Embodiments of the present invention will be described hereinbelow with respect to the drawings.
Constitution of the wireless transceiver device First, the constitution of the wireless transceiver device according to this embodiment will be described. As shown in
The wireless transmitter 1 has a function for generating and transmitting a wireless signal so that the wireless signal that is transmitted has second or higher-order statistic properties that are unique to the group to which the wireless signal belongs. The wireless receiver 2 has a function for calculating second or higher-order statistic properties that the received wireless signal possesses and a function for discriminating the group to which the wireless signal belongs based on the second or higher-order statistic properties thereof and pre-stored second or higher-order statistic properties for each group.
The respective functional elements will be described in detail hereinbelow by using
The ID signal storage 21 of the wireless transmitter 1 stores ID signal data with second or higher-order statistic properties that are unique to the group to which the transmitted signal belongs. Second or higher-order statistic properties are properties that appear in statistic quantities such as a frequency correlation, time correlation, cyclic autocorrelation, cumulant, and moment, and second or higher-order statistic properties with two or more dimensions are relevant. Here, the ID signal storage 21 stores the sine wave with a specified frequency as the ID signal data so that the characteristic appears as the cyclic autocorrelation characteristic, for example. The cyclic autocorrelation characteristic for the time signal x(t) with respect to the delay time T and the cycle frequency a is given by:
and, when the delay time is 0, the cyclic autocorrelation characteristic for the sine wave is as follows:
and the cyclic autocorrelation characteristic has a peak at the cycle frequency of two times the frequency of the sine wave, and becomes 0 for other cycle frequencies.
The data generator 20 generates the transmitted data signal D1 and outputs the generated data signal D1 to the data modulator 22.
The data modulator 22 modulates the transmitted data signal D1 in a format that is suited to wireless communications and outputs the signal that is modulated (called ‘modulated signal’ hereinbelow) to the wireless signal ID assigner 23. Further, although an example in which the wireless transmitter 1 comprises data generator 20 has been described in this embodiment, there is no requirement that the wireless transmitter 1 should comprise data generator 20. For example, an aspect in which the transmitted data signal D1 is input from the outside to the wireless transmitter 1 may also be adopted.
The wireless signal ID assigner 23 generates a signal for transmission by adding the sine wave which is held by the ID signal storage 21 to the input modulated signal and outputs the signal that has been generated for transmission to the wireless signal transmitter 24.
The wireless signal transmitter 24 transmits the wireless signal S that has undergone signal processing to wireless receiver 2 which is the communication partner via an antenna 24A after performing predetermined signal processing such as amplification, band-limiting, and frequency conversion on the transmission signal.
The wireless signal receiver 31 of the wireless receiver 2 shown in
Further, the wireless signal S is known as a ‘transmission signal’ when seen from the perspective of the wireless transmitter 1 and is called a ‘received signal’ when viewed from the perspective of the wireless receiver 2.
As shown in
The wireless signal group discriminator 33 calculates the cyclic autocorrelation characteristic for the received signal after the predetermined signal processing by the wireless signal receiver 31 and, by comparing the cyclic autocorrelation characteristic obtained using this calculation with the feature quantities of the second or higher-order statistic properties stored in the second or higher-order statistic properties database 32, discriminates the group to which the received wireless signal belongs.
Here, the feature quantity of the second or higher-order statistic properties is, for example, the frequency shift amount with which the power peak of frequency autocorrelation characteristic appears and, in cases where a sine wave is added as an ID signal, a frequency that is two times the frequency of the sine wave corresponds to the frequency shift amount. The second or higher-order statistic properties database 32 stores the frequency shift amount as the feature quantity for each group. Here, the power of the second or higher-order statistic properties of the received signal can be observed in the frequency shift amount constituting the feature quantity that is unique to each group to which the signal probably belongs and the group corresponding to the frequency shift amount at which the power peak appears can be discriminated as the group to which the received signal belongs, by comparing the magnitudes of the observed power.
Furthermore, in cases where the power peak of the second or higher-order statistic properties appears for a plurality of frequency shifts in one ID signal, the frequency shift amounts at which the power peak appears and the corresponding power values are stored in the second or higher-order statistic properties database 32. The wireless signal group discriminator 33 calculates the second or higher-order statistic properties for the received signal and performs detection of correlations between (1) the power values of the second or higher-order statistic properties of the calculation result and (2) the frequency shift amounts and corresponding to the power values stored in the second or higher-order statistic properties database 32, and discriminates the group corresponding to the feature quantity with the highest correlation among the feature quantities stored in the second or higher-order statistic properties database 32 as the group to which the received signal belongs.
