Patent Grant
7286600
1. Field of the Invention
The present invention relates to a data transmission method and a data transmission device. Specifically, the present invention relates to a data transmission method and a data transmission device that can be applied to a power line carrier communication modem and the like for high speed data communication using a power line, wherein a leak electromagnetic field (electromagnetic wave) that is radiated from the power line at the time of signal transmission can be suppressed. That is, the present invention relates to a data transmission method and a data transmission device that have a function of suppressing a leak electromagnetic field to reduce a noise applied to other receivers, while signal transmission is performed therethrough.
2. Description of the Related Art
In this power line carrier communication system, an optical fiber is provided between an access node 9-11 of the power distribution transformer substation 9-1 and a modem inside the pole transformer 9-3 so as to enable data transmission with an optical signal. Further, data transmission can be performed between the pole transformer 9-3 and a modem of the house 9-6 whose plug is inserted into an outlet of the house 9-6, via the low-voltage power distribution line 9-4, the service line 9-5, and wiring 9-7 in the house 9-6.
Plural home electric appliances are connected to the low-voltage power distribution line 9-4, the service line 9-5, and the wiring 9-7, so that switching power sources and inverter circuits of these home electric appliances randomly generate noises to deteriorate communication quality in the above data transmission. For this reason, the following techniques are applied. That is, an FM modulation method, an FSK modulation method, a PSK modulation method, a spectrum diffusion method, and the like that are robust against noises are used. Alternatively, a multi-carrier modulation method, OFDM (Orthogonal Frequency Division Multiplexing), and the like are introduced to perform communication while avoiding use of carrier bands having many noises.
Meanwhile, in such a power line carrier communication system, a radiated leak electromagnetic field generated from the power line at the time of the signal transmission can adversely affect broadcasting media or other communications. Particularly, the noises can adversely affect a receiver for short-wave broadcasting to deteriorate quality in a voice of the broadcasting.
In order to reduce deterioration of the quality of the other communications caused by the radiated leak electromagnetic field, the transmission level in the power line carrier communication may be lowered. However, when the transmission level in the power line carrier communication is lowered, communication quality in the power line carrier communication is substantially lowered by noises generated from the switching sources and the inverters of the various home electric appliances.
Furthermore, there are many branching points on the power line. Accordingly, multi-paths (that are described hereinafter) are formed, so that a transmission signal of a particular frequency is reflected at the branching point, and the reflected signal is returned to the transmitter with the reflected signal having the opposite phase.
The “n” number of reflected waves that are generated by the reflection at many branching points spend respective delay times Δt1 through Δtn, and then are returned to the power line at the side of the pole transformer modem transmission unit 10-1 to be combined. With respect to a transmission signal of a certain frequency, the reflected wave and the carrier wave of the transmission signal overlap to generate a point where a voltage value becomes zero, that is, a point where the impedance becomes zero. Accordingly, at this point, a large current signal flows to generate a large leak electromagnetic field.
Furthermore, in the power line carrier communication system, a low-voltage power distribution line can function as an inductor for the pole transformer modem, and a service line and wiring in a house can function as a condenser for the pole transformer modem. In addition, a noise preventing condenser of each home electronic appliance connected to the wiring in the house is provided between AC 100V lines, so that each home electric appliance generates a large capacitance load.
Accordingly, for the pole transformer modem, the power line can function as a series resonance circuit including an output impedance, i.e., including R, L, and C.
In
Furthermore, the power line becomes a distributed constant circuit, and branching circuits form a plurality of series resonance circuits that have different resonance frequencies, respectively.
Furthermore, each branching circuit functions as an antenna. For example, when the resonance frequency is 30 MHz, the transmission speed of the radio wave becomes 3×108 [m/s], and the wave length of the radio wave becomes 10 m. As shown in
In addition, frequencies having values that are integral multiples of the resonance frequency also cause the resonance. Accordingly, large leak electromagnetic fields are generated at intervals of half wave lengths of these resonance frequencies. Since the electric home appliance has capacity load, a large electromagnetic field is generated at intervals of the half wave length of the resonance frequency larger than about 100 kHz.
Accordingly, it is a general object of the present invention to provide a data transmission method and a data transmission device for suppressing a leak electromagnetic field. Specifically, in the data transmission method and the data transmission device, at the time of transmitting a signal by a communication line such as a power line, a telephone line, and a coaxial transmission line that generates a reflected wave, a large current caused by the reflected wave and caused by intersymbol interference can be prevented from flowing to suppress the leak electromagnetic field.
According to one aspect of the present invention, there is provided a method of transmitting data, comprising the steps of:
According to another aspect of the present invention, the step (a) comprises the step (c) of performing the predetermined processing on the transmission data on the frequency axis such that the inverted signal and at least one zero signal point are inserted between the transmission signals on the time axis.
