular frequencies ω_C2+ω_B2 and ω_C2−ω_B2. The device A2 performs reception in the heterodyne scheme using the signal generated by the local oscillator of the device A2.

The distance between the transmission device and the reception device is represented as 2R to correspond to the distance in the case in which the reflected wave is used. Initial phases of a transmission signal having the angular frequency ω_C1+ω_B1 and a transmission signal having the angular frequency ω_C1−ω_B1 transmitted from the device A1 are respectively represented as θ_1H and θ_1L. Initial phases of two signals having the angular frequencies ω_C2+ω_B2 and ω_C2−ω_B2 of the device A2 are respectively represented as θ_2H and θ_2L.

First, a phase is considered concerning the transmission signal having the angular frequency ω_C1+ω_B1. The transmission signal represented by Equation (1) described above is output from the device A1. The received signal rx2(t) in the device A2 is represented by the following Equation (11):rx2(t)=cos {(ω_C1+ω_B1)t+θ_1H−θ_2×Hτ1}  (11)

The device A2 multiplies together two signals cos {(ω_C2+ω_B2)t+θ_2H} and sin {(ω_C2+ω_B2)t+θ_2H} and a received wave of Equation (11) to thereby separate the received wave into an in-phase component (an I signal) and a quadrature component (a Q signal). A phase of the received wave (hereinafter referred to as detected phase or simply referred to as phase) can be easily calculated from the I and Q signals. That is, a detected phase θ_H1(t) is represented by the following Equation (12). Note that, in the following Equation (12), since a term of harmonics near an angular frequency ω_C1+ω_C2 is removed during demodulation, the term is omitted.θ_H1(t)=tan⁻¹(Q(t)/I(t))=−{((ω_C1−ω_C2)t+(ω_B1−ω_B2)t+θ_1H−θ_2×Hτ1}  (12)

Similarly, when the transmission signal having the angular frequency ω_C1-ω_B1 is transmitted from the device A1, a detected phase θ_L1(t) calculated from the I and Q signals obtained in the device A2 is represented by the following Equation (13). Note that, in the following Equation (13), since a term of harmonics near the angular frequency ω_C1+ω_C2 is removed during demodulation, the term is omitted.θ_L1(t)=tan⁻¹(Q(t)/I(t))=−{(ω_C1−ω_C2)t−(ω_B1−ω_B2)t+θ_1L−θ_2L−θ_2×Lτ1}  (13)

A phase difference between these two detected phases (hereinafter referred to as detected phase difference or simply referred to as phase difference) θ_H1(t)−θ_L1(t) is represented by the following Equation (14):θ_H1(t)−θ_L1(t)=−2(ω_B1−ω_B2)t+(θ_1H−θ_1L)−(θ_2H−θ_2L)+(θ_2×Hτ1−θ_2×Lτ1)  (14)

In the distance measuring device in the past that measures a distance using a reflected wave, the device A1 and the device A2 are the same device and share the local oscillator. Therefore, the following Equations (15) to (17) are satisfied:ω_B1=ω_B2  (15)θ_1H=θ_2H  (16)θ_1L=θ_2L  (17)

When Equations (15) to (17) hold, Equation (14) is equal to Equation (7) described above. The distance R between the device A1 and the device A2 can be calculated according to a phase difference calculated by I and Q demodulation processing for the received signal in the device A2.

However, since the device A1 and the device A2 are provided to be separated from each other and the local oscillators operate independently from each other, Equations (15) to (17) described above are not satisfied. In this case, unknown information such as a difference between initial phases is included in Equation (14). A distance cannot be correctly calculated.

(Distance Measuring Method of the Embodiment)

The signals having the two angular frequencies explained above transmitted by the first device are received in the second device and phases of the respective signals are calculated. The signals having the two angular frequencies explained above transmitted by the second device are received in the first device and phases of the respective signals are calculated. Further, phase information is transmitted from either one of the first device and the second device to the other. In the present embodiment, as explained below, the distance R between the first device and the second device is calculated by adding up a phase difference between the two signals calculated by the reception of the first device and a phase difference between the two signals calculated by the reception of the second device. Note that the phase information may be the I and Q signals or may be information concerning phases calculated from the I and Q signals or may be information concerning a difference between phases calculated from two signals having different frequencies.

(Configuration)

In FIG. 1, the first device 1 (hereinafter referred to as device 1 as well) and the second device 2 (hereinafter referred to as device 2 as well) are disposed to be separated from each other by the distance R. At least one of the device 1 and the device 2 is movable. The distance R changes according to the movement. A control section 11 is provided in the device 1. The control section 11 controls respective sections of the device 1. The control section 11 is configured of a processor including a CPU. The control section 11 may operate according to a computer program stored in a not-shown memory and control the respective sections.

An oscillator 13 is controlled by the control section 11 and generates oscillation signals (local signals) having two frequencies on a basis of a reference oscillator incorporated in the oscillator 13. The respective oscillation signals from the oscillator 13 are supplied to a transmitting section 14 and a receiving section 15. Angular frequencies of the oscillation signals generated by the oscillator 13 are set to angular frequencies necessary for generating two waves of ω_C1+ω_B1 and ω_C1−ω_B1 as angular frequencies of transmission waves of the transmitting section 14.

The transmitting section 14 can be configured of, for example, a quadrature modulator. The transmitting section 14 is controlled by the control section 11 to be capable of outputting two transmission waves of a transmission signal having the angular frequency ω_C1+ω_B1 and a transmission signal having the angular frequency ω_C1−ω_B1. The transmission waves from the transmitting section 14 are supplied to an antenna circuit 17.

The antenna circuit 17 includes one or more antennas and can transmit the transmission waves transmitted from the transmitting section 14. The antenna circuit 17 receives transmission waves from the device 2 explained below and supplies received signals to the receiving section 15.

The receiving section 15 can be configured of, for example, a quadrature demodulator. The receiving section 15 is controlled by the control section 11 to be capable of receiving and demodulating a transmission wave from the device 2 using, for example, signals having angular frequencies oct and fat from the oscillator 13 and separating and outputting an in-phase component (an I signal) and a quadrature component (a Q signal) of the received wave.

A configuration of the device 2 is the same as the configuration of the device 1. That is, a control section 21 is provided in the second device. The control section 21 controls respective sections of the device 2. The control section 21 is configured of a processor including a CPU. The control section 21 may operate according to a computer program stored in a not-shown memory and control the respective sections.

An oscillator 23 is controlled by the control section 21 to generate oscillation signals having two frequencies on a basis of a reference oscillator incorporated in the oscillator 23. The respective oscillation signals from the oscillator 23 are supplied to a transmitting section 24 and a receiving section 25. Angular frequencies of the oscillation signals generated by the oscillator 23 are set to angular frequencies necessary for generating two waves of ω_C2+ω_B2 and ω_C2−ω_B2 as angular frequencies of transmission waves of the transmitting section 24.

The transmitting section 24 can be configured of, for example, a quadrature modulator. The transmitting section 24 is controlled by the control section 21 to be capable of outputting two transmission waves of a transmission signal having an angular frequency ω_C2+ω_B2 and a transmission signal having an angular frequency ω_C2−ω_B2. The transmission waves from the transmitting section 24 are supplied to an antenna circuit 27.

The antenna circuit 27 includes one or more antennas and can transmit the transmission waves transmitted from the transmitting section 24. The antenna circuit 27 receives transmission waves from the device 1 and supplies received signals to the receiving section 25.

The receiving section 25 can be configured of, for example, a quadrature demodulator. The receiving section 25 is controlled by the control section 21 to be capable of receiving and demodulating a transmission wave from the device 1 using, for example, signals having angular frequencies ω_C2 and ω_B2 from the oscillator 23 and separating and outputting an in-phase component (an I signal) and a quadrature component (a Q signal) of the received wave.

FIG. 4 is a circuit diagram showing an example of specific configurations of the transmitting section 14 and the receiving section 15 shown in FIG. 1. FIG. 5 is a circuit diagram showing an example of specific configurations of the transmitting section 24 and the receiving section 25 shown in FIG. 1. FIGS. 4 and 5 show a transceiver of an image suppression scheme. However, the transceiver is not limited to the configuration.

Note that a configuration of the image suppression scheme is publicly known. As characteristics of the image suppression scheme, when a higher angular frequency band is demodulated centering on a local angular frequency for a high frequency, that is, ω_C1 or ω_C2, a signal in a lower angular frequency band is attenuated and, when a lower angular frequency band is demodulated, a signal in a higher angular frequency band is attenuated. This filtering effect is due to signal processing. The same applies to transmission. When the higher angular frequency band is demodulated centering on ω_C1 or ω_C2, sin(ω_B1+θ_B1) or sin(ω_B2t+θ_B2) shown in FIGS. 4 and 5 is used. When the lower angular frequency band is demodulated, −sin(ω_B1t+θ_B1) or −sin(ω_B2t+θ_B2) shown in FIGS. 4 and 5 is used. The frequency band demodulated is decided by change of such polarity.

Note that, in a receiver of the image suppression scheme, a term of harmonics near the angular frequency ω_C1+ω_C2 is removed during demodulation. Therefore, in an operation explained below, this term is omitted.

The transmitting section 14 is configured of multipliers TM11 and TM12 and an adder TS11. Oscillation signals having an angular frequency ω_C1 and having phases 90 degrees different from each other are respectively given to the multipliers TM11 and TM12 from the oscillator 13. Oscillation signals having an angular frequency ω_B1 and having phases 90 degrees different from each other are respectively given to the multipliers TM11 and TM12 from the oscillator 13. An inverted signal of the oscillation signal having the angular frequency ω_B1 is also given to the multiplier TM12 from the oscillator 13.

The multipliers TM11 and TM12 respectively multiply together the two inputs and give multiplication results to the adder TS11. The adder TS11 adds up outputs of the multipliers TM11 and TM12 and outputs an addition result as a transmission wave tx1.

The receiving section 15 is configured of multipliers RM11 to RM16 and adders RS11 and RS12. A transmission wave of the device 2 is input to the multipliers RM11 and RM12 via the antenna circuit 17 as a received signal rx1. Oscillation signals having the angular frequency ω_C1 and phases 90 degrees different from each other are respectively given to the multipliers RM11 and RM12 from the oscillator 13. The multiplier RM11 multiplies together the two inputs and gives a multiplication result to the multipliers RM13 and RM14. The multiplier RM12 multiplies together the two inputs and gives a multiplication result to the multipliers RM15 and RM16.

An oscillation signal having the angular frequency (a local angular frequency for baseband processing) ω_B1 is given to the multipliers RM13 and RM15 from the oscillator 13. The multiplier RM13 multiplies together the two inputs and gives a multiplication result to the adder RS11. The multiplier RM14 multiplies together the two inputs and gives a multiplication result to the adder RS12.

An oscillation signal having the angular frequency ω_B1 or an inverted signal of the oscillation signal, that is, a signal orthogonal to the oscillation signal having the angular frequency ω_B1 given to the multiplier RM13 is given to the multipliers RM14 and RM16 from the oscillator 13. The multiplier RM14 multiplies together the two inputs and gives a multiplication result to the adder RS12. The multiplier RM16 multiplies together the two inputs and gives a multiplication result to the adder RS11.

The adder RS11 adds up outputs of the multipliers RM13 and RM16 and outputs an addition result as an I signal. The adder RS12 adds up outputs of the multipliers RM14 and RM15 and outputs an addition result as a Q signal. The I and Q signals from the receiving section 15 are supplied to the control section 11.

The circuits shown in FIGS. 4 and 5 are the same circuit. That is, in FIG. 5, the configurations of the multipliers TM21, TM22, and RM21 to RM26 and the adders TS21, RS21, and RS22 are respectively the same as the configurations of the multipliers TM11, TM12, and RM11 to RM16 and the adders TS11, RS11, and RS12 shown in FIG. 4. The configurations are only different in that, since the frequency and the phase of the oscillation signal of the oscillator 23 are different from the frequency and the phase of the oscillation signal of the oscillator 13, in FIG. 5, a local angular frequency for baseband ω_B2 is input instead of the angular frequency ω_C1 shown in FIG. 4 and ω_C2 is input instead of the angular frequency ω_C1 shown in FIG. 4. The I and Q signals from the receiving section 25 are supplied to the control section 21.

In the present embodiment, the control section 11 of the device 1 controls the transmitting section 14 to transmit two transmission waves having angular frequencies ω_C1+ω_B1 and ω_C1-ω_B1 via the antenna circuit 17.

On the other hand, the control section 21 of the device 2 controls the transmitting section 24 to transmit two transmission waves having angular frequencies ω_C2+ω_B2 and ω_C2−ω_B2 via the antenna circuit 27.

The control section 11 of the device 1 controls the receiving section 15 to receive the two transmission waves from the device 2 and acquires the I and Q signals. The control section 11 calculates a difference between two phases calculated from the I and Q signals respectively obtained by two received signals.

Similarly, the control section 21 of the device 2 controls the receiving section 25 to receive the two transmission waves from the device 1 and acquires the I and Q signals. The control section 21 calculates a difference between two phases calculated from the I and Q signals respectively obtained by two received signals.

In the present embodiment, the control section 11 of the device 1 gives phase information based on the acquired I and Q signals to the transmitting section 14 and causes the transmitting section 14 to transmit the phase information. Note that, as explained above, as the phase information, for example, a predetermined initial value may be given. The phase information may be I and Q signals calculated from the two received signals, may be information concerning phases calculated from the I and Q signals, or may be information concerning a difference between the phases.

For example, the control section 11 may generate I and Q signals based on phase information of a received signal having an angular frequency ω_B2 and supplies the I and Q signals respectively to the multipliers TM11 and TM12 to transmit the phase information.

During output of the oscillation signal having the angular frequency ω_B1, the control section 11 may generate I and Q signals obtained by adding phase information of the received signal having the angular frequency ω_B2 to an initial phase of the oscillation signal having angular frequency ω_B1 and supply the I and Q signals respectively to the multipliers TM11 and TM12 to transmit the phase information.

The receiving section 25 of the device 2 receives the phase information transmitted by the transmitting section 14 via the antenna circuit 27. The receiving section 25 demodulates a received signal and obtains I and Q signals of the phase information. The I and Q signals are supplied to the control section 21. The control section 21 obtains, according to the phase information from the receiving section 25, a value including the phase difference acquired by the control section 11 of the device 1. The control section 21 functioning as a calculating section adds up the phase difference obtained by the reception result of the receiving section 25 and the phase difference based on the phase information transmitted from the device 2 to calculate the distance R between the first device 1 and the second device 2.

Note that, in FIG. 1, an example is shown in which both of the first device 1 and the second device 2 have a function of transmitting phase information and a function of giving received phase information to the control section and calculating the distance R. However, it is sufficient that one of the first device 1 and the second device 2 has the function of transmitting phase information and the other has the function of giving received phase information to the control section and calculating the distance R.

An operation in the configuration configured as explained above is explained with reference to a flowchart of FIG. 6. In FIG. 6, an operation of the device 1 is shown on a left side and an operation of the device 2 is shown on a right side. In FIG. 6, an arrow connecting steps of the devices 1 and 2 indicates that communication is performed between the devices 1 and 2. Note that steps S4, S5, S14, and S15 are substantially simultaneously executed.

In step S1, the control section 11 of the device 1 determines whether an instruction for a distance measurement start is received. When the instruction for the distance measurement start is received, the control section 11 controls the oscillator 13 to start an output of a necessary oscillation signal. In step S11, the control section 21 of the device 2 determines whether an instruction for a distance measurement start is received. When the instruction for the distance measurement start is received, the control section 21 controls the oscillator 23 to start an output of a necessary oscillation signal.

Note that, as explained below, in step S9, the control section 11 ends oscillation. In step S20, the control section 21 ends oscillation. Control of a start and an end of oscillation in the control sections 11 and 21 indicates that oscillation of the oscillators 13 and 23 is not stopped during transmission and reception periods for distance measurement. Actual start and end timings of the oscillation are not limited to the flow shown in FIG. 6. In a period in which the oscillation of the oscillators 13 and 23 continues, initial phases of the respective oscillators 13 and 23 are not set anew.

The control section 11 of the device 1 generates two transmission signals in step S3 and causes the antenna circuit 17 to transmit the transmission signals as transmission waves (step S4). The control section 21 of the device 2 generates two transmission signals in step S13 and causes the antenna circuit 27 to transmit the transmission signals as transmission waves (step S14).

