JP2019169904A - Receiver unit, communication device, and signal-to-noise ratio calculation device - Google Patents

Abstract

To calculate the signal-to-noise ratio (SNR) of an input signal subjected to direct spread spectrum.SOLUTION: An input signal is subjected to frequency conversion in a RF section 110, before being converted into a signal SR1 by an A/D converter 120. A back diffusion part 130 outputs a signal SR2 by executing back-diffusion of the signal SR1 with a spread code of code length L. A first power calculation section 160 calculates a first reception power P1, i.e., the power of the signal SR1 before diffusion. A second power calculation section 165 calculates a second reception power P2, i.e., the power of the signal SR2 after back-diffusion. A SNR calculation part 170 calculates the SNR so as to become a value obtained by dividing a value (P2-P1/L), subtracting a value dividing the first reception power P1 by the code length L from the second reception power P2, by a value (P1-P2) obtained by subtracting the second reception power P2 from the first reception power P1.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a receiving apparatus, a communication apparatus, and a signal-to-noise ratio calculating apparatus, and more specifically, to calculate a signal-to-noise ratio (SNR) of a received direct spread spectrum signal. About.

  In recent years, in a communication system that realizes long-distance communication, a direct spread spectrum method that suppresses noise by despreading on the receiving side after direct transmission of a modulated signal is often used (for example, Non-patent document 1).

  In Japanese Patent Laid-Open No. 8-32552 (Patent Document 1), in a system employing a direct spread spectrum system, noise power (N) is approximated by the power of a received signal, and signal power ( S) is approximated to calculate SNR, which is the ratio of noise power to signal power.

JP-A-8-32552 (paragraph 0018)

Nakagawa Masao and Otsuki Tomoaki, “Mobile Communication (Electronic Information and Communication Lecture Series D-5)”, edited by the Institute of Electronics, Information and Communication Engineers, March 31, 2009, p. 66

  However, the technique described in Patent Document 1 has a problem that the SNR estimation accuracy deteriorates in the case of short-range communication in which the noise power cannot be approximated by the power of the received signal. Similarly, even when the spreading code length for spreading the modulation signal is short, the signal power cannot be approximated by the power after despreading, and there is a problem that the estimation accuracy of SNR deteriorates.

  The present invention has been made in view of the above-described problems, and an object of the present invention is to calculate the SNR of a directly spread spectrum received signal with high accuracy.

  One aspect of the present invention is a receiving device that directly receives a spread spectrum signal, and includes a despreading unit, first and second power calculation units, and a signal-to-noise ratio calculation unit. The despreading unit despreads the received signal, which is a direct spread spectrum signal, with a spreading code having a code length of L bits (L: natural number). The first power calculation unit calculates first received power that is the power of the received signal before despreading. The second power calculating unit calculates second received power that is the power of the received signal after despreading by the despreading unit. The signal-to-noise ratio calculation unit calculates a signal-to-noise ratio obtained by dividing the signal power of the received signal by the noise power based on the output of the first power calculation unit and the output of the second power calculation unit. The signal-to-noise ratio calculation unit subtracts the value obtained by dividing the first received power by L (code length) from the second received power, and the value obtained by subtracting the second received power from the first received power. The signal-to-noise ratio is calculated so as to be a value divided by.

  In another aspect of the present invention, a communication device that directly communicates with a spread spectrum signal includes the receiving device and a transmitting device. The transmission device includes a modulation unit and a spreading unit. The modulation unit modulates transmission data by one modulation method selected from a plurality of predetermined modulation methods according to the signal-to-noise ratio calculated by the signal-to-noise ratio calculation unit of the receiving apparatus. A modulation signal is generated. The spreader outputs a transmission signal by directly spectrum-spreading the modulated signal modulated by the modulator using a spread code having a code length of L bits.

  In still another aspect of the present invention, there is provided a signal-to-noise ratio calculation apparatus for calculating a signal-to-noise ratio of a reception signal that is a direct spread spectrum signal, wherein the first reception is the power of the reception signal before despreading. A first value obtained by subtracting the second received power, which is the power of the signal after despreading of the received signal by the spreading code having a code length of L bits, from the power, and the first received power is L (code length) The signal-to-noise ratio is calculated so as to be a value obtained by dividing a second value obtained by subtracting the divided value from the second received power.

