Transmitter and Transmitter Program

Abstract

This disclosure aims to suppress abrupt deterioration of characteristics such as the error rate of received bits, while suppressing an increase in the overall system delay of the receiving device and the amount of computation per demodulated symbol when switching the modulation method from a fixed-envelope modulation signal to a non-fixed-envelope modulation signal in order to compensate for the nonlinear distortion of the modulated signal. [Solution] In this disclosure, the modulator 1 of the transmitting device T maps a fixed envelope modulated signal to multiple envelope levels and adjusts the frequency of mapping to multiple envelope levels. Then, when the receiving device R switches between receiving a fixed envelope modulated signal and a non-fixed envelope modulated signal, the equalizer 3 of the receiving device R can adjust the weight coefficients of the equalization filter to be equal, thereby suppressing abrupt deterioration of characteristics such as the error rate of the received bits.

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 Documents 1 and 2. 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 amount of computation, an equalizer that approximates the Volterra series with a memory polynomial is used to compensate for the nonlinear distortion of the modulated signal, and the filter coefficients of the equalizer are calculated using a known signal with fewer symbols than the number of taps of the equalizer. In Patent Document 2, nonlinear distortion is compensated by performing error correction on a received signal that does not contain a known signal with the same signal point arrangement as the data section, and then performing the equalization process. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] International Publication No. 2019 / 171655 [Patent Document 2] International Publication No. 2016 / 056395 [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. [Overview of the project] [Problems that the invention aims to solve]

[0007] Incidentally, the modulation method may be switched between the pull-in process and the data transmission process. Furthermore, depending on the transmission path conditions, the modulation method may be switched using the ACM (Adaptive Coding and Modulation) method. For example, the modulation method may be switched between a fixed-envelope modulated signal (such as QPSK or 8PSK) and a non-fixed-envelope modulated signal (such as 32APSK or 64QAM).

[0008] However, Non-Patent Documents 1 and 2 and Patent Documents 1 and 2 do not explicitly state that the modulation method is switched between a fixed-envelope modulation signal and a non-fixed-envelope modulation signal. Furthermore, in Non-Patent Documents 1 and 2 and Patent Document 1, even if the modulation method is switched from a fixed-envelope modulation signal to a non-fixed-envelope modulation signal, the characteristics such as the error rate of the received bits deteriorate rapidly. Moreover, in Patent Document 2, even if the modulation method is switched from a fixed-envelope modulation signal to a non-fixed-envelope modulation signal, it is necessary to perform error correction and then equalization processing, which increases the system delay of the entire receiving device and the amount of computation per demodulated symbol.

[0009] Therefore, in order to solve the aforementioned problems, the present disclosure aims to suppress a rapid deterioration of characteristics such as the error rate of received bits while suppressing an increase in the overall system delay of the receiving device and the amount of computation per demodulated symbol when switching the modulation method from a fixed-envelope modulation signal to a non-fixed-envelope modulation signal in order to compensate for the nonlinear distortion of the modulated signal. [Means for solving the problem]

[0010] To solve the aforementioned problem, the modulator in the transmitting device maps the fixed-envelope modulated signal to multiple envelope levels and adjusts the frequency of mapping to multiple envelope levels. Then, when the receiving device switches between receiving the fixed-envelope modulated signal and the non-fixed-envelope modulated signal, the equalizer in the receiving device can adjust the weight coefficients of the equalization filter to be equal, thereby suppressing abrupt deterioration of characteristics such as the error rate of the received bits.

[0011] Specifically, the present disclosure relates to a transmitting device that switches between a constant envelope modulated signal and a non-constant envelope modulated signal and transmits them to a receiving device that switches between receiving a constant envelope modulated signal and a non-constant envelope modulated signal, comprising: a modulator that switches between generating a constant envelope modulated signal and a non-constant envelope modulated signal; and an amplifier that amplifies the constant envelope modulated signal and the non-constant envelope modulated signal, wherein the modulator maps the constant envelope modulated signal to a plurality of envelope levels and adjusts the frequency of occurrence of mapping to the plurality of envelope levels, so that when the receiving device switches between receiving a constant envelope modulated signal and a non-constant envelope modulated signal, the non-linear equalizer provided in the receiving device adjusts the weight coefficients of the equalization filter to be equal. This transmitting device is applicable to wireless or wired communication.

[0012] This configuration makes it possible to suppress the rapid deterioration of characteristics such as the error rate of received bits when switching the modulation method from a fixed-envelope modulation signal to a non-fixed-envelope modulation signal. Furthermore, since it is not always necessary to perform equalization processing after error correction, it is possible to suppress the overall system delay of the receiving device and the increase in the amount of computation per demodulated symbol.

[0013] Furthermore, the present disclosure is a transmitting device characterized in that, when the receiving device switches between receiving the fixed envelope modulated signal and the non-fixed envelope modulated signal, the modulator maps the fixed envelope modulated signal to the plurality of envelope levels and adjusts the frequency of occurrence of mapping to the plurality of envelope levels so as to adjust the expected value of the α-power value of the transmitted signal level (where α is a natural number of 2 or greater) to be equal.