The wireless signal group discriminator 33 outputs a control signal corresponding with the discrimination result to the switch 34. More specifically, in cases where, as a result of the discrimination of the group to which the received signal belongs, the received signal is a signal for the wireless receiver 2, the wireless signal group discriminator 33 outputs a control signal that turns the switch 34 ON. However, in cases where the received signal is not a signal for the wireless receiver 2, the wireless signal group discriminator 33 outputs a control signal that turns the switch 34 OFF. In addition, the wireless signal group discriminator 33 outputs the result of discriminating the group to which the received signal belongs to the data demodulator 35 in cases where the received signal is a signal for the wireless receiver 2.
The switch 34 is turned ON and OFF in accordance with the control signal that is input via the wireless signal group discriminator 33. As a result, in cases where the received signal is a signal for the wireless receiver 2, the received signal input via the wireless signal receiver 31 is output to the data demodulator 35 and, in cases where the received signal is transmitted for other receivers, the received signal is not output to the data demodulator 35 and the processing is terminated.
When the result of discriminating the group to which the received signal belongs is input from the wireless signal group discriminator 33, the data demodulator 35 extracts the waveform of the ID signal corresponding to the group from the second or higher-order statistic properties database 32 and subtracts the waveform of the extracted ID signal from the received signal and obtains the data signal D2 by demodulating the signal of the subtraction result.
Operation Relating to the Wireless Transmission/Reception
Thereafter, the operation relating to the wireless transmission/reception method that is executed between a plurality of wireless transceiver devices 10 (called the ‘wireless transmission/reception operation’ hereinbelow) will be described.
In the wireless transmission/reception operation according to this embodiment, when an ID is assigned to a wireless signal (that is, a signal for transmission is generated by assigning second or higher-order statistic properties corresponding to the ID signal to the modulated signal that is associated with the ID signal), first, in the wireless transceiver 1, the data generator 20 generates a data signal D1 (S51), the data modulator 22 modulates the data signal D1 to the format suited to wireless communications, and outputs the modulated data signal D1 to the wireless signal ID assigner 23 (S52).
The wireless signal ID assigner 23 extracts a sine wave with a specified frequency as an ID signal with second or higher-order statistic properties unique to the group to which the signal for transmission belongs that is stored in the ID signal storage 21 and adds the extracted sine wave to the modulated data signal (that is, assigns an ID signal to the data signal), whereby a signal for transmission is generated (S53). The signal for transmission is output to the wireless signal transmitter 24.
The wireless signal transmitter 24 performs predetermined signal processing such as amplification, band limiting and frequency conversion and so forth with respect to the signal for transmission and transmits the wireless signal S that has undergone signal processing to the wireless receiver 2 constituting the communication partner via the antenna 24A (S54).
The wireless signal S is received by the wireless receiver 2 that exists at the periphery of the wireless transmitter 1 (in reality, the wireless transceiver device 10 in
In the wireless receiver 2, the wireless signal receiver 31 performs predetermined signal processing such as amplification, band limiting, and frequency conversion on the wireless signal S after receiving the wireless signal S (S55). Further, the wireless signal group discriminator 33 calculates the second or higher-order statistic properties (here, the cyclic autocorrelation characteristic) pertaining to the received wireless signal S (S56). Thereafter, the wireless signal group discriminator 33 compares the feature quantities of the second or higher-order statistic properties (here, the cyclic autocorrelation characteristic) unique to the group to which the received signal probably belongs that is stored in the second or higher-order statistic properties database 32 with the second or higher-order statistic properties obtained from the calculation of step S56 (S57) and discriminates the group to which the received wireless signal S belongs on the basis of the comparison result (S58). In the comparison processing and discrimination processing at this time, the wireless signal group discriminator 33 performs pattern matching by means of correlation detection and so forth between the feature quantity of the second or higher-order statistic properties stored in the second or higher-order statistic properties database 32 (here, a cyclic autocorrelation appearance pattern 62) and the cyclic autocorrelation value 61 that is obtained by means of a calculation, as per
Thereafter, the wireless signal group discriminator 33 determines whether the received wireless signal S is a signal for the wireless receiver 2 on the basis of the discrimination result in step S58 (S59). Here, in cases where the wireless signal S is a signal for the wireless receiver 2, the switch 34 is turned ON so that wireless signal S is input to the data demodulator 35 and data demodulator 35 performs data demodulation processing with respect to the wireless signal S as described hereinbelow (S60) and the processing is terminated. Thereupon, the wireless signal group discriminator 33 outputs the result of discriminating the group to which the wireless signal S belongs to the data demodulator 35 and the data demodulator 35 performs demodulation processing by extracting an ID signal waveform that is stored in the second or higher-order statistic properties database 32 on the basis of the group discrimination result and subtracting the extracted ID signal waveform from the wireless signal S. Further, in the step S59, in cases where the received wireless signal S is not a signal for the wireless receiver 2, the processing is terminated without performing demodulation processing.
