Receiving device and receiving program

Abstract

This disclosure aims to improve error correction capability when compensating for nonlinear distortion in a modulated signal, particularly at low modulation orders, by avoiding unnecessary distortion compensation processing and, conversely, not introducing nonlinear distortion. [Solution] In this disclosure, the equalizer 4 provided in the receiving device R controls the degree of freedom for compensating for the nonlinear distortion of the modulated signal to be lower as the modulation order of the modulated signal decreases, and controls the degree of freedom for compensating for the nonlinear distortion of the modulated signal to be higher as the modulation order of the modulated signal increases.

Description

[Technical Field]

[0001] This disclosure relates to a technique for compensating for nonlinear distortion in modulated signals. [Background technology]

[0002] In amplifiers equipped with transmitting or relaying devices, high power utilization efficiency can be achieved by setting the operating point near the saturation region. However, modulated signals with nonlinear distortion cause radiation outside the transmission band and degrade the error rate of received bits.

[0003] Therefore, techniques for compensating for the nonlinear distortion of modulated signals are disclosed in Non-Patent Documents 1 and 2 and Patent Document 1. Non-Patent Document 1 compensates for the nonlinear distortion of modulated signals using an equalizer that utilizes a Volterra series. Non-Patent Document 2 compensates for the nonlinear distortion of modulated signals using an equalizer that approximates the Volterra series with a memory polynomial in order to reduce the amount of computation.

[0004] In Patent Document 1, in order to reduce the computational load, an equalizer that approximates the Volterra series with a memory polynomial is used to compensate for the nonlinear distortion of the modulated signal. In this method, the filter coefficients of the equalizer are calculated using a known signal with fewer symbols than the number of taps in the equalizer. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] International Publication No. 2019 / 171655 [Non-patent literature]

[0006] [Non-Patent Document 1] S. Benedetto and E. Biglieri, “Nonlinear Equalization of Digital Satellite Channels,” IEEE Journal on Selected Areas in Communications, vol. 1, No. 1, pp. 57-62, Jan 1983. [Non-Patent Document 2] Yasuyoshi Noda, Shunsuke Uehashi, Shigenori Tani, Katsuyuki Motoyoshi, and Atsushi Okamura, "An Adaptive Equalization Method Applicable to Single-Carrier Broadband Transmission with Nonlinear Distortion," IEICE Technical Report, WBS2018-2, vol.118, No.51, pp.7-12, May 2018. [Non-Patent Document 3] “ETSI EN 302 307-1 V1.4.1 (2014-11)”, [online], EUROPEAN STANDARD, [Retrieved December 4, 2024], Internet <URL:https: / / www.etsi.org / deliver / etsi_en / 302300_302399 / 30230701 / 01.04.01_60 / en_30230701v010401p.pdf> [Overview of the project] [Problems that the invention aims to solve]

[0007] Incidentally, depending on the transmission path conditions (CNR: Carrier-to-Noise Ratio), the modulation scheme and error correction coding rate can be adaptively controlled using the ACM (Adaptive Coding and Modulation) method. For example, as an error correction code, an LDPC (Low-Density Parity-Check) code, which has strong resistance to AWGN (Additive White Gaussian Noise), can be applied. Here, in order to calculate the log-likelihood ratio (LLR) etc. in the pre-decoder stage, it is desirable to compensate for the nonlinear distortion of the modulated signal in the pre-likelihood ratio calculation stage.

[0008] However, Non-Patent Documents 1 and 2 and Patent Document 1 treat the degree of freedom for compensating for the nonlinear distortion of the modulated signal equally for all modulation schemes. Here, when the backoff during amplification is constant, the lower / higher the modulation order, the smaller / larger the nonlinear distortion, and therefore distortion compensation is unnecessary / necessary. Thus, especially when the modulation order is low, unnecessarily performing distortion compensation can actually introduce nonlinear distortion and degrade the error correction capability.

[0009] Therefore, in order to solve the aforementioned problems, this disclosure aims to improve error correction capability when compensating for nonlinear distortion in a modulated signal, especially when the modulation order is low, without unnecessarily performing distortion compensation processing and without introducing nonlinear distortion. [Means for solving the problem]

[0010] To solve the aforementioned problem, the equalizer in the receiving device controls the degree of freedom for compensating for the nonlinear distortion of the modulated signal to be lower as the modulation order of the modulated signal decreases, and controls the degree of freedom for compensating for the nonlinear distortion of the modulated signal to be higher as the modulation order of the modulated signal increases.

[0011] Specifically, the present disclosure relates to a receiving device for receiving a modulated signal from a transmitting device that transmits a modulated signal, comprising: an equalizer for compensating for the nonlinear distortion of the modulated signal; a demodulator for demodulating the modulated signal from which the nonlinear distortion has been compensated; and an error corrector for performing error correction on the demodulated signal, wherein the equalizer controls the degree of freedom of the compensation process for the nonlinear distortion of the modulated signal to be lower the lower the modulation order of the modulated signal, and controls the degree of freedom of the compensation process for the nonlinear distortion of the modulated signal to be higher the higher the modulation order of the modulated signal, and is applicable to wireless communication or wired communication.

[0012] This configuration allows for improved error correction capability, especially at low modulation orders, by avoiding unnecessary distortion compensation processing without introducing nonlinear distortion. Furthermore, at high modulation orders, sufficient distortion compensation processing can be performed to remove nonlinear distortion while simultaneously improving error correction capability.