  According to the present invention, it is possible to calculate the SNR of a received signal with high accuracy even in short-range communication in which noise power cannot be approximated by the power of the received signal, and even when the spreading code length is short.

2 is a block diagram showing a configuration of a receiving apparatus that receives a direct spread spectrum signal according to Embodiment 1. FIG. It is a functional block diagram which shows the structure of the de-spreading part shown by FIG. It is a block diagram explaining the 1st structural example of the signal noise electric power calculation part shown by FIG. It is a block diagram explaining the 2nd structural example of the signal noise power calculation part shown by FIG. 6 is a block diagram showing a configuration of a communication apparatus according to Embodiment 2. FIG.

  Embodiments of the present invention will be described below in detail with reference to the drawings. In the following, the same or corresponding parts in the drawings are denoted by the same reference numerals, and the description thereof will not be repeated in principle.

Embodiment 1 FIG.
FIG. 1 is a block diagram illustrating a configuration of a receiving apparatus that receives a direct spread spectrum signal according to the first embodiment.

  Referring to FIG. 1, receiving apparatus 100 includes an RF (Radio Frequency) unit 110, an A / D (Analog / Digital) converter 120, a despreading unit 130, a demapping unit 140, and an error correction decoding unit 150, A first power calculation unit 160, a second power calculation unit 165, and an SNR calculation unit 170 are provided. The SNR calculation unit 170 includes a signal noise power calculation unit 180 and a ratio calculation unit 190.

  The RF unit 110 performs frequency conversion on a reception signal (direct spectrum spread signal) generated from a radio wave received by an antenna (not shown) to generate a reception signal having a spread code frequency. Further, the RF unit 110 amplifies the received signal having the frequency of the spread code to a necessary signal level and outputs the amplified signal. The A / D converter 120 converts the analog reception signal output from the RF unit 110 into a digital signal, and outputs a signal SR1 that is a digital signal.

  Despreading section 130 despreads signal SR1 with a spreading code having a predetermined code length, and outputs signal SR2 that is a signal after despreading. By this despreading process, the noise power included in the signal SR2 is reduced to 1 / L according to the code length (L bits, L: natural number) of the spread code as compared with the noise power included in the signal SR1 before despreading. .

FIG. 2 is a functional block diagram showing the configuration of the despreading unit 130.
Referring to FIG. 2, despreading section 130 includes low-pass filters (denoted as LPF in the figure) 131, 132, clock oscillator 133, spreading code generator 134, and multiplier 135.

  The cutoff frequencies of the low-pass filters 131 and 132 are designed to remove noise outside the signal band before despreading from the signal SR1. The clock oscillator 133 generates a clock signal having a spread code frequency. The spread code generator 134 generates a spread code having a code length of L bits, which is the same as that used on the direct spread spectrum signal transmission side according to the clock signal. The multiplier 135 outputs a signal obtained by multiplying the output signal of the low-pass filter 131 and the spreading code by the spreading code generator 134. By despreading, the original narrowband signal can be obtained. The output signal of the multiplier 135 is further passed through the low-pass filter 132, and the despread signal SR2 is output as the output signal of the despreading unit 130.

  Referring to FIG. 1 again, demapping section (demodulating section) 140 demaps signal SR2 after despreading and converts it to a bit string. The demapping unit (demodulating unit) 140 generates a bit string of a digital value from the signal SR2 by demodulation according to the modulation method. As a modulation method, any digital modulation method such as BPSK (Binary Phase Shift Keying), QPSK (Quadrature Phase Shift Keying), or QAM (Quadrature Amplitude Modulation) can be used.

  The error correction decoding unit 150 outputs received data by performing error correction decoding of the demapped bit string. The error correction decoding unit 150 generates a final received data string by performing error correction decoding according to the error correction code scheme employed at the time of transmission. Any method can be applied to the error correction code.