The effects of this embodiment will be described next. In the wireless transmission/reception processing, the wireless signal ID assigner 23 of the wireless transmitter 1 adds a sine wave as an ID signal to the data signal that is to be transmitted and the wireless signal group discriminator 33 of the wireless receiver 2 computes the cyclic autocorrelation characteristic as the second or higher-order statistic properties of the received wireless signal and discriminates the group to which the received wireless signal belongs on the basis of the cyclic autocorrelation characteristic.
Modified Example of Wireless Transceiver Device
A variety of modified examples of the wireless transceiver device according to this embodiment will be described next.
A first modified example uses a plurality of sine waves as ID signals in the wireless transceiver device 10. In other words, the ID signal storage 21 stores, as an ID signal, a multiplexed wave that is obtained by adding a plurality of sine waves and the wireless signal ID assigner 23 generates a transmission signal by adding the ID signal stored in the ID signal storage 21 (a multiplexed wave to which a plurality of sine waves have been added) to a modulated signal that is obtained by modulating the data signal, and outputs the transmission signal thus generated. As a result, the cyclic autocorrelation characteristic is such that a correlation value peak appears at a cycle frequency that corresponds to the difference in frequency of a plurality of sine waves and, even when the number of target groups (the number of groups to which the data signal can belong) increases, a unique ID signal that is allocated to each group can be secured.
A second modified example uses a modulated signal with a predetermined signal bandwidth as an ID signal in the wireless transceiver device 10. In other words, the ID signal storage 21 stores a modulated signal with a predetermined bandwidth as an ID signal and the wireless signal ID assigner 23 generates a transmission signal by adding the ID signal stored in the ID signal storage 21 (modulated signal with a predetermined bandwidth) to the modulated signal obtained by modulating the data signal, and outputs the transmission signal thus generated. As a result, whereas, for the cyclic autocorrelation characteristic, a correlation value power peak appears close to delay time 0 (zero) at a cycle frequency that corresponds with the signal bandwidth of the ID signal, there is no correlation when the delay time is large. Accordingly, because a correlation value characteristic that differs from that with a sine wave appears, even when the number of target groups (the number of groups to which the data signal belongs) increases, a unique ID signal that is allocated to each group can be secured.
A third modified example is an example that uses a frequency autocorrelation characteristic instead of a cyclic autocorrelation characteristic as second or higher-order statistic properties in the wireless transceiver device 10. Thereupon, the ID signal storage 21 of the wireless transmitter 1 stores an ID signal with a frequency autocorrelation characteristic that is unique to the group to which the data signal belongs and the wireless signal ID assigner 23 generates a transmission signal by modulating the data signal and adding the ID signal stored in the ID signal storage 21 to the modulated signal thus obtained. In addition, the second or higher-order statistic properties database 32 of the wireless receiver 2 stores the feature quantity of the frequency autocorrelation characteristic that is unique to groups to which the received signal possibly belongs and the wireless signal group discriminator 33 computes the frequency autocorrelation characteristic for the received signal received by the wireless signal receiver 31 and compares the frequency autocorrelation characteristic obtained in the calculation and the feature quantity of the frequency autocorrelation characteristic for each group stored in the second or higher-order statistic properties database 32, before discriminating the group to which the received signal belongs.
C
x(α)=Ef[X(f)X*(f+α)] (3)
when the frequency characteristic 81 of the received signal is X(f). Here, Ef represents the expected value for the frequency f and a represents the frequency shift. Further, the bispectrum 83, which is a special example of a third-order frequency autocorrelation, is obtained by multiplying the frequency characteristic for the signal, the frequency characteristic for a signal that has undergone a frequency shift of a first predetermined amount, and a frequency characteristic for a signal that has undergone a frequency shift of a second predetermined amount. The numerical definition of the bispectrum 83 is given by:
B(f1, f2)=X(f1)X(f2)X*(f1+f2) (4)
when the frequency characteristic 81 of the received signal is X(f). By using the frequency autocorrelation characteristic in this manner, in cases where a plurality of sine waves are used as the ID signal in particular, a frequency autocorrelation peak appears at a frequency that corresponds with the frequency difference in a plurality of sine waves and, therefore, although the generation of a sine wave of a correct frequency, such as the generation of a sine wave by means of a local oscillator, is difficult, in a situation where the relative frequency difference can be accurately determined, the frequency at which the frequency autocorrelation peak appears can be accurately determined.