It is assumed that an initial phase of an oscillation signal having the frequency ω_C1 output from the oscillator 13 of the device 1 is θ_c1 and an initial phase of an oscillation signal having the frequency ω_B1 is θ_B1. Note that, as explained above, the initial phases θ_c1 and θ_B1 are not set anew as long as the oscillation of the oscillator 13 continues.

Note that it is assumed that an initial phase of an oscillation signal having the frequency ω_C2 output from the oscillator 23 of the device 2 is θ_c2 and an initial phase of an oscillation signal having the frequency ω_B2 is θ_B2. The initial phases θ_c2 and θ_B2 are not set anew as long as the oscillation of the oscillator 23 continues.

Note that, when simultaneous transmission and simultaneous reception of two frequencies are assumed, two wireless sections shown in FIG. 4 are necessary in the device 1 and two wireless sections shown in FIG. 5 are necessary in the device 2. Alternatively, a radio of a superheterodyne scheme or the like is used. However, the respective oscillators use the same radio section.

(Transmission and Reception of a Transmission Wave Having the Angular Frequency ω_C1+ω_B1 from the Device 1)

Two transmission waves having the angular frequencies ω_C1+ω_B1 and ω_C1−∫_B1 are output from the transmitting section 14 of the device 1, and the transmitting section 14 is composed of the multipliers TM11 and TM12 and the adder TS11. The transmission signal tx1(t) having the angular frequency ω_C1+ω_B1 is represented by the following Equation (18):

$\begin{array}{cc}\begin{array}{c}\mathrm{tx}1\left(t\right)=\cos \left({\omega }_{C1}t+{\theta }_{C1}\right)\cos \left({\omega }_{B1}t+{\theta }_{B1}\right)-\\ \sin \left({\omega }_{C1}t+{\theta }_{c1}\right)\sin \left({\omega }_{B1}t+{\theta }_{B1}\right)\\ =\cos \left\{\left({\omega }_{C1}+{\omega }_{B1}\right)t+{\theta }_{C1}+{\theta }_{B1}\right\}\end{array}& \left(18\right)\end{array}$

When the distance between the devices 1 and 2 is represented as R and a delay until a transmission wave from the device 1 is received by the device 2 is represented as τ₁, the received signal rx2(t) of the device 2 can be represented by the following Equations (19) and (20):

$\begin{array}{cc}\begin{array}{c}\mathrm{rx}2\left(t\right)=\cos \left\{\left({\omega }_{C1}+{\omega }_{B1}\right)\left(t-{\tau }_1\right)+{\theta }_{C1}+{\theta }_{B1}\right\}\\ =\cos \left\{\left({\omega }_C+{\omega }_{B1}\right)t+{\theta }_{C1}+{\theta }_{B1}-{\theta }_{\tau H1}\right\}\end{array}& \left(19\right)\\ {\theta }_{\tau H1}=\left({\omega }_{C1}+{\omega }_{B1}\right){\tau }_1& \left(20\right)\end{array}$

The received signal rx2(t) is received by the antenna circuit 27 and supplied to the receiving section 25. In the receiver shown in FIG. 5, the received signal rx2(t) is input to the multipliers RM21 and RM22. Subsequently, signals in respective nodes of the receiver shown in FIG. 5 are sequentially calculated. Outputs of the multipliers RM21, RM23, and RM24 are respectively represented as I₁(t), I₂(t), and I₃(t), outputs of the multipliers RM22, RM26, and RM25 are respectively represented as Q₁(t), Q₂(t), and Q₃(t), and outputs of the adders RS21 and RS22 are respectively represented as I(t) and Q(t). The outputs are represented by the following Equations (21) to (26):I₁(t)=cos(ω_C2t+θ_C2)×cos {(ω_C1+ω_B1)t+θ_c1+θ_B1−θ_τH1}  (21)Q₁(t)=sin(ω_C2t+θ_C2)×cos {(ω_C1+ω_B1)t+θ_c1+θ_B1−θ_τH1}  (22)I₂(t)=I₁(t)×cos(ω_B2t+θ_B2)  (23)Q₂(t)=Q₁(t)×sin(ω_B2t+θ_B2)  (24)I₃(t)=I₁(t)×sin(ω_B2t+θ_B2)  (25)Q₃(t)=Q₁(t)×cos(ω_B2t+θ_B2)  (26)

An output I(t) of the adder RS21 is I(t)=I₂(t)+Q₂(t). An output Q(t) of the adder RS22 is Q(t)=I₃(t)−Q₃(t). A phase θ_H1(t) obtained from I(t) and Q(t) is represented by the following Equation (27):θ_H1(t)=tan⁻¹(Q(t)/I(t))=−{(ω_C1−ω_C2)t+(ω_B1−ω_B2)t+θ_C1−θ_C2+θ_B1−θ_B2−θ_τH1}   (27)(Transmission and Reception of a Transmission Wave Having the Angular Frequency ω_C2+ω_B2 from the Device 2)

Similarly, when the signal tx2(t) having the angular frequency ω_C2+ω_B2 transmitted from the device 2 is received by the device 1 after a delay 72, a phase θ_H2(t) obtained from the signals I(t) and Q(t) detected by the device 1 is calculated.

$\begin{array}{cc}\begin{array}{c}\mathrm{tx}2\left(t\right)=\cos \left({\omega }_{C2}t+{\theta }_{C2}\right)\cos \left({\omega }_{B2}t+{\theta }_{B2}\right)-\\ \sin \left({\omega }_{C2}t+{\theta }_{c2}\right)\sin \left({\omega }_{B2}t+{\theta }_{B2}\right)\\ =\cos \left\{\left({\omega }_{C2}+{\omega }_{B2}\right)t+{\theta }_{C2}+{\theta }_{B2}\right\}\end{array}& \left(28\right)\\ \begin{array}{c}\mathrm{rx}1\left(t\right)=\cos \left\{\left({\omega }_{C2}+{\omega }_{B2}\right)\left(t-{\tau }_2\right)+{\theta }_{C2}+{\theta }_{B2}\right\}\\ =\cos \left\{\left({\omega }_{C2}+{\omega }_{B2}\right)t+{\theta }_{C2}+{\theta }_{B2}-{\theta }_{\tau H2}\right\}\end{array}& \left(29\right)\\ {\theta }_{\tau H2}=\left({\omega }_{C2}+{\omega }_{B2}\right){\tau }_2& \left(30\right)\end{array}$

The received signal rx1(t) is received by the antenna circuit 17 and supplied to the receiving section 15. In the receiver shown in FIG. 4, the received signal rx1(t) is input to the multipliers RM11 and RM12. Subsequently, signals in respective nodes of the receiver shown in FIG. 4 are sequentially calculated. Outputs of the multipliers RM11, RM13, and RM14 are respectively represented as I₁(t), I₂(t), and I₃(t), outputs of the multipliers RM12, RM16, and RM15 are respectively represented as Q₁(t), Q₂(t), and Q₃(t), and outputs of the adders RS11 and RS12 are respectively represented as I(t) and Q(t). The outputs are represented by the following Equations (31) to (36):I₁(t)=cos(ω_C1t+θ_C1)×cos {(ω_C2+ω_B2)t+θ_c2+θ_B2−θ_τH2}  (31)Q₁(t)=sin(ω_C1t+θ_C1)×cos {(ω_C2+ω_B2)t+θ_c2+θ_B2−θ_τH2}  (32)I₂(t)=I₁(t)×cos(ω_B1t+θ_B1)  (33)Q₂(t)=Q₁(t)×sin(ω_B1t+θ_B1)  (34)I₃(t)=I₁(t)×sin(ω_B1t+θ_B1)  (35)Q₃(t)=Q₁(t)×cos(ω_B1t+θ_B1)  (36)

An output I(t) of the adder RS11 is I(t)=I₂(t)+Q₂(t). An output Q(t) of the adder RS12 is Q(t)=I₃(t)−Q₃(t). A phase θ_H2(t)=tan⁻¹(Q(t)/I(t)) obtained from I(t) and Q(t) is represented by the following Equation (37):θ_H2(t)=(ω_C1ω_C2)t+(ω_B1−ω_B2)t+θ_C1−θ_C2+θ_B1−θ_B2+θ_τH2  (37)(Transmission and Reception of a Transmission Wave Having the Angular Frequency ω_C1-ω_B1 from the Device 1)

The signal tx1(t) having the angular frequency ω_C1-ω_B1 transmitted from the device 1 is calculated in the same manner.

$\begin{array}{cc}\begin{array}{c}\mathrm{tx}1\left(t\right)=\cos \left({\omega }_{C1}t+{\theta }_{C1}\right)\cos \left({\omega }_{B1}t+{\theta }_{B1}\right)+\\ \sin \left({\omega }_{C1}t+{\theta }_{c1}\right)\sin \left({\omega }_{B1}t+{\theta }_{B1}\right)\\ =\cos \left\{\left({\omega }_{C1}-{\omega }_{B1}\right)t+{\theta }_{C1}-{\theta }_{B1}\right\}\end{array}& \left(38\right)\end{array}$

Since the distance between the devices 1 and 2 is R and the delay time is τ₁, the received signal rx2(t) in the device 2 is represented by the following Equations (39) and (40):

$\begin{array}{cc}\begin{array}{c}\mathrm{rx}2\left(t\right)=\cos \left\{\left({\omega }_{C1}-{\omega }_{B1}\right)\left(t-{\tau }_1\right)+{\theta }_{C1}-{\theta }_{B1}\right\}\\ =\cos \left\{\left({\omega }_{C1}-{\omega }_{B1}\right)t+{\theta }_{C1}-{\theta }_{B1}-{\theta }_{\tau L1}\right\}\end{array}& \left(39\right)\\ {\theta }_{\tau L1}=\left({\omega }_{C1}-{\omega }_{B1}\right){\tau }_1& \left(40\right)\end{array}$

Signals of the respective nodes of the device 2 can be represented by the following Equations (41) to (47):I₁(t)=cos(ω_C2t+θ_C2)×cos {(ω_C1−ω_B1)t+θ_c1−θ_B1−θ_τL1}  (41)Q₁(t)=sin(ω_C2t+θ_C2)×cos {(ω_C1−ω_B1)t+θ_c1−θ_B1−θ_τL1}  (42)I₂(t)=I₁(t)×cos(ω_B2t+θ_B2)  (43)Q₂(t)=Q₁(t)×−sin(ω_B2t+θ_B2)  (44)I₃(t)=I₁(t)×−sin(ω_B2t+θ_B2)  (45)Q₃(t)=Q₁(t)×cos(ω_B2t+θ_B2)  (46)

A phase θ_H1(t)=tan⁻¹(Q(t)/I(t)) detected by the device 2 from I(t)=I₂(t)−Q₂(t) obtained from the adder RS21 and Q(t)=I₃(t)+Q₃(t) obtained from the adder RS22 is represented by the following Equation (47):θ_L1(t)=tan⁻¹{(Q(t)/I(t))=−(ω_C1−ω_C2)t−(ω_B1−ω_B2)t+θ_C1−θ_C2−(θ_B1−θ_B2)−θ_τL1}   (47)(Transmission and Reception of a Transmission Wave Having the Angular Frequency ω_C2−ω_B2 from the Device 2)

Similarly, when the signal tx2(t) having the angular frequency ω_C2-ω_B2 transmitted from the device 2 is received by the device 1 after a delay τ₂, a phase θ_L2(t) obtained from I(t) and Q(t) detected by the device 1 is calculated.

$\begin{array}{cc}\begin{array}{c}\mathrm{tx}2\left(t\right)=\cos \left({\omega }_{C2}t+{\theta }_{C2}\right)\cos \left({\omega }_{B2}t+{\theta }_{B2}\right)+\\ \sin \left({\omega }_{C2}t+{\theta }_{C2}\right)\sin \left({\omega }_{B2}t+{\theta }_{B2}\right)\\ =\cos \left\{\left({\omega }_{C2}-{\omega }_{B2}\right)t+{\theta }_{C2}-{\theta }_{B2}\right\}\end{array}& \left(48\right)\\ \begin{array}{c}\mathrm{rx}1\left(t\right)=\cos \left\{\left({\omega }_{C2}-{\omega }_{B2}\right)\left(t-{\tau }_2\right)+{\theta }_{C2}-{\theta }_{B2}\right\}\\ =\cos \left\{\left({\omega }_{C2}-{\omega }_{B2}\right)t+{\theta }_{C2}-{\theta }_{B2}-{\theta }_{\tau L2}\right\}\end{array}& \left(49\right)\\ {\theta }_{\tau L2}=\left({\omega }_{C2}-{\omega }_{B2}\right){\tau }_2& \left(50\right)\end{array}$

Signals of the respective nodes of the device 1 can be represented by the following Equations (53) to (57):I₁(t)=cos(ω_C1t+θ_C1)×cos {(ω_C2−ω_B2)t+θ_c2−θ_B2−θ_τL2}  (51)Q₁(t)=sin(ω_C1t+θ_C1)×cos {(ω_C2−ω_B2)t+θ−θ_B2−θ_τL2}  (52)I₂(t)=I₁(t)×cos(ω_B1t+θ_B1)  (53)Q₂(t)=Q₁(t)×−sin(ω_B1t+θ_B1)  (54)I₃(t)=I₁(t)×−sin(ω_B1t+θ_B1)  (55)Q₃(t)=Q₁(t)×cos(ω_B1t+θ_B1)  (56)

A phase θ_H1(t)=tan⁻¹(Q(t)/I(t)) detected by the device 1 from I(t)=I₂(t)−Q₂(t) obtained from the adder RS11 and Q(t)=I₃(t)+Q₃(t) obtained from the adder RS12 is represented by the following Equation (57):θ_L2(t)=(ω_C1−ω_C2)t−(ω_B1−ω_B2)t+θ_C1−θ_C2−(θ_B1−θ_B2)+θ_τL2  (57)

In step S6 in FIG. 6, the control section 11 of the device 1 acquires the I and Q signals received by the receiving section 15. In step S7, the control section 11 calculates the phases θ_τH1(t) and θ_τL1(t) represented by Equations (27) and (47) described above. In step S16 in FIG. 6, the control section 21 of the device 2 acquires the I and Q signals received by the receiving section 25. In step S17, the control section 21 calculates the phases θ_τH2(t) and θ_τL2(t) represented by Equations (37) and (57) described above.

The control section 11 gives acquired phase information to the transmitting section 14 and causes the transmitting section 14 to transmit the phase information (step S8). For example, the control section 11 supplies the I and Q signals based on the phase information instead of the oscillation signals supplied to the multipliers TM11 and TM12 shown in FIG. 4. As described later, the phase information are given to I_T, Q_T signals in FIG. 50 and FIG. 51. Note that another transmitter for transmitting the phase information may be used.

In step S18, the control section 21 of the device 2 receives the phase information from the device 1. As explained above, the phase information may be the I and Q signals from the receiving section 15 of the device 1, may be information concerning phases obtained from the I and Q signals, or may be information concerning a difference between the phases.

In step S19, the control section 21 performs an operation of the following Equation (58) to calculate a distance. The following Equation (58) is an Equation for adding up a difference between Equation (27) and Equation (47) and a difference between Equation (37) and Equation (57).{θ_H1(t)−θ_L1(t)}+{θ_H2(t)−θ_L2(t)}=(θ_τH1−θτ_L1)+(θ_τH2−θ_τL2)  (58)

The following Equations (59) and (60) hold:

$\begin{array}{cc}\begin{array}{c}{\theta }_{\tau H1}-{\theta }_{\tau L1}=\left({\omega }_{C1}+{\omega }_{B1}\right){\tau }_1-\left({\omega }_{C1}-{\omega }_{B1}\right){\tau }_1\\ =2{\omega }_{B1\tau 1}\end{array}& \left(59\right)\\ \begin{array}{c}{\theta }_{\tau H2}-{\theta }_{\tau L2}=\left({\omega }_{C2}+{\omega }_{B2}\right){\tau }_2-\left({\omega }_{C2}-{\omega }_{B2}\right){\tau }_2\\ =2{\omega }_{B2\tau 2}\end{array}& \left(60\right)\end{array}$

The delays τ₁ and τ₂ of radio waves between the devices 1 and 2 are the same irrespective of a traveling direction. Therefore, the following Equation (61) is obtained from Equation (58):

$\begin{array}{cc}\left\{{\theta }_{H1}\left(t\right)-{\theta }_{L1}\left(t\right)\right\}+\left\{{\theta }_{H2}\left(t\right)-{\theta }_{L2}\left(t\right)\right\}=\left({\theta }_{\tau H1}-{\theta }_{\tau L1}\right)+\left({\theta }_{\tau H2}-{\theta }_{\tau L2}\right)=2\times \left({\omega }_{B1}+{\omega }_{B2}\right){\tau }_1& \left(61\right)\end{array}$

Equation (61) described above indicates that a value proportional to a double of the distance R is calculated by addition of a phase difference between two frequencies by the I and Q signals detected by the device 2 and a phase difference between two frequencies by the I and Q signals detected by the device 1. In general, the angular frequency ω_B1 by the oscillator 13 of the device 1 and the angular frequency ω_B2 by the oscillator 13 of the device 2 can be matched with an error in the order of several ten ppm. Therefore, the distance R by Equation (61) described above can be calculated at resolution of equal to or higher than at least approximately 1 m.