[0013] Furthermore, this disclosure provides a receiving device characterized in that the equalizer controls the degree of freedom of the compensation process for the nonlinear distortion of the modulated signal to be lower the higher the coding rate of error correction of the modulated signal, and controls the degree of freedom of the compensation process for the nonlinear distortion of the modulated signal to be higher the lower the coding rate of error correction of the modulated signal.

[0014] This configuration allows for improved error correction capability, especially when the error correction coding rate is high, by avoiding unnecessary distortion compensation processing without introducing nonlinear distortion. Furthermore, when the error correction coding rate is low, sufficient distortion compensation processing can be performed to remove nonlinear distortion while simultaneously improving error correction capability.

[0015] Furthermore, this disclosure provides a receiving device characterized in that the equalizer controls the degree of freedom of the compensation process for the nonlinear distortion of the modulated signal to be lower the smaller the backoff during amplification of the modulated signal, and controls the degree of freedom of the compensation process for the nonlinear distortion of the modulated signal to be higher the larger the backoff during amplification of the modulated signal.

[0016] This configuration allows for improved error correction capability without introducing nonlinear distortion, especially when the backoff during amplification is small, by avoiding unnecessary distortion compensation processing. Furthermore, when the backoff during amplification is large, sufficient distortion compensation processing can be performed to remove nonlinear distortion while simultaneously improving error correction capability.

[0017] Furthermore, this disclosure provides a receiving device characterized in that the equalizer adjusts the weight coefficients of the first-order and third-order or higher equalizing filters to minimize an evaluation function that includes the squared error between the modulated signal, which has been compensated for nonlinear distortion, and the demodulated signal or known signal, and a regularization term of the weight coefficients of the first-order and third-order or higher equalizing filters, thereby controlling the degree of freedom of the compensation process for the nonlinear distortion of the modulated signal to a lower degree by setting a larger regularization parameter of the regularization term of the weight coefficients of the equalizing filters, and controlling the degree of freedom of the compensation process for the nonlinear distortion of the modulated signal to a higher degree by setting a smaller regularization parameter of the regularization term of the weight coefficients of the equalizing filters.

[0018] With this configuration, the degrees of freedom for compensating for the nonlinear distortion of the modulated signal can be controlled by including the regularization term of the weight coefficients of the first-order and third-order or higher equalization filters in the evaluation function.

[0019] Furthermore, this disclosure is a receiving program installed on a computer to cause the equalizer in the receiving device described above to control the degrees of freedom for compensating for the nonlinear distortion of the modulated signal.

[0020] This configuration makes it possible to provide a program that has the effects described above.

[0021] Furthermore, the inventions disclosed above can be combined as much as possible. [Effects of the Invention]

[0022] Thus, this disclosure makes it possible to improve error correction capability when compensating for nonlinear distortion in a modulated signal, especially at low modulation orders, without unnecessarily performing distortion compensation processing and without introducing nonlinear distortion. [Brief explanation of the drawing]

[0023] [Figure 1] This diagram shows the configuration of the transmission and reception system disclosed herein. [Figure 2]This figure shows the procedures for transmission and reception processing as described herein. [Figure 3] This figure shows the pre-processing and post-processing steps for distortion compensation according to this disclosure. [Figure 4] This figure shows the control of the regularization parameter according to the modulation order of this disclosure. [Figure 5] This figure shows the control of regularization parameters in response to backoff in this disclosure. [Figure 6] This figure shows the control of regularization parameters according to the coding rate of this disclosure. [Figure 7] This figure shows the amplitude and coding rate of the modulated signal in this disclosure. [Figure 8] This figure shows the amplitude and coding rate of the modulated signal in this disclosure. [Figure 9] This figure shows a table of regularization parameters for the disclosure. [Figure 10] This figure shows the interpolation curve for the regularization parameter of this disclosure. [Figure 11] This figure shows the distortion compensation of the modulated signal according to the prior art and the present disclosure. [Figure 12] This figure shows the distortion compensation of the modulated signal according to the prior art and the present disclosure. [Figure 13] This figure shows the distortion compensation of the modulated signal according to the prior art and the present disclosure. [Modes for carrying out the invention]

[0024] Embodiments of the present disclosure will be described with reference to the attached drawings. The embodiments described below are examples of the implementation of the present disclosure, and the present disclosure is not limited to these embodiments.

[0025] (Configuration of the transmission and reception system in this disclosure) Figure 1 shows the configuration of the transmission / reception system of this disclosure. Figure 2 shows the transmission and reception procedures of this disclosure. The transmission / reception system S is applicable to wireless or wired communication and comprises a transmitting device T and a receiving device R. The transmitting device T comprises an encoder 1, a modulator 2, and an amplifier 3. The receiving device R comprises an equalizer 4, a demodulator 5, an error corrector 6, a switch 7, and a regularization parameter control unit 8. In particular, in order to have the regularization parameter control unit 8 execute step S4, the receiving program for step S4 can be installed in a computer.

[0026] Transmitter T, when transmitting a modulated signal, writes the modulation scheme, backoff during amplification, and error correction coding rate into the frame header, etc. (Step S1). Encoder 1 performs encoding of the transmission signal. Modulator 2 generates the encoded modulated signal. Amplifier 3 amplifies the encoded modulated signal (Step S2).

