JP2014033291A - Spectral diffusion receiving device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve a problem that it is assumed that sequence length of a diffusion code and the diffusion code are known in a conventional spectral diffusion receiving device, and demodulation of a received spectral diffusion signal cannot be performed when the sequence length of the diffusion code is not known.SOLUTION: In a spectral diffusion receiving device, a cycle of a diffusion code is obtained by estimating a peak period of a correlation output between a received spectral diffusion signal and a signal that is extracted from the received signal in a peak period estimation part 117.

Description

The present invention relates to a spread spectrum receiver for estimating a sequence length of a spread code.

In a conventional spread spectrum receiver, spread spectrum demodulation is performed on the assumption that the sequence length of a spread code is known when a spread spectrum signal is received.

As an example, the prior art described in Non-Patent Document 1 will be described. FIG. 15 shows a configuration example of a transmission / reception apparatus of a conventional spread spectrum communication system. In FIG. 15, 170 is an information modulation unit, 171 is a spread spectrum modulation unit, 172 is a spread code generation unit, 173 is a transmission antenna, 174 is a reception antenna, 175 is a spread spectrum demodulation unit, 176 is a spread code generation unit, and 177 is Represents an information demodulator. Data to be transmitted is input to the information modulation unit 170, and after information modulation, input to the spread spectrum modulation unit 171. The spread spectrum modulation section 171 performs spread modulation with the known spread code generated by the spread code generation section 172, and the spread spectrum signal subjected to the spread modulation is transmitted from the transmission antenna.

  On the receiving side, the signal received by the receiving antenna 174 is input to the spread spectrum demodulator 175. The spread code generation unit 176 generates a spread code after predicting the propagation delay time or synchronizing the spread code. Using the output from the spread code generator 176, the spread spectrum code generator 175 performs a despreading process to generate a signal that can be demodulated. The output of the spread spectrum demodulator 175 is input to an information demodulator 177 where demodulation processing for obtaining information data is performed.

Mitsuo Yokoyama “Spread Spectrum Communication System” Science and Technology Publishers, pp. 471-477 (May 1988).

  It is assumed that the spread spectrum receiver in the above-described prior art has a known spread code and a known sequence length of the spread code. Therefore, when the spread code or the sequence length of the spread code is unknown, there arises a problem that spread spectrum demodulation cannot be performed even if a spread spectrum signal is received.

  The present invention has been made to solve the above-described problem, and an object of the present invention is to provide a spread spectrum receiver that estimates the sequence length of a spreading code on the receiving side even when the sequence length of the spreading code is unknown. . Note that the spread spectrum signal is often information-modulated, and an object of the present invention is to obtain a spread-spectrum receiver capable of accurately estimating the sequence length of a spread code having periodicity from the information-modulated spread spectrum signal. .

  In order to achieve the above object, a spread spectrum receiving apparatus according to the present invention includes a spread spectrum receiving means for receiving a signal including a spread spectrum signal as a received signal, a signal extracting means for extracting a part of the received signal, And estimating means for estimating a spread sequence length of a spread spectrum signal included in the received signal using the signal extracted by the signal extracting means and the received signal.

The spread spectrum receiver according to the present invention can uniquely detect the spread sequence length without knowing the spread sequence length of the spread spectrum signal in advance.

1 shows a configuration of a spread spectrum signal transmission station assumed in the first embodiment. 1 is a basic configuration diagram of a spread spectrum receiving apparatus according to Embodiment 1. FIG. 3 is a flowchart showing the operation of the spread spectrum receiving apparatus according to the first embodiment. The figure which shows the relationship between the transmission-and-reception signal in the spread spectrum receiver of Embodiment 1, and the extracted received signal series. The figure which shows the output of correlation power when there is no phase shift at the time of correlation calculation in Embodiment 1. The figure which shows the output of correlation power in case there exists a phase shift at the time of correlation calculation in Embodiment 1. FIG. Output of correlation power at the peak detection unit output of the first embodiment. FIG. 3 is a basic configuration diagram of a spread spectrum receiving apparatus according to a second embodiment. The result of having converted the output of the electric power calculation part into the frequency domain in the spread spectrum receiver of the second embodiment. The state of the power peak value in the frequency domain when there is no phase shift during correlation calculation in the second embodiment. The state of the power peak value in the frequency domain when there is a phase shift during correlation calculation in the second embodiment. FIG. 5 is a basic configuration diagram of a spread spectrum receiver according to a third embodiment. 10 is a flowchart showing the operation of the spread spectrum reception apparatus according to the third embodiment. 10 is a flowchart showing the operation of the spread spectrum reception apparatus according to the fourth embodiment. The basic block diagram of the spread-spectrum receiver in a prior art.