In step S9, the control section 11 stops the oscillator 13. In step S20, the control section 21 stops the oscillator 23. Note that, as explained above, the control sections 11 and 21 only have to continue the oscillation in a period of transmission and reception in steps S4, S5, S14, and S15. Start and end timings of the oscillation of the oscillators 13 and 23 are not limited to the example shown in FIG. 6.

(Calculation of a Distance by a Residue of 2π)

Incidentally, when the addition of the phase differences detected by the device 1 and the device 2 is performed, a result of the addition is sometimes equal to or smaller than −π(rad) or larger than π(rad). In this case, it is possible to calculate a correct distance R with respect to a detected phase by calculating a residue of 2π.

FIGS. 7 and 8 are explanatory diagrams for explaining a method of calculating a distance using a system of residue.

For example, when R=11 m and ω_B1=ω_B2=2π×5M, a detected phase difference Δθ₁₂ obtained by the device 1 and a detected phase difference Δθ₂₁ obtained by the device 2 are respectively as represented by the following Equations (62) and (63):Δθ₁₂=θ_τH1−θ_τL1=−1.8849  (62)Δθ₂₁=θ_τH2−θ_τL2=−6.0737  (63)

The following Equation (61a) is obtained from Equation (61) described above:(½)[{Δθ₁₂}+{Δθ₂₁}]=(ω_B1+ω_B2)(R/c)  (61a)

FIG. 7 shows a phase relation between Equations (62) and (63) described above. A phase of a sum of Δθ₂₁ indicated by an arrow on inner most side and Δθ₁₂ indicated by a second arrow from the inner side rotating in a clockwise direction on a basis of a phase 0 degree is a phase indicated by a third arrow from the inner side. A half angle of this phase is a phase of a thick line indicated by an arrow on the outermost side.

From Equation (61a), −0.3993=(ω_B1+ω_B2)(R/c) is obtained. When this Equation is solved, R=−19 m. It is seen that a distance cannot be correctly calculated because a detected phase difference is larger than −π(rad).

Therefore, in the present embodiment, in such a case, as shown in FIG. 8, 2π is added to both of Δθ₁₂ and Δθ₂₁. That is, a phase of a sum of 2π+Δθ₂₁ indicated by an arrow on inner most side and 2π+Δθ₁₂ indicated by a second arrow from the inner side rotating in a counterclockwise direction on a basis of the phase 0 degree is a phase indicated by a third arrow from the inner side. A half angle of this phase is a phase of a thick line indicated by an arrow on the outermost side.2π+(Δθ₁₂+Δθ₂₁)/2=2.3008From Equation (61a), R is calculated as R=11 m.

Consequently, in the present embodiment, when the detected phase differences are added up, a residue of 2π only has to be calculated to calculate the distance R. Note that the method of using the residue of 2π in the phase addition is applicable in other embodiments.

(Selection from a Plurality of Distance Candidates)

Incidentally, a detected phase difference exceeding 2π cannot be detected. Therefore, a plurality of distance candidates are present with respect to a calculated detected phase difference. As a method of selecting a correct distance from the plurality of distance candidates, a method of transmitting three transmission waves having different angular frequencies and a method of determining a distance according to received power exist.

FIG. 9 is an explanatory diagram showing an example in which a distance is plotted on the horizontal axis and a phase is plotted on the vertical axis and the third transmission wave having a different angular frequency is transmitted.

The following Equation (64) is obtained from Equation (61) described above:(½)×{(θ_τH1−θ_τL1)+(θ_τH2−θ_τL2)}=(ω_B1+ω_B2)×(R/c)  (64)

When a left side is described as θ_det, a relation between the distance R and θ_det is as indicated by a solid line in FIG. 9. However, although a sum θ_det of detected phase differences calculated by Equation (64) described above can take a value other than a value between −π(rad) and π(rad), the sum θ_det of the phase differences is a value converted into a value between −π(rad) and π(rad). In general, this is because a phase angle is displayed within a range [−π(rad), π(rad)].

Referring to FIG. 9, candidates of a distance by the sum θ_det of the detected phase differences include R₁, R₂, and R₃. The sum θ_det of the detected phase differences is an addition and subtraction result of phases obtained by transmission and reception of respective transmission waves having angular frequencies ω_C1+ω_B1, ω_C1−ω_B1, ω_C2+ω_B2, and ω_C2−ω_B2. However, an addition and subtraction result of phases obtained by transmission and reception of transmission waves having angular frequencies ω_C1+ω_B1/Q and ω_C2+ω_B2/Q is considered anew. Q is a rational number satisfying the following Inequality (65):Q>1  (65)

A relation between detected phases at the new angular frequencies and the distance R can be indicated by a broken line shown in FIG. 9. To select a correct distance from the candidates R₁, R₂, and R₃ of the distance, a result of the detected phases obtained at the new angular frequencies is referred to. That is, if θ_det1 is detected, the correct distance is determined as the distance R₁. If θ_det2 is detected, the correct distance is determined as the distance R₂. Note that, if a coverage of a radio wave is kept small, the inspection by the phase aliasing is unnecessary. Note that the transmission at the different three frequencies is explained above. However, the same can be realized by transmitting different three or more frequencies.

A method of selecting a correct distance according to amplitude observation of a detected signal is explained with reference to the explanatory diagram of FIG. 10.

In Equation (8) described above, the amplitude is attenuated at the attenuation L₁ according to the distance R. However, propagation attenuation in a free space is represented by the following Equation (66):L₁=(λ/4πR)²  (66)where λ is a wavelength. According to Equation (66), if the distance R is large, the attenuation L₁ is also large and, if the distance R is small, the attenuation L1 is also small. FIG. 10 shows this relation. When it is assumed that an antenna gain of transmission and reception is 1 and transmission power is P₀, received power P₁ at the distance R₁ and received power P₂ at the distance R₂ are respectively represented by the following Equations (67) and (68):P₁=(λ/4πR₁)²×P₀  (67)P₂=(λ/4πR₂)²×P₀  (68)

It is possible to distinguish the distances R₁ and R₂ from the sum θ_det of the detected phase differences and the received power.

Note that, in this case, it is possible to perform sure distance measurement by using the residue of 2π in the phase addition as well.

As explained above, in the present embodiment, the signals having the two angular frequencies are transmitted from the first device and the second device to the second device and the first device respectively, and the two phases of the two received signals having different angular frequencies are respectively calculated in the first and second devices. Any one of the first device and the second device transmits calculated phase information to the other. The device that receives the phase information accurately calculates the distance between the first device and the second device irrespective of initial phases of the oscillators of the first device and the second device according to an addition result of a phase difference between the two received signals received by the first device and a phase difference between the two received signals received by the second device. In the distance measuring system, a reflected wave is not used. The accurate distance measurement is performed by only one direction from the first device and the second device. It is possible to increase a measurable distance.

Second Embodiment

FIG. 11A is a flowchart according to a second embodiment of the present invention. FIGS. 11B to 15 are explanatory diagrams according to the second embodiment. A hardware configuration in the present embodiment is the same as the hardware configuration in the first embodiment. A method of transmitting two transmission waves and receiving the transmission waves in both the devices 1 and 2 and calculating a distance according to an addition result of phase differences detected from received signals is the same as the method in the first embodiment.{θ_H1(t)−θ_L1(t)}+{θ_H2(t)−θ_L2(t)}=(θ_τH1−θ_τL1)+(θ_τH2−θ_τL2)  (58)In the first embodiment, Equation (61) described above for calculating a distance from addition of detected phase differences is calculated assuming that the delays τ₁ and τ₂ of the radio wave are the same in Equation (58) described above. However, Equation (58) is an example in the case in which transmission and reception processing is simultaneously performed in the devices 1 and 2.

However, because of the provision of the Radio Law in the country, a frequency band in which simultaneous transmission and reception cannot be performed is present. For example, a 920 MHz band is an example of the frequency band. When distance measurement is performed in such a frequency band, transmission and reception has to be performed in time-series processing. In the present embodiment, an example adapted to such time-series transmission and reception is explained.

(Problems in the Time-Series Transmission and Reception)

When it is specified that only one wave can be transmitted and received at the same time between the devices 1 and 2, it is necessary to carry out, in time-series processing, transmission and reception of at least four waves necessary for distance measurement. However, when the time-series transmission and reception is carried out, a phase equivalent to a delay that occurs in time-series processing is added to a detected phase. A phase required for propagation cannot be calculated. A reason for this is explained by modifying Equation (58) explained above.

Note that a broken line portion of FIG. 6 is substantially simultaneously executed. However, when transmission and reception of one wave is performed in time-series processing, the broken line portion is as shown in FIG. 11A.

As in the first embodiment, in the devices 1 and 2 separated from each other by the distance R, a phase (shift amount) at the time when a signal having the angular frequency ω_C1+ω_B1 transmitted from the device 1 is detected in the device 2 is represented as θ_H1, a phase at the time when a signal having the angular frequency ω_C1-ω_B1 transmitted from the device 1 is detected in the device 2 is represented as θ_L1, a phase (shift amount) at the time when a signal having the angular frequency ω_C2+ω_B2 transmitted from the device 2 is detected in the device 1 is represented as θ_H2, and a phase at the time when a signal having the angular frequency ω_C2-ω_B2 transmitted from the device 2 is detected in the device 1 is represented as θ_L2.

For example, phase detection order is set as θ_H1, θ_L2, θ_H2, and θ_L1. As shown in FIGS. 11B and 11C, respective transmission signals are transmitted and received while being shifted by a time T. In this case, a time is substituted in (t) of Equations (27), (37), (47), and (57) described above. The following Equation (120) obtained by modifying Equation (58) described above holds:{θ_H1((t)−θ_L1(t+3T)}+{θ_H2(t+2T)−θ_L2(t+T)}=(θ_τH1−θ_τL1)+(θ_τH2−θ_τL2)+(ω_C1−ω_C2)4T  (120)

A last term of Equation (120) described above is a phase added by the time-series transmission and reception. The added phase is a multiplication result of error angular frequencies between the local angular frequencies used in the device 1 and the device 2 and a delay 4T, where the local frequencies are almost the same frequencies as the RF frequencies used in the device 1 and the device 2. When a local frequency is set to 920 MHz, a frequency error is set to 40 ppm, and a delay T is set to 0.1 ms, the added phase is 360°×14.7. It is seen that an error due to the added phase is too large and distance measurement cannot be correctly performed.

The phase detection order is set as θ_H1, θ_L1, θ_H2, and θ_L2. FIGS. 12A and 12B show an example of this case. In this case, the following Equation (121) is obtained by modifying Equation (58) described above:{θ_H1(t)−θ_L1(t+T)}+{θ_H2(t+2T)−θ_L2(t+3T)}=(θ_τH1−θ_τL1)+(θ_τH2−θ_τL2)+(ω_B1−ω_B2)4T  (121)

A last term of Equation (121) described above is a phase added by the time-series transmission and reception. The added phase is a multiplication result of error angular frequencies between the local angular frequencies for baseband processing used in the device 1 and the device 2 and a delay 4T, where the local frequencies for baseband processing are almost the same frequencies as the baseband frequencies used in the device 1 and the device 2. When a local frequency for baseband processing is set to 5 MHz, a frequency error is set to 40 ppm, and the delay T is set to 0.1 ms, the added phase is 360°×0.08=28.8°. It is seen from precedence that distance measurement can be correctly performed.

However, in this case, it depends on a system whether an error is within an allowable error of system specifications. The present embodiment presents a time-series procedure for reducing a distance error that occurs because of the time-series transmission and reception. Note that the present embodiment indicates a procedure that takes into account the regulation of transmission and reception specified by the Radio Law.

(Specific Procedure)

First, an influence due to a transmission delay is considered.

The following Equation (122) is obtained by modifying Equation (58) described above:{θ_H1(t)+θ_H2(t)}−{θ_L1(t)+θ_L2(t)}=(θ_τH1+θ_τH2)−(θ_τL1+θ_τL2)  (122)

In the equation,θ_H1(t)+θ_H2(t)=θ_τH1+θ_τH2  (123)θ_L1(t)+θ_L2(t)=θ_τL1+θ_τL2  (124)

In wireless communication, there is a provision that, when a signal addressed to oneself is received, a reply can be transmitted without carrier sense. According to the provision, after transmission of a signal from the device 1 to the device 2 ends, a reply is immediately transmitted from the device 2 to the device 1. To simplify an analysis, it is assumed that the device 2 transmits a reply to the device 1 after to from the transmission by the device 1. The following Equation (125) is obtained from Equations (27) and (37):θ_H1(t)+θ_H2(t+t₀)=θ_τH1+θ_τH2+{(ω_B1−ω_B2)+(ω_C1−ω_C2)}t₀  (125)

A delay t₀ is a shortest time period and includes a time period in which a signal having the angular frequency ω_C1+ω_B1 is transmitted from the device 1 to the device 2, a transmission and reception timing margin, and a propagation delay. A third term and a fourth term on a right side are phase errors due to the delay t₀. The fourth term is particularly a problem because a frequency is high. This is referred to below.

The delay T is further added to a left side of Equation (125). FIG. 13 shows such a transmission procedure. As shown in FIG. 13, an addition value of a detected phase in this case is the same irrespective of the addition of the delay T. Therefore, the following Equation (126) is obtained:θ_H1(t+T)+θ_H2(t+t₀+T)=θ_τH1+θ_τH2+{(ω_B1−ω_B2)+(ω_C1−ω_C2)}t₀  (126)

A right side of Equation (126) described above and a right side of Equation (125) described above are the same. That is, if a relative time difference is the same (in the example explained above, T), an addition result of a phase in which a signal transmitted from the device 1 is received by the device 2 and a phase in which a signal transmitted from the device 2 is received by the device 1 does not change irrespective of the delay T. That is, the addition result of the phases is a value that does not depend on the delay T.

Transmission and reception of the angular frequency ω_C1−ω_B1 signal between the device 1 and the device 2 is explained the same. That is, the following Equations (127) and (128) are obtained from Equations (47) and (57) described above:θ_L1(t)+θ_L2(t+t₀)=θ_τL1+θ_τL2+{−(ω_B1−ω_B2)+(ω_C1−ω_C2)}t₀  (127)θ_L1(t+T)+θ_L2(t+t₀+T)=θ_τL1+θ_τL2+{−(ω_B1−ω_B2)+(ω_C1−ω_C2)}t₀  (128)

From the above examination, a sequence is considered in which, after transmission and reception in both directions of the angular frequency ω_C1+ω_B1 signal, transmission of reception of the angular frequency ω_C1-ω_B1 a signal is performed. When a transmission start time of the angular frequency ω_C1-ω_B1 signal from the device 1 is represented as T on a basis of a transmission start time of the angular frequency ω_C1+ω_B1 signal, the following Equation (129) is obtained from Equations (125) and (128) describe above, where T>t₀ is assumed.θ_H1(t)+θ_H2(t+t₀)−{θ_L1(t+T)+θ_L2(t+t₀+T)}=θ_τH1−θ_τL1+θ_τH2−θ_τL2+2(ω_B1−ω_B2)t₀  (129)

A last term of a left side of Equation (129) described above is a phase error due to a transmission delay. A delay error due to a received local frequency for high-frequency is cancelled by calculating a difference between the angular frequency ω_C1+ω_B1 signal and the angular frequency ω_C1−ω_B1 signal. Therefore, the phase error is, in terms of time series, multiplication of a shortest delay time t₀ and an error of a local angular frequency (e.g., 2π×5 MHz) for a baseband processing. If the delay time t₀ is set small, the error is small. Therefore, depending on a value of the delay time t₀, practically, it is considered possible to perform distance measurement without a problem in accuracy.

A method of removing the last term of Equation (129) described above, which is a distance estimation error factor, is explained.