According to another aspect of the present invention, the step (a) comprises the step (d) of copying the transmission data on the frequency axis, and the step (b) comprises the step (e) of processing the transmission data and the copied transmission data in parallel.
According to another aspect of the present invention, the step (a) comprises the step (f) of performing the predetermined processing on the transmission data such that the transmission signal of the transmission data is delayed by a predetermined time, and the delayed transmission signal is subtracted from the transmission signal.
According to another aspect of the present invention, the method further comprises the step (g) of decreasing a roll-off rate of frequency characteristics in the processing of the step (f).
According to another aspect of the present invention, the step (b) comprises the step (h) of transforming the transmission data processed in the step (a) into the time-axis signal by using inverse fast Fourier transform processing.
According to another aspect of the present invention, the step (d) comprises the step (i) of determining a first number of points that are assigned to the transmission data such that data of both the transmission data and the copied transmission data corresponds to a second number of points that is a number of carriers used in the inverse fast Fourier transform processing.
According to another aspect of the present invention, the step (d) comprises the step (j) of adjusting the number of times of copying the transmission data, the number of times of copying being the number of times of generating transmission data by copying the transmission data.
According to another aspect of the present invention, there is provided a data transmission device, comprising:
According to another aspect of the present invention, the frequency-axis processing means perform the predetermined processing on the transmission data on the frequency axis such that the inverted signal and at least one zero signal point are inserted between the transmission signals of the transmission data on the time axis.
According to another aspect of the present invention, the frequency-axis processing means comprise copying means for copying the transmission data on the frequency axis, and the time-axis transform means process the transmission data and the copied transmission data in parallel.
According to another aspect of the present invention, the frequency-axis processing means comprise delay finite-difference means for delaying the transmission signal, and subtracting the delayed transmission signal from the transmission signal.
According to another aspect of the present invention, the delay finite-difference means use a decreased roll-off rate of frequency characteristics in the frequency-axis processing means.
According to another aspect of the present invention, the time-axis transform means transform the transmission data processed by the frequency-axis processing means into the time-axis signal by using inverse fast Fourier transform processing.
According to another aspect of the present invention, the copying means determine a first number of points that are assigned to the transmission data such that data of both the transmission data and the copied transmission data corresponds to a second number of points that is a number of carriers used in the inverse fast Fourier transform processing.
According to another aspect of the present invention, the copying means adjust the number of copies of the transmission data generated by the copying means.
Thereby, before the data on the frequency axis can be transformed into the data on the time axis by an inverse fast Fourier transform process and the like, the zero point inserting process or the inverted signal point inserting process can be performed. Furthermore, the number of signal points to which the transmission data is assigned can be determined such that the data obtained after the zero point inserting process or the inverted signal point inserting process agrees with the number (the carrier number) of the points that are used when the data on the frequency axis is transformed into the data on the time axis. Accordingly, the configuration for transforming the data on the frequency axis into the data on the time axis can be made so as to process the fixed number of the points, resulting in the simplified configuration.
Therefore, with the simple configuration, it is possible to provide a data transmission method in which the leak electromagnetic field suppressing effect can be controlled, and the leak electromagnetic field can be effectively suppressed.
Other objects, features, and advantages of the present invention will become more apparent from the following detailed description when read in conjunction with the accompanying drawings.
First, the related technique disclosed in Japanese Patent Application No. 2002-015098 (Title of the invention is “Leak Electromagnetic Field Suppressing Method, Leak Electromagnetic Field Suppressing Transmission Method, and Apparatus”) filed by the applicant of the present application in the Japanese Patent Office on Jan. 24, 2002 will be described. This technique will be described with reference to
As describe above, a power line becomes an equivalent circuit as shown in
In the transmission band ranging from 1.7 MHz to 30 MHz as shown in
Furthermore, as shown in
Furthermore, a first impulse is transmitted, and a second impulse having a phase (inverted phase) that is shifted from the phase of the first impulse by 180 degrees is then transmitted so as to reduce the reflected waves and suppress a leak electromagnetic field. This leak electromagnetic field suppression is shown in
When the first impulse is transmitted as shown in
The reflected wave shape of the first impulse and the reflected wave shape of the second impulse are inverted from each other to negate each other, so that a leak electromagnetic field generated by the reflected wave can be reduced, as shown in
The vector sum circuit performs signal conversion from a Gray binary code G into a natural binary code (N) on the input parallel signal. Further, the vector sum circuit performs a vector sum operation corresponding to a vector difference circuit (difference N/G) used at the reception side for detecting a phase, and outputs the processed signal to a signal point generation unit 4-1.