[0014] In this configuration, when the receiving device switches between receiving a fixed-envelope modulated signal and a non-fixed-envelope modulated signal, the modulator in the transmitting device adjusts the expected value of the α-power value of the transmitted signal level (where α is a natural number greater than or equal to 2) to be equal. As a result, the equalizer in the receiving device can adjust the weight coefficients of the equalization filter to be equal, as described above.

[0015] Furthermore, the present disclosure relates to a transmitting device characterized in that, when the receiving device receives the constant envelope modulated signal which the receiving device has determined to have small nonlinear distortion, the modulator maps the constant envelope modulated signal to the plurality of envelope levels and adjusts the frequency of occurrence of mapping to the plurality of envelope levels so that the nonlinear equalizer provided in the receiving device adjusts the weight coefficient of the equalization filter of order 3 or higher to 0.

[0016] In this configuration, when the receiving device receives a constant envelope modulated signal that it has determined to have small nonlinear distortion, the modulator in the transmitting device maps the constant envelope modulated signal to multiple envelope levels at a predetermined frequency. As a result, the equalizer in the receiving device can adjust the weight coefficients of the third-order or higher equalization filter to be equal to zero, as described above.

[0017] Furthermore, this disclosure provides a transmitting device characterized in that, when generating the constant envelope modulated signal, the modulator performs only phase modulation without performing amplitude modulation regardless of the plurality of envelope levels, or performs both amplitude modulation and phase modulation according to the plurality of envelope levels.

[0018] In this configuration, the modulator in the transmitting device maps the constant envelope modulated signal to multiple envelope levels at a predetermined frequency. As the original constant envelope modulated signal, it can perform only phase modulation without performing amplitude modulation, or it can perform both amplitude modulation and phase modulation in accordance with the multiple envelope levels.

[0019] Furthermore, this disclosure relates to a transmission program installed on a computer for causing the modulator of the transmission device described above to map the constant envelope modulation signal to the plurality of envelope levels and to adjust the frequency of occurrence of the mapping to the plurality of envelope levels.

[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, in compensating for the nonlinear distortion of the modulated signal, this disclosure makes it possible to suppress a rapid deterioration of characteristics such as the error rate of the received bits while suppressing an increase in the overall system delay of the receiving device and the amount of computation per demodulated symbol when switching the modulation method from a fixed-envelope modulated signal to a non-fixed-envelope modulated signal. [Brief explanation of the drawing]

[0023] [Figure 1] This diagram shows the configuration of the transmission and reception system disclosed herein. [Figure 2]This diagram shows the procedure for sending and receiving data according to this disclosure. [Figure 3] This figure shows the weight coefficients of a conventional third-order equalization filter. [Figure 4] This figure shows the mapping of the constant envelope modulated signal in the first embodiment. [Figure 5] This diagram shows distortion compensation during switching of modulation methods in conventional technology. [Figure 6] This figure shows the distortion compensation during switching of the modulation scheme in the first embodiment. [Figure 7] This figure shows the MER characteristics when switching between the conventional technology and the modulation scheme of the first embodiment. [Figure 8] This figure shows the distortion compensation during switching of the modulation scheme in the first embodiment. [Figure 9] This figure shows the MER characteristics when switching between the conventional technology and the modulation scheme of the first embodiment. [Figure 10] This figure shows the transmission signal level of the non-deterministic envelope modulation signal in the second embodiment. [Figure 11] This figure shows the mapping of the constant envelope modulation signal in the second embodiment. [Figure 12] This diagram shows distortion compensation during switching of modulation methods in conventional technology. [Figure 13] This figure shows the distortion compensation during switching of the modulation scheme in the first embodiment. [Figure 14] This figure shows the distortion compensation during the switching of the modulation scheme in the second embodiment. [Figure 15] This figure shows the MER characteristics when switching between the modulation methods of the prior art and the first and second embodiments. [Figure 16] This figure shows the MER characteristics when switching between the modulation methods of the prior art and the first and second embodiments. [Figure 17] This figure shows the weighting coefficients when switching modulation schemes in the first embodiment. [Figure 18] This figure shows the weighting coefficients when switching the modulation scheme in the second embodiment. [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 procedure for transmission / reception processing 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 a modulator 1 and an amplifier 2. The receiving device R comprises an equalizer 3, a demodulator 4 and a switch 5. In order to execute step S1 on the modulator 1, the transmission program for step S1 can be installed on a computer.

[0026] Transmitter T switches between transmitting a fixed-envelope modulated signal and a non-fixed-envelope modulated signal. Modulator 1 switches between generating a fixed-envelope modulated signal and a non-fixed-envelope modulated signal (step S1). Amplifier 2 amplifies the fixed-envelope modulated signal and the non-fixed-envelope modulated signal (step S2).

[0027] The receiving device R receives by switching between a fixed-envelope modulated signal and a non-fixed-envelope modulated signal. The equalizer 3 compensates for the nonlinear distortion of the fixed-envelope modulated signal and the non-fixed-envelope modulated signal (step S3). The demodulator 4 demodulates by switching between a fixed-envelope modulated signal and a non-fixed-envelope modulated signal (step S4). The switch 5 outputs a known signal such as a pilot signal during the pull-in process and the hard judgment value of the demodulator 4 during the data transmission process, as a reference signal as described later.

[0028] The equalizer 3 comprises a first-order equalizer filter 31, a weight coefficient calculation unit 32, a cube value calculation unit 33, a third-order equalizer filter 34, a weight coefficient calculation unit 35, an adder 36, and a subtractor 37. As a modified example, the equalizer 3 may include an equalizer filter of order 3 or higher.