A fourth modified example is an example in which both a frequency autocorrelation characteristic and a cyclic autocorrelation characteristic are used as the second or higher-order statistic properties in the wireless transceiver 10. In this case, the ID signal storage 21 of the wireless transmitter 1 stores an ID signal having both a frequency autocorrelation characteristic and a cyclic autocorrelation characteristic that are unique to the group to which the data signal belongs and the wireless signal ID assigner 23 generates a transmission signal by adding the ID signal that is stored in the ID signal storage 21 to the modulated signal obtained by modulating the data signal. The second or higher-order statistic properties database 32 of the wireless receiver 2 stores both the feature quantities of the frequency autocorrelation characteristic and the cyclic autocorrelation characteristic that are unique to the groups that the received signal possibly belongs to and the wireless signal group discriminator 33 computes both the frequency autocorrelation characteristic and cyclic autocorrelation characteristic for the received signal received by the wireless signal receiver 31 and performs a comparison of both the frequency autocorrelation characteristic and cyclic autocorrelation characteristic obtained in this calculation and both the feature quantities of the frequency autocorrelation characteristic and the cyclic autocorrelation characteristic stored in the second or higher-order statistic properties database 32, and discriminates the group to which the received signal belongs. As a result, even for a plurality of received signals that possess different cyclic autocorrelation characteristics while holding the same frequency autocorrelation characteristic, discrimination of the IDs of these received signals is possible and, even when the number of target groups (the number of groups to which the data signal can belong) increases, a unique ID signal that is allocated to each group can be secured.
A fifth modified example is such that the wireless signal ID assigner 23 of the wireless transmitter 1 performs ID assignment by modulating the data signal and multiplying the modulated signal thus obtained by the ID signal. ‘Multiply’ as it used here means multiplying the modulated signal s(t) obtained by modulating the data signal by the ID signal gid(t) for each period, where the transmission signal x(t) may be
x(t)=gid(t)s(t) (5)
or, multiplied on the frequency axis (equivalent to a convolution operation on the time axis), may be as follows.
x(t)=∫gid(τ)s(t−τ)dτ (6)
Here, the ID signal storage 21 stores, as an ID signal, the ID signal so that predetermined second or higher-order statistic properties appear by modulating the data signal and multiplying the modulated signal by the ID signal. The wireless signal ID assigner 23 generates a transmission signal by modulating the data signal and multiplying the modulated signal by the ID signal stored in the ID signal storage 21. Furthermore, the second or higher-order statistic properties database 32 of the wireless receiver 2 stores feature quantities of the cyclic autocorrelation characteristic for a group to which the received signal possibly belongs and the signal waveform pattern of the ID signal. The data demodulator 35 is able to demodulate the data signal component without being affected by the ID signal component by dividing the received signal by the waveform pattern of the ID signal of the group to which the received signal belongs that is stored in the second or higher-order statistic properties database 32.
x(t)=s(t)+s(t)ej2πf
then the cyclic autocorrelation characteristic 94 when the time difference is zero is expressed by:
For this reason, when the cycle frequency a matches the frequency shift amount fc of the ID signal 92 or two times the frequency shift amount (that is, 2 fc), the correlation peak appears. Thus, by multiplying the ID signal by the data signal, the second or higher-order statistic properties can be allocated characteristically to each group to which the data signal belongs and ID allocation and discrimination can be carried out.