Embodiment 1 FIG.
The present embodiment relates to a spread spectrum receiving apparatus, and a spread code sequence length estimation method of the apparatus will be described with reference to FIGS.

FIG. 1 shows the configuration of a spread spectrum transmitter assumed in this embodiment, where 100 is an information modulation unit, 101 is a spread spectrum modulation unit, 102 is a spread sequence unit, and 103 is a spread spectrum signal. FIG. 2 shows the configuration of the spread sequence length estimation unit of the spread spectrum reception apparatus according to the present embodiment, where 110 is a spread signal reception unit, 111 is an extracted signal length setting unit, 112 is a signal extraction unit, and 113 is a spread sequence. A length estimation unit, 114 is a correlator, 115 is a power calculation unit, 116 is a peak detection unit, and 117 is a peak period estimation unit. FIG. 3 shows a processing flow of spread sequence length estimation of the spread spectrum receiver according to the present embodiment. FIG. 4 shows an example of the relationship between the received signal and the extracted received signal sequence. (A) shows no phase shift (time shift), and (b) shows a phase shift (time shift) (symbol). (C) shows the case where there is a phase shift (time shift) (when the symbol changes). FIG. 5 shows a waveform example when there is no phase shift (time shift) between the received signal and the extracted received signal sequence during correlation calculation, and FIG. 6 shows a waveform example when there is a phase shift (time shift). FIG. 7 shows the relationship between the threshold value and the peak value for detecting the peak value of the correlation power of the correlator output.

Hereinafter, the reception process according to the present embodiment will be described with reference to FIGS. First, FIG. 1 shows a configuration of a spread spectrum transmission apparatus assumed in the present embodiment, and information is modulated by an information modulation unit 100 in a transmission station. Specifically, the information to be transmitted is modulated in units of time symbols for a fixed time using a modulation scheme such as BPSK (Binary Phase Shift Keying), QPSK (Quadrature Phase Shift Keying), or the like. Also, in the spread spectrum modulation section 101, the information modulated by the information modulation section 100 is spread spectrum modulated by the spread spectrum sequence generated by the spread sequence section 102 and transmitted. The spread spectrum signal 103 to be transmitted is a signal that changes in units of chip time, and there are a large number of chips in one data symbol time. As a result, the frequency band in which the spread spectrum signal subjected to the spread modulation is transmitted is wider than the frequency band of the information-modulated data symbol. The receiving apparatus according to the present embodiment assumes a transmission signal subjected to spread spectrum modulation in this way.

The control procedure of the present embodiment will be described with reference to FIGS. In the spread spectrum receiver, the received signal obtained by sampling the spread spectrum signal at a predetermined time interval is stored in the spread signal receiving unit 110 (step 120). Next, the extracted signal length setting unit 111 sets a signal length N (N is a positive integer) to be extracted from the accumulated signal (step 121). Here, the signal length is usually expressed by the number of samples, but other methods may be used. The signal extraction unit 112 extracts a signal corresponding to the signal length N from the signals accumulated in the spread signal reception unit 110 according to the signal length N set by the extraction signal length setting unit 111 (step 122). Here, the signal length set by the extracted signal length setting unit 111 needs to be shorter than the original spreading period of the spread signal. The spread sequence length estimation unit 113 uses the signal extracted by the signal extraction unit 112 as a reference signal, measures the correlation value between the reference signal and the reception signal while shifting the reception signal samples accumulated in the spread signal reception unit 110, The time period of the peak of the correlation value is estimated as the spreading sequence length (step 123).

Specific processing in step 123 will be described. The spread sequence length estimation unit 113 uses the complex conjugate value of the signal extracted by the signal extraction unit 112 in the correlator 114 as a reference signal, and performs a correlation operation with the received signal sample accumulated in the spread signal reception unit 110. Here, correlator 114 is configured as a correlator having N stages (N is a value set by extraction signal length setting section 111). Specifically, the correlation calculation with the reference signal is performed while shifting the received signal samples accumulated in the spread signal receiving unit 110 in time, and the correlation coefficient is calculated with respect to various timings of the received signal samples. The output of the correlator 114 is input to the power calculation unit 115, and the correlation power is calculated.

FIG. 4 shows an example of the relationship between the received signal and the extracted received signal sequence. In FIG. 4, “no phase shift” is a state in which a received signal sequence is extracted from one information symbol, and “having a phase shift” is a state in which a received signal sequence is extracted from two straddling information symbols. Represents. Depending on the presence / absence of this phase shift, the temporal output waveform of the correlation power, which is the output of the power calculation unit 115, changes.