[0027] When the receiving device R receives the modulated signal, it reads the modulation scheme, the backoff during amplification, and the coding rate for error correction from the frame header, etc. (step S3). The equalizer 4 compensates for the nonlinear distortion of the modulated signal. The demodulator 5 demodulates the modulated signal from which the nonlinear distortion has been compensated. The error corrector 6 performs error correction on the demodulated signal (step S4). The switch 7 outputs a known signal such as a pilot signal during the pull-in process and the hard judgment value of the demodulator 5, etc., as a reference signal, as described later. The regularization parameter control unit 8 will be described later.

[0028] In other words, the transmission / reception system S can adaptively control the modulation scheme and error correction coding rate using the ACM method according to the transmission path conditions (CNR). For example, the error corrector 6 can apply an LDPC code, which has strong resistance to AWGN, as the error correction code. Here, the error corrector 6 compensates for the nonlinear distortion of the modulated signal in the stage before the likelihood ratio calculation unit in order to calculate the log-likelihood ratio (LLR) etc. in the stage before the decoder.

[0029] In the prior art, regardless of the modulation method of the modulation signal, the back-off during amplification, and the coding rate of error correction, the degree of freedom of the compensation process for the non-linear distortion of the modulation signal is made equal. In the present disclosure, the regularization parameter control unit 8 controls the degree of freedom of the compensation process for the non-linear distortion of the modulation signal according to the modulation method of the modulation signal, the back-off during amplification, and the coding rate of error correction (step S4).

[0030] Then, particularly, when (1) the modulation order is low, (2) the back-off during amplification is small, or (3) the coding rate of error correction is high, by not performing the distortion compensation process unnecessarily, the error correction ability can be improved without imparting non-linear distortion.

[0031] On the other hand, particularly, when (1) the modulation order is high, (2) the back-off during amplification is large, or (3) the coding rate of error correction is low, by sufficiently performing the distortion compensation process, after sufficiently removing the non-linear distortion, the error correction ability can be improved.

[0032] (Procedure of the processing during distortion compensation of the present disclosure) The equalizer 4 includes a first-order equalization filter 41, a weight coefficient calculation unit 42, a cube value calculation unit 43, a third-order equalization filter 44, a weight coefficient calculation unit 45, an adder 46, and a subtractor 47. As a modification, the equalizer 4 may include an equalization filter of the third order or higher.

[0033] The first-order equalization filter 41 inputs the modulation signal and the additive noise x 1、n +z n as an input signal y n (see the first equation of Equation 1). The cube value calculation unit 43 calculates the cube value |x n +z n | 2 (x n +z n ). The third-order equalization filter 44 inputs the modulation signal and the additive noise x 2、n +z n as an input signal y n and the cube value |x 2 (x n +z nEnter ) (see the second equation in equation 1).

number

[0034] The first-order equalization filter 41 and the third-order equalization filter 44 can be fitted with FIR (Finite Impulse Response) filters, etc. Modulated signal and additional noise x n +z n The sample may be taken at the symbol timing of the aperture point of the eye pattern, or it may be oversampled at a sampling frequency that is P times the symbol timing.

[0035] The weight coefficient calculation unit 42 calculates the weight coefficient vector w1 of the first-order equalization filter 41, as described later (see the first equation of Equation 2, where 0, 1, ..., and M1-1 indicate tap numbers). The weight coefficient calculation unit 45 calculates the weight coefficient vector w2 of the third-order equalization filter 44, as described later (see the second equation of Equation 2, where 0, 1, ..., and M2-1 indicate tap numbers).

number

[0036] The first-order equalization filter 41 uses a weight coefficient vector w1 and an input signal vector y 1、n The inner product w1 between and T y 1、n The following is calculated (see the first equation of Equation 3 and the first term on the right-hand side of Equation 4). The third-order equalization filter 44 uses the weight coefficient vector w2 and the input signal vector y 2、n The dot product w2 between and T y 2、n Calculate (see the second equation of Equation 3 and the second term on the right side of Equation 4). Adder 46 calculates the inner product w1 T y 1、n And the dot product w2 T y 2、n The added value x between and n ^ Calculate (see formula 4).

number

number

[0037] Demodulator 5 adds up x n ^ Restore hardness judgment value etc x n-m It outputs the reference signal x. Switch 7 outputs the reference signal x n-m During the pull-in process, known signals such as pilot signals x n-m It outputs the hard judgment value of demodulator 5, etc. during the data transmission process. n-m It outputs the following. Subtractor 47 adds x n ^ And, reference signal x n-m The error value e between and n Calculate (see formula 5).

number

[0038] In this disclosure, the first-order equalization filter 41 and the third-order equalization filter 44, when ROF (Roll Off Filter) is not applied, w in one m. 1、m and w 2、m This is defined as non-zero. Here, when m=0, the reference signal x n-m The value at the same time as the present is adopted, and when m=1, the reference signal x n-m The value from one time step prior to the present is adopted. As an example, the first-order equalization filter 41 and the third-order equalization filter 44, when applying ROF, use multiple values ​​for m, for example, at the central tap of ROF, w 1、m and w 2、m It may be treated as non-zero.