[0029] The first-order equalization filter 31 processes the input signal y 1、n The modulated signal and the added noise x n +z nInput it (refer to the first equation of Equation 1). The cube value calculation unit 33 calculates the cube value |x n +z n | 2 (x n +z n ). The third-order equalization filter 34 uses the cube value |x 2、n of the modulation signal and the added noise as the input signal y n +z n | 2 (x n +z n ) (refer to the second equation of Equation 1).

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[0030] The first-order equalization filter 31 and the third-order equalization filter 34 can apply a FIR (Finite Inpulse Response) filter or the like. The modulation signal x n may be sampled at the symbol timing of the aperture point of the eye pattern, or may be oversampled at a sampling frequency that is P times the symbol timing. The added noise z n may assume AWGN (Additive White Gaussian Noise) or the like.

[0031] As will be described later, the weight coefficient calculation unit 32 calculates the weight coefficient vector w1 of the first-order equalization filter 31 (refer to the first equation of Equation 2, where 0, 1, ···, M1-1 indicate tap numbers). As will be described later, the weight coefficient calculation unit 35 calculates the weight coefficient vector w2 of the third-order equalization filter 34 (refer to the second equation of Equation 2, where 0, 1, ···, M2-1 indicate tap numbers).

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[0032] The first-order equalization filter 31 calculates the inner product w1 1、n between the weight coefficient vector w1 and the input signal vector y T y 1、nThe 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 34 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 36 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).

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[0033] Demodulator 4 adds up x n ^ Restore hardness judgment value etc x n-m It outputs the reference signal x. Switch 5 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 4, etc. x during the data transmission process. n-m It outputs the following. Subtractor 37 adds x n ^ And, reference signal x n-m The error value e between and n Calculate (see formula 5).

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[0034] In this disclosure, the first-order equalization filter 31 and the third-order equalization filter 34, 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-mThe value from one time step prior to the present is adopted. As an example, the first-order equalization filter 31 and the third-order equalization filter 34, 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.

[0035] The weight coefficient calculation unit 32 calculates the error value e n The expected value of the squared value E[|e n | 2 The weight coefficient vector w1 of the first-order equalization filter 31 is set to minimize ] ^ The weight coefficient calculation unit 35 calculates the error value e n The expected value of the squared value E[|e n | 2 The weight coefficient vector w2 of the third-order equalization filter 34 is set to minimize ] ^ Calculate (see the second term on the left side of equation 6).

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[0036] In this disclosure, the weight coefficient calculation units 32 and 35 calculate the weight coefficient vector w1 in accordance with the MMSE (Minimum Mean Square Error) standard. ^ w2 ^ As such, Wiener solution w1 ^ w2 ^ The following is calculated. As a modified example, the weight coefficient calculation units 32 and 35 calculate the weight coefficient vector w1 according to the LMS (Least Mean Square) standard or the RLS (Recursive Least Square) standard. ^ w2 ^ The following can also be calculated: In other words, the weight coefficient calculation units 32 and 35 calculate the error value e n The squared value of |e n | 2 To minimize this, the weight coefficient vector w1 ^ w2 ^ You just need to calculate that.

[0037] Weight coefficient vector w1 of the first-order equalization filter 31 ^ This is expressed as shown in equation 7. The weight coefficient vector w2 of the cubic equalization filter 34. ^ 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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[0038] 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 α-th power of 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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[0039] Incidentally, when the receiving device R switches between receiving a fixed-envelope modulated signal and a non-fixed-envelope modulated signal, if the equalizer 3 provided in the receiving device R can adjust the weight coefficient vectors w1 and w2 of the first-order equalizing filter 31 and the third-order equalizing filter 34 (or, as a modified example, the weight coefficient vectors of the third-order or higher equalizing filters) to be equal, then a rapid deterioration of characteristics such as the error rate of the received bits can be suppressed.

[0040] Therefore, the modulator 1 in the transmitting device T maps the constant envelope modulation signal to multiple envelope levels s and adjusts the frequency p of the mapping to the multiple envelope levels s (step S1). Specifically, the modulator 1 in the transmitting device T performs the mapping of the constant envelope modulation signal in the first and second embodiments. The first and second embodiments will be described below.

[0041] In this way, when switching the modulation method from a fixed-envelope modulation signal to a non-fixed-envelope modulation signal, it is possible to suppress a rapid deterioration of characteristics such as the error rate of the received bits. Furthermore, since it is not always necessary to perform equalization processing after error correction, it is possible to suppress the increase in the overall system delay of the receiving device R and the amount of computation per demodulated symbol.

[0042] (Mapping of the constant envelope modulated signal in the first embodiment) Figure 3 shows the weight coefficients of a conventional third-order equalization filter. The expected value E[|x| of the alpha power of the constant envelope modulation signal x] α ] is expressed as in the first equation of Equation 12. The signal-to-noise ratio CNR is expressed as in the second equation of Equation 12. Modulated signal power P x While variable on long-term scales, it is constant (e.g., 1) on short-term scales (switching between constant-envelope modulated signals and non-constant-envelope modulated signals) (see Equation 3 of Equation 12).