A sixth modified example uses a frequency autocorrelation characteristic as the second or higher-order statistic properties in place of the cyclic autocorrelation characteristic of the fifth modified example. Here, the ID signal storage 21 of the wireless transmitter 1 stores, as an ID signal, the ID signal such that a frequency autocorrelation characteristic that is unique to the group to which the data signal belongs is added by multiplying the transmission signal by the ID signal. The wireless signal ID assigner 23 generates a transmission signal by modulating the data signal and multiplying the ID signal that is stored in the ID signal storage 21 by the modulated signal thus obtained. In addition, the second or higher-order statistic properties database 32 of the wireless receiver 2 stores an ID signal waveform and the feature quantity of the frequency autocorrelation characteristic that is unique to the groups to which the received signal possibly belongs. The wireless signal group discriminator 33 computes a frequency autocorrelation characteristic for the received signal that is received by the wireless signal receiver 31 and performs a comparison between the feature quantities of the frequency autocorrelation characteristic obtained through computation and the frequency autocorrelation characteristic stored in the second or higher-order statistic properties database 32, thereby discriminating the group to which the received signal belongs. By using the frequency autocorrelation characteristic in this manner, in cases where a plurality of sine waves are used as the ID signal in particular, because the frequency autocorrelation peak appears at a frequency that corresponds to the frequency difference of the plurality of sine waves, although the generation of a sine wave of the correct frequency, such as the generation of a sine wave by means of a local oscillator, is difficult, in a situation where the relative frequency difference can be accurately determined, the frequency at which the frequency autocorrelation peak appears can be accurately determined.
A seventh modified example is an example in which both a frequency autocorrelation characteristic and a cyclic autocorrelation characteristic are used as the second or higher-order statistic properties of the fifth modified example. In this case, the ID signal storage 21 of the wireless transmitter 1 stores, as the ID signal, an ID signal such that both a frequency autocorrelation characteristic and a cyclic autocorrelation characteristic that are unique to the group to which the data signal belongs are added by multiplying the transmission signal by the ID signal. The wireless signal ID assigner 23 generates a transmission signal by modulating the data signal and multiplying the ID signal that is stored in the ID signal storage 21 by the modulated signal thus obtained. The second or higher-order statistic properties database 32 of the wireless receiver 2 stores the feature quantities of both a frequency autocorrelation characteristic and a cyclic autocorrelation characteristic that are unique to the groups to which the received signal possibly belongs. The wireless signal group discriminator 33 computes both a frequency autocorrelation characteristic and also a cyclic autocorrelation characteristic for the received signal that is received by the wireless signal receiver 31 and performs a comparison between the feature quantities of both the frequency autocorrelation characteristic and also the cyclic autocorrelation characteristic obtained through computation and the both the frequency autocorrelation characteristic and also the cyclic autocorrelation characteristic stored in the second or higher-order statistic properties database 32, thereby discriminating the group to which the received signal belongs. As a result, even for a plurality of received signals that possess different cyclic autocorrelation characteristics while holding the same frequency autocorrelation characteristic, discrimination of the IDs of these received signals is possible and, even when the number of target groups (the number of groups to which the data signal can belong) increases, a unique ID signal that is allocated to each group can be secured.
An eighth modified example is such that, when the wireless transmitter 1 transmits a wireless signal by means of multicarrier transmission, the transmission content of each subcarrier is established on the basis of the assigned ID signal (in other words, the assignment of an ID is carried out according to the transmission content of the subcarriers for multicarrier transmission). As the relationship between ID assignment at the time of multicarrier transmission and second or higher-order statistic properties according to this modified example, the relationship between ID assignment and a second-order frequency autocorrelation characteristic will be described hereinbelow. Further, ID assignment can also be carried out using the same procedure in cases where second or higher-order statistic properties other than the second-order frequency autocorrelation characteristic are used.
In multicarrier transmission, a plurality of subcarriers are transmitted in parallel with frequency spacing of Δf. Here, the transmission signal that is transmitted in the multicarrier transmission is expressed by:
Here, Sk(t) represents a transmission signal waveform for the subcarrier k; Ts represents the sampling rate, and K represents the number of subcarriers. The frequency characteristic of the transmission signal is then:
S
k(f)=0, f≧Δf or f<0, for ∀k (11)
Here, the second-order frequency autocorrelation characteristic is:
and, if we assume that α=βΔf (βεZ),
In other words, the result of multiplying each of the source signal and β adjacent subcarrier signals and then taking the sum thereof is the second-order frequency autocorrelation characteristic. However, under the condition that the sampling time interval cannot be made sufficiently small, the high frequency component that is removed from the observed frequency band determined by the sampling rate appears within a low frequency range. Here, if we assume that the observed frequency band is 0≦f≦KΔf, Equation (13) is as follows.
This modified example utilizes this characteristic, and by changing the content of the symbols transmitted so that (1) the second-order frequency autocorrelation characteristic becomes close to 0, or alternatively, (2) conversely, the peak appears, given a predetermined frequency shift amount, an ID can be assigned to the group to which the data signal belongs so that the second-order frequency autocorrelation characteristics differ.