  When the error correction code is not used, the receiving apparatus does not have an error correction decoding unit, and the data sequence converted by the demapping unit (demodulation unit) 140 is used as it is as a final received data sequence.

First power calculating section 160 calculates signal SR1, that is, power P1 of the received signal before despreading. Here, assuming that the signal power is S and the noise power N, the power P1 calculated by the first power calculation unit is expressed by the following equation (1).
P1 = S + N (1)

Second power calculation section 165 calculates signal SR2 output from despreading section 130, that is, power P2 of the received signal after despreading. The power P2 calculated by the second power calculation unit 165 is expressed by the following equation (2).
P2 = S + N / L (2)

  The power P1 corresponds to “first received power”, and the power P2 corresponds to “second received power”. The SNR calculator 170 calculates the SNR of the received signal based on the powers P1 and P2 output from the first and second power calculators 160 and 165. That is, the SNR calculation unit 170 corresponds to an example of a “signal to noise calculation unit”.

  Here, assuming only long-distance transmission and assuming that the noise power N is very large with respect to the signal power S (S << N), the equation (1) is obtained by approximating S + N≈N. Can be considered as P1 = N. Further, assuming that the spreading code length L is sufficiently long and the noise component can be sufficiently reduced by despreading (L >> N), P2 in the equation (2) is obtained by approximating N / L≈0. = S. Therefore, when these assumptions are satisfied, the SNR can be estimated by the calculation of P1 / P2, as in Patent Document 1.

  However, when a direct spread spectrum signal is transmitted and received at a short distance, the noise power N applied during transmission is not so large with respect to the signal power S, and it is not appropriate to approximate S + N≈N. Also, when the spreading code length is short, it is not appropriate to approximate N / L≈0. Therefore, in these cases, the error with respect to the actual (S / N) becomes large in the SNR estimation value according to (P1 / P2) in Patent Document 1.

  Therefore, in the present embodiment, the signal noise power calculation unit 180 uses the simultaneous equations of the equations (1) and (2) for the powers P1 and P2 by the first power calculation unit 160 and the second power calculation unit 165. By solving, the signal power S and the noise power N are calculated.

Here, the results of solving equations (1) and (2) for S and N are shown by the following equations (3) and (4).
S = (L / (L-1)) * P2- (1 / (L-1)) * P1 (3)
N = (L / (L-1)) * P1- (L / (L-1)) * P2 (4)

FIG. 3 shows a first configuration example of the signal noise power calculation unit 180.
Referring to FIG. 3, the signal noise power calculation unit 180 includes a first multiplication unit 181, a second multiplication unit 182, a third multiplication unit 183, a first subtraction unit 186, and a second subtraction unit. 187.

  The first multiplication unit 181 outputs a value obtained by multiplying the power P2 output from the second power calculation unit 165 by a coefficient L / (L−1) based on the spreading code length L. Second multiplication section 182 outputs a value obtained by multiplying power P1 output from first power calculation section 160 by coefficient 1 / (L−1) based on spreading code length L. The third multiplication unit 183 outputs a value obtained by multiplying the power P1 output from the first power calculation unit 160 by a coefficient L / (L−1) based on the spreading code length L.

  The first subtracting unit 186 subtracts the output of the second multiplying unit 182 from the output of the first multiplying unit 181 to calculate the power estimated value Q1 = (L / (L−1)) × P2− (1 / (L-1)) × P1 is output. The second subtraction unit 187 subtracts the output of the first multiplication unit 181 from the output of the third multiplication unit 183 to estimate the power value Q2 = (L / (L−1)) × P1− (L / (L-1)) × P2 is output. As a result, the estimated power values Q1 and Q2 output from the first subtracting unit 186 and the second subtracting unit 187 as output signals from the signal noise power calculating unit 180 are the right sides of the equations (3) and (4). Therefore, Q1 = S and Q2 = N. That is, the power estimated values Q1 and Q2 are estimated values of the signal power S and the noise power N.