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[0043] In a constant envelope modulated signal x, the weight coefficient w of the third-order equalization filter 34. 2、m ^ Based on equations 8-12, it is expressed as shown in equation 13. In the upper left column of Figure 3, the weight coefficient w of the cubic equalization filter 34 is shown. 2、m ^ When the signal-to-noise ratio (CNR) is low, it approaches 0; when the CNR is high, it approaches -0.5; and when the CNR is within the expected range of -10 to 30 dB, it can take a value less than 0 and greater than -0.5. [Number]

[0044] That is, in Equation 8, contrary to the assumption that the nonlinear distortion of the non-constant envelope modulation signal x is extremely small, the weight coefficient w of the third-order equalization filter 34 2、m ^ can take a non-zero value.

[0045] The expected value E[|x| α of the α-th power value of the non-constant envelope modulation signal x (in FIG. 3, 16QAM signal, 32APSK signal or 64QAM signal) is not expressed as in the first equation of Equation 12. The signal-to-noise ratio CNR is expressed as in the second equation of Equation 12. The modulation signal power P x is variable on a long-time scale, but is constant (e.g., 1) on a short-time scale (switching between the constant envelope modulation signal and the non-constant envelope modulation signal) (see the third equation of Equation 12).

[0046] In the non-constant envelope modulation signal x (in FIG. 3, 16QAM signal, 32APSK signal or 64QAM signal), the weight coefficient w of the third-order equalization filter 34 2、m ^ is expressed in a form different from Equation 13 based on Equations 8 to 11. In the upper right column, lower left column and lower right column of FIG. 3, in any case, the weight coefficient w of the third-order equalization filter 34 2、m ^ approaches 0 when the signal-to-noise ratio CNR is low or high, and can take a value smaller than 0 and larger than about -0.1 when the signal-to-noise ratio CNR is within the assumed -10 to 30 dB, but does not take a value as small as -0.5.

[0047] That is, in Equation 8, in response to the assumption that the nonlinear distortion of the non-constant envelope modulation signal x is extremely small, the weight coefficient w of the third-order equalization filter 34 2、m ^ can be said to take a value close to zero.

[0048] Therefore, in the prior art, when the receiving device R switches between receiving a constant envelope modulation signal and a non-constant envelope modulation signal, the equalizer 3 included in the receiving device R adjusts the weight coefficient vector w2 of the third-order equalization filter 34 (as a modification example, the weight coefficient vector of an equalization filter of the third order or higher) to different values, so that it is impossible to suppress a sharp deterioration in characteristics such as the error rate of received bits.

[0049] The mapping of the constant envelope modulation signal in the first embodiment is shown in FIG. 4. The modulator 1 included in the transmitting device T maps the constant envelope modulation signal to a plurality of envelope levels s and adjusts the occurrence frequency p of the mapping to the plurality of envelope levels s (step S1).

[0050] Then, when the receiving device R receives a constant envelope modulation signal determined to have small non-linear distortion, the equalizer 3 included in the receiving device R can adjust the weight coefficient vector w2 of the third-order equalization filter 34 (as a modification example, the weight coefficient vector of an equalization filter of the third order or higher) to 0.

[0051] In the constant envelope modulation signal x (in FIG. 4, a QPSK signal), the weight coefficient w of the third-order equalization filter 34 2、m ^ is adjusted to 0 (see the first equation of Equation 14). For this reason, the expected value E[|x| of the fourth power value of the constant envelope modulation signal x 4 is adjusted as in the second equation of Equation 14. Moreover, the weight coefficient w of the first-order equalization filter 31 1、m ^ is adjusted as in the third equation of Equation 14.

Equation

[0052] In the left column of FIG. 4, in the constant envelope modulation signal x (QPSK signal) before mapping, one envelope level is s. In the right column of FIG. 4, in the constant envelope modulation signal x (QPSK signal) after mapping, two envelope levels are s1 and s2, and the occurrence frequencies of the mapping to the two envelope levels s1 and s2 are p1 and p2 (see Equation 15).

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[0053] In the right column of Figure 4, the expected value E[|x| of the squared value of the constant envelope modulation signal x is shown. 2 ] is the modulated signal power P x It is expressed as the first equation of Equation 16, and is the expected value E[|x| of the fourth power of the constant envelope modulation signal x]. 4 ] is expressed by the second equation of equation 16, based on the second equation of equation 14.

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[0054] In the right column of Figure 4, the mapping frequencies p1 and p2 to the two envelope levels s1 and s2 are known, and the two envelope levels s1 and s2 are unknown, and the result can be obtained as shown in Equation 17. As a variation, one of the two envelope levels s1 and s2 is known, and the mapping frequencies p1 and p2 to the two envelope levels s1 and s2, and the other envelope level s1 and s2 are unknown, and the result can be obtained in the same way as Equation 17. However, if the inner envelope level s1 is known, then 0 ≤ s1 < √P x It is necessary that the outer envelope level s2 is a known number, and if √(2P) x It is necessary that )≦s2. Also, it is necessary that p1≧p2.

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[0055] Furthermore, in order for the receiving device R to determine that the nonlinear distortion of the constant envelope modulated signal x is small, it may refer to the backoff condition of the transmitted signal level using the frame header, etc. (the smaller the backoff, the smaller the nonlinear distortion is determined to be), or it may refer to the modulation order of the constant envelope modulated signal x (the lower the modulation order, the smaller the nonlinear distortion is determined to be). In addition, the modulator 1 provided in the transmitting device T may map the constant envelope modulated signal to three or more envelope levels s, and may adjust the frequency p of mapping to three or more envelope levels s.