The following Equation (130) is obtained from Equations (27) and (37) described above:θ_H1(t+t₀)+θ_H2(t)=θ_τH1+θ_τH2−{(ω_B1−ω_B2)+(ω_C1−ω_C2)}t₀  (130)

Even if a predetermined delay D is added to a left side of Equation (130), as explained above, a value of a right side does not change. Therefore, the following Equation (131) is obtained:θ_H1(t+t₀+D)+θ_H2(t+D)=θ_τH1+θ_τH2−{(ω_B1−ω_B2)+(ω_C1−ω_C2)}t₀  (131)

When the Equations (125) and (131) are added up, the following Equation (132) is obtained:θ_H1(t)+θ_H2(t+t₀)+θ_H1(t+t₀+D)+θ_H2(t+D)=2(θ_τH1+θ_τH2)  (132)

A left side of FIG. 14 shows a state of Equation (132) described above. When D=t₀ in Equation (132), the following Equation (133) is obtained:θ_H1(t)+2θ_H2(t+t₀)+θ_H1(t+2t₀)=2(θ_τH1+θ_τH2)  (133)

A right side of Equation (133) described above is only a term of a radio wave propagation delay corresponding to a distance that does not depend on time.

From Equations (47) and (57) described above, the following Equation (134) is obtained:θ_L1(t+t₀)+θ_L2(t)=θ_τL1+θ_τL2−{−(ω_B1−ω_B2)+(ω_C1−ω_C2)}t₀  (134)

Even if the predetermined delay D is added to a left side of Equation (134), a value of a right side does not change. Therefore, the following Equation (135) is obtained:θ_L1(t+t₀+D)+θ_L2(t+D)=θ_τL1+θ_τL2−{−(ω_B1−ω_B2)+(ω_C1−ω_C2)}t₀  (135)

When Equations (127) and (135) described above are added up, the following Equation (136) is obtained:θ_L1(t)+θ_L2(t+t₀)=θ_L1(t+t₀+D)+θ_L2(t+D)=2(θ_τL1+θ_τL2)  (136)

In Equation (136), when D=t₀, the following Equation (137) is obtained:θ_L1(t)+2θ_L2(t+t₀)+θ_L(t+2t₀)=2(θ_τL1+θ_τL2)  (137)

A right side of Equation (137) described above is only a term of a radio wave propagation delay corresponding to a distance that does not depend on time.

Equations (133) and (137) described above mean a sequence for performing phase detection of a transmission signal of the device 1 in the device 2, performing phase detection of a transmission signal of the device 2 in the device 1 after t₀, and performing the phase detection of the transmission signal of the device 1 in the device 2 again after 2 t₀. In the following explanation, the process in which transmission of the transmission signal of the device 1 and phase detection in the device 2 for the transmission signal and transmission of the transmission signal of the device 2 and phase detection in the device 1 for the transmission signal alternate and the phase detections are measured again by shifting time is referred to as “repeated alternation”.

That is, the repeated alternation for respectively transmitting and receiving two carrier signals in the devices 1 and 2 and transmitting and receiving the carrier signals again at a t₀ interval from the device 1 or 2 to the other device is performed. Consequently, although the order and time of the transmission are limited, it is possible to perform accurate distance measurement that does not depend on time.

Further, depending on a transmission and reception sequence of carrier signals, even if the repeated alternation is not performed at the to interval, it is possible to perform accurate distance measurement that does not depend on time.

That is, even if a fixed delay T is added to a left side of Equation (136) described above, a right side is fixed. Therefore, the following Equation (138) is obtained:θ_L1(t+T)+θ_L2(t+t₀+T)+θ_L1(t+t₀+D+T)+θ_L2(t+D+T)=2(θ_τL1+θ_τL2)  (138)

The following Equation (139) is obtained from Equations (132) and (138) described above:

$\begin{array}{cc}{\theta }_{H1}\left(t\right)+{\theta }_{H2}\left(t+t_0\right)+{\theta }_{H1}\left(t+t_0+D\right)+{\theta }_{H2}\left(t+D\right)-\left\{{\theta }_{L1}\left(t+T\right)+{\theta }_{L2}\left(t+t_0+T\right)+{\theta }_{L1}\left(t+t_0+D+T\right)+{\theta }_{L2}\left(t+D+T\right)\right\}=2\left\{\left({\theta }_{\tau H1}-{\theta }_{\tau L1}\right)+\left({\theta }_{\tau H2}-{\theta }_{\tau L2}\right)\right\}=4\times \left({\omega }_{B1}+{\omega }_{B2}\right){\tau }_1& \left(139\right)\end{array}$

Equation (139) described above indicates a sequence for, after performing the repeated alternation of reciprocation of the angular frequencies ω_C1+ω_B1 signal and ω_C2+ω_B2 signal at the time interval D, performing the repeated alternation of reciprocation of the angular frequencies ω_C1−ω_B1 signal and ω_C2−ω_B2 signal at the time interval D after T from a measurement start. By adopting this sequence, it is possible to remove a distance estimation error factor of the last term of Equation (129) described above and perform accurate distance measurement.

FIGS. 14 and 15 show the sequence. It is possible to extract only a propagation delay component by measuring a phase in such a sequence. That is, the control section 11 of the device 1 transmits a transmission wave having the angular frequency ω_C1+ω_B2 (hereinafter referred to as transmission wave H1A) at predetermined timing. Immediately after receiving the transmission wave H1A, the control section 21 of the device 2 transmits a transmission wave having the angular frequency ω_C2+ω_B2 (hereinafter referred to as transmission wave H2A). Further, after transmitting the transmission wave H2A, the control section 21 of the device 2 transmits a transmission wave having the angular frequency ω_C2+ω_B2 (hereinafter referred to as transmission wave H2B). After receiving the second transmission wave H2B, the control section 11 of the device 1 transmits a transmission wave having the angular frequency ω_C1+ω_B1 (hereinafter referred to as transmission wave H1B).

Further, the control section 11 transmits a transmission wave having the angular frequency ω_C1−ω_B1 (hereinafter referred to as transmission wave L1A). Immediately after receiving the transmission wave L1A, the control section 21 of the device 2 transmits a transmission wave having the angular frequency ω_C2−ω_B2 (hereinafter referred to as transmission wave L2A). Further, after transmitting the transmission wave L2A, the control section 21 of the device 2 transmits a transmission wave having the angular frequency ω_C2−ω_B2 (hereinafter referred to as transmission wave L2B). After receiving the second transmission wave L2B, the control section 11 of the device 1 transmits a transmission wave having the angular frequency ω_C1−ω_B1 (hereinafter referred to as transmission wave L1B).

In this way, as shown in FIGS. 14 and 15, the control section 21 of the device 2 acquires a phase θ_H1(t) based on the transmission wave H1A in a predetermined time from a predetermined reference time 0, acquires a phase θ_H1(t+t₀+D) based on the transmission wave H1B in a predetermined time from a time t₀+D, acquires a phase θ_L1(t+T) based on the transmission wave L1A in a predetermined time from the time T, and acquires a phase θ_L1(t+t₀+D+T) based on the transmission wave L1B in a predetermined time from a time t₀+D+T.

The control section 11 of the device 1 acquires a phase θ_H2(t+t₀) based on the transmission wave H2A in a predetermined time from a time t₀, acquires a phase θ_H2(t+D) based on the transmission wave H2B in a predetermined time from a time D, acquires a phase θ_L2(t+t₀+T) based on the transmission wave L2A in a predetermined time from a time t₀+T, and acquires a phase θ_L2(t+D+T) based on the transmission wave L2B in a predetermined time from a time D+T.

At least one of the devices 1 and 2 transmits phase information, that is, calculated four phases or two phase differences or an operation result of Equation (139) described above of the phase differences. The control section of the device 1 or 2, which receives the phase information, calculates a distance according to an operation of Equation (139) described above. Note that, although “calculate a phase difference” is described in steps S7 and S17 in FIG. 6, in this case, it is not always necessary to calculate a phase difference in steps S7 and S17. A phase difference may be calculated during the distance calculation in S19.

In this way, in the present embodiment, by repeatedly alternating the carrier signals from the first device and the second device, even when the carrier signals cannot be simultaneously transmitted and received, it is possible to perform accurate distance measurement. For example, the first device and the second device respectively transmit signals having two angular frequencies twice to the second device and the first device in a predetermined sequence and calculate phase differences respectively in the first and second devices. Any one of the first device and the second device transmits calculated phase information to the other. The device, which receives the phase information, calculates a distance between the first device and the second device on a basis of eight phases calculated by the first device and the second device. Consequently, the distance between the first device and the second device is accurately calculated irrespective of initial phases of the oscillators of the first device and the second device. In this way, even when signals having respective angular frequencies are not simultaneously transmitted and are transmitted and received at timings shifted from each other, it is possible to remove an error of distance estimation and perform accurate distance measurement.

Third Embodiment

FIG. 16 is a block diagram showing a third embodiment of the present invention. FIG. 16 shows a transceiver adopted instead of the transceiver by the transmitting section 14 and the receiving section 15 shown in FIG. 1 and the transceiver by the transmitting section 24 and the receiving section 25 shown in FIG. 1. In the present embodiment, a configuration of the transceiver is only different from the configuration of the transceiver in the first embodiment.

In the first embodiment, the device 2 receives the transmission signal two waves having the angular frequencies ω_C1+ω_B1 and ω_C1−ω_B1 from the device 1 and detects the phases θ_H1(t) and θ_L1(t) and the device 1 receives the transmission signal two waves having the angular frequencies ω_C2+ω_B2 and ω_C2−ω_B2 from the device 2 and detects the phases θ_H2(t) and θ_L2(t). The distance is calculated using these four phases.

However, in general, a band-pass filter (BPF) that suppresses frequency components other than a frequency component near a desired wave is inserted between the transceiver and the antenna. Since the filter is requested to have a steep frequency characteristic, in general, an order of the filter is high. Therefore, a delay of a signal passing through the filter is large. For example, a delay of approximately 10 ns occurs in a BPF in a 900 MHz band. If τ₁ increases by 10 ns because of a delay of the BPF of the transceiver, a calculated distance increases by 3 m. Moreover, a delay amount of the BPF has a temperature characteristic and involves an increase or a decrease of 10% or more according to an ambient environment. Therefore, unless a BPF delay time is not compensated during distance measurement, a distance cannot be accurately calculated. The present embodiment compensates for such a BPF delay time.

In FIG. 16, a multiplier TMIX1 is equivalent to the multipliers TM11 and TM21 shown in FIG. 4 or 5. Similarly, multipliers TMIX2 and RMIX1 to RMIX6 are equivalent to the multipliers TM12 and 22 and the multipliers RM11 and 21 to RM16 and 26. Adders TSUM1, RSUM1, and RSUM2 are equivalent to the adders TS11 and TS21, the adders RS11 and RS21, and the adders RS12 and RS22.

A transmitter including the multipliers TMIX1 and TMIX2 and the adder TSUM1 and a receiver including the multipliers RMIX1 to RMIX6 and the adders RSUM1 and RSUM2 adopt the image suppression scheme like the transmitter and the receiver shown in FIGS. 4 and 5. In the present embodiment, multipliers RSMIX1 and RSMIX2 are provided in parallel to multipliers RMIX1 and RMIX2.

An RF (high-frequency) input terminal RX1 is connected to an RX terminal of a switch SW1. An RF output terminal TX1 is connected to a TX terminal of the switch SW1. An FIL terminal of the switch SW1 is connected to an input terminal of the band-pass filter BPF. A DET terminal of a switch SW2 is connected to a common input terminal of an added RF input terminal sRX1, that is, a common input terminal of the multiplier RMIX1 and the multiplier RMIX2. An FIL_I terminal of the switch SW2 is coupled to an input terminal of the band-pass filter BPF by a not-shown coupler. An FIL_O terminal of the switch SW2 is coupled to an output terminal of the band-pass filter BPF by a not-shown coupler. The output terminal of the band-pass filter BPF is connected to an antenna ANT terminal. Note that the switches SW1 and SW2 are controlled by the control section 11 (or the control section 21).

In the present embodiment, a delay time of the band-pass filter BPF (hereinafter referred to as BPF delay time) is measure in advance. The delay time is subtracted from a delay time calculated during phase detection to perform accurate distance measurement. The BPF delay time is obtained according to a difference between a signal delay time calculated by giving a transmission signal from the transmitter to the receiver via the switches SW1 and SW2 and a signal delay time calculated by giving the transmission signal to the receiver via the switch SW1, the band-pass filter BPF, and the switch SW2.

That is, when the BPF delay time is measured, the switch SW1 selects the TX terminal and the switch SW2 is connected to either one of the FIL_I terminal and the FIL_O terminal. In this state, the control sections 11 and 21 operate the transmitter. The receiver turns off only the multipliers RMIX1 and RMIX2 and operates the other circuit blocks.

The BPF delay time is calculated by detecting a transmission signal from the transmitter via the switch SW2 and the multipliers RSMIX1 and RSMIX2. The multiplier RMIX1 and the multiplier RMIX2 are turned off in order to prevent an error from increasing because a situation in which a signal leaks from the TX terminal to the RX terminal of the switch SW1 and is added to a detection signal. If the multiplier RMIX1 and the multiplier RMIX2 are turned off, isolation of the multiplier RMIX1 and the multiplier RMIX2 is added to isolation of the switch SW1. Therefore, it is possible to greatly attenuate a signal directly leaking from the transmitter.

In order to detect the BPF delay time, the switch SW2 is connected to the FIL_I terminal first to detect a signal via the FIL_I terminal and thereafter connected to the FIL_O terminal to detect a signal via the FIL_O terminal. Alternatively, the opposite sequence may be adopted. However, in the following explanation, the switch SW2 is connected to the FIL_I terminal and thereafter connected to the FIL_O terminal. Note that the transmitter and the receiver that detect the BPF delay time are present in the same device and can use a common local signal. Therefore, there is no problem concerning an initial phase and a frequency shift.

When an angular frequency of a transmission wave is represented as ω_C1+ω_B1 and an initial phase is represented as θ_C1+θ_B1, a signal of the TX1 terminal is represented by the following Equation (169):tx1(t)=cos {(ω_C1+ω_B1)t+θ_C1+θ_B1}  (169)

A signal delay due to the switch SW1, the not-shown couplers, and the switch SW2 can be neglected. Therefore, the signal represented by Equation (169) is input to the multipliers RSMIX1 and RSMIX2. The phase θ_H1I(t) detected in this case is calculated by Equation (27) described above. That is, the phase θ_H1I(t) is a result obtained by applying condition ω_C1=ω_C2, ω_B1=ω_B2, θ_C1=θ_C2, θ_B1=θ_B2, and θ_τH1=0.θ_H1I(t)=0  (170)Similarly, when an angular frequency of a transmission wave is represented as ω_C1−ω_B1 and an initial phase is represented as θ_C1−θ_B1, a signal of the TX1 terminal is represented by the following Equation (171):tx1(t)=cos {(ω_C1−ω_B1)t+θ_C1−θ_B1}  (171)

In this case, signals input to the multipliers RSMIX1 and RSMIX2 are the same as the signal represented by Equation (171). A phase θ_L11(t) detected in this case is calculated from Equation (47) described above. That is, the θ_H11(t) is a result obtained by applying conditions ω_C1=ω_C2, ω_B1=ω_B2, θ_C1=θ_C2, θ_B1=θ_B2, and θ_τL1=0.θ_L1I(t)=0  (172)

Subsequently, the switch SW2 is connected to the FIL_O terminal. When a BPF delay is represented as τ_BPF, signals having two frequencies input to the multipliers RSMIX1 and RSMIX2 via the switch SW1, the not-shown couplers, and the switch SW2 are respectively represented by the following Equations (173) and (174):rx1(t)=cos {(ω_C1+ω_B1)t+θ_C1+θ_B1−θ_BPFH}  (173)rx1(t)=cos {(ω_C1−ω_B1)t+θ_C1−θ_B1−θ_BPFL}  (174)In the equations,θ_BPFH=(ω_C1+ω_B1)τ_BPF  (175)θ_BPFL=(ω_C1−ω_B1)τ_BPF  (176)

From Equations (27) and (47) described above, phases θ_H10(t) and θ_L10(t) are represented by the following Equations (177) and (178):θ_H10(t)=θ_BPF  (177)θ_L10(t)=θ_BPFL  (178)

The following Equation (179) is derived from Equations (170), (171), (177), and (178):{θ_H10(t)−θ_L10(t)}−{θ_H1I(t)−θ_L1I(t)}=θ_BPFH−θ_BPFL=2ω_B1τ_BPF  (179)

A BPF delay time is calculated by Equation (179). The other components and action are the same as the components and the action in the first embodiment. That is, during actual use, the control sections 11 and 21 cause the switch SW1 to select the TX terminal during transmission and select RX terminal during reception.