[0039] The regularization parameter control unit 8 sets the regularization parameters λ1 and λ2 of the regularization terms of the weight coefficient vectors w1 and w2 of the first-order equalization filter 41 and the third-order equalization filter 44 (see the second and third terms on the right-hand side of equations 6 and 12). Generally, the regularization parameter control unit 8 sets the regularization parameters of the regularization terms of the weight coefficient vectors of the equalization filters to be larger, thereby increasing the modulation signal x n The degree of freedom for compensating for the nonlinear distortion is controlled to be lower (see the right-hand side of equations 6 and 12). On the other hand, the regularization parameter control unit 8 sets the regularization parameter of the regularization term of the weight coefficient vector of the equalization filter to a smaller value, thereby reducing the modulated signal x n This allows for greater control over the degrees of freedom in the compensation process for nonlinear distortion (see the right-hand side of equations 6 and 12).

[0040] As a first specific example, the regularization parameter control unit 8 sets the regularization parameters λ1 and λ2 of the regularization terms of the weight coefficient vectors w1 and w2 of the first-order equalization filter 41 and the third-order equalization filter 44 to be larger, thereby increasing the modulation signal x n The degree of freedom for compensating for the nonlinear distortion is controlled to be lower (see the second and third terms on the right-hand side of equations 6 and 12). On the other hand, the regularization parameter control unit 8 sets the regularization parameters λ1 and λ2 of the regularization terms of the weight coefficient vectors w1 and w2 of the first-order equalization filter 41 and the third-order equalization filter 44 to be smaller, thereby reducing the modulated signal x n This allows for greater control over the degrees of freedom in the compensation process for nonlinear distortion (see the second and third terms on the right-hand side of equations 6 and 12).

[0041] As a second specific example, the regularization parameter control unit 8 sets only the regularization parameter λ2 of the regularization term of the weight coefficient vector w2 of the third-order equalization filter 44 to a larger value, thereby increasing the modulated signal x n The degree of freedom for compensating for the nonlinear distortion is controlled to be lower (see the third term on the right-hand side of equations 6 and 12). On the other hand, the regularization parameter control unit 8 sets only the regularization parameter λ2 of the regularization term of the weight coefficient vector w2 of the third-order equalization filter 44 to be smaller, thereby reducing the modulated signal x nThis allows for greater control over the degrees of freedom in compensating for nonlinear distortion (see the third term on the right-hand side of equations 6 and 12). The first specific example is used below, but the second specific example may also be used.

[0042] The weight coefficient calculation unit 42 calculates the error value e n The expected value of the squared value E[|e n | 2 The evaluation function that minimizes the regularization term of the weight coefficient vectors w1 and w2 of the first-order equalizer filter 41 is set to minimize the weight coefficient vector w1 ^ The weight coefficient calculation unit 45 calculates the error value e n The expected value of the squared value E[|e n | 2 The evaluation function that minimizes the regularization term of the weight coefficient vectors w1 and w2 of the cubic equalization filter 44 is determined by the weight coefficient vector w2 ^ The following is calculated (see the second term on the left side of equation 6). In other words, the weight coefficient calculation units 42 and 45 calculate the weight coefficient vector w1 according to the MMSE (Minimum Mean Square Error) standard. ^ w2 ^ As such, Wiener solution w1 ^ w2 ^ It is calculating this.

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[0043] Weight coefficient vector w1 of the first-order equalization filter 41 ^ This is expressed as shown in equation 7. The weight coefficient vector w2 of the cubic equalization filter 44. ^ This can be expressed as shown in equation 8. Here, the modulation signal x n The nonlinear distortion is extremely small, and the added noise z n It is assumed that it is an AWGN.

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[0044] In equations 7 and 8, P 11 , P 12 , P 22 r1 and r2 are expressed as shown in equations 10 and 11. Here, P x P is the modulated signal power. z This is the additional noise power (see Equation 9). And E[|x| α ](α≧2) is the modulated signal x n It is the expected value of the alpha power of, and E[|z| 2 ] is additional noise z n This is the expected value of the square of (see formulas 9-11).

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number

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[0045] Thus, the regularization parameters λ1 and λ2 of the regularization terms of the weight coefficient vectors w1 and w2 of the first-order equalization filter 41 and the third-order equalization filter 44 are mutually equal to the weight coefficient vector w1 of the first-order equalization filter 41 and the third-order equalization filter 44. ^ w2 ^ This controls the regularization parameters λ1 and λ2. The regularization parameters λ1 and λ2 may be equal or different; in the prior art they were 0, but in this disclosure they are positive. As an alternative, for equalization filters of order 3 or higher, the regularization parameter of the regularization term of the weight coefficient vector can also be controlled.

[0046] The weight coefficient calculation unit 42 calculates the error value e n The squared value of |e n | 2 The weight coefficient vector w1 of the first-order equalization filter 41 is set such that the evaluation function including the regularization terms of the weight coefficient vectors w1 and w2 is minimized. ^ You may also calculate (see the first term on the left side of equation 12). The weight coefficient calculation unit 45 calculates the error value e n The squared value of |en | 2 And, the weight coefficient vector w2 of the third-order equalization filter 44 is calculated so as to minimize an evaluation function including the regularization terms of the weight coefficient vectors w1 and w2. ^ (Refer to the second term on the left side of Equation 12). That is, the weight coefficient calculation units 42 and 45 may calculate the weight coefficient vectors w1 ^ , w2 ^ in accordance with the LMS (Least Mean Square) norm or the RLS (Recursive Least Square) norm.