[0056] Thus, when the receiving device R receives a constant envelope modulated signal that it has determined to have small nonlinear distortion, the modulator 1 of the transmitting device T maps the constant envelope modulated signal to multiple envelope levels at a predetermined frequency. As a result, the equalizer 3 of the receiving device R can adjust the weight coefficients of the third-order or higher equalization filter to be equal to zero, as described above.

[0057] In the right column of Figure 4, when modulator 1 generates a constant envelope modulated signal x, it either performs only phase modulation without performing amplitude modulation regardless of the multiple envelope levels s, or it performs both amplitude modulation and phase modulation depending on the multiple envelope levels s.

[0058] In the former case, modulator 1 is equipped with a QPSK mapper, and demodulator 4 is equipped with a QPSK demapper, and both refer only to phase information without referring to amplitude information. In the latter case, modulator 1 is equipped with an 8APSK mapper, and demodulator 4 is equipped with an 8APSK demapper, and both refer to amplitude information and phase information.

[0059] Thus, the modulator 1 of the transmitting device T maps the constant envelope modulated signal to multiple envelope levels at a predetermined frequency. As the original constant envelope modulated signal, it can perform only phase modulation without performing amplitude modulation, or it can perform both amplitude modulation and phase modulation in accordance with the multiple envelope levels.

[0060] Figures 5 and 6 show the distortion compensation during the switching between the modulation methods of the prior art and the first embodiment, respectively. Figure 7 shows the MER (Modulation Error Ratio) characteristics during the switching between the modulation methods of the prior art and the first embodiment. In Figures 5-7, there is no nonlinear distortion, the CNR is 25 dB, and the modulation method switches from a QPSK signal to a 64QAM signal. The upper left and upper right columns of Figures 5 and 6 show the constellations of the ideal and distortion-compensated QPSK signals, respectively. The lower left and lower right columns of Figures 5 and 6 show the constellations of the ideal and distortion-compensated 64QAM signals, respectively.

[0061] In conventional techniques (see Figures 5 and 7), in the distortion-compensated QPSK signal, the signal points are compressed in the amplitude direction, so the signal point deviation characteristic MER from the ideal point appears to improve, but the weight coefficient vector w2 of the third-order equalization filter 34 is over-tuned to the QPSK signal only. After switching the modulation scheme, in the distortion-compensated 64QAM signal, the weight coefficient vector w2 of the third-order equalization filter 34 is over-tuned to the QPSK signal only, so the signal points are compressed in both the amplitude and phase directions, and the signal point deviation characteristic MER from the ideal point deteriorates rapidly.

[0062] In the first embodiment (see Figures 6 and 7), in the distortion-compensated QPSK signal, the signal points are not compressed in the amplitude direction, so the signal point deviation characteristic MER from the ideal point is sufficient, and the weight coefficient vector w2 of the third-order equalization filter 34 is not over-tuned to the original QPSK signal. After switching the modulation scheme, in the distortion-compensated 64QAM signal, the weight coefficient vector w2 of the third-order equalization filter 34 is not over-tuned to the original QPSK signal, so the signal points are not compressed in either the amplitude or phase direction, and the signal point deviation characteristic MER from the ideal point does not change.

[0063] Figure 8 shows the distortion compensation during modulation scheme switching in the first embodiment. Figure 9 shows the MER characteristics during modulation scheme switching in the prior art and the first embodiment. In Figure 8, there is some nonlinear distortion, CNR = 25 dB, and the modulation scheme switches from a QPSK signal to a 64QAM signal. The upper left, upper middle, and upper right columns of Figure 8 show the ideal constellations of the QPSK signal after distortion addition and distortion compensation, respectively. The lower left, lower middle, and lower right columns of Figure 8 show the ideal constellations of the 64QAM signal after distortion addition and distortion compensation, respectively.

[0064] In the conventional technique (see Figure 9), in the distortion-compensated QPSK signal, the signal points are compressed in the amplitude direction, so the signal point deviation characteristic MER from the ideal point appears to improve, but the weight coefficient vector w2 of the third-order equalization filter 34 is over-tuned to the QPSK signal only. After switching the modulation scheme, in the distortion-compensated 64QAM signal, the weight coefficient vector w2 of the third-order equalization filter 34 is over-tuned to the QPSK signal only, so the signal points are compressed in both the amplitude and phase directions, and the signal point deviation characteristic MER from the ideal point deteriorates rapidly.

[0065] In the first embodiment (see Figures 8 and 9), in the distortion-compensated QPSK signal, the signal points are not compressed in the amplitude direction, so the signal point deviation characteristic MER from the ideal point is sufficient, and the weight coefficient vector w2 of the third-order equalization filter 34 is not over-tuned to the original QPSK signal. After switching the modulation scheme, in the distortion-compensated 64QAM signal, the weight coefficient vector w2 of the third-order equalization filter 34 is not over-tuned to the original QPSK signal, so the signal points are not compressed in either the amplitude or phase direction, and the signal point deviation characteristic MER from the ideal point does not change. However, in Figures 8 and 9, unlike Figures 5 to 7, there is some nonlinear distortion, so the signal point deviation characteristic MER from the ideal point changes slightly before and after switching the modulation scheme.