The control sections 11 and 21 correct τ₁ in the calculation of Equation (61) described above with the BPF delay time calculated from Equation (179) and thereafter calculate the distance R.

Note that, in the above explanation, the phase of the band-pass filter BPF input terminal is calculated assuming that the phase is equal to the TX output phase. However, if there is a delay in the switch SW, the coupler 1, or the like, a phase difference is detected taking into account the delay. However, even during the actual use, a signal including a delay of the switch SW1, the coupler, or the like appear at a band-pass filter BPF output end and is supplied to the antenna ANT. Therefore, even if there is a delay before a band-pass filter BPF input end, it is possible to correctly perform measurement. Note that the control sections 11 and 21 may calculate a BPF delay time, for example, during a start of the actual use.

Incidentally, as an environment depending element, the band-pass filter BPF is mainly conceivable. Therefore, if a phase at the time when the switch SW2 is connected to the FIL_I terminal, that is, a phase at the band-pass filter BPF input end less easily affected by an environment is saved in a memory in advance, there is no problem even if a value saved in the memory is used during subsequent calculation of a BPF delay time. That is, in this case, after the phase detection at the band-pass filter BPF input end, it is possible to always connect the switch SW2 to the FIL_O terminal (the band-pass filter BPF output end). Consequently, it is possible to prevent a situation in which a power step change occurs and a large spurious occurs because the switch SW2 is switched during transmission.

As explained above, in the present embodiment, effects same as the effects in the respective embodiments explained above. Further, there is an advantage that it is possible to perform accurate distance measurement by removing the influence of a delay time due to the band-pass filter.

Note that, in the present embodiment, in order to avoid a measurement error due to a lack of isolation of the switch SW1, the multiplier RSMIX1 and the multiplier RSMIX2 used during calculation of a BPF delay time are adopted. However, if sufficient isolation of the switch SW1 can be secured, it is also possible to connect the DET terminal of the switch SW2 to the RX1 terminal and measure a delay via the multiplier RMIX1 and the multiplier RMIX2. In this case, during reception, the switch SW1 is connected to the RX1 terminal and the switch SW2 is connected to the FIL_I terminal or opened. In this case, the multiplier RSMIX1 and the multiplier RSMIX2 may be omitted.

Fourth Embodiment

FIGS. 17 and 18 are explanatory diagrams showing a fourth embodiment of the present invention. The present embodiment indicates an example in which the respective distance measuring systems are applied to a smart entry system.

In FIG. 17, a key 31 can transmit, by radio, a signal for enabling unlocking and locking of a door of an automobile 32 and a start of an engine of the automobile 32. That is, the key 31 includes a not-shown data transmitting/receiving section and can transmit encrypted peculiar data for authentication with the data transmitting/receiving section. A radio wave from the data transmitting/receiving section of the key 31 is received in a not-shown vehicle control device 35 mounted on the automobile 32.

As shown in FIG. 18, a control section 36 is provided in the vehicle control device 35. The control section 36 controls respective sections of the vehicle control device 35. The control section 36 is configured of a processor including a CPU. The control section 36 may operate a computer program stored in a memory 38 and control the respective sections.

A data transmitting/receiving section 37 is provided in the vehicle control device 35. The data transmitting/receiving section 37 can perform wireless communication with the data transmitting/receiving section of the key 31 via an antenna 35a. The data transmitting/receiving section 37 receives the peculiar data transmitted from the key 31 and transmits predetermined response data to the key 31 to perform authentication of the key 31 and the automobile 32.

The data transmitting/receiving section 37 can finely set electric field intensity. The authentication is not performed unless the key 31 is located in a relatively close position where the key 31 is capable of receiving transmission data of the data transmitting/receiving section 37, that is, near the automobile 32.

For example, as indicated by a broken line in FIG. 17, it is assumed that the key 31 is located sufficiently close to the automobile 32. In this case, the data transmitting/receiving section 37 is capable of communicating with the key 31. The data transmitting/receiving section 37 authenticates the key 31 through collation with peculiar data recorded in a memory 37a. The data transmitting/receiving section 37 outputs a signal indicating that the key 31 is authenticated to the control section 36. Consequently, the control section 36 controls an unlocking/locking device 39 to give permission of locking or unlocking.

In FIG. 17, attackers of a relay attack carry relay devices 33 and 34. The relay device 33 is capable of communicating with the key 31. The relay device 34 is capable of communicating with the data transmitting/receiving section 37 in the automobile 32. The relay devices 33 and 34 relay communication between the key 31 and the data transmitting/receiving section 37. Consequently, even when the key 31 is sufficiently separated from the automobile 32 as shown in FIG. 17 and direct communication between the key 31 and the data transmitting/receiving section 37 cannot be performed, the data transmitting/receiving section 37 can authenticate the key 31 through the relay devices 33 and 34.

Therefore, in the present embodiment, the control section 36 determines on a basis of an authentication result of the data transmitting/receiving section 37 and a distance measurement result from the second device 2 whether unlocking and locking, a start of the engine, and the like are permitted.

The second device 2 in the respective embodiments is incorporated in the key 31. On the other hand, the device 1 in the respective embodiments is mounted on the vehicle control device 35. A transmission wave from the device 1 is received in the device 2 via an antenna 27a. A transmission wave from the device 2 is received in the device 1 via the antenna 27a. The transmission wave from the device 1 is directly received by the antenna 27a in some case and is received by the antenna 27a through the relay devices 33 and 34 in other cases. Similarly, the transmission wave from the second device 2 is directly received by the device 1 from the antenna 27a in some case and is received by the device 1 from the antenna 27a through the relay devices 33 and 34.

When it is assumed that phases of the transmission waves from the device 1 and the device 2 do not change in the relay devices 33 and 34, the device 2 can calculate a distance from the key 31 on a basis of the phases calculated in the devices 1 and 2. The device 2 outputs the calculated distance to the control section 36. A distance threshold for permitting authentication of the key 31 is stored in the memory 38. When the distance calculated by the device 2 is within the distance threshold read out from the memory 38, the control section 36 assumes that the key 31 is authenticated and permits unlocking and locking, a start of the engine, and the like. When the distance calculated by the device 2 is larger than the distance threshold read out from the memory 38, the control section 36 does not permit the authentication of the key 31. Therefore, in this case, the control section 36 does not permit unlocking and locking, a start of the engine, and the like.

Note that the relay devices 33 and 34 can change the phases of the transmission waves from the device 1 and the device 2. Even in this case, since initial phases of the devices 1 and 2 are unknown, the relay devices 33 and 34 cannot calculate a phase shift amount necessary for keeping the distance calculated by the device 2 within the distance threshold read out from the memory 38. Therefore, even if the relay devices 33 and 34 are used, possibility that the authentication of the key 31 is permitted is sufficiently small.

As explained above, in the present embodiment, by using the distance measuring system in the respective embodiments, it is possible to prevent unlocking and the like of a vehicle from being performed by a relay attack to the smart entry system.

(Transmission Sequence)

FIGS. 19 to 44 are explanatory diagrams showing various sequences adoptable in the respective embodiments.

(Examples of Two Waves)

First, various sequences for transmitting two waves from each of the devices 1 and 2 are explained with reference to FIGS. 19 to 32.

Two transmission waves output from the device 1 are represented as transmission waves A1 and A2. Frequencies of the transmission waves A1 and A2 are respectively represented as f_A1 and f_A2. Two transmission waves output from the device 2 are represented as transmission waves B1 and B2. Frequencies of the transmission waves B1 and B2 are respectively represented as f_B1 and f_B2. As explained above, taking into account the presence of a frequency band in which simultaneous transmission and reception is prohibited in the Radio Law, the transmission waves A1, A2, B1, and B2 are transmitted in time-series processing in a predetermined sequence.

FIG. 19 shows a sequence in which carrier sense is performed, a response is absence, and the repeated alternation is absent.

The device 1 carries out the carrier sense at the frequency f_A1 for, for example, 128 μS (second) and thereafter transmits the transmission wave A1. Further, the device 1 carries out the carrier sense at the frequency f_A2 for, for example, 128 μS and thereafter transmits the transmission wave A2.

The device 2 carries out the carrier sense at the frequency f_Ba for, for example, 128 μS after a predetermined period after the transmission of the transmission wave A2 from the device 1 without responding to reception of the transmission wave A2 (a response is absent) and thereafter transmits the transmission wave B1. Further, the device 2 carries out the carrier sense at the frequency f_B2 for, for example, 128 μS and thereafter transmits the transmission wave B2. Note that a phase detected in the device 2 may be reflected in phases of the transmission waves B1 and B2 in a predetermined period (which may include a carrier sense period) after the transmission of the transmission wave A2 from the device 1.

This example of the sequence is an example in which presence or absence of a distance measurement frequency is determined by the carrier sense. When the distance measurement frequency is sensed by the carrier sense, (a) the sequence may be started from the beginning again after a predetermined time (e.g., several milliseconds) or (b) may be started in a carrier sense exception sequence explained below.

FIG. 20 shows a sequence in which the carrier sense is performed, a response is absent, and the repeated alternation is present.

The device 1 carries out the carrier sense at the frequency f_A1 for, for example, 128 μS and thereafter transmits the transmission wave A1. Further, the device 1 carries out the carrier sense at the frequency f_A2 for, for example, 128 μS without waiting for a response of a transmission wave from the device 2 and thereafter transmits the transmission wave A2. Further, the device 1 carries out the carrier sense at the frequency f_A1 for, for example, 128 μS without waiting for a response of a transmission wave from the device 2 and thereafter transmits the transmission wave A1 again (the repeated alternation is present).

On the other hand, the device 2 carries out the carrier sense at the frequency f_B1 for, for example, 128 μS after a predetermined period after the transmission of the transmission wave A2 from the device 1 and thereafter transmits the transmission wave B1. Further, the device 2 carries out the carrier sense at the frequency f_B2 for, for example, 128 μS without a response of a transmission wave from the device 1 and thereafter transmits the transmission wave B2. Further, the device 2 carries out the carrier sense at the frequency f_B1 for, for example, 128 μS without a response of a transmission wave from the device 1 and thereafter transmits the transmission wave B1 again (the repeated alternation is present).

This example of the sequence is also an example in which presence or absence of a distance measurement frequency is determined by the carrier sense. When the distance measurement frequency is sensed by the carrier sense, (a) the sequence may be started from the beginning again after a predetermined time (e.g., several milliseconds) or (b) may be started in the carrier sense exception sequence.

FIG. 21 shows a sequence in which the carrier sense is performed, a response is present, and the repeated alternation is absent.

The device 1 carries out the carrier sense at the frequency f_A1 for, for example, 128 μS and thereafter transmits the transmission wave A1. When receiving the transmission wave A1 from the device 1, the device 2 transmits the transmission wave B1 after, for example, 0 microsecond to 2 milliseconds from the reception without carrying out the carrier sense in response to the reception of the transmission wave A1.

The device 1 carries out the carrier sense at the frequency f_A2 for, for example, 128 μS after a predetermined period after reception of the transmission wave B1 from the device 2 and thereafter transmits the transmission wave A2. When receiving the transmission wave A2 from the device 1, the device 2 transmits the transmission wave B2 after, for example, 0 microsecond to 2 milliseconds from the reception without carrying out the carrier sense in response to the reception of the transmission wave A2. Note that, in an idle time until the response, the device 2 may reflect a received and detected phase on phases of the transmission waves B1 and B2.

This example of the sequence is also an example in which presence or absence of a distance measurement frequency is determined by the carrier sense. When the distance measurement frequency is sensed by the carrier sense, (a) the sequence may be started from the beginning again after a predetermined time (e.g., several milliseconds) or (b) may be started in the carrier sense exception sequence.

FIG. 22 shows a sequence in which the carrier sense is performed, a response is present, and the repeated alternation is present.

The device 1 carries out the carrier sense at the frequency f_A1 for, for example, 128 μS and thereafter transmits the transmission wave A1. When receiving the transmission wave A1 from the device 1, the device 2 transmits the transmission wave B1 after, for example, 0 microsecond to 2 milliseconds from the reception without carrying out the carrier sense in response to the reception of the transmission wave A1.

The device 1 carries out the carrier sense at the frequency f_A2 for, for example, 128 μS after a predetermined period after reception of the transmission wave B1 from the device 2 and thereafter transmits the transmission wave A2. When receiving the transmission wave A2 from the device 1, the device 2 transmits the transmission wave B2 after, for example, 0 microsecond to 2 milliseconds from the reception without carrying out the carrier sense in response to the reception of the transmission wave A2.

Further, in this example, the device 1 carries out the carrier sense at the frequency f_A1 for, for example, 128 μS after a predetermined period after reception of the transmission wave B2 from the device 2 and thereafter transmits the transmission wave A1 again (the repeated alternation is present). When receiving the transmission wave A1 from the device 1, the device 2 transmits the transmission wave B1 again after, for example, 0 microsecond to 2 milliseconds from the reception without carrying out the carrier sense in response to the reception of the transmission wave A1. Note that, in an idle time until the response, the device 2 may reflect a received and detected phase on phases of the transmission waves B1 and B2.

This example of the sequence is also an example in which presence or absence of a distance measurement frequency is determined by the carrier sense. When the distance measurement frequency is sensed by the carrier sense, (a) the sequence may be started from the beginning again after a predetermined time (e.g., several milliseconds) or (b) may be started in the carrier sense exception sequence.

FIG. 23 shows a sequence in which the carrier sense is performed in some case and is not performed in other cases, a response is absent, and the repeated alternation is absent.

The device 1 carries out the carrier sense at the frequency f_A1 for, for example, 128 μS and thereafter continuously transmits the transmission waves A1 and A2.

The device 2 carries out the carrier sense at the frequency f_B1 for, for example, 128 μS after a predetermined period after reception of the transmission wave A2 from the device 1 and thereafter continuously transmits the transmission waves B1 and B2. Note that, in an idle time until the response, the device 2 may reflect a received and detected phase on phases of the transmission waves B1 and B2.

This example of the sequence is an example in which presence or absence of a distance measurement frequency is determined by the carrier sense only at a start time of transmission. When the distance measurement frequency is sensed by the carrier sense, (a) the sequence may be started from the beginning again after a predetermined time (e.g., several milliseconds) or (b) may be started in the carrier sense exception sequence.

FIG. 24 shows a sequence in which the carrier sense is performed in some case and is not performed in other cases, a response is present, and the repeated alternation is absent.

The device 1 carries out the carrier sense at the frequency f_A1 for, for example, 128 μS and thereafter transmits the transmission wave A1. When receiving the transmission wave A1 from the device 1, the device 2 transmits the transmission wave B1 after, for example, 0 microsecond to 2 milliseconds from the reception without carrying out the carrier sense in response to the reception of the transmission wave A1. When receiving the transmission wave B1 from the device 2, the device 1 transmits the transmission wave A2 after, for example, 0 microsecond after the reception without carrying out the carrier sense.

When receiving the transmission wave A2 from the device 1, the device 2 transmits the transmission wave B2 after, for example, 0 microsecond to 2 milliseconds from the reception without carrying out the carrier sense in response to the reception of the transmission wave A2. Note that, in an idle time until the response, the device 2 may reflect a received and detected phase on phases of the transmission waves B1 and B2.

This example of the sequence is an example in which presence or absence of a distance measurement frequency is determined by the carrier sense only at a start time of transmission. When the distance measurement frequency is sensed by the carrier sense, (a) the sequence may be started from the beginning again after a predetermined time (e.g., several milliseconds) or (b) may be started in the carrier sense exception sequence.

FIG. 25 shows a sequence in which the carrier sense is absent, a response is absent, and the repeated alternation is absent.

The device 1 transmits the transmission wave A1 without carrying out the carrier sense. Further, the device 1 transmits the transmission wave A2 after several ten milliseconds after the transmission of the transmission wave A1 without carrying out the carrier sense. The device 2 transmits the transmission wave B1 after, for example, 100 milliseconds after reception of the transmission wave A2 from the device 1 without carrying out the carrier sense. Further, the device 2 transmits the transmission wave B2 after several ten milliseconds after the transmission of the transmission wave B1 without carrying out the carrier sense.

FIG. 26 shows a sequence in which the carrier sense is absent, a response is absent, and the repeated alternation is absent.