When there is no phase shift between the received signal and the extracted received signal sequence as shown in FIG. 4 (a), a correlation value peak regularly exceeding the power of 50 dB is obtained for each period as shown in FIG. It is done. In FIG. 5, the horizontal axis represents the sample timing of the received signal for correlation calculation, and the vertical axis represents the output value of the correlation power. On the other hand, when there is a phase shift, a received signal sequence is extracted from two straddling information symbols as shown in FIG. This extracted received sequence has a large correlation value when two information symbols have the same value (corresponding to FIG. 4B), and has a different value when the two information symbols have different values (FIG. 4C). Correspondence) is a small correlation value. As a result, as shown in FIG. 6, the peak value of the correlation power occurs irregularly.

The output of the power calculation unit 115 in FIG. 2 is input to the peak detection unit 116, and peak detection is performed. FIG. 7 shows an example of a peak occurrence situation in order to explain the operation of the peak detection unit 116. Here, the peak value generation time interval (sample interval) is M, which is larger than the extracted signal length N set by the extracted signal length setting unit 111 and is not known. In FIG. 7, the peak values P (1), P (M + 1), and P (2M + 1) are obtained in the order of the sample time. Here, P (M + 1) has the maximum value among the three peak values. The peak detection unit 116 sets a threshold value Pth of the following expression, regards a value higher than Pth as a peak, and extracts a time (sample number) at which the peak appears.

Pth = α · Pmax (1)
Here, Pmax is a maximum peak value, and α is a coefficient of 0 <α <1.

Information regarding the peak value detected by the peak detection unit 116 and its sample number is input to the peak period estimation unit 117. The peak period estimation unit 117 takes a statistical value relating to the time interval (or sample interval) of the peak value, and estimates and outputs a statistically frequent time interval as the sequence length of the spreading code. However, those having a peak value generation cycle shorter than N are not estimated values.

As described above, it is possible to estimate the sequence length of the spread code on the receiving side by measuring the correlation with the received signal sequence extracted for various received signal timings and calculating the peak period of the correlation. A possible spread spectrum receiver is obtained.

Embodiment 2. FIG.
While the first embodiment relates to a spread spectrum receiver that estimates the spread sequence length in the time domain, this embodiment discloses a spread spectrum receiver that estimates the spread sequence length in the frequency domain.

FIG. 8 shows the configuration of the spreading sequence length estimation unit in the present embodiment. In FIG. 8, 140 is a spread signal receiving unit, 141 is an extracted signal length setting unit, 142 is a signal extraction unit, 143 is a spread sequence length estimation unit, 144 is a correlator, 145 is a power calculation unit, and 146 is a time-frequency domain. Conversion 147 indicates a peak detection unit, and 148 indicates a peak period estimation unit. The operation of the time-frequency domain conversion unit 146, the peak detection unit 147, and the peak period estimation unit 148 that are different from the configuration of the present embodiment and the first embodiment will be mainly described.

In the present embodiment, the output of power calculation unit 145 after the correlation calculation is input to time-frequency domain conversion unit 146. A process of converting the time sample from the time domain to the frequency domain is performed on the time sample by the output of the power calculation unit 145 input to the time-frequency domain conversion unit 146. For the process of converting from the time domain to the frequency domain, for example, FFT (Fast Fourier Transform) may be used. In FFT, for example, calculation is generally performed in units of powers of 2 (number of points: K). FIG. 9 shows the result of converting the output of the power calculator 145 from the time domain to the frequency domain. When a peak value with periodicity occurs in the power of the correlation calculation, a peak with periodicity occurs even when converted into the frequency domain. The peak generation period F in the frequency domain seen in FIG. 9 has the relationship shown in Expression (2).

F = K / M (2)

Here, M is the peak generation period in the time domain, and is the sequence length of the spreading code. FIG. 10 shows the state of power peak values in the frequency domain when there is no phase shift at the time of correlation calculation and FIG. 11 shows the phase shift at the time of correlation calculation. In the frequency domain, a peak value of periodic power is obtained for both cases where there is a phase shift between the received signal and the extracted received signal series.