The subcarrier thus determined (the subcarrier that is used in the ID signal transmission) and the content of the ID signal that is transmitted using the subcarrier are stored in the ID signal storage 21 of the wireless transmitter 1 and the second or higher-order statistic properties database 32 of the wireless receiver 2 stores the feature quantity and the signal waveform of the frequency autocorrelation characteristic that appears.
Here, a specific example of the content of the ID signal content will be described. For example, a case where an ID signal is transmitted on five subcarriers may be considered. Here, the frequency characteristic of the signal that is transmitted on these five subcarriers is Sk(f). Here, k is the index of the subcarrier that transmits an ID signal and k={0,1,2,3,4}. Further, these five subcarriers exist spaced apart at intervals of a predetermined frequency interval Δf. Here, when we assume that the frequency characteristic of the predetermined time signal gid(t) is Gid(f), and the signal to be transmitted on the five subcarriers is given by
{S0(f),S1(f),S2(f),S3(f),S4(f)}={Gid(f),Gid(f),Gid(f),Gid(f),Gid(f)} (15) then,
{S0(f),S1(f),S2(f),S3(f),S4(f)}={Gid(f),−Gid(f),Gid(f),Gid(f),Gid(f)} (17)
then,
{s0(t), s1(t),s2(t),s3(t),s4(t)}={gid(t),gid(t),gid(t),gid(t),gid(t)} (19)
using a predetermined time signal waveform gid(t). Further, in order for the feature of the frequency autocorrelation of Equation (18) to appear, the content of the ID signal of the five subcarriers, based on Equation (17), then becomes:
{s0(t),s1(t),s2(t),s3(t),s4(t)}={gid(t),−gid(t),gid(t),gid(t),gid(t)} (20).
In addition, in the modified example, the wireless signal ID assigner 23 sets the content of the ID signal that is transmitted on the subcarriers used in the ID signal transmission as the content that is stored in the ID signal storage 21 and generates a transmission signal so that the modulated signal obtained through modulation of the data signal is transmitted on another subcarrier. Further, the wireless signal group discriminator 33 computes the frequency autocorrelation characteristic, compares the frequency autocorrelation characteristic obtained through computation with the second or higher-order statistic properties that are unique to each group stored in the second or higher-order statistic properties database 32, and, based on the comparison result, discriminates the group to which the received signal belongs. Here, the data demodulator 35 is able to estimate the transmission path of the received signal based on the ID signal waveform of the discriminated group that is stored in the second or higher-order statistic properties database 32 and perform highly accurate data demodulation by utilizing the ID signal waveform. Further, in this modified example, if the subcarrier for transmitting the ID signal and the subcarrier for transmitting the data signal are divided, the ID signal can be transmitted at the same time as the data signal is transmitted. However, if only the ID signal is transmitted on the subcarrier, IDs that are unique to a multiplicity of groups can be allocated.
In addition, in this modified example, the wireless signal ID assigner 23 are also able to set the signal that is transmitted on the subcarrier used for the ID signal transmission so that there is a concentration of signal energy in a predetermined frequency component. Specifically, a sine wave of a predetermined frequency is stored in the ID signal storage 21 and, as a result of the wireless signal ID assigner 23 making settings so that a stored sine wave of a predetermined frequency is transmitted on the subcarrier that is used for ID signal transmission, there is a concentration of signal energy in a predetermined frequency component within the subcarrier. As a result of the concentration of signal energy in the predetermined frequency component, second or higher-order statistic properties that are unique to the group to which the received signal belongs can be made to appear prominently and highly accurate ID detection can be carried out. Further, settings may also be made to transmit an ith transmission symbol of a digital signal instead of using the sine wave as the transmission signal
a(i)=ej2πki (21).
Here, an example of transmission symbols when k=⅛ is shown in
A ninth modified example uses only some of the subcarriers during multicarrier transmission, that is, the symbol input to the unused subcarriers is zero (no input). Here, the ID signal storage 21 stores non-input subcarriers and ‘0’ which is the input symbol of the non-input subcarrier. The wireless signal ID assigner 23 generates a transmission signal so that the signals of the non-input subcarriers stored in the ID signal storage 21 are ‘0’ and so that a modulated signal is transmitted on subcarriers other than those designated as non-input subcarriers. In this case, as shown in
Using 802.11a wireless LAN, a short training signal is transmitted by using some subcarriers in order to establish synchronization and automatic frequency control and, after effecting frequency error compensation in order to establish symbol timing synchronization and establish carrier frequency synchronization by using short training, the MAC address of the signal transmission destination can be acquired by performing error correction decoding after FFT-processing a data portion of a wireless signal frame that is transmitted using all the subcarriers, whereby the group to which the received signal belongs can be obtained.