[0066] (Mapping of the constant envelope modulation signal in the second embodiment) Figure 10 shows the transmission signal level of the non-constant envelope modulation signal of the second embodiment. Figure 11 shows the mapping of the constant envelope modulation signal of the second embodiment. The modulator 1 of the transmitting device T maps the constant envelope modulation signal to multiple envelope levels s regardless of the presence or absence of nonlinear distortion, and adjusts the frequency p of mapping to multiple envelope levels s (step S1).

[0067] Then, when the receiving device R switches between receiving a fixed-envelope modulated signal and a non-fixed-envelope modulated signal, the modulator 1 in the transmitting device T can adjust the expected value of the α-power value of the transmitted signal level (where α is a natural number greater than or equal to 2, depending on the order of the equalization filter) to be equal.

[0068] When there is no nonlinear distortion, the weight coefficient w of the third-order equalization filter 34 2、m ^ This is expressed by equations 8-11. Here, in the case of a fixed envelope modulated signal and a non-fixed envelope modulated signal, of the terms in equations 8-11, the modulated signal power P x Since they are equally tuned (see Equation 1 of Equation 18), the signal-to-noise ratio (CNR) is also automatically equal (see Equation 2 of Equation 18).

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[0069] Therefore, in both fixed-envelope modulated signals and non-fixed-envelope modulated signals, the expected value E[|x| of the modulated signal x to the power of 4 is obtained from each term in equations 8 to 11. 4 If ] are equally adjusted, and the expected value E[|x| of the modulated signal x to the power of 6 is equal to E[|x| 6 If ] are equally adjusted, (the weight coefficient w of the first-order equalization filter 31) 1、m ^ (Of course) the weight coefficient w of the 3rd order equalization filter 34 2、m ^ These should also be adjusted equally (see Equation 19).

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[0070] When there is nonlinear distortion, the weight coefficient vector w2 of the third-order equalization filter 34 becomes more complex than equations 8-11. However, in the case of fixed-envelope modulated signals and non-fixed-envelope modulated signals, among the terms in the weight coefficient equations, the modulated signal power P x Since they are equally tuned (see Equation 1 of Equation 18), the signal-to-noise ratio (CNR) is also automatically equal (see Equation 2 of Equation 18).

[0071] Therefore, in both fixed-envelope modulated signals and non-fixed-envelope modulated signals, the expected value E[|x| of the modulated signal x to the power of 4 is obtained from each term in the formula for the weight coefficient. 4 If ] are equally adjusted, and the expected value E[|x| of the modulated signal x to the power of 6 is equal to E[|x| 6 If ] are equally adjusted, then it can be assumed that the weight coefficient vector w2 of the cubic equalization filter 34 (as well as the weight coefficient vector w1 of the first-order equalization filter 31) will also be equally adjusted (see Equation 19).

[0072] Figures 12-18 demonstrate that even with nonlinear distortion, if equation 19 holds, the signal point deviation characteristic MER from the ideal point does not change before and after switching the modulation scheme. Therefore, even with nonlinear distortion, if equation 19 holds, it can be empirically seen that the weight coefficient vector w2 of the third-order equalizer filter 34 (as well as the weight coefficient vector w1 of the first-order equalizer filter 31) remains equal before and after switching the modulation scheme.

[0073] In the left or right column of Figure 10, the three envelope levels for the non-deterministic envelope modulation signal x (16QAM signal or 32APSK signal) are s1, s2, and s3, and the frequencies of mapping to the three envelope levels s1, s2, and s3 are p1, p2, and p3.

[0074] In the left or right column of Figure 10, the expected value E[|x| of the fourth power of the non-deterministic envelope modulation signal x (16QAM signal or 32APSK signal) is shown. 4 E[|x|] is expressed by the first equation of equation 20 and is the expected value of the sixth power of the non-deterministic envelope modulation signal x (16QAM signal or 32APSK signal). 6 ] is expressed by the second equation of equation 20. Here, γk This is the first envelope level s1 relative to the kth envelope level s k This is the ratio. As the first step, the calculation of Equation 20 is performed on the non-deterministic envelope modulation signal x (16QAM signal or 32APSK signal).

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[0075] In the left column of Figure 11, one envelope level in the constant envelope modulated signal x (QPSK signal) before mapping is s. In the right column of Figure 11, the two envelope levels in the constant envelope modulated signal x (QPSK signal) after mapping are s1 and s2, and the mapping frequencies to the two envelope levels s1 and s2 are p1 and p2 (see Equation 15).

[0076] In the right column of Figure 11, the expected value E[|x|] of the fourth power of the constant envelope modulation signal x (QPSK signal) after mapping is shown. 4 E[|x|] is expressed by the first equation of equation 20, and is the expected value of the sixth power of the constant envelope modulation signal x (QPSK signal) after mapping. 6 This is expressed by the second equation of Equation 20, where γ2 is the ratio of the second envelope level s2 to the first envelope level s1. In the second step, s1, s2, p1, and p2 are calculated based on Equations 19 and 20 for the mapped constant envelope modulated signal x (QPSK signal).