The signal point generation unit 4-1 divides the transmission data into data groups each having a predetermined bit number by a predetermined modulation unit, and generates one signal point corresponding to this bit number. For example, when the transmission data is divided by two bits, the signal point generation unit 4-1 generates one signal point out of signal points whose number is 22=4, as shown in
As shown in
The thus-output transmission signal is modulated by a modulation circuit (MOD), and is converted from a digital signal into an analog signal by a D/A converter (D/A). Thereafter, a low pass filter (LPF) extracts a signal of a low frequency band including a frequency band of the power line carrier wave, and outputs the extracted signal to a transmission line (TX-line).
A corresponding modem receives, via a reception line (RX-line), the transmission signal output to the transmission line (TX-line). Next, a band pass filter (BPF) extracts only predetermined frequency band components, and an A/D converter (A/D) converts the signal into the digital signal.
This digitalized reception signal is converted into a signal of a baseband by a demodulation circuit (DEM), and the wave shape of this signal is then adjusted by a roll-off filter (ROF2). Thereafter, the roll-off filter outputs the signal to a VCXO (Voltage Controlled Crystal Oscillator) type phase lock loop circuit (PLL VCXO).
This VCXO type phase lock loop circuit extracts the phase of the zero point, and provides the phase of the zero point as a sampling timing signal to the A/D converter (A/D) and to a clock (RX-CLK) distribution unit 4-3 of the reception unit.
The zero point of the signal output from the roll-off filter (ROF2) of the reception unit is deleted by a zero point deleting unit 4-4, and the gain of the signal is then controlled to be a predetermined level by an automatic gain controlling unit (AGC). Thereafter, an automatic carrier phase controlling unit (CAPC) aligns the phase. Furthermore, a determining circuit (DEC) performs signal determination of the reception signal, and outputs a result of the signal determination to a vector difference circuit (difference N/G).
This vector difference circuit performs a vector difference operation on the signal corresponding to the signal output with the natural binary code (N) by the vector sum circuit (G/N) of the transmission unit. Then, this vector difference circuit returns the code to the Gray binary code (G), and outputs this signal to a descrambler (P/S DSCR). The descrambler (P/S DSCR) converts this parallel gray code into a serial signal to perform a descrambling process so as to obtain a reception signal (RD).
Furthermore, in the transmission unit, a transmission clock distribution circuit (TX-CLK) distributes the transmission clock signal to the zero point inserting unit 4-2, the D/A converter (D/A), and other transmission circuit units. In the reception unit, a reception clock (RX-CLK) distribution unit 4-3 extracts a reception clock signal from the VCXO type phase lock loop circuit (PLL VCXO), and distributes the extracted reception clock signal to the zero point deleting unit 4-4, and other reception circuit unit.
The reception clock (RK-CLK) distribution unit 4-3 only passes the sampling timing signal that indicates the phase of the zero point and is extracted from the VCXO type phase lock loop circuit (PLL VCXO). This sampling timing signal is a mere symbol timing signal.
1/(1+k1×Z−1+k2×Z−2+. . . +kn×Z−n).
The multi-path equalizing unit 6-1 is configured so as to include a filter of a transfer function that is the inverse function of the transfer function of the communication line 6-2 so that the modem of the pole transformer can negate the reflected waves. That is, a FIR (Finite Pulse Response) filter whose transfer function is “1+C1×Z−1+C2×Z−2+. . . +Cn×Z−n)” is used as the filter of the multi-path equalizing unit 6-1.
The multi-path equalizing unit 6-1 includes the “n” number of delay elements 6-11 corresponding to estimated maximum delay times, and a multiplying unit 6-12 that multiplies, by predetermined coefficients, respective output from the “n” number of the delay elements 6-11. The multi-path equalizing unit 6-1 further includes a coefficient correction unit 6-13 that calculates and corrects each coefficient by a least square method (LSM), and an error calculating unit 6-14 that compares the input transmission signal with the output transmission signal to output an error signal generated based on this comparison to the coefficient correcting unit 6-13. The multi-path equalizing unit 6-1 further includes a combining adding unit 6-15 that adds the combined signal to the transmission signal with the phase of the combined signal being opposite. This combined signal is generated by combining the respective signals that are produced by multiplying the output from the respective delay elements by the respective predetermined coefficients.