The device 1 transmits the transmission wave A1 without carrying out the carrier sense. Further, the device 1 once suspends the transmission after the transmission of the transmission wave A1 and thereafter transmits the transmission wave A2 without carrying out the carrier sense. In the figure, a transmission suspension section is described as 0 microsecond to 2 milliseconds. The device 2 immediately transmits the transmission wave B1 after reception of the transmission wave A2 from the device 1 without carrying out the carrier sense. In the figure, the device 2 transmits the transmission wave B1 after, for example, 0 microsecond to 2 milliseconds after the reception of the transmission wave A2 from the device 1. Further, the device 2 once suspends transmission after the transmission of the transmission wave B1 and thereafter transmits the transmission wave B2 without carrying out the carrier sense. In the figure, a transmission suspension section is described as 0 microsecond to 2 milliseconds.

FIG. 27 shows a sequence in which the carrier sense is absent, a response is absent, and repeated alternation is present.

The device 1 transmits the transmission wave A1 without carrying out the carrier sense. The device 1 transmits the transmission wave A2 after several ten milliseconds after the transmission of the transmission wave A1 without carrying out the carrier sense. Further, the device 1 transmits the transmission wave A1 again after several ten milliseconds after the transmission of the transmission wave A2 without carrying out the carrier sense. The device 2 transmits the transmission wave B1 after, for example, 100 milliseconds after reception of the transmission wave A1 from the device 1 without carrying out the carrier sense. Further, the device 2 transmits the transmission wave B2 after, for example, 100 milliseconds after the transmission of the transmission wave B1 without carrying out the carrier sense. Further, the device 2 transmits the transmission wave B1 after, for example, 100 milliseconds after the transmission of the transmission wave B2 without carrying out the carrier sense.

FIG. 28 shows a sequence in which the carrier sense is absent, a response is present, and the repeated alternation is absent.

The device 1 transmits the transmission wave A1 without carrying out the carrier sense. When receiving the transmission wave A1 from the device 1, the device 2 transmits the transmission wave B1 after, for example, 0 microsecond to 2 milliseconds from the reception without carrying out the carrier sense in response to the reception of the transmission wave A1. The device 1 transmits the transmission wave A2 after several ten milliseconds after the transmission of the transmission wave A1 without carrying out the carrier sense. When receiving the transmission wave A2 from the device 1, the device 2 transmits the transmission wave B2 after, for example, 0 microsecond to 2 milliseconds from the reception without carrying out the carrier sense in response to the reception of the transmission wave A2.

FIG. 29 shows a sequence in which the carrier sense is absent, a response is present, and the repeated alternation is present.

The device 1 transmits the transmission wave A1 without carrying out the carrier sense. When receiving the transmission wave A1 from the device 1, the device 2 transmits the transmission wave B1 after, for example, 0 microsecond to 2 milliseconds from the reception without carrying out the carrier sense in response to the reception of the transmission wave A1. The device 1 transmits the transmission wave A2 after several ten milliseconds after the transmission of the transmission wave A1 without carrying out the carrier sense. When receiving the transmission wave A2 from the device 1, the device 2 transmits the transmission wave B2 after, for example, 0 microsecond to 2 milliseconds from the reception without carrying out the carrier sense in response to the reception of the transmission wave A2. Further, the device 1 transmits the transmission wave A1 again after several ten milliseconds after the transmission of the transmission wave A2 without carrying out the carrier sense. When receiving the transmission wave A1 from the device 1, the device 2 transmits the transmission wave B1 again after, for example, 0 microsecond to 2 milliseconds from the reception without carrying out the carrier sense in response to the reception of the transmission wave A1.

FIG. 30 shows a sequence in which the carrier sense is performed in some case and is not performed in other cases, a response is present, and the repeated alternation is present.

The device 1 carries out the carrier sense at the frequency f_A1 for, for example, 128 μS and thereafter transmits the transmission wave A1. When receiving the transmission wave A1 from the device 1, the device 2 transmits the transmission wave B1 after, for example, 0 microsecond to 2 milliseconds from the reception without carrying out the carrier sense in response to the reception of the transmission wave A1. After reception of the transmission wave B1 after several ten milliseconds after the transmission of the transmission wave A1, the device 1 carries out the carrier sense at the frequency f_A2 for, for example, 128 μS and thereafter transmits the transmission wave A2. When receiving the transmission wave A2 from the device 1, the device 2 transmits the transmission wave B2 after, for example, 0 microsecond to 2 milliseconds from the reception without carrying out the carrier sense in response to the reception of the transmission wave A2. After the reception of the transmission wave B1 after several ten milliseconds after the transmission of the transmission wave A1, the device 1 transmits the transmission wave A1 again without carrying out the carrier sense this time. When receiving the transmission wave A1 from the device 1, the device 2 transmits the transmission wave B1 again after, for example, 0 microsecond to 2 milliseconds after the reception without carrying out the carrier sense in response to the reception of the transmission wave A1. Note that, in an idle time until the response, the device 2 may reflect a received and detected phase on phases of the transmission waves B1 and B2.

This example of the sequence is an example in which presence or absence of a distance measurement frequency is determined by the carrier sense only before the repeated alternation. When the distance measurement frequency is sensed by the carrier sense, (a) the sequence may be started from the beginning again after a predetermined time (e.g., several milliseconds) or (b) may be started in the carrier sense exception sequence.

FIG. 31 shows a sequence in which the carrier sense is performed in some case and is not performed in other cases, a response is absent, and the repeated alternation is absent.

The device 1 carries out the carrier sense at the frequency f_A1 for, for example, 128 μS and thereafter continuously transmits the transmission waves A1 and A2. The device 2 carries out the carrier sense at the frequency f_B1 for, for example, 128 μS after reception of the transmission wave A2 from the device 1 and thereafter continuously transmits the transmission waves B1 and B2. Further, the device 2 carries out the carrier sense at the frequency f_B1 for, for example, 128 μS after, for example, 100 milliseconds from the transmission of the transmission wave B2 and thereafter continuously transmits the transmission waves B1 and B2 again. After receiving the transmission wave B2 from the device 2, the device 1 carries out the carrier sense at the frequency f_A1 for, for example, 128 μS and thereafter continuously transmits the transmission waves A1 and A2. Note that, in an idle time until the response, the device 2 may reflect a received and detected phase on phases of the transmission waves B1 and B2.

This example of the sequence is an example in which presence or absence of a distance measurement frequency is determined by the carrier sense only at start times of respective transmissions. When the distance measurement frequency is sensed by the carrier sense, (a) the sequence may be started from the beginning again after a predetermined time (e.g., several milliseconds) or (b) may be started in the carrier sense exception sequence.

FIG. 32 shows a sequence in which the carrier sense is performed in some case and is not performed in other cases, a response is present, and the repeated alternation is absent.

The device 1 carries out the carrier sense at the frequency f_A1 for, for example, 128 μS and thereafter transmits the transmission wave A1. After receiving the transmission wave A1 from the device 1, the device 2 transmits the transmission wave B1 after, for example, 0 microsecond to 2 milliseconds from the reception without carrying out the carrier sense in response to the reception of the transmission wave A1. After receiving the transmission wave B1 from the device 2, the device 1 transmits the transmission wave A2 without carrying out the carrier sense. When receiving the transmission wave A2 from the device 1, the device 2 transmits the transmission wave B2 after, for example, 0 microsecond to 2 milliseconds from the reception without carrying out the carrier sense in response to the reception of the transmission wave A2.

Further, the device 2 carries out the carrier sense at the frequency f_B1 for, for example, 128 μS after, for example, 100 milliseconds after the transmission of the transmission wave B2 and transmits the transmission wave B1. When receiving the transmission wave B1 from the device 2, the device 1 transmits the transmission wave A1 without carrying out the carrier sense in response to the reception of the transmission wave B1. After receiving the transmission wave A1 from the device 1, the device 2 transmits the transmission wave B2 without carrying out the carrier sense. When receiving the transmission wave B2 from the device 2, the device 1 transmits the transmission wave A2 without carrying out the carrier sense in response to the reception of the transmission wave B2. Note that, in an idle time until the response, the device 2 may reflect a received and detected phase on phases of the transmission waves B1 and B2.

This example of the sequence is an example in which presence or absence of a distance measurement frequency is determined by the carrier sense only at start times of the devices 1 and 2. When the distance measurement frequency is sensed by the carrier sense, (a) the sequence may be started from the beginning again after a predetermined time (e.g., several milliseconds) or (b) may be started in the carrier sense exception sequence.

FIG. 33 shows a sequence in which the carrier sense is present, a response is present, and the repeated alternation is present.

The device 1 carries out the carrier sense at the frequency f_A1 for, for example, 128 μS and thereafter transmits the transmission wave A1. When receiving the transmission wave A1 from the device 1, the device 2 transmits the transmission wave B1 after, for example, 0 microsecond to 2 milliseconds from the reception without carrying out the carrier sense in response to the reception of the transmission wave A1. After the transmission of the transmission wave B1, the device 2 carries out the carrier sense at the frequency f_B1 for, for example, 128 μS and thereafter transmits the transmission wave B1. When receiving the transmission wave B from the device 2, the device 1 transmits the transmission wave A1 without carrying out the carrier sense in response to the reception of the transmission wave B1. Further, after transmitting the transmission wave A1, the device 1 carries out the carrier sense at the frequency f_A2 for, for example, 128 μS and thereafter transmits the transmission wave A2. When receiving the transmission wave A2 from the device 1, the device 2 transmits the transmission wave B2 after, for example, 0 microsecond to 2 milliseconds from the reception without carrying out the carrier sense in response to the reception of the transmission wave A2. Further, after the transmission of the transmission wave B2, the device 2 carries out the carrier sense at the frequency f_B2 for, for example, 128 μS and thereafter transmits the transmission wave B2. When receiving the transmission wave B2 from the device 2, the device 1 transmits the transmission wave A2 without carrying out the carrier sense in response to the reception of the transmission wave B2.

This example of the sequence is an example in which presence or absence of a distance measurement frequency is determined by the carrier sense. When the distance measurement frequency is sensed by the carrier sense, (a) the sequence may be started from the beginning again after a predetermined time (e.g., several milliseconds) or (b) may be started in the carrier sense exception sequence.

(Examples of Three Waves)

Various sequences for transmitting three waves from each of the devices 1 and 2 are explained with reference to FIGS. 34 to 44.

Three transmission waves output from the device 1 are represented as transmission waves A1, A2, and A3. Frequencies of the transmission waves A1, A2, and A3 are respectively represented as f_A1, f_A2, and f_A3. Three transmission waves output from the device 2 are represented as transmission waves B1, B2, and B3. Frequencies of the transmission waves B1, B2, and B3 are respectively represented as f_B1, f_B2, and f_B3. As explained above, taking into account the presence of a frequency band in which simultaneous transmission and reception is prohibited in the Radio Law, the transmission waves A1 to A3 and B1 to B3 are transmitted in time-series processing in a predetermined sequence.

Note that a method of describing sequences of transmission and reception in FIGS. 34 to 44 is the same as the method shown in FIGS. 19 to 32. In the following explanation, explanation is omitted concerning specific sequences of transmission and reception.

FIG. 34 shows a sequence in which the carrier sense is performed, a response is absent, and the repeated alternation is absent. This example of the sequence is an example in which presence or absence of a distance measurement frequency is determined by the carrier sense. When the distance measurement frequency is sensed by the carrier sense, (a) the sequence may be started from the beginning again after a predetermined time (e.g., several milliseconds) or (b) may be started in the carrier sense exception sequence.

FIG. 35 shows a sequence in which the carrier sense is performed, a response is absent, and the repeated alternation is present. This example of the sequence is also an example in which presence or absence of a distance measurement frequency is determined by the carrier sense. When the distance measurement frequency is sensed by the carrier sense, (a) the sequence may be started from the beginning again after a predetermined time (e.g., several milliseconds) or (b) may be started in the carrier sense exception sequence.

FIG. 36 shows a sequence in which the carrier sense is performed, a response is present, and the repeated alternation is absent. This example of the sequence is also an example in which presence or absence of a distance measurement frequency is determined by the carrier sense. When the distance measurement frequency is sensed by the carrier sense, (a) the sequence may be started from the beginning again after a predetermined time (e.g., several milliseconds) or (b) may be started in the carrier sense exception sequence.

FIG. 37 shows a sequence in which the carrier sense is performed, a response is present, and the repeated alternation is present. This example of the sequence is also an example in which presence or absence of a distance measurement frequency is determined by the carrier sense. When the distance measurement frequency is sensed by the carrier sense, (a) the sequence may be started from the beginning again after a predetermined time (e.g., several milliseconds) or (b) may be started in the carrier sense exception sequence.

FIG. 38 shows a sequence in which the carrier sense is absent, a response is absent, and the repeated alternation is absent.

FIG. 39 shows a sequence in which the carrier sense is absent, a response is present, and the repeated alternation is present.

FIG. 40 shows a sequence in which the carrier sense is absent, a response is present, and the repeated alternation is absent.

FIG. 41 shows a sequence in which the carrier sense is absent, a response is present, and the repeated alternation is present.

FIG. 42 shows a sequence in which the carrier sense is present in some case and is absent in other cases, a response is present, and the repeated alternation is absent. This example of the sequence is also an example in which presence or absence of a distance measurement frequency is determined by the carrier sense. When the distance measurement frequency is sensed by the carrier sense, (a) the sequence may be started from the beginning again after a predetermined time (e.g., several milliseconds) or (b) may be started in the carrier sense exception sequence.

FIG. 43 shows a sequence in which the carrier sense is performed, a response is present, and the repeated alternation is present. This example of the sequence is also an example in which presence or absence of a distance measurement frequency is determined by the carrier sense. When the distance measurement frequency is sensed by the carrier sense, (a) the sequence may be started from the beginning again after a predetermined time (e.g., several milliseconds) or (b) may be started in the carrier sense exception sequence.

FIG. 44 shows a sequence in which the carrier sense is performed, a response is present, and the repeated alternation is present. This example of the sequence is also an example in which presence or absence of a distance measurement frequency is determined by the carrier sense. When the distance measurement frequency is sensed by the carrier sense, (a) the sequence may be started from the beginning again after a predetermined time (e.g., several milliseconds) or (b) may be started in the carrier sense exception sequence.

(Modification)

FIGS. 45 to 47 show a modification. In the modification, a period in which an initial phase should be fixed is explained. FIG. 45 is an explanatory diagram showing a relation between a transmission sequence and a period in which an initial phase is maintained. FIG. 46 is an explanatory diagram showing a carrier frequency used for distance measurement. FIG. 47 is a flowchart for explaining the modification.

In the first embodiment, the simultaneous transmission and the simultaneous reception of the respective two frequencies from the devices 1 and 2 are assumed. In a period of the transmission and reception, the oscillators 13 and 23 are caused to continue oscillation such that the initial phase does not change. On the other hand, in the second embodiment, between the devices 1 and 2, it is specified that only one wave can be transmitted and received at the same time, transmission and reception of at least four waves necessary for distance measurement is carried out in time-series processing, and carrier signals from the devices 1 and 2 are repeatedly alternated to enable accurate distance measurement even when the time-series transmission and reception is performed.

For example, as explained above, in the example shown in FIG. 15, the transmission and reception of the transmission wave having the angular frequency ω_C1+ω_B1 from the device 1, the two times of transmission and reception of the transmission wave having the angular frequency ω_C2+ω_B2 from the device 2, and the transmission and reception of the transmission wave having the angular frequency ω_C1+ω_B1 from the device 1 are performed.

Further, the transmission and reception of the transmission wave having the angular frequency ω_C1-ω_B1 from the device 1, the two times of transmission and reception of the transmission wave having the angular frequency ω_C2-ω_B2 from the device 2, and the transmission and reception of the transmission wave having the angular frequency ω_C1−ω_B1 from the device 1 are performed.

An addition result of phases obtained in the devices 1 and 2 according to first transmission and reception of four waves in FIG. 15 is shown in a former half portion (first to fourth terms) of Equation (139) described above. The addition result of the first to fourth terms is 2(θ_τH1+θ_τH2) as shown in Equation (132) described above. As shown in Equations (20) and (30) described above, the addition result does not include a term of an initial phase. That is, information concerning the initial phase is not included in an operation result of phases obtained by the first transmission and reception of the four waves in FIG. 15. Therefore, in an operation of the first to fourth terms of Equation (139) described above, a correct result is obtained if the initial phase is not changed only in the transmission and reception period of the four waves.