[0077] Furthermore, the receiving device R can apply the second embodiment regardless of whether the nonlinear distortion of the constant envelope modulated signal x is small or large, in contrast to the first embodiment, which can only be applied when the nonlinear distortion of the constant envelope modulated signal x is small. In addition, the modulator 1 provided in the transmitting device T may map the constant envelope modulated signal to three or more envelope levels s, and the frequency p of mapping to three or more envelope levels s may be adjusted.

[0078] Thus, when the receiving device R switches between receiving a fixed-envelope modulated signal and a non-fixed-envelope modulated signal, the modulator 1 of the transmitting device T adjusts the expected value of the α-power value of the transmitted signal level (where α is a natural number greater than or equal to 2, depending on the order of the equalization filter) to be equal. As a result, the equalizer 3 of the receiving device R can adjust the weight coefficients of the equalization filter to be equal, as described above.

[0079] In the right column of Figure 11, when modulator 1 generates a constant envelope modulated signal x, it either performs only phase modulation without performing amplitude modulation regardless of the multiple envelope levels s, or it performs both amplitude modulation and phase modulation depending on the multiple envelope levels s.

[0080] In the former case, modulator 1 is equipped with a QPSK mapper, and demodulator 4 is equipped with a QPSK demapper, and both refer only to phase information without referring to amplitude information. In the latter case, modulator 1 is equipped with an 8APSK mapper, and demodulator 4 is equipped with an 8APSK demapper, and both refer to amplitude information and phase information.

[0081] Thus, the modulator 1 of the transmitting device T maps the constant envelope modulated signal to multiple envelope levels at a predetermined frequency. As the original constant envelope modulated signal, it can perform only phase modulation without performing amplitude modulation, or it can perform both amplitude modulation and phase modulation in accordance with the multiple envelope levels.

[0082] Figures 12-14 show the distortion compensation during modulation method switching in the prior art, the first embodiment, and the second embodiment, respectively. Figures 15 and 16 show the MER characteristics during modulation method switching in the prior art, the first embodiment, and the second embodiment. In Figures 12-16, there is some nonlinear distortion, CNR = 18 dB, and the modulation method switches from a QPSK signal to a 16QAM signal. The upper left, upper middle, and upper right columns of Figures 12-14 show the ideal constellations of the QPSK signal after distortion addition and distortion compensation, respectively. The lower left, lower middle, and lower right columns of Figures 12-14 show the ideal constellations of the 16QAM signal after distortion addition and distortion compensation, respectively. In Figures 15 and 16, after the modulation method switching in the first embodiment, the weight coefficient vector w2 of the third-order equalization filter 34 is fixed to 0 / updated from 0, respectively.

[0083] In conventional techniques (see Figures 12, 15, and 16), in the distortion-compensated QPSK signal, the signal points are compressed in the amplitude direction, so the signal point deviation characteristic MER from the ideal point appears to improve, but the weight coefficient vector w2 of the third-order equalization filter 34 is over-tuned to the QPSK signal only. After switching the modulation scheme, in the distortion-compensated 16QAM signal, the weight coefficient vector w2 of the third-order equalization filter 34 is over-tuned to the QPSK signal only, so the signal points are compressed in both the amplitude and phase directions, and the signal point deviation characteristic MER from the ideal point deteriorates rapidly. Furthermore, in Figure 12, unlike Figure 5, there is some nonlinear distortion, so the signal point deviation characteristic MER from the ideal point deteriorates even more rapidly before and after switching the modulation scheme.

[0084] In the first embodiment (see Figures 13, 15, and 16), in the distortion-compensated QPSK signal, the signal points are not compressed in the amplitude direction, so the signal point deviation characteristic MER from the ideal point is sufficient, and the weight coefficient vector w2 of the third-order equalization filter 34 is not over-tuned to the original QPSK signal. After switching the modulation scheme, in the distortion-compensated 16QAM signal, the weight coefficient vector w2 of the third-order equalization filter 34 is not over-tuned to the original QPSK signal, so the signal points are not compressed in either the amplitude or phase direction, and the signal point deviation characteristic MER from the ideal point does not change. However, in Figure 13, unlike Figure 6, there is some nonlinear distortion, so the signal point deviation characteristic MER from the ideal point changes slightly before and after switching the modulation scheme.

[0085] In the second embodiment (see Figures 14, 15, and 16), in the distortion-compensated QPSK signal, the signal points are not compressed in the amplitude direction, so the signal point deviation characteristic MER from the ideal point is sufficient, and the weight coefficient vector w2 of the third-order equalization filter 34 is not over-tuned to the original QPSK signal. After switching the modulation scheme, in the distortion-compensated 16QAM signal, the weight coefficient vector w2 of the third-order equalization filter 34 is not over-tuned to the original QPSK signal, so the signal points are not compressed in either the amplitude or phase direction, and the signal point deviation characteristic MER from the ideal point does not change. Furthermore, in Figure 14, unlike Figure 13, although there is some nonlinear distortion, the signal point deviation characteristic MER from the ideal point remains almost unchanged before and after switching the modulation scheme.