However, because this series of data demodulation processes is required, there is the problem that a long processing time is required to discriminate the group to which the data signal belongs. In contrast, according to the present invention, an ID is allocated to each group to which the wireless signal belongs by changing the placement of the subcarriers used in order to obtain different second or higher-order statistic properties and only these second or higher-order statistic properties are determined, IDs being discriminated based on the second or higher-order statistic properties thus determined. As a result, the group to which the received signal belongs can be discriminated at high speed. In this case, as per a conventional 802.11a wireless LAN, the short training symbols can be used in order to discriminate the group to which the received signal belongs at the same time as being utilized to establish symbol synchronization and carrier frequency synchronization.
A tenth modified example is such that an ID signal that fluctuates with respect to time is transmitted when the wireless transmitter 1 transmits a transmission signal. More specifically, the ID signal storage 21 stores an ID signal that adds second or higher-order statistic properties so that the frequency at which the power peak of the second or higher-order statistic properties appears changes according to the difference in the delay time. The wireless signal ID assigner 23 generates, using the ID signal stored in the ID signal storage 21, a transmission signal with second or higher-order statistic properties such that the frequency at which the power peak of the second or higher-order statistic properties appears varies according to the difference in the delay time. Further, the second or higher-order statistic properties database 32 of the wireless receiver 2 stores the feature quantities of the second or higher-order statistic properties that vary according to the delay time difference and the frequency. The wireless signal group discriminator 33 performs discrimination of the group to which the received signal belongs by computing the second or higher-order statistic properties of the received signal by varying the delay time difference and frequency and comparing the feature quantities of the second or higher-order statistic properties obtained through computation and the second or higher-order statistic properties stored in the second or higher-order statistic properties database 32.
A more specific example will be described hereinbelow.
Here, the frequency autocorrelation characteristic of signals A and B of
and the second-order frequency characteristic that considers the time difference is defined by:
C
x(α,τ,t0)=Ef[X(f,t0)X*(f+α,t0+τ) (23).
Here, if we assume that the time interval T0 of the interval integral in Equation (22) is τ0 and the frequency characteristic XA(f, t) of signal A is:
hold true for k=0,1,2, . . . ,M−1, and 0≦t0≦(M−k)τ0 . It is clear from Equation (25) that the second-order frequency autocorrelation characteristic of signal A is not dependent on the time difference kτ0 and
C
x(α,0,t0)=Cx(α,τ0,t0)=Cx(α,2τ0,t0)= . . . =Cx(α(M−1)τ0,t0) (26)
holds true for an arbitrary α. In contrast, if we assume that the frequency characteristic XB (f,t) of signal B is:
are valid for k=0,1,2, . . . ,M−1, and 0≦t0≦(M−2k−1)τ0. In other words, it can be seen that the second-order frequency autocorrelation characteristic of signal B fluctuates according to the time difference. Thus, it is clear that the second or higher-order statistic properties can vary according to the difference in the delay time (the manner in which the second or higher-order statistic properties appear changes as a result of considering the delay time). According to the modified example, by utilizing this characteristic and changing the frequency characteristic of the transmission signal using a fixed pattern according to time, the second or higher-order statistic properties are varied in accordance with the difference in the delay time. Accordingly, the assignment of an ID signal with unique second or higher-order statistic properties to groups to which the data signal possibly belongs is possible and the number of IDs that can be allocated can be increased.
An eleventh modified example uses a third or higher-order frequency autocorrelation characteristic as the second or higher-order statistic properties of the tenth modified example. Here, the ID signal storage 21 of the wireless transmitter 1 stores an ID signal that adds a frequency autocorrelation characteristic of a third or higher-order that is unique to the group to which the data signal belongs together with information on the subcarrier used for the transmission of the ID signal. The wireless signal ID assigner 23 generates a transmission signal such that the ID signal is transmitted using the subcarrier stored in the ID signal storage 21 and the modulated signal obtained through modulation of the data signal is transmitted on the other carriers. In addition, the second or higher-order statistic properties database 32 of the wireless receiver 2 stores a feature quantity of a third or higher-order frequency autocorrelation characteristic that is unique to the groups to which the signal possibly belongs. The wireless signal group discriminator 33 computes a third or higher-order frequency autocorrelation characteristic for the received signal that is received by the wireless receiver 31 and, by comparing the feature quantities of the third or higher-order frequency autocorrelation characteristic obtained through computation and the third or higher-order frequency autocorrelation characteristic that is unique to the groups to which the received signal stored in the second or higher-order statistic properties database 32 possibly belongs, the wireless signal group discriminator 33 discriminates the group to which the received signal belongs. Thus, by using a third or higher-order frequency autocorrelation characteristic, the effect of noise on the ID discrimination can be reduced and highly accurate ID discrimination is possible.