Equation

[0047] The weight coefficient vector w1 of the first-order equalization filter 41 ^ may be expressed as in Equation 13. The weight coefficient vector w2 of the third-order equalization filter 44 ^ may be expressed as in Equation 14. Here, w in Equation 13 1、n ^ and w in Equation 14 2、n ^ are estimated values at time n, and Δw in Equation 13 1、n ^ and Δw in Equation 14 2、n ^ are update amounts at time n, and μ1 in Equation 13 and μ2 in Equation 14 are parameters indicating the step size in the LMS norm.

Equation

Equation

[0048] Thus, the regularization parameters λ1 and λ2 of the regularization terms of the weight coefficient vectors w1 and w2 of the first-order equalization filter 41 and the third-order equalization filter 44 are each independently the weight coefficient vectors w1 of the first-order equalization filter 41 and the third-order equalization filter 44 ^ , w2 ^The regularization parameters λ1 and λ2 may be equal or different; in the prior art they were 0, but in this disclosure they are positive. As an example of modification, the regularization parameters of the regularization term of the weight coefficient vector can also be controlled for equalization filters of order 3 or higher.

[0049] (Preprocessing procedure for distortion compensation in this disclosure) The pre-processing and post-processing procedures for distortion compensation described herein are shown in Figure 3. In the pre-processing for distortion compensation, prior to the post-processing for distortion compensation, the regularization parameters λ1 and λ2 are optimized for each modulation scheme of the modulated signal, the backoff during amplification, and the coding rate of error correction (see the left column of Figure 3). In the post-processing for distortion compensation, the regularization parameters λ1 and λ2 are controlled to the optimized values ​​for each modulation scheme of the modulated signal, the backoff during amplification, and the coding rate of error correction (see the right column of Figure 3).

[0050] First, the distortion compensation preprocessing will be explained. Modulator 2, amplifier 3, and encoder 1 each fix the modulation scheme of the modulated signal, the backoff during amplification, and the coding rate of error correction to various schemes and values ​​(step S11). The regularization parameter control unit 8 changes the regularization parameters λ1 and λ2 to various values, then the equalizer 4 compensates for the nonlinear distortion of the modulated signal, the demodulator 5 demodulates the modulated signal with the nonlinear distortion compensated, and the error corrector 6 performs error correction on the demodulated signal and evaluates the error rate of the demodulated signal (step S12). The regularization parameter control unit 8 optimizes the regularization parameters λ1 and λ2 for each modulation scheme of the modulated signal, the backoff during amplification, and the coding rate of error correction (step S13). Details will be explained in Figures 4 to 10.

[0051] Next, the distortion compensation process will be explained. The receiving device R reads the modulation scheme of the modulated signal, the backoff during amplification, and the coding rate for error correction from the frame header, etc. (step S14). The regularization parameter control unit 8 controls the regularization parameters λ1 and λ2 to optimized values ​​for each modulation scheme, backoff during amplification, and coding rate for error correction of the modulated signal. Then, the equalizer 4 compensates for the nonlinear distortion of the modulated signal, the demodulator 5 demodulates the modulated signal with the nonlinear distortion compensated, and the error corrector 6 performs error correction on the demodulated signal (step S15).

[0052] Figure 4 shows the control of the regularization parameter according to the modulation order of this disclosure. The amplifier 3 and encoder 1 fix the coding rate of backoff and error correction during amplification of the modulated signal to a single value, and the modulator 2 changes the modulation method of the modulated signal to various methods (step S11).

[0053] Then, when modulator 2 sets the modulation order of the modulated signal to a lower value, and regularization parameter control unit 8 changes the regularization parameters λ1 and λ2 to various values, the error rate of the demodulated signal is lowest with larger regularization parameters λ1 and λ2 (steps S12, S13). Therefore, the regularization parameter control unit 8 sets the regularization parameters λ1 and λ2 to be larger (the regularization parameters of the third-order or higher equalization filter are also set to be larger) as the modulation order of the modulated signal decreases (step S14), thereby controlling the degree of freedom of the compensation process for the nonlinear distortion of the modulated signal to be lower (step S15).

[0054] On the other hand, when modulator 2 sets the modulation order of the modulated signal to a higher value, and regularization parameter control unit 8 changes the regularization parameters λ1 and λ2 to various values, the error rate of the demodulated signal is lowest with the smaller regularization parameters λ1 and λ2 (steps S12, S13). Therefore, the regularization parameter control unit 8 sets the regularization parameters λ1 and λ2 to be smaller (and the regularization parameters of the equalization filter of order 3 or higher) as the modulation order of the modulated signal increases (step S14), thereby increasing the degree of freedom in the compensation process for the nonlinear distortion of the modulated signal (step S15).

[0055] Furthermore, when the regularization parameters λ1 and λ2 are excessively large, the degrees of freedom for compensating for the nonlinear distortion of the modulated signal are excessively low, resulting in an excessively high error rate in the demodulated signal regardless of the modulation order of the modulated signal. Conversely, when the regularization parameters λ1 and λ2 are excessively small, the degrees of freedom for compensating for the nonlinear distortion of the modulated signal are excessively high, causing the weight coefficient vector w2 to be over-tuned, and the error rate of the demodulated signal to take an asymptotic value higher than the minimum, regardless of the modulation order of the modulated signal.