  Therefore, the ratio calculation unit 190 in FIG. 1 can calculate the SNR (S / N) by calculating the ratio (Q1 / Q2) of the power estimation values Q1 and Q2 by the signal noise power calculation unit 180.

FIG. 4 shows a second configuration example of the signal noise power calculation unit 180.
Referring to FIG. 4, the signal noise power calculation unit 180A includes a fourth multiplication unit 184, a fifth multiplication unit 185, a third subtraction unit 188, and a fourth subtraction unit 189.

  The fourth multiplier 184 outputs a value obtained by multiplying the power P2 output from the second power calculator 165 by the code length L of the spreading code. The fifth multiplier 185 outputs a value obtained by multiplying the power P1 output from the first power calculator 160 by the code length L.

  The third subtracting unit 188 subtracts the power P1 output from the first power calculating unit 160 from the output of the fourth multiplying unit 184. The fourth subtractor 189 subtracts the output of the fourth multiplier from the output of the fifth multiplier 185.

Through the above processing, the power estimation values Q3 and Q4 output from the third subtraction unit 188 and the fourth subtraction unit 189 are Q3 = L × P2−P1 and Q4 = L × (P1−P2).
Here, when Expressions (3) and (4) are modified, Expressions (5) and (6) are obtained.
S = (L / (L-1)) * (P2-P1 / L) (5)
N = (L / (L-1)) * (P1-P2) (6)

  In light of the equations (5) and (6), the power estimation values Q3 and Q4 output from the signal noise power calculation unit 180A are Q3 = (L−1) × S and Q4 = (L−1) × N. It is understood that it corresponds. As a result, the ratio of the power estimation values Q1 and Q2 calculated by the ratio calculation unit 190 in FIG. 1 is calculated by replacing Q1 with Q3 and Q2 with Q4, so that Q3 / Q4 = ((L−1) × S) / ((L-1) × N) = S / N.

  That is, according to the configuration example of FIG. 4, the SNR (S / N) estimation ratio can be calculated by calculating the ratio (Q3 / Q4) of the power estimation values Q3 and Q4 by the signal noise power calculation unit 180. it can. In the equations (3), (4) and (5), (6), S / N = (P2-P1 / L) / (P1-P2) can be calculated, so the signal noise power in FIG. 3 or FIG. It is understood that in the SNR calculation unit 170 configured by the calculation unit 180 and the ratio calculation unit 190, the SNR is calculated to be a value obtained by dividing (P2-P1 / L) by (P1-P2).

  As described above, according to the receiving apparatus that receives the direct spread spectrum signal according to the first embodiment, the noise power N is very large with respect to the signal power S that is a premise in Patent Document 1 (S << N ), The SNR can be estimated with high accuracy even in an environment that does not satisfy the above condition, that is, an environment of short-range communication. Further, when the condition that the code length L as a premise in Patent Document 1 is sufficiently long and the noise power N / L after despreading can be ignored (N / L≈0) is not satisfied, that is, the spreading code length is short. Even in this case, the SNR can be estimated with high accuracy.

  According to the configuration example of FIG. 4, the multiplication process by the signal noise power calculation unit 180 is simplified by specializing in the calculation of the ratio (SNR) between the values of the signal power S and the noise power N itself. be able to. As a modification of the configuration example of FIG. 3, even if a value obtained by multiplying the values multiplied by the first multiplier 181, the second multiplier 182, and the third multiplier 183 by an arbitrary number α is used, the SNR Can be calculated. That is, the first multiplier 181 multiplies the coefficient α × (L / (L−1)), the second multiplier 182 multiplies the coefficient α / (L−1), and the third multiplier 183. May be multiplied by a coefficient α × (L / (L−1)). Note that the SNR calculated by the SNR calculation unit 170 is displayed on a display unit (not shown) of the receiving apparatus 100, and used for grasping and monitoring the quality of received signals (propagation path characteristics such as a propagation environment) by an operator or the like. Is possible.

Embodiment 2. FIG.
A communication apparatus that employs an adaptive modulation scheme can be configured using highly accurate SNR estimation by the receiving apparatus according to the first embodiment.