Next, the output of the time-frequency domain conversion unit 146 is input to the peak detection unit 147, and peak detection is performed as in the first embodiment. The output of the peak detection unit 147 is input to the peak period estimation unit 148, and the peak generation period on the frequency domain is estimated by the same method as in the first embodiment. The difference from the first embodiment regarding the peak period estimation unit 148 needs to be converted into the estimation result of the peak generation period on the time domain based on the estimation result F of the peak generation period on the frequency domain. There is a point. Specifically, by using the relationship of Equation (2), the estimation result of the peak generation period on the frequency domain is used to estimate the sequence length of the spreading code in the time domain based on Equation (3). It needs to be converted to the value M ′.

M '= K / F (3)

As described above, in the present invention, the sequence length of a spread code having periodicity can be estimated from an information-modulated spread spectrum signal. Even when peaks occur irregularly in the time domain, when converted to the frequency domain, a stable peak generation interval F can be obtained, and the generation interval F can be stably measured. As a result, it is possible to obtain a spread spectrum receiver that can estimate the period of peak power by correlation calculation after conversion from the time domain to the frequency domain, and can improve the estimation accuracy of the sequence length of the spread code.

Embodiment 3 FIG.
In the first and second embodiments, the sequence length period of the spreading code is estimated, whereas in this embodiment, the spreading sequence is determined by determining whether the sequence length period can be estimated and estimating the spreading period. The length estimation process will be described.

FIG. 12 shows the configuration of the spread spectrum transmitter assumed in the present embodiment, and a spread sequence length estimation availability determination unit 118 is further added to the configuration of the spread spectrum receiver in FIG. 1 (FIG. 1). Yes. Further, a configuration in which a spreading sequence length estimation availability determining unit is added to the configuration of the spread spectrum receiving apparatus (FIG. 8) in the second embodiment is also included in the present embodiment, but the description is omitted. FIG. 13 shows an operation flow in the present embodiment. Hereinafter, the present embodiment will be described with reference to FIGS.

As shown in the flow of FIG. 13, the spread spectrum receiving apparatus accumulates the received signals input at a predetermined sampling interval in the spread signal receiving unit 110 (step 150). Next, the extracted signal length setting unit 111 sets a signal length N (N is a positive integer) to be extracted from the accumulated signal (step 151). Here, the signal length N is assumed to be shorter than the period M of the spreading sequence (N <M). The operation for extracting the received signal sequence (step 152) and the operation for estimating the spread sequence length (step 153) are the same as those in the first and second embodiments, and therefore will not be described.

The signal length N set in step 151 may be sufficiently smaller than the number of samples M corresponding to the original spreading sequence period. In this case, since the S / N of the peak value of the power of the correlator output may not be sufficiently obtained, there is a possibility that the sequence length of the spreading code cannot be estimated. Therefore, in the present embodiment, the signal length N set by the extracted signal length setting unit 111 is sequentially changed (for example, increased by a power of 2), and is repeated until a spread sequence length estimation result is obtained (step 154). . Specifically, the spread sequence length estimation availability determination unit 118 in the spread spectrum transmitter (FIG. 12) receives an output related to the peak period and the accuracy of the peak period from the peak period estimation unit 117, and based on the accuracy information Determine if length estimation was done properly. If spread sequence length estimation is not properly performed in the spread sequence length estimation enable / disable determining unit 118 (step 154), the signal length N set by the extracted signal length setting unit 111 is sequentially changed (for example, a power of 2) This is repeated until the spreading sequence length estimation result is obtained (step 155). If it is determined that the estimated spreading sequence length is appropriate, the spreading sequence length estimation process is stopped (step 154).

  As described above, in the present invention, in order to estimate the sequence length of a spread code having periodicity from an information-modulated spread spectrum signal, the sequence length of a repeated spread code is changed while changing the sequence length setting that defines the number of correlators. By performing the estimation, it is possible to obtain a spread spectrum receiver capable of improving the estimation accuracy of the sequence length of the spread code.

Embodiment 4 FIG.
In the third embodiment, the signal length N is sequentially updated depending on whether or not the spread sequence length estimation is properly performed. In the present embodiment, however, the spread sequence length is further increased when the signal length N reaches the maximum value. An embodiment in which a measure for stopping estimation is provided.

As shown in the flow of FIG. 14, the received signal input at a predetermined sampling interval is input to the spread signal receiving unit 110 (step 160). Next, the extracted signal length setting unit 111 sets a signal length N (N is a positive integer) to be extracted from the accumulated signal (step 161). The set signal length N is shorter than the original spreading sequence length M (N <M). The operation for extracting the received signal sequence (step 162), the operation for estimating the spread sequence length (step 163), and the operation to be repeated until the spread sequence length estimation result is obtained (step 164) are the same as in the third embodiment. Therefore, the explanation is omitted.