[0056] Thus, particularly when the modulation order of the modulated signal is low, avoiding unnecessary distortion compensation can improve error correction capability without introducing nonlinear distortion. Conversely, particularly when the modulation order of the modulated signal is high, performing sufficient distortion compensation can effectively remove nonlinear distortion while simultaneously improving error correction capability.

[0057] Figure 5 shows the control of the regularization parameter in response to the backoff of the present disclosure. The modulator 2 and encoder 1 fix the modulation scheme and error correction coding rate of the modulated signal to one scheme and value, while the amplifier 3 changes the backoff during amplification of the modulated signal to various values ​​(step S11).

[0058] Then, when amplifier 3 sets the backoff during amplification to a smaller value, and the regularization parameter control unit 8 changes the regularization parameters λ1 and λ2 to various values, the error rate of the demodulated signal is lowest with larger regularization parameters λ1 and λ2 (steps S12, S13). Therefore, the smaller the backoff during amplification (step S14), the larger the regularization parameters λ1 and λ2 are set (the regularization parameters of the third-order or higher equalization filter are also set), thereby controlling the degree of freedom of the compensation process for the nonlinear distortion of the modulated signal to be (step S15).

[0059] On the other hand, when amplifier 3 sets a larger backoff during amplification, and regularization parameter control unit 8 changes the regularization parameters λ1 and λ2 to various values, the error rate of the demodulated signal is lowest with the smaller regularization parameters λ1 and λ2 (steps S12, S13). Therefore, the larger the backoff during amplification (step S14), the smaller the regularization parameters λ1 and λ2 are set (the regularization parameters of the third-order or higher equalization filter are also set), thereby increasing the degree of freedom in compensating for the nonlinear distortion of the modulated signal (step S15).

[0060] Furthermore, when the regularization parameters λ1 and λ2 are excessively large, the degrees of freedom for compensating for the nonlinear distortion of the modulated signal are excessively low, resulting in an excessively high error rate of the demodulated signal regardless of backoff during amplification. Conversely, when the regularization parameters λ1 and λ2 are excessively small, the degrees of freedom for compensating for the nonlinear distortion of the modulated signal are excessively high, causing the weight coefficient vector w2 to be over-tuned, and the error rate of the demodulated signal to take an asymptotic value higher than the minimum, regardless of backoff during amplification.

[0061] Thus, by avoiding unnecessary distortion compensation processing, especially when the backoff during amplification is small, it is possible to improve error correction capability without introducing nonlinear distortion. Furthermore, by performing sufficient distortion compensation processing, especially when the backoff during amplification is large, it is possible to improve error correction capability while sufficiently removing nonlinear distortion.

[0062] Figure 6 shows the control of the regularization parameters according to the coding rate of this disclosure. Modulator 2 and amplifier 3 fix the modulation method and backoff during amplification of the modulated signal to one method and value, while encoder 1 changes the coding rate for error correction of the modulated signal to various values ​​(step S11).

[0063] Then, when the encoder 1 sets a higher error correction coding rate, and the regularization parameter control unit 8 changes the regularization parameters λ1 and λ2 to various values, the error rate of the demodulated signal is lowest with larger regularization parameters λ1 and λ2 (steps S12, S13). Therefore, the higher the error correction coding rate (step S14), the larger the regularization parameters λ1 and λ2 are set (the regularization parameters of the third-order or higher equalization filters are also set), and the lower the degree of freedom for compensating for the nonlinear distortion of the modulated signal (step S15).

[0064] On the other hand, when the encoder 1 sets the error correction coding rate to a lower value, and the regularization parameter control unit 8 changes the regularization parameters λ1 and λ2 to various values, the error rate of the demodulated signal is lowest with the smaller regularization parameters λ1 and λ2 (steps S12, S13). Therefore, the lower the error correction coding rate (step S14), the smaller the regularization parameters λ1 and λ2 are set (the regularization parameters of the third-order or higher equalization filters are also set), thereby controlling the degree of freedom of the compensation process for the nonlinear distortion of the modulated signal to be (step S15).

[0065] Figures 7 and 8 show the amplitude and coding rate of the modulated signals of this disclosure. In the 16APSK signal constellation shown in Figure 7, the amplitude of the modulated signal decreases slightly as the error correction coding rate increases in the order of R=2 / 3, 3 / 4, 4 / 5, 5 / 6, and 8 / 9. In the 32APSK signal constellation shown in Figure 8, the amplitude of the modulated signal decreases slightly as the error correction coding rate increases in the order of R=3 / 4, 4 / 5, 5 / 6, 8 / 9, and 9 / 10. The 16APSK and 32APSK signal constellations shown in Figures 7 and 8 use sections 5.4.3 and 5.4.4 of the DVB-S2 standard shown in Non-Patent Literature 3 as examples.

[0066] Therefore, when the error correction coding rate is higher, the regularization parameter control unit 8 sets the regularization parameters λ1 and λ2 in the same way as when the backoff during amplification is smaller, thereby controlling the degree of freedom for compensating for the nonlinear distortion of the modulated signal. On the other hand, when the error correction coding rate is lower, the regularization parameter control unit 8 sets the regularization parameters λ1 and λ2 in the same way as when the backoff during amplification is larger, thereby controlling the degree of freedom for compensating for the nonlinear distortion of the modulated signal.