FIG. 5 is a block diagram illustrating a configuration of a communication apparatus according to the second embodiment.
Referring to FIG. 5, communication apparatus 300 according to Embodiment 2 includes reception apparatus 100 and transmission apparatus 200 according to Embodiment 1.

  As described in Embodiment 1, when receiving a spread spectrum signal directly, receiving apparatus 100 generates a reception data sequence by despreading processing of the received signal, and at the same time, signal noise power calculation section 180 and ratio calculation section 190 SNR is calculated.

  Transmitting apparatus 200 includes error correction coding section 210, mapping section (modulation section) 220, and spreading section 230.

  The error correction coding unit 210 performs error correction coding on the transmission data according to the adopted error correction coding method. The error correction coding is paired with error decoding by the error correction decoding unit 150 (FIG. 1) on the receiving device side. Note that when the error correction code is not used, the error correction decoding unit 150 and the error correction code unit 210 are omitted. That is, the transmission data may be input to the mapping unit (modulation unit) 220 without being error encoded.

  Mapping section 220 employs an adaptive modulation scheme that selects a modulation scheme based on the quality of the received signal, and switches the modulation scheme in accordance with the SNR calculated in receiving apparatus 100. That is, mapping section 220 maps the transmission data after error correction code (or transmission data that has not been error encoded) according to the modulation scheme selected according to the SNR, and generates a modulated signal.

  The spreading unit 230 outputs a transmission signal by directly spectrum-spreading the modulated signal output from the mapping unit (modulating unit) 220 using a spreading code having a code length L. The transmission signal output from the spreading unit 230 is amplified by an amplifier (not shown) and then radiated from an antenna (not shown) to space.

  In the adaptive modulation method in the mapping unit 220, based on the monitoring of the propagation environment due to the radio wave environment or the like (typically, the monitoring of the SNR), among the modulation methods satisfying the required line quality (for example, bit error rate), One modulation scheme with the highest frequency utilization efficiency is selected. Therefore, when the SNR is low, a modulation method with a small multi-value number is selected, and when the SNR is high, a modulation method with a large multi-value number is selected. For example, according to the comparison between the SNR calculated by the receiving apparatus 100 and a plurality of predetermined threshold values for stratification, the higher the SNR, the more BPSK, QPSK, 16-value QAM, 64-value QAM, and It is possible to switch to using a modulation scheme having a large multilevel number in the order of 256-level QAM. That is, the mapping unit (modulation unit) 220 selects the modulation method so that the multi-value number of the modulation method to be selected increases monotonously when the SNR increases. Monotonically increasing means that the same modulation scheme is selected for a range of SNRs, and the modulation scheme selected in a larger SNR range is selected in a smaller SNR range. Means greater than.

  As described above, the adaptive modulation method is a method for realizing a transmission capacity suitable for the SNR of the communication line. However, if the estimation accuracy of the SNR is poor, the optimum transmission capacity is realized by erroneously selecting the modulation method. There is a problem that it becomes impossible.

  On the other hand, according to the communication apparatus according to the second embodiment, data communication using an appropriate modulation scheme is performed by using the SNR calculated with high accuracy from the received signal by the receiving apparatus according to the first embodiment. Therefore, the adaptive modulation method can be appropriately operated.

  In the present embodiment, the function of each block described in each of FIG. 1 to FIG. 5 is a software process in which a processor executes a program stored in advance, or an FPGA (Field-Programmable Gate Array), It can be realized by hardware processing using an LSI (Large-Scale Integrated circuit) or the like, or a combination of software processing and hardware processing.

  Also, from the configuration described in the first embodiment, the SNR calculation unit 170 (or the first and second power calculation units 160 and 165 and the SNR calculation unit 170) is extracted and “signal-to-noise ratio calculation device” is extracted. It is also possible to configure.