[0086] In Figure 15, after switching the modulation scheme in the first embodiment, the weight coefficient vector w2 of the third-order equalization filter 34 is fixed to 0. Therefore, the signal point deviation characteristic MER from the ideal point remains almost unchanged from immediately after switching the modulation scheme to after switching the modulation scheme. In Figure 16, after switching the modulation scheme in the first embodiment, the weight coefficient vector w2 of the third-order equalization filter 34 is updated from 0. Therefore, from immediately after switching the modulation scheme to after switching the modulation scheme, the signal point deviation characteristic MER from the ideal point converges to a similar extent as in the second embodiment.

[0087] Figures 17 and 18 show the weight coefficients during the switching of the modulation scheme in the first and second embodiments, respectively. In Figures 17 and 18, there is some nonlinear distortion, the CNR is 18 dB, and the modulation scheme switches from a QPSK signal to a 16QAM signal. In Figure 17, after the switching of the modulation scheme in the first embodiment, the weight coefficient vector w2 of the third-order equalization filter 34 is updated from 0. Figures 17 and 18 also show the weight coefficient vector w1 of the first-order equalization filter 31.

[0088] In the first embodiment (see Figure 17), the weight coefficient |w of the first-order equalization filter 31 is determined from just before the modulation method is switched, through just after the modulation method is switched, to when the weight coefficient converges. 1、m | remains almost unchanged, but the weight coefficients |w of the third-order equalization filter 34 are still the same. 2、m | converges to a small value. Here, because there is some nonlinear distortion, the weight coefficient |w of the third-order equalization filter 34 2、m The | symbol is non-zero in multiple m values ​​and at the central tap of ROF.

[0089] In the second embodiment (see Figure 18), the weight coefficients |w| of the first-order equalization filter 31 are determined from just before the modulation method is switched, through just after the modulation method is switched, to when the weight coefficients converge. 1、m | has remained almost unchanged, and the weight coefficient |w of the 3rd order equalization filter 34 2、m | has also remained almost unchanged. Here, in the first embodiment (see Figure 17), compared to the second embodiment (see Figure 18), the weight coefficient |w of the cubic equalization filter 34 at the time of convergence of the weight coefficients 2、m | converges to a similar degree.

[0090] Figures 12-18 demonstrate that, even with nonlinear distortion, if equation 19 holds, the signal point deviation characteristic MER from the ideal point does not change before and after switching modulation schemes. Furthermore, it was empirically found that, even with nonlinear distortion, if equation 19 holds, the weight coefficient vector w2 of the third-order equalizer filter 34 (as well as the weight coefficient vector w1 of the first-order equalizer filter 31) remains equal before and after switching modulation schemes. [Industrial applicability]

[0091] The transmitting device and transmitting program of this disclosure, when compensating for nonlinear distortion of the modulated signal, can suppress a rapid deterioration of characteristics such as the error rate of the received bits while suppressing an increase in the overall system delay of the receiving device and the amount of computation per demodulated symbol when switching the modulation method from a fixed-envelope modulated signal to a non-fixed-envelope modulated signal. [Explanation of Symbols]

[0092] S: Transmit / Receive System T: Transmitter R: Receiver 1: Modulator 2: Amplifier 3: Equalizer 4: Demodulator 5: Switch 31:1st-order equalization filter 32: Weight coefficient calculation unit 33: Calculation unit for the cubed value 34:3rd order equalization filter 35: Weight coefficient calculation unit 36: Adder 37: Subtractor

Claims

1. A transmitting device that switches between a fixed-envelope modulated signal and a non-fixed-envelope modulated signal to a receiving device that switches between receiving a fixed-envelope modulated signal and a non-fixed-envelope modulated signal, A modulator that generates by switching between the fixed envelope modulation signal and the non-fixed envelope modulation signal, The system includes an amplifier that amplifies the fixed envelope modulation signal and the non-fixed envelope modulation signal, When the receiving device switches between receiving the constant envelope modulated signal and the non-constant envelope modulated signal, the modulator maps the constant envelope modulated signal to multiple envelope levels and adjusts the frequency of mapping to the multiple envelope levels so that the nonlinear equalizer in the receiving device adjusts the weight coefficients of the equalization filter to be equal. A transmitting device applicable to wireless or wired communications, characterized by the above features.

2. When the receiving device switches between receiving the fixed-envelope modulated signal and the non-fixed-envelope modulated signal, the modulator maps the fixed-envelope modulated signal to the multiple envelope levels and adjusts the frequency of mapping to the multiple envelope levels so that the expected value of the α-power of the transmitted signal level (where α is a natural number greater than or equal to 2) is equal. The transmitting device according to claim 1, characterized in that

3. When the receiving device receives the constant envelope modulated signal, which it has determined has low nonlinear distortion, the modulator maps the constant envelope modulated signal to the multiple envelope levels and adjusts the frequency of mapping to the multiple envelope levels, so that the nonlinear equalizer in the receiving device adjusts the weight coefficients of the equalization filter of order 3 or higher to zero. A transmitting device according to claim 1 or 2, characterized in that...

4. When the modulator generates the constant envelope modulated signal, it either performs only phase modulation without amplitude modulation, regardless of the multiple envelope levels, or performs both amplitude modulation and phase modulation depending on the multiple envelope levels. The transmitting device according to claim 1, characterized in that

5. A transmission program installed on a computer to cause the modulator of the transmitting device according to claim 1 to map the constant envelope modulation signal to the plurality of envelope levels and to adjust the frequency of occurrence of the mapping to the plurality of envelope levels.

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