Similarly, an addition result of phases obtained in the devices 1 and 2 by last transmission and reception of fourth waves in FIG. 15 is shown in a latter half portion (fifth to eighth terms) of Equation (139) described above. The addition result of the fifth to eighth terms is 2(θ_τL1+θ_τL2) as shown in Equation (138) described above. As shown in Equations (40) and (50) described above, the addition result does not include a term of an initial phase. That is, information concerning the initial phase is not included in an operation result of phases obtained by last transmission and reception of the four waves in FIG. 15. Therefore, in an operation of the fifth to eighth terms of Equation (139) described above, a correct result is obtained if the initial phase is not changed only in the transmission and reception period of the four waves.

FIG. 45 shows this state and indicates that an initial phase is maintained fixed in a distance measurement period in which the angular frequencies ω_C1+ω_B1 and ω_C2+ω_B2 are used and an initial phase is maintained fixed in a distance measurement period in which the angular frequencies ω_C1−ω_B1 and ω_C2−ω_B2 are used.

That is, for example, when the sequence of FIG. 15 is adopted, it is sufficient to cause the oscillators 13 and 23 to continue oscillation such that the initial phase does not change in a period of the first transmission and reception of the four waves and cause the oscillators 13 and 23 to continue oscillation such that the initial phase does not change in a period of last transmission and reception of the four waves. Even if the oscillation of the oscillators 13 and 23 stops and the initial phase changes until transmission and reception of a fifth wave from transmission and reception of a fourth wave, an accurate distance can be calculated on a basis of Equation (139) described above.

On the other hand, even if the oscillators 13 and 23 continuously operate, the initial phase changes if a frequency setting is not changed in the ω_C+ω_B distance measurement section and if a frequency setting is not changed in the ω_C−ω_B distance measurement section. This is explained in detail below (concerning two carrier signals).

Incidentally, in the respective embodiments, the example is explained in which the two carrier signals transmitted by the devices 1 and 2 has a frequency of a sum of or a difference between, for example, the relatively high angular frequencies ω_C1 and ω_C2 and, for example, the relatively low angular frequencies ω_B1 and ω_B2. Note that the angular frequencies ω_C1 and ω_C2 are Set to substantially the same frequency and the angular frequencies ω_B1 and ω_B2 are set to substantially the same frequency.

(Concerning Two Carrier Signals)

However, in the distance measurement in the respective embodiments, as explained below, the devices 1 and 2 only have to transmit two carrier signals respectively having predetermined frequency differences.

An angular frequency ω_C+ω_B and an angular frequency ω_C−ω_B can be modified as described below.ω_C+ω_B=(ω_C−Δω_c)+(Δω_C+ω_B)=ω′_C+ω_H  (201)ω_C−ω_B=(ω_C−Δω_c)+(Δω_C+ω_B)=ω′_C+ω_H  (202)

When transmission waves having the angular frequency ω_C and the angular frequency ω_B are represented as f_C and f_B on a frequency axis, transmission waves having the angular frequency ω_C+ω_B and the angular frequency ω_C−ω_B are as shown on a left side of FIG. 46.

Equations (201) and (202) described above indicate that a representation method is changed without changing a frequency. The transmission wave having the angular frequency ω_C+ω_B is obtained by a sum of transmission waves having an angular frequency ω′_C and an angular frequency ω_H. The transmission wave having the angular frequency ωC−ω_B is obtained by a sum of transmission waves having the angular frequency ω′_C and an angular frequency ω_L.

The center in FIG. 46 shows transmission waves based on this representation. The transmission waves having the angular frequencies ω′_C, ω_H, and ω_L are respectively represented as f_C, f_H, and f_L on the frequency axis. A transmission wave having a frequency f_C−f_B and a transmission wave having a frequency f_C+f_B on the left side of FIG. 46 respective indicates that the transmission waves can be represented as a transmission wave having the same frequency f_C+f_L and a transmission wave having the same frequency f_C+f_H.

That is, Equations (201) and (202) described above indicate that two carriers transmitted by the devices 1 and 2 do not need to be obtained by a sum of and a difference between two frequencies and the devices 1 and 2 only have to generate two carriers having a predetermined frequency difference and transmit the carriers.

As an example in which the transmission waves having the angular frequency ω_C+ω_B and the angular frequency ω_C−ω_B shown on the left side of FIG. 46 are obtained, for example, the oscillators 13 and 23 shown in FIG. 1 only have to generate a local signal having the angular frequency ω_C as a relatively high local frequency (hereinafter referred to as RF-LO frequency) and a local signal having the angular frequency ω_B as a relatively low local frequency (hereinafter referred to as IF-LO frequency) and the transmitting section 14 and 24 only have to generate signals having a sum of or a difference between the local frequencies as transmission signals.

On the other hand, the transmission waves in the center of FIG. 46 are obtained by generating a local signal having the angular frequency ω′_C as the RF-LO frequency and generating two local signals having the angular frequencies ω_L and ω_H as the IF-LO frequency and generating, in the transmitting sections 14 and 24, signals having a sum of these local frequencies as transmission signals. That is, the transmission waves in the center of FIG. 46 are obtained by fixing the RF-LO frequency and changing the IF-LO frequency.

The angular frequency ω_C-ω_B can be modified as shown below.ω_C−ω_B=(ω_C−2ω_B)+(2ω_B−ω_B)=ω″_C+ω_B  (203)

A right side of FIG. 46 shows transmission waves based on the representation of Equation (203) and indicates that, when a transmission wave having an angular frequency ω″_C is represented as f″_C on the frequency axis, the transmission wave having the frequency f_C-f_B on the left side of FIG. 46 can be represented as a transmission wave having the same frequency f″_C+f_B.

For example, the transmission waves on the right side of FIG. 46 are obtained by generating a local signal having the angular frequency ω′c and a local signal having the angular frequencies ω″_C as the RF-LO frequency and generating a local signal having the angular frequency ω_B as the IF-LO frequency and generating, in the transmitting sections 14 and 24, signals having a sum of these local frequencies as transmission signals. That is, the transmission waves on the right side of FIG. 46 are obtained by fixing the IF-LO frequency and changing the RF-LO frequency.

(Change of the Carrier Frequencies)

In this way, the devices 1 and 2 only have to transmit the two carrier signals respectively having the predetermined frequency difference in the distance measurement. Moreover, when transmission and reception of a carrier having a higher frequency of the two carriers is alternately performed and transmission and reception of a carrier having a low frequency is subsequently alternately performed as in the sequence shown in FIG. 15, initial phases may be different in the transmission and reception of the carrier having the high frequency and the transmission and reception of the carrier having the low frequency.

Further, only the carrier having the high frequency is used for an operation of Equation (132) described above obtained by decomposing Equation (139) described above and only the carrier having the low frequency is used for an operation of Equation (138) described above. That is, the operation of Equation (132) described above and the operation of Equation (138) described above only have to be independently performed. The local frequencies may be changed between a transmission and reception period of the carrier having the high frequency and a transmission and reception period of the carrier having the low frequency.

When the change in the initial phase and the change in the carrier angular frequency are allowed, a flow shown in FIG. 47 can be adopted instead of the flow shown in FIG. 11A.

In the flow shown in FIG. 47, the device 1 sets a first local (LO) frequency before one wave transmission signal generation and the device 2 sets a first local (LO) frequency before reception of one wave transmission wave from the device 1. The device 1 generates a carrier having a high frequency, for example, as one wave transmission signal using the local signal having the first LO frequency. The device 2 receives the one wave transmission wave using the carrier having the high frequency and acquires I and Q signals.

After acquisition of the I and Q signals based on the transmission signal having the high frequency from the device 2 and before generation of the next one wave transmission signal, the device 1 sets a second local (LO) frequency. Similarly, after the transmission of the one wave transmission wave to the device 1 and before reception of the next one wave transmission wave, the device 2 sets a second local (LO) frequency. The device 1 generates a carrier having a low frequency, for example, as one wave transmission signal using the local signal having the second LO frequency. The device 2 receives the transmission wave of the device 1 using the carrier having the low frequency and acquires I and Q signals.

(Configuration Example of the Oscillators and the Transceivers)

In this way, the devices 1 and 2 only have to be capable of generating and transmitting the two carrier signals having the predetermined frequency difference. Circuits having various configurations can be adopted as the oscillators 13 and 23, the transmitting sections 14 and 24, and the receiving sections 15 and 25 in FIG. 1.

FIG. 48A is an explanatory diagram showing, in a simplified manner, an example of the configurations of the oscillator 13, the transmitting section 14, and the receiving section 15 of the device 1. FIG. 48B is an explanatory diagram showing, in a simplified manner, an example of the configurations of the oscillator 23, the transmitting section 24, and the receiving section 25 of the device 2.

As shown in FIGS. 48A and 48B, the device 1 and the device 2 include an oscillator that generates an IF-LO frequency and an oscillator that generates an RF-LO frequency. Oscillation frequencies of the oscillators are, for example, fixed. Two carrier signals having a frequency difference can be generated by adding the IF-LO frequency to or subtracting the IF-LO frequency from the RF-LO frequency.

FIG. 49A is an explanatory diagram showing, in a simplified manner, an example of the configurations of the oscillator 13, the transmitting section 14, and the receiving section 15 of the device 1. FIG. 49B is an explanatory diagram showing, in a simplifier manner, an example of the configurations of the oscillator 23, the transmitting section 24, and the receiving section 25 of the device 2.

The examples shown in FIGS. 49A and 49B are examples in which two carrier signals having a frequency difference are generated by an oscillator having a variable frequency and a frequency divider (N-div).

FIG. 50 is a circuit diagram more specifically showing an example of a circuit that generates signals given to the multipliers TM11 and TM12 in FIG. 4. FIG. 51 is a circuit diagram more specifically showing an example of a circuit that generates signals given to the multipliers TM21 and TM22 in FIG. 5.

In FIG. 50, a multiplier TM15 gives, to an adder TS15, a multiplication result of an I_T signal and a local signal cos(ω_B1t+θ_B1) from the oscillator 13. A multiplier TM16 gives, to the adder TS15, a multiplication result of a Q_T signal and a local signal ±sin(ω_B1t+θ_B1) from the oscillator 13. The adder TS15 adds up the two inputs and gives an addition result to the multiplier TM11.

A multiplier TM17 gives, to an adder TS16, a multiplication result of the I_T signal and the local signal ±sin(ω_B1t+θ_B1) from the oscillator 13. A multiplier TM18 gives, to the adder TS16, a multiplication result of the Q_T signal and the local signal cos(ω_B1t+θ_B1) from the oscillator 13. The adder TS16 subtracts the output of a multiplier TM18 from the output of the multiplier TM17 and gives a subtraction result to the multiplier TM12. The other components are the same as the components shown in FIG. 4.

In FIG. 51, a multiplier TM25 gives, to an adder TS25, a multiplication result of the I_T signal and a local signal cos(ω_B2t+θ_B2) from the oscillator 23. A multiplier TM26 gives, to the adder TS25, a multiplication result of the Q_T signal and a local signal ±sin(ω_B2t+θ_B2) from the oscillator 23. The adder TS25 adds up the two inputs and gives an addition result to the multiplier TM21.

A multiplier TM27 gives, to an adder TS26, a multiplication result of the I_T signal and the local signal ±sin(ω_B2t+θ_B2) from the oscillator 23. A multiplier TM28 gives, to the adder TS26, a multiplication result of the Q_T signal and the local signal cos(ω_B2t+θ_B2) from the oscillator 23. The adder TS26 subtracts the output of the multiplier TM28 from the output of the multiplier TM27 and gives a subtraction result to the multiplier TM22. The other components are the same as the components shown in FIG. 5.

FIG. 52 is a circuit diagram showing an example of specific configurations of the transmitting section 14 and the receiving section 15 shown in FIG. 1. FIG. 53 is a circuit diagram showing an example of specific configurations of the transmitting section 24 and the receiving section 25 shown in FIG. 1. Note that FIGS. 52 and 53 show transceivers having a heterodyne configuration.

In FIG. 52, a multiplier TM1A gives, to an adder TS1A, a multiplication result of the I_T signal and the local signal cos(ω_B1+θ_B1) from the oscillator 13. A multiplier TM1B gives, to the adder TS1A, a multiplication result of the Q_T signal and the local signal sin(ω_B1t+θ_B1) from the oscillator 13. The adder TS1A subtracts the output of the multiplier TM1B from the output of the multiplier TM1A and gives a subtraction result to a multiplier TM1C. The multiplier TM1C multiplies together the output of the adder TS1A and a local signal cos(ω_C1t+θ_C1) and outputs a multiplication result as the transmission signal tx1.

A multiplier RM1A multiplies together the received signal rx1 and the local signal cos(ω_C1+θ_C1) to obtain an I₁ signal and outputs the I₁ signal to multipliers RM1B and RM1C. The multiplier RM1B outputs a multiplication result of the I₁ signal and the local signal cos(ω_B1t+θ_B1) as an I signal. The multiplier RM1C outputs a multiplication result of the I₁ signal and the local signal sin(ω_B1t+θ_B1) as a Q signal.

In FIG. 53, a multiplier TM2A gives, to an adder TS2A, a multiplication result of the I_T signal and the local signal cos(ω_B2t+θ_B2) from the oscillator 23. A multiplier TM2B gives, to the adder TS2A, a multiplication result of the Q_T signal and the local signal sin(ω_B2t+θ_B2) from the oscillator 23. The adder TS2A subtracts the output of the multiplier TM2B from the output of the multiplier TM2A and gives a subtraction result to a multiplier TM2C. The multiplier TM2C multiplies together the output of the adder TS2A and a local signal cos(ω_C2t+θ_C2) and outputs a multiplication result as the transmission signal tx2.

A multiplier RM2A multiplies together the received signal rx2 and the local signal cos(ω_C2t+θ_C2) to obtain the I₁ signal and outputs the I₁ signal to multipliers RM2B and RM2C. The multiplier RM2B outputs a multiplication result of the I₁ signal and the local signal cos(ω_B2t+θ_B2) as the I signal. The multiplier RM2C outputs a multiplication result of the I₁ signal and the local signal sin(ω_B2t+θ_B2) as the Q signal.

FIG. 54 is a circuit diagram showing an example of the specific configurations of the transmitting section 14 and the receiving section 15 shown in FIG. 1. FIG. 55 is a circuit diagram showing an example of the specific configurations of the transmitting section 24 and the receiving section 25 shown in FIG. 1. Note that FIGS. 54 and 55 show transceivers in which a direct conversion scheme is adopted.

In FIG. 54, a multiplier TM1D gives, to an adder TS1C, a multiplication result of the I_T signal and the local signal cos(ω_C1t+θ_C1) from the oscillator 13. A multiplier TM1E gives, to the adder TS1C, a multiplication result of the Q_T signal and the local signal sin(ω_C1t+θ_C1) from the oscillator 13. The adder TS1C subtracts the output of the multiplier TM1E from the output of the multiplier TM1D and outputs a subtraction result as the transmission signal tx1.

A multiplier RMID multiplies together the received signal rx1 and the local signal cos(ω_C1t+θ_C1) and outputs a multiplication result as the I signal. A multiplier RMIE multiplies together the received signal rx1 and the local signal sin(ω_C1t+θ_C1) and outputs a multiplication result as the Q signal.

In FIG. 55, a multiplier TM2D gives, to the adder TS2C, a multiplication result of the I_T signal and the local signal cos(ω_C2t+θ_C2) from the oscillator 23. A multiplier TM2E gives, to the adder TS2C, a multiplication result of the Q_T signal and the local signal sin(ω_C2t+θ_C2) from the oscillator 23. The adder TS2C subtracts the output of the multiplier TM2E from the output of the multiplier TM2D and outputs a subtraction result as the transmission signal tx2.

A multiplier RM2D multiplies together the received signal rx2 and the local signal cos(ω_C2t+θ_C2) and outputs a multiplication result as the I signal. A multiplier RM2E multiplies together the received signal rx2 and the local signal sin(ω_C2t+θ_C2) and outputs a multiplication result as the Q signal.

(Transmission Example of Phase Information)

In the respective embodiments, the phase information is transmitted from either one of the first device and the second device to the other. However, as explained above, a method of transmitting the phase information is not particularly limited. For example, the phase information may be transmitted by shifting by a phase obtained from a received signal, a phase of a carrier signal to be transmitted.

For example, in this case, it is possible to adopt a flow in which the broken line portion of FIG. 6 is replaced with a flow shown in FIG. 56 and steps S7, S8, and S18 in FIG. 6 are omitted.