  The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

  100 receiver, 110 RF unit, 120 A / D converter, 130 despreading unit, 131, 132 low-pass filter (LPF), 133 clock oscillator, 134 spreading code generator, 135 multiplier, 140 demapping unit (demodulation) Section), 150 error correction decoding section, 160 first power calculation section, 165 second power calculation section, 170 SNR calculation section (signal to noise ratio calculation section), 180, 180A signal noise power calculation section, 181 first Multiplication unit, 182 second multiplication unit, 183 third multiplication unit, 184 fourth multiplication unit, 185 fifth multiplication unit, 186 first subtraction unit, 187 second subtraction unit, 188 third Subtraction unit, 189 fourth subtraction unit, 190 ratio calculation unit, 200 transmission device, 210 error correction code unit, 220 mapping unit (modulation unit), 230 spreading unit, 300 Communication device, L spreading code length, N noise power, P1, P2 power, Q1, Q2, Q3, Q4 power estimation value, S signal power, SR1 signal (before inverse transformation), SR2 signal (after inverse transformation).

Claims (6)

A receiving device that directly receives a spread spectrum signal,
A despreading unit that despreads the received signal, which is the direct spread spectrum signal, with a spreading code having a code length of L bits (L: natural number);
A first power calculator that calculates a first received power that is the power of the received signal before despreading;
A second power calculator that calculates second received power that is the power of the received signal after despreading by the despreading unit;
Signal-to-noise ratio calculation for calculating a signal-to-noise ratio obtained by dividing the signal power of the received signal by noise power based on the first and second received power calculated by the first and second power calculators With
The signal-to-noise ratio calculator is
A value obtained by subtracting the value obtained by dividing the first received power by L from the second received power is a value obtained by dividing the value by subtracting the second received power from the first received power. A receiving device that calculates the signal-to-noise ratio. The signal-to-noise ratio calculator is
A first multiplier that outputs a value obtained by multiplying the second received power by L / (L-1);
A second multiplier that outputs a value obtained by multiplying the first received power by 1 / (L-1);
A third multiplier that outputs a value obtained by multiplying the first received power by L / (L-1);
A first subtractor that outputs a value obtained by subtracting the output of the second multiplier from the output of the first multiplier;
A second subtractor that outputs a value obtained by subtracting the output of the first multiplier from the output of the third multiplier;
The receiving apparatus according to claim 1, further comprising: a ratio calculation unit that calculates the signal-to-noise ratio by dividing the output of the first subtraction unit by the output of the second subtraction unit. The signal-to-noise ratio calculator is
A fourth multiplier for outputting a value obtained by multiplying the second received power by L;
A fifth multiplier that outputs a value obtained by multiplying the first received power by L;
A third subtractor that outputs a value obtained by subtracting the first received power from the output of the fourth multiplier;
A fourth subtractor that outputs a value obtained by subtracting the output of the fourth multiplier from the output of the fifth multiplier;
The receiving apparatus according to claim 1, further comprising: a ratio calculation unit that calculates the signal-to-noise ratio by dividing the output of the third subtraction unit by the output of the fourth subtraction unit. A communication device that directly communicates with a spread spectrum signal,
The receiving device according to any one of claims 1 to 3,
The signal-to-noise ratio calculated by the receiving device is input, and transmission data is modulated by one modulation method selected according to the signal-to-noise ratio from a plurality of predetermined modulation methods. A modulation unit that generates a modulation signal, and a spreading unit that outputs a transmission signal by directly spreading the spectrum using a spreading code having a code length of L bits,
A communication device comprising a transmission device.   The modulation unit selects one modulation method so that the multi-value number of the selected modulation method increases monotonously when the signal-to-noise ratio increases, and modulates the transmission data by modulating the selected modulation method. The communication apparatus according to claim 4, wherein the communication apparatus generates a signal. A signal-to-noise ratio calculation device that calculates a signal-to-noise ratio of a received signal that is a direct spread spectrum signal,
Second received power that is the power of the signal after despreading of the received signal by a spreading code having a code length of L bits (L: natural number) from the first received power that is the power of the received signal before despread The signal-to-noise ratio is set to a value obtained by dividing a value obtained by dividing the first received power by the L by a first value obtained by subtracting the first received power from the second received power. A signal-to-noise ratio calculation apparatus characterized by calculating.

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