A twelfth modified example uses a cyclic autocorrelation characteristic as the second or higher-order statistic properties of the tenth modified example. Here, the ID signal storage 21 of the wireless transmitter 1 stores an ID signal to which a cyclic autocorrelation characteristic that is unique to the group to which the data signal belongs together with information on the subcarrier that is used for the transmission of the ID signal. The wireless signal ID assigner 23 generates the transmission signal such that the ID signal is transmitted on the subcarrier stored in the ID signal storage 21 and the modulated signal obtained through modulation of the data signal is transmitted on another carrier. Further, the second or higher-order statistic properties database 32 of the wireless receiver 2 stores a feature quantity of the cyclic autocorrelation characteristic that is unique to the group to which the received signal possibly belongs. The wireless signal group discriminator 33 computes a cyclic autocorrelation characteristic for the received signal that is received by the wireless signal receiver 31 and, by comparing the feature quantities of the cyclic autocorrelation characteristic obtained through computation and a cyclic autocorrelation characteristic that is unique to the groups to which the received signal possibly belongs which is stored in the second or higher-order statistic properties database 32, the wireless signal group discriminator 33 discriminates the group to which the received signal belongs. By using the cyclic autocorrelation in this way, there is no longer a need to perform a “Fourier transform of the received signal” which is required in a case where a frequency autocorrelation characteristic is employed. Hence, ID discrimination can be performed using a simple constitution.
A thirteenth modified example uses both a frequency autocorrelation characteristic and a cyclic autocorrelation characteristic as the second or higher-order statistic properties of the tenth modified example. In this case, the second or higher-order statistic properties database 32 of the wireless receiver 2 stores feature quantities of both the frequency autocorrelation characteristic and cyclic autocorrelation characteristic that are unique to the groups to which the received signal possibly belongs. The wireless signal group discriminator 33 computes both a frequency autocorrelation characteristic and a cyclic autocorrelation characteristic for the received signal that is received by the wireless signal receiver 31 and, by comparing the feature quantities of both the frequency autocorrelation characteristic and the cyclic auto correlation characteristic obtained through computation and a frequency autocorrelation characteristic and cyclic autocorrelation characteristic for each group stored in the second or higher-order statistic properties database 32, the wireless signal group discriminator 33 discriminates the group to which the received signal belongs. As a result, ID discrimination is also possible for a plurality of received signals with the same frequency autocorrelation characteristic and different cyclic autocorrelation characteristics, and the number of IDs can be secured with respect to an increase in the number of groups.
A fourteenth modified example is constituted to determine the frequency shift amount at which the peak of the second or higher-order statistic properties appears by matching the error correcting code to the feature quantities of the second or higher-order statistic properties in the wireless transceiver device and to determine the format of the ID signal in accordance with the position of this peak.
More specifically, as shown in
Further, an ID is allocated simply according to the existence of a second or higher-order statistic properties peak by using two values of 0 and 1 as the error correcting code in the fourteenth modified example. However, the size of the second or higher-order statistic properties (the power thereof) may also be allocated to multivalued error correcting code. In this case, even when the number of groups increases as a result of correspondence with multivalued error correcting code, the number of IDs can be secured and ID discrimination errors can be reduced.
Moreover, according to the fourteenth modified example, information may also be provided for the phase of the second or higher-order statistic properties. In this case, by allocating different IDs according to the phase of the second or higher-order statistic properties, the number of IDs that can be allocated can be increased. The method of providing information on the phases is particularly effective because the relative values of the phases do not vary with frequency in a flat phasing environment.
The disclosure of Japanese Patent Application No. 2006-208679 filed on Jul. 31, 2006 including specification, drawings and claims and the disclosure of Japanese Patent Application No. 2006-286741 filed on Oct. 20, 2006 including specification, drawings and claims are incorporated herein by reference in its entirety.
Number | Date | Country | Kind |
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P2006-208679 | Jul 2006 | JP | national |
P2006-286741 | Oct 2006 | JP | national |