If the original spreading sequence length M is not known, N may be sufficiently smaller than M. In this case, since the S / N of the peak value of the power of the correlator output may not be sufficiently obtained, there is a possibility that the sequence length of the spreading code cannot be estimated. Therefore, when the spreading sequence length estimation is not properly performed (step 164), the spreading sequence is changed while sequentially changing the signal length N set by the extracted signal length setting unit 111 (for example, increasing by a power of 2). The process is repeated until a length estimation result is obtained (step 165). The extracted signal length setting unit 111 determines whether or not the signal length N has reached the maximum signal length setting (step 166). If the maximum sequence length has not been reached, the process returns to step 161 while sequentially increasing the signal length N. If the extracted signal length setting unit 111 determines that the signal length N has reached the maximum sequence length setting value, the spread sequence length estimation process is stopped.

With the above control, the sequence length of the repetitive spreading code can be estimated while changing the sequence length setting that defines the number of correlator stages within the range of the signal length N up to the set maximum value. As a result, it is possible to obtain a spread spectrum receiver capable of improving the estimation accuracy of the sequence length of the spread code within the range of the signal length N up to the set maximum value.

100: information modulation unit 101: spread spectrum modulation unit 102: spread sequence unit 103: spread spectrum signal 110: spread signal reception unit 111: extracted signal length setting unit 112: signal extraction unit 113: spread sequence length estimation unit 114: correlator 115: Power calculation unit 116: Peak detection unit 117: Peak period estimation unit 118: Spreading sequence length estimation availability determination unit 130, 132, 134: Transmission / reception signal 131, 133, 135: Extracted received signal sequence 140: Spreading signal Reception unit 141: Extracted signal length setting unit 142: Signal extraction unit 143: Spreading sequence length estimation unit 144: Correlator 145: Power calculation unit 146: Time-frequency domain conversion 147: Peak detection unit 148: Peak period estimation unit 170: Information modulator 171: Spread spectrum modulator 172: Spread code generator 173, 174: Antenna 175: Spectrum Le spread demodulation unit 176: spreading code generating unit 177: information demodulating unit

Claims (7)

Spread spectrum receiving means for receiving a signal including a spread spectrum signal as a received signal;
Signal extraction means for extracting a part of the received signal;
Estimating means for estimating a spread sequence length of a spread spectrum signal included in the received signal using the signal extracted by the signal extracting means and the received signal;
A spread spectrum signal receiving apparatus comprising: The estimation means includes
Correlation calculation means for performing a correlation calculation with the received signal using the signal extracted by the signal extraction means as a reference signal;
Power calculating means for calculating the power value of the output of the correlation calculating means;
Peak detection means for detecting the peak value of the power value based on the output of the power calculation means;
A peak period estimating means for estimating a period of occurrence of a peak based on an output of the peak detecting means and outputting as a sequence length of a spreading code;
The spread spectrum receiver according to claim 1, further comprising: The estimation means includes
Correlation calculation means for performing a correlation calculation with the received signal using the signal extracted by the signal extraction means as a reference signal;
Power calculating means for calculating a power value for the output of the correlation calculating means;
Time-frequency domain conversion means for converting the output of the power calculation means from the time domain to the frequency domain;
Peak detection means for detecting a peak value of power based on the output of the time-frequency domain conversion means;
A peak period estimation means for estimating a period in which a peak occurs in the frequency domain using the output of the peak detection means, and converting and outputting the sequence length of a spreading code in the time domain;
The spread spectrum receiver according to claim 1, further comprising: The correlation calculation means includes
Complex conjugate calculation means for converting the signal extracted by the signal extraction means into a complex conjugate value;
Arithmetic means for performing a correlation operation with the received signal using the signal converted into a complex conjugate value by the complex conjugate calculation means as a reference signal;
The spread spectrum receiver according to claim 2, comprising: 2. An estimation capability determination unit that determines whether estimation is possible based on a result of estimation by the estimation unit, and that determines whether to repeatedly estimate a sequence length of a spread code based on the determination. The spread spectrum signal receiver described. It is provided with signal length determination means for determining whether or not the signal length extracted by the signal extraction means has reached a set maximum value, and determining whether or not to repeatedly estimate the sequence length of the spread code based on the determination. The spread spectrum signal receiving apparatus according to claim 5. A spread spectrum receiving step for receiving a signal including a spread spectrum signal as a received signal;
A signal extraction step of extracting a portion of the received signal;
An estimation step of estimating a spread sequence length of a spread spectrum signal included in the reception signal using the signal extracted by the signal extraction step and the reception signal;
A spread spectrum signal receiving method comprising:

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