[0067] Furthermore, when the regularization parameters λ1 and λ2 are excessively large, the degrees of freedom for compensating for the nonlinear distortion of the modulated signal are excessively low, resulting in an excessively high error rate in the demodulated signal, regardless of the error correction coding rate. Conversely, when the regularization parameters λ1 and λ2 are excessively small, the degrees of freedom for compensating for the nonlinear distortion of the modulated signal are excessively high, causing the weight coefficient vector w2 to be over-tuned, and the error rate of the demodulated signal to take an asymptotic value higher than the minimum, regardless of the error correction coding rate.

[0068] Thus, particularly when the error correction coding rate is high, avoiding unnecessary distortion compensation processing can improve error correction capability without introducing nonlinear distortion. Conversely, particularly when the error correction coding rate is low, performing sufficient distortion compensation processing can improve error correction capability while effectively removing nonlinear distortion.

[0069] A table of regularization parameters for this disclosure is shown in Figure 9. When the modulation scheme and error correction coding rate of the modulated signal are QPSK (R=R1_1, ..., R1_N1), 16APSK (R=R2_1, ..., R2_N2), or 32APSK (R=R3_1, ..., R3_N3), and the backoff during amplification of the modulated signal is X_1 [dB], X_2 [dB], ..., X_L [dB], a table of regularization parameters λ1, λ2 (λ1=λ2 or λ1≠λ2) is stored in the regularization parameter control unit 8.

[0070] Figure 10 shows the interpolation curves for the regularization parameters of this disclosure. When the modulation scheme and error correction coding rate of the modulated signal are fixed to one scheme and value, while the backoff during amplification of the modulated signal is discretely varied to X_1[dB], X_2[dB], ..., X_L[dB], a curve interpolation formula or a linear interpolation formula based on a table of regularization parameters λ1, λ2 (λ1=λ2 or λ1≠λ2) is stored in the regularization parameter control unit 8.

[0071] In this embodiment, the regularization parameter control unit 8 sets regularization parameters λ1 and λ2 according to the modulation scheme of the modulated signal, the coding rate of error correction, and the backoff during amplification, thereby controlling the degree of freedom for compensating for the nonlinear distortion of the modulated signal. As a modified example, the regularization parameter control unit 8 may set regularization parameters λ1 and λ2 according to the transmission line conditions (CNR) and the backoff during amplification of the modulated signal, thereby controlling the degree of freedom for compensating for the nonlinear distortion of the modulated signal.

[0072] The reason why modifications are possible is that the transmitting / receiving system S adaptively controls the modulation method of the modulated signal and the coding rate of error correction according to the transmission path conditions (CNR). Therefore, the conditions of the transmission path conditions (CNR) are equivalent to the conditions of the modulation method of the modulated signal and the coding rate of error correction.

[0073] Here, the regularization parameter control unit 8 should set the regularization parameters λ1 and λ2 to be larger (and the regularization parameters of the third-order or higher equalization filter to be larger) as the transmission path condition (CNR) deteriorates, thereby controlling the degree of freedom of the compensation process for the nonlinear distortion of the modulated signal to be lower.

[0074] On the other hand, the regularization parameter control unit 8 should set the regularization parameters λ1 and λ2 smaller (and the regularization parameters of the third-order or higher equalization filter) as the transmission path conditions (CNR) are better, thereby increasing the degree of freedom in compensating for the nonlinear distortion of the modulated signal.

[0075] The receiving device R only needs to perform a process to estimate the transmission path condition (CNR). The regularization parameter control unit 8 only needs to store the table of regularization parameters λ1 and λ2 shown in Figure 9, using the transmission path condition (CNR) and the backoff during amplification of the modulated signal as variables, and may also store the curve interpolation formula or linear interpolation formula for the regularization parameters λ1 and λ2 shown in Figure 10.

[0076] (Distortion compensation of modulated signals in prior art and in this disclosure) Figure 11 shows distortion compensation of modulated signals in the prior art and in this disclosure. In Figure 11, there is no nonlinear distortion and a QPSK scheme with a lower modulation order is applied. The upper left and upper right columns of Figure 11 show constellations of the ideal and transmitted QPSK signals, respectively (similar in the prior art and in this disclosure). The lower left and lower right columns of Figure 11 show constellations of the distortion-compensated QPSK signals in the prior art and in this disclosure, respectively.

[0077] In the conventional technology, the regularization parameters λ1 and λ2 are 0, resulting in an excessively high degree of freedom in compensating for the nonlinear distortion of the modulated signal. This causes the weight coefficient vector w2 to be over-tuned, and in the QPSK signal after distortion compensation, the signal points are significantly compressed in the amplitude direction. In this disclosure, the regularization parameters λ1 and λ2 are larger positive values, resulting in a moderately low degree of freedom in compensating for the nonlinear distortion of the modulated signal. As a result, in the QPSK signal after distortion compensation, the signal points are not compressed in the amplitude direction and are almost the same as during transmission. Thus, when compensating for distortion in QPSK signals with lower modulation orders, this disclosure, compared to the conventional technology, uses larger regularization parameters λ1 and λ2 and has a lower degree of freedom in compensating for the nonlinear distortion of the modulated signal, thus preventing the addition of nonlinear distortion.

[0078] Distortion compensation of modulated signals in the prior art and in this disclosure is also shown in Figure 12. In Figure 12, a QPSK scheme with nonlinear distortion and a lower modulation order is applied. The upper left and upper right columns of Figure 12 show the constellations of the ideal and transmitted QPSK signals, respectively (similar in the prior art and in this disclosure). The lower left and lower right columns of Figure 12 show the constellations of the distortion-compensated QPSK signals in the prior art and in this disclosure, respectively.