FIG. 56 is a flowchart for explaining an example corresponding to FIG. 11A in which the second device transmits phase information to the first device. FIG. 56 includes a step of adding up a received phase and an initial phase between the acquisition step for the I and Q signals and the one wave transmission signal generating step in the second device shown in FIG. 11A. Consequently, a carrier signal in which a phase detected from a received signal is added to the initial phase of the device 2 is generated. The device 1 can acquire phase information calculated by the device 2 by receiving the carrier signal from the device 2 and calculating a phase.

As extension of the addition of the received phase and the initial phase, for example, in the eight-times repeated alternating sequence shown in FIG. 15, a sequence of θ_L2, θ_L2, and θ_L1 is considered, that is, after the device 2 transmits signals to the device 1 twice, the device 1 transmits a signal to the device 2. A received phase added to the initial phase during last θ_L1 transmission may be a phase of the immediately preceding θ_L2 but may be a value obtained by taking into account a phase detection result of θ_L2 immediately preceding θ_L2. That is, in addition to simply reflecting an immediately preceding received result, a result reflecting phases in the past may be added. In this case, in general, a result obtained by performing a predetermined operation on detected phase in the past is added to the initial phase. Further, in the case of the sequence shown in FIG. 15, since the device 2 receives a signal last, the device 2 is a device that calculates a distance. In this case, the device 1 does not always need to calculate a distance.

FIG. 57 is a flowchart for explaining an example corresponding to FIG. 47. A flow shown in FIG. 57 includes a step of adding up a received phase and an initial phase between the acquisition step for I and Q signals and the one wave transmission signal generating step in the device 2 shown in FIG. 47. When the eight-time repeated alternating sequence shown in FIG. 15 is assumed, as explained above, a predetermined calculation result with respect to detected phases in the past is added to the initial phase. Further, the device 2 is a device that calculates a distance. In this way, even when the carrier frequency is changed halfway in the distance measurement, the phase information may be transmitted while being included in the information concerning the phase of the carrier signal transmitted for the distance measurement.

(Doubling of a Measurement Distance)

Incidentally, the result of Equation (139) described above is a value in a system of residue of 2π, that is, a value between 0 and 2π. The distance R is R=τ₁/C. When a left side of Equation (139) described above is represented as S_A and R is calculated, the following Equation (210) is obtained:R=(S_A/4)×{c/(ω_B1+ω_B2)}  (210)

A maximum of S_A of Equation (210) described above is 2π. When (ω_B1+ω_B2)=2πΔf, a maximum R_MAX of the distance R is represented by the following Equation (211):R_MAX=c/4Δf  (211)

That is, Equation (211) described above indicates a maximum distance measurable without adopting the methods shown in FIGS. 9 and 10 in the sequence shown in FIG. 15 for transmitting two carriers having different frequencies four times from each of the device 1 and the device 2, eight times in total (hereinafter referred to as eight-time alternate sequence). On the other hand, when four waves are simultaneously transmitted and a distance is calculated by Equation (61) described above, R_MAX=c/2Δf. That is, in the eight-time alternate sequence shown in FIG. 15, a measurable distance is a half of a measurable distance during the four-wave simultaneous transmission.

Therefore, a method of increasing the measurable distance in the eight-time alternate sequence shown in FIG. 15 is examined. When ω_B1−ω_B2 represents a beat angular frequency and a result obtained by multiplying the time t₀ with a double of the beat angular frequency is represented as A(=2(ω_B1−ω_B2)t₀). A can be calculated by the following Equation (212) in which measured eight phases are used:A=[mod {(θ_H1(t)+θ_H2(t+t₀)−θ_H1(t+t₀+D)−θ_H2(t+D)−(θ_L1(t+T)+θ_L2(t+t₀+T)−θ_L1(t+t₀+D+T)−θ_L2(t+D+T))+π,2π}−π]/2  (212)

When the following Equation (213) is satisfied, Equation (129) is modified to represent a distance with the following Equation (214):|2(ω_B1−ω_B2)t₀|≤π/2  (213)R=[{θ_H1(t)+θ_H2(t+t₀)−(θ_L1(t+T)+θ_L2(t+t₀+T))−A}/2]×c/(ω_B1+ω_B2)  (214)

Therefore, the maximum R_MAX of the distance R in this case is represented by the following Equation (215):R_MAX=c/2Δf  (215)That is, by performing distance measurement using Equation (214) described above, in the eight-time alternate sequence shown in FIG. 15, it is possible to set a transmittable and measurable maximum distance to a measurement distance same as the measurement distance during the four-wave simultaneous transmission without adopting the methods shown in FIGS. 9 and 10.

For example, if ω_B1=2π×5 [MHz], an error of 0B2 with respect to ω_B1 is 40 [ppm], and t₀=100 [μs], a left side of Equation (213) described above is 2(ω_B1−ω_B2)t₀=2×2π×5×40×10×100=0.08π. It is relatively easy to perform system design to satisfy Equation (213) described above.

[Notes]

[Note 1]

A distance measuring device that calculates a distance on a basis of carrier phase detection, the distance measuring device including a calculating section configured to calculate, on a basis of phase information acquired by a first device and a second device, at least one of which is movable, a distance between the first device and the second device, wherein

the first device includes:

• • a first reference signal source; and
  • a first transceiver configured to transmit two or more first carrier signals and receives two or more second carrier signals using an output of the first reference signal source,

the second device includes:

• • a second reference signal source configured to operate independently from the first reference signal source; and
  • a second transceiver configured to transmit the two or more second carrier signals and receives the two or more first carrier signals using an output of the second reference signal source, and

the calculating section calculates the distance on a basis of a phase detection result obtained by reception of the first and second carrier signals.

[Note 2]

The distance measuring device according to the note 1, wherein the calculating section calculates the distance by calculating a residue of 2π concerning an addition result of a residue result of 2π concerning the first phase difference and a residue result of 2π concerning the second phase difference.

[Note 3]

The distance measuring device according to the note 1, wherein

the first and second reference signal sources generate two kinds of local signals, and

the first and second transceivers are configured of a wireless receiver of an image suppression scheme in which the two kinds of local signals are used.

[Note 4]

The distance measuring device according to the note 1, further including:

a band-pass filter provided between the first transceiver and an antenna; and

a switch circuit that switches a first route for giving an output of a transmitter in the first transceiver to a receiver in the first transceiver via the band-pass filter and a second route for giving the output to the receiver in the first transceiver not via the band-pass filter, wherein

a receiver of the first transceiver includes two inputs, one of which is connected to an output of the switch circuit, and

the calculating section calculates a delay time due to the band-pass filter on a basis of a phase of the first carrier signal that passes the first route and a phase of the first carrier signal that passes the second route.

[Note 5]

The distance measuring device according to the note 1, wherein

the first carrier signal is two or more carrier signals having different frequencies,

the second carrier signal is two or more carrier signals having frequencies respectively corresponding to the two or more carrier signals of the first carrier signal, and

the first and second transceivers do not change initial phases and frequencies of the first and second carrier signals during a period in which carrier signals having frequencies corresponding to each other of the first and second carrier signals are transmitted and received.

[Note 6]

The distance measuring device according to the note 1, wherein one device of the first and second devices generates a carrier signal obtained by adding, to an initial phase, a phase detection result obtained by reception of a carrier signal from another device of the first and second devices and transmits the carrier signal to the other device, and the device that receives the carrier signal last in a distance measurement sequence is a device that performs distance measurement calculation.

While certain embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions. Indeed, the novel devices and methods described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the embodiments described herein may be made without departing from the spirit of the inventions. The accompanying claims and their equivalents are intended to cover such forms or modification as would fall within the scope and spirit of the inventions.

Claims

1. A distance measuring device that calculates a distance on a basis of carrier phase detection, the distance measuring device comprising a processor configured to calculate, on a basis of phase information acquired by a first device and a second device, at least one of which is movable, a distance between the first device and the second device, wherein the first device includes: a first reference signal source; anda first transceiver configured to transmit two or more first carrier signals having frequencies different from each other and receive two or more second carrier signals having frequencies that are the same as the respective frequencies of the two or more first carrier signals using an output of the first reference signal source,the second device includes: a second reference signal source configured to operate independently from the first reference signal source; anda second transceiver configured to transmit the two or more second carrier signals and receive the two or more first carrier signals using an output of the second reference signal source,the processor calculates the distance by a phase calculation using a phase detection result obtained by reception of the first and second carrier signals having the same frequencies, andthe first and second reference signal sources continuously operate during a period in which the first and second carrier signals are transmitted and received by the first and second transceivers, and, as a result, respective phases of the first and second carrier signals continuously change.

2. The distance measuring device according to claim 1, wherein a receiver of the first transceiver includes a first phase detector that detects phases of the two or more second carrier signals, anda receiver of the second transceiver includes a second phase detector that detects phases of the two or more first carrier signals.

3. The distance measuring device according to claim 2, wherein the first and second phase detectors are each configured of a quadrature demodulator.

4. The distance measuring device according to claim 1, wherein the first transceiver transmits two or more first carrier signals and receives two or more second carrier signals using the output of the first reference signal source,the second transceiver transmits the two or more second carrier signals and receives the two first carrier signals using the output of the second reference signal source, andthe processor calculates the distance on a basis of four or more phase detection results obtained by reception of the first and second carrier signals.

5. The distance measuring device according to claim 4, wherein the processor calculates the distance by adding up one or more first phase differences between phases of the two or more second carrier signals obtained by the first transceiver and one or more second phase differences between phases of the two or more first carrier signals obtained by the second transceivers.

6. The distance measuring device according to claim 4, wherein the first transceiver transmits a first wave of the first carrier signals using the output of the first reference signal source,the second transceiver receives the first wave from the first transceiver using the output of the second reference signal source and thereafter transmits a first wave of the second carrier signals and thereafter transmits the first wave of the second carrier signals again,the first transceiver receives the first wave from the second transceiver twice using the output of the first reference signal source and thereafter transmits the first wave of the first carrier signals again and thereafter transmits a second wave of the first carrier signals, the second wave being different from the first wave;the second transceiver receives the first wave and the second wave from the first transceiver in order using the output of the second reference signal source and thereafter transmits a second wave of the second carrier signals, the second wave being different from the first wave, and thereafter transmits the second wave of the second carrier signals again,the first transceiver receives the second wave from the second transceiver twice using the output of the first reference signal source and thereafter transmits the second wave of the first carrier signals again, andthe second transceiver receives the second wave from the first transceiver using the output of the second reference signal source.

7. The distance measuring device according to claim 6, wherein the processor calculates the distance using a detected phase error component due to a beat angular frequency, which is a difference between a frequency of the first wave transmitted from the first transceiver and a frequency of the first wave transmitted from the second transceiver, a first phase detection result by the second device that receives the first wave transmitted from the first transceiver, a second phase detection result by the first device that receives the first wave transmitted from the second transceiver, a third phase detection result by the second device that receives the second wave transmitted from the first transceiver, a fourth phase detection result by the first device that receives the second wave transmitted from the second transceiver, and a frequency of a sum of the frequency of the first wave transmitted from the first transceiver and the frequency of the first wave transmitted from the second transceiver.

8. The distance measuring device according to claim 1, wherein the first transceiver transmits three or more first carrier signals and receives three or more second carrier signals using the output of the first reference signal source,the second transceiver transmits the three or more second carrier signals and receives the three or more first carrier signals using the output of the second reference signal source, andthe processor calculates the distance on a basis of six or more phase detection results obtained by reception of the first and second carrier signals.

9. The distance measuring device according to claim 8, wherein the processor calculates the distance by adding up two or more first phase differences between one phase and other two or more phases of the three or more second carrier signals obtained by the first transceiver and two or more second phase differences between one or more phase and other two or more phases of the three first carrier signals obtained by the second transceiver.

10. The distance measuring device according to claim 1, wherein the processor calculates the distance using amplitudes of received signals of the first and second transceivers.

11. The distance measuring device according to claim 1, wherein at least one of the first and second devices includes the processor, andthe first and second devices include communication sections for transmitting the phase information to the processor.

12. The distance measuring device according to claim 1, wherein the first transceiver transmits a first wave of the first carrier signals using the output of the first reference signal source,the second transceiver receives the first wave from the first transceiver using the output of the second reference signal source and thereafter transmits a first wave of the second carrier signals,the first transceiver receives the first wave from the second transceiver using the output of the first reference signal source and thereafter transmits a second wave of the first carrier signals, the second wave being different from the first wave;the second transceiver receives the second wave from the first transceiver using the output of the second reference signal source and thereafter transmits a second wave of the second carrier signals, the second wave being different from the first wave, andthe first transceiver receives the second wave from the second transceiver using the output of the first reference signal source.

13. The distance measuring device according to the claim 1, further comprising: a band-pass filter provided between the first transceiver and an antenna; anda switch circuit configured to switch a first route for giving an output of a transmitter in the first transceiver to a receiver in the first transceiver via the band-pass filter and a second route for giving the output to the receiver in the first transceiver not via the band-pass filter, whereinthe processor calculates a delay time due to the band-pass filter on a basis of phases of the first carrier signals that pass the first route and phases of the first carrier signals that pass the second route.

14. The distance measuring device according to claim 1, wherein one device of the first and second devices generates a carrier signal obtained by adding, to an initial phase, a phase detection result obtained by reception of a carrier signal from another device of the first and second devices and transmits the carrier signal to the other device.

15. The distance measuring device according to claim 1, wherein the two or more first carrier signals have frequencies different from each other,each of the two or more second carrier signals has a frequency corresponding to each frequency of the two or more first carrier signals,the first and second reference signal sources generate two kinds of local signals,the first and second transceivers are configured of a wireless transceiver of a heterodyne scheme in which the two kinds of local signals are used and change a frequency of at least one kind of the local signal of the two kinds of the local signals to be capable of changing each frequency of the first two or more carrier signals and each frequency of the two or more second carrier signals, andthe first and second reference signal sources continuously generate the two kinds of the local signals during a period in which carrier signals having frequencies corresponding to each other of the two or more first and second carrier signals are transmitted and received.

16. The distance measuring device according to claim 1, wherein the two or more first carrier signals have frequencies different from each other,each of the two or more second carrier signals has a frequency corresponding to each frequency of the two or more first carrier signals,the first and second reference signal sources generate one kind of a local signal,the first and second transceivers are configured of a wireless transceiver of a direct conversion scheme in which the one kind of the local signal is used and change a frequency of the one kind of the local signal to be capable of changing each frequency of the first two or more carrier signals and each frequency of the two or more second carrier signals, andthe first and second reference signal sources continuously generate the one kind of the local signal in a period in which carrier signals having frequencies corresponding to each other of the two or more first and second carrier signals are transmitted and received.

17. A distance measuring method for calculating a distance on a basis of carrier phase detection, the distance measuring method comprising: in a first device, transmitting two or more first carrier signals using an output of a first reference signal source;in a second device, transmitting two or more second carrier signals having frequencies that are the same as respective frequencies of the two or more first carrier signals using an output of a second reference signal source;in the first device, receiving the two or more second carrier signals and obtaining two or more first phase detection results;in the second device, receiving the two or more first carrier signals and obtaining two or more second phase detection results;transmitting the first and second phase detection results to a processor;in the processor, calculating a distance between the first device and the second device on a basis of the first and second phase detection results, andcausing the first and second reference signal sources to continuously operate during a period in which the first and second carrier signals are transmitted and received by the first and second transceivers, in order to continuously change respective phases of the first and second carrier signals.

18. The distance measuring method according to claim 17, wherein the processor calculates the distance by adding up two or more first phase differences based on the two or more first phase detection results and two or more second phase difference based on the two or more second phase detection results.

19. The distance measuring method according to claim 17, wherein one of the first and the second transceivers transmits a single carrier signal in a time-division manner, and the other of the first and second transceivers receives the transmitted single carrier signal.

20. The distance measuring method according to claim 17, wherein one of the first and the second transceivers transmits a single carrier signal in a time-division manner, the other of the first and second transceivers receives the transmitted single carrier signal, and the first and second transceivers transmit and receive the single carrier signal in the time-division manner at least four or more times.

21. The distance measuring method according to claim 17, wherein one of the first and the second transceivers transmits a single carrier signal in a time-division manner, the other of the first and second transceivers receives the transmitted single carrier signal, and the first and second transceivers execute an initial phase correction by transmitting and receiving the single carrier signal in the time-division manner at least four or more times.

22. The distance measuring method according to claim 17, wherein, one of the first and the second transceivers transmits a single carrier signal in a time-division manner, the other of the first and second transceivers receives the transmitted single carrier signal, and the first and second transceivers execute a frequency difference correction and an initial phase correction by transmitting and receiving the single carrier signal in the time-division manner at least five or more times.