The coefficient correcting unit 6-13 calculates the respective coefficients C1, C2, . . . Cn so as to minimize the error signal output from the error calculating unit 6-14. In this manner, K1 becomes equal to C1, K2 becomes equal to C2, . . . , and Kn becomes equal to Cn so that a transfer function of an entire transmission that includes the multi-path equalizing unit 6-1 and the communication line 6-2 becomes “1”. As a result, the resonance points where the impedance becomes zero (as shown in
As shown in
On the other hand, as shown in
In this guard interval addition, without changing a sub-channel frequency interval, the symbol period is made to be longer by the guard interval that is determined based on an assumed delay time of the multi-path wave. In the reception unit, symbol data of the guard interval part that is assumed to be affected by the intersymbol interference is not used, and the remaining symbol data is used to demodulate orthogonal frequency division multiplexing (OFDM) data, so that the influence by the noises can be removed.
According to the present invention, there is provided a data transmission method in which a leak electromagnetic field in the power line carrier system can be more effectively suppressed.
Problems in this configuration will be described in the following.
The number of the zero points inserted by the zero point inserting unit 4-2 is determined by an environment to which the data transmission device is applied, types of the power lines for the power line carrier, the length of the power line, and the like. However, the number of points that is the number of carriers (carrier waves) in the inverse fast Fourier transform unit needs to be changed depending on the number of the inserted zero points. In other words, for example, when no zero point is inserted between two signal points, the inverse fast Fourier transform is performed with a process of 128 points (this is assumed to be a standard condition). When one zero point is inserted between respective two signal points, the signal transmission speed becomes the half of the signal transmission speed in the standard condition, so that the inverse fast Fourier transform needs to be performed by a process of 64 points that is half of the number in the standard condition. Similarly, when three zero points are inserted between respective two signal points, the inverse fast Fourier transform needs to be performed by a process of 32 points that is the one fourth of the number in the standard condition. When seven zero points are inserted between the respective two signal points, the inverse fast Fourier transform needs to be performed by a process of 16 points that is one eighth of the number in the standard condition. Thus, when zero points are inserted between the signal points, it is necessary to provide a configuration that copes with the inverse Fourier transform of many different types of the point number. As a result, a circuit required for the inverse Fourier transform unit 7-1 becomes large in a size.
The finite-difference function unit 6-1 generally has finite-difference function characteristics in
y=x−x*Z−1=x(1−Z−1).
In the first equation, “x” designates an amplitude of the input signal of the finite-difference function unit 6-1, and “y” designates an amplitude of the output signal of the finite-difference function unit. Furthermore, a second equation where “ω” designates an angular frequency, and when “T” is a delay time of a delay tap T, “Z” becomes “ejωT” is obtained from the first equation. That is, the second equation is:
Accordingly, the finite-difference function unit 6-1 shown in
In the modem of
Accordingly, as described with reference to
The zero point inserting advantage that is obtained by signal point copying will be described with reference to
In other words, when the data constituted by 64 points is copied once, and the data corresponding to a total of 128 points on the frequency axis is input to the inverse fast Fourier transform unit 7-1, the signal in which one zero point is inserted between two signal points on the time axis is formed. Similarly, when data constituted by 32 points is copied three times, and the data corresponding to a total of 128 points on the frequency axis is input to the inverse fast Fourier transform unit 7-1, the signal in which three zero points are inserted between two signal points on the time axis is formed. In these cases, the inverse fast Fourier transform unit may be configured so as to always perform the process corresponding to 128 points. Accordingly, it is possible to simplify the configuration of the inverse fast Fourier transform unit 7-1.
As shown in
Meanwhile, according to the first embodiment, the output from the copying unit 8-1 is input to the finite-difference function unit 6-1 where the finite-difference function process is performed. Thereafter, the output from the finite-difference function unit 6-1 is input to the inverse fast Fourier transform unit 7-1 where the inverse fast Fourier transform is performed to transform the input signal into the signal on the time axis shown in
Next, a second embodiment of the present invention will be described. In the second embodiment, the 100 percent cosine square characteristics (shown in
The equation showing the frequency characteristics shown in
On the other hand, the imaginary component Hi(ω) is expressed by the fourth equation:
According to the embodiments of the present invention, it is possible to perform the inverse fast Fourier transform with the same point number either in the case where one or more zero points are inserted between two signal points of the original signal without outputting the inverted signal as shown in
In the configuration in which the prevention of the intersymbol interference, and the negating of the reflected wave can be carried out by outputting the signal inverted by 180 degrees from the original signal on the time axis after the original signal, it is possible to arbitrarily adjust the number of the zero points inserted between two original signal points or between the original signal point and the inverted signal point without changing the number of the points processed in the inverse fast Fourier transform process, as shown in
As described with reference to
Furthermore, as described with reference to
This patent application is based on Japanese priority patent application No. 2002-246840 filed on Aug. 27, 2002, the entire contents of which are hereby incorporated by reference.
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| Number | Date | Country | |
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| 20040042391 A1 | Mar 2004 | US |