[0079] In the conventional technology, the regularization parameters λ1 and λ2 are 0, resulting in an excessively high degree of freedom in the compensation process for the nonlinear distortion of the modulated signal. This causes the weight coefficient vector w2 to be over-tuned, and in the QPSK signal after distortion compensation, the signal points are somewhat compressed in the amplitude direction. In this disclosure, the regularization parameters λ1 and λ2 are larger positive values, resulting in a moderately low degree of freedom in the compensation process for the nonlinear distortion of the modulated signal. In the QPSK signal after distortion compensation, the signal points are not compressed in the amplitude direction and are somewhat similar to those at the time of transmission. Thus, when compensating for distortion in QPSK signals with lower modulation orders, this disclosure, compared to the conventional technology, has larger regularization parameters λ1 and λ2 and a lower degree of freedom in the compensation process for the nonlinear distortion of the modulated signal, thus preventing the addition of nonlinear distortion.

[0080] Distortion compensation of modulated signals in the prior art and in this disclosure is also shown in Figure 13. In Figure 13, a 32APSK scheme with nonlinear distortion and a higher modulation order is applied. The upper left and upper right columns of Figure 13 show the constellations of the ideal and transmitted 32APSK signals, respectively (similar in the prior art and in this disclosure). The lower left and lower right columns of Figure 13 show the constellations of the distortion-compensated 32APSK signals in the prior art and in this disclosure, respectively.

[0081] In the prior art, the regularization parameters λ1 and λ2 are 0, and the degree of freedom for compensating for the nonlinear distortion of the modulated signal is moderately high. As a result, in the distortion-compensated 32APSK signal, the inner signal points (excluding the outer ones) are in a better state compared to the transmission state. In this disclosure, the regularization parameters λ1 and λ2 are smaller positive values, and the degree of freedom for compensating for the nonlinear distortion of the modulated signal is moderately high. As a result, in the distortion-compensated 32APSK signal, the inner signal points (excluding the outer ones) are in a better state compared to the transmission state. Thus, when compensating for distortion in a 32APSK signal with a higher modulation order, in this disclosure, compared to the prior art, the regularization parameters λ1 and λ2 are almost equal, and the degree of freedom for compensating for the nonlinear distortion of the modulated signal is almost equal, so the nonlinear distortion can be sufficiently removed. [Industrial applicability]

[0082] The receiving device and receiving program of this disclosure can improve error correction capability, especially when the modulation order is low, by compensating for nonlinear distortion in a modulated signal without unnecessarily performing distortion compensation processing and without introducing nonlinear distortion. [Explanation of symbols]

[0083] S: Transmit / Receive System T: Transmitter R: Receiver 1: Encoder 2: Modulator 3: Amplifier 4: Equalizer 5: Demodulator 6: Error Corrector 7: Switch 8: Regularization parameter control unit 41:1st-order equalization filter 42: Weight coefficient calculation unit 43: Calculation unit for the cubed value 44:3rd order equalization filter 45: Weight coefficient calculation unit 46: Adder 47: Subtractor

Claims

1. A receiving device that receives a modulated signal from a transmitting device that transmits a modulated signal, The system comprises an equalizer for compensating for the nonlinear distortion of the modulated signal, a demodulator for demodulating the modulated signal from which the nonlinear distortion has been compensated, and an error corrector for performing error correction on the demodulated signal. The equalizer controls the degree of freedom for compensating for the nonlinear distortion of the modulated signal to be lower as the modulation order of the modulated signal decreases, and controls the degree of freedom for compensating for the nonlinear distortion of the modulated signal to be higher as the modulation order of the modulated signal increases. A receiving device applicable to wireless or wired communication, characterized by the above.

2. The equalizer controls the degree of freedom for compensating for the nonlinear distortion of the modulated signal to be lower the higher the coding rate of error correction of the modulated signal, and controls the degree of freedom for compensating for the nonlinear distortion of the modulated signal to be higher the lower the coding rate of error correction of the modulated signal. The receiving device according to claim 1, characterized in that

3. The equalizer controls the degree of freedom for compensating for the nonlinear distortion of the modulated signal to be lower the smaller the backoff during amplification of the modulated signal, and controls the degree of freedom for compensating for the nonlinear distortion of the modulated signal to be higher the larger the backoff during amplification of the modulated signal. A receiving device according to claim 1 or 2, characterized in that

4. The equalizer adjusts the weight coefficients of the first-order and third-order or higher equalizing filters to minimize an evaluation function that includes the squared error between the modulated signal, which has been compensated for nonlinear distortion, and the demodulated signal or known signal, and a regularization term of the weight coefficients of the first-order and third-order or higher equalizing filters. By setting a larger regularization parameter in the regularization term of the weight coefficients of the equalization filter, the degree of freedom for compensating for the nonlinear distortion of the modulated signal can be controlled to be lower, and by setting a smaller regularization parameter in the regularization term of the weight coefficients of the equalization filter, the degree of freedom for compensating for the nonlinear distortion of the modulated signal can be controlled to be higher. The receiving device according to claim 1, characterized in that

5. A receiving program installed on a computer to cause the equalizer in the receiving device according to claim 1 to control the degrees of freedom of the compensation process for the nonlinear distortion of the modulated signal.

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