Transmitting device and transmitting program

Abstract

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

Description

[Technical Field]

[0001] The present disclosure relates to techniques for compensating for nonlinear distortion in modulated signals. [Background technology]

[0002] In the amplifiers of transmitters or repeaters, high power utilization efficiency can be achieved by setting the operating point near the saturation region. However, a modulated signal with nonlinear distortion generates radiation outside the transmission band and degrades the error rate of the received bit.

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

[0004] In Patent Document 1, in order to reduce the amount of calculation, an equalizer that approximates a Volterra series with a memory polynomial is used to compensate for nonlinear distortion of a modulated signal, and the filter coefficients of the equalizer are calculated using known signals with a number of symbols smaller than the number of taps of the equalizer.In Patent Document 2, nonlinear distortion is compensated for by performing error correction and then equalization processing on received signals that do not contain known signals with the same signal point arrangement as the data section. [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] Y. Noda, S. Uehashi, S. Tani, K. Motoyoshi, and A. Okamura, "An adaptive equalization method for single-carrier wideband transmission with nonlinear distortion," IEICE Technical Report, WBS2018-2, vol. 118, No. 51, pp. 7-12, May 2018. Summary of the Invention [Problem to be solved by the invention]

[0007] Meanwhile, the modulation method may be switched between the acquisition process and the data transmission process. Furthermore, the modulation method may be switched using an ACM (Adaptive Coding and Modulation) method depending on the transmission path conditions. For example, the modulation method may be switched between a constant envelope modulated signal (such as QPSK or 8PSK) and a non-constant 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 switching of the modulation scheme between a constant envelope modulated signal and a non-constant envelope modulated signal. Furthermore, Non-Patent Documents 1 and 2 and Patent Document 1 state that even if the modulation scheme is switched from a constant envelope modulated signal to a non-constant envelope modulated signal, characteristics such as the error rate of the received bits will rapidly deteriorate. Furthermore, Patent Document 2 states that even if the modulation scheme is switched from a constant envelope modulated signal to a non-constant envelope modulated signal, it is necessary to perform error correction and then equalization, which increases the system delay of the entire receiving device and the amount of calculation per demodulated symbol.

[0009] Therefore, in order to solve the above problem, the present disclosure aims to suppress a sudden deterioration in characteristics such as the error rate of received bits when switching the modulation method from a constant envelope modulated signal to a non-constant envelope modulated signal in compensating for non-linear distortion of a modulated signal, while suppressing an increase in the system delay of the entire receiving device and the amount of calculation per demodulated symbol. [Means for solving the problem]

[0010] To solve the above problem, a modulator included in a transmitting device maps a constant envelope modulated signal to a plurality of envelope levels and adjusts the frequency of mapping to the plurality of envelope levels. As a result, when a receiving device switches between receiving a constant envelope modulated signal and a non-constant envelope modulated signal, an equalizer included in the receiving device can equally adjust the weighting coefficients of an equalization filter, thereby suppressing a sudden deterioration in characteristics such as the error rate of received bits.

[0011] Specifically, the present disclosure relates to a transmitting device that transmits a constant envelope modulated signal and a non-constant envelope modulated signal by switching between them to a receiving device that receives the signal by switching between the constant envelope modulated signal and the non-constant envelope modulated signal, the transmitting device comprising: a modulator that generates the constant envelope modulated signal and the non-constant envelope modulated signal by switching between them; and an amplifier that amplifies the constant envelope modulated signal and the non-constant envelope modulated signal, wherein when the receiving device receives the constant envelope modulated signal and the non-constant envelope modulated signal by switching between them, 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 a non-linear equalizer included in the receiving device equally adjusts the weighting coefficients of an equalization filter.

[0012] This configuration can suppress a sudden deterioration in characteristics such as the error rate of received bits when switching the modulation method from a constant envelope modulated signal to a non-constant envelope modulated signal. Furthermore, since it is not necessarily necessary to perform equalization processing after performing error correction, it is possible to suppress an increase in the system delay of the entire receiving device and the amount of calculation per demodulated symbol.

[0013] The present disclosure also provides a transmitting device characterized in that, 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 the plurality of envelope levels and adjusts the frequency of occurrence of mapping to the plurality of envelope levels so as to equally adjust the expected values ​​of the α-th power values ​​of the transmission signal levels (where α is a natural number greater than or equal to 2).

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

[0015] The present disclosure also provides a transmitting device characterized in that, when the receiving device receives the constant envelope modulated signal 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 mapping to the plurality of envelope levels so that the nonlinear equalizer included in the receiving device adjusts the weighting coefficient of the equalization filter of third order or higher to 0.

[0016] According to this configuration, when the receiving device receives a constant envelope modulated signal that has been determined to have small nonlinear distortion, the modulator included in the transmitting device maps the constant envelope modulated signal to multiple envelope levels with a predetermined occurrence frequency, and therefore the equalizer included in the receiving device can adjust the weighting coefficients of third-order or higher equalization filters to be equal to 0, as described above.

[0017] The present disclosure also 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 multiple envelope levels, or performs both amplitude modulation and phase modulation in accordance with the multiple envelope levels.

[0018] According to this configuration, the modulator provided in the transmitting device maps the constant envelope modulated signal to a plurality of envelope levels at a predetermined occurrence frequency, and can perform only phase modulation without performing amplitude modulation as the original constant envelope modulated signal, or can perform both amplitude modulation and phase modulation according to the plurality of envelope levels.

[0019] The present disclosure also provides a transmission program installed on a computer to cause the modulator provided in the transmission device described above to map the constant envelope modulated signal to the plurality of envelope levels and adjust the frequency of occurrence of mapping to the plurality of envelope levels.

[0020] According to this configuration, it is possible to provide a program having the above-described effects.

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

[0022] In this way, when compensating for nonlinear distortion in a modulated signal, the present disclosure can suppress a sudden deterioration in characteristics such as the error rate of received bits while suppressing an increase in the system delay of the entire receiving device and the amount of calculation per demodulated symbol when switching the modulation method from a constant envelope modulated signal to a non-constant envelope modulated signal. [Brief explanation of the drawings]

[0023] [Figure 1] FIG. 1 is a diagram illustrating a configuration of a transmission / reception system according to the present disclosure. [Figure 2]FIG. 2 is a diagram showing a procedure of a transmission and reception process according to the present disclosure. [Figure 3] FIG. 1 is a diagram illustrating weighting coefficients of a third-order equalization filter according to the prior art. [Figure 4] FIG. 3 is a diagram illustrating mapping of a constant envelope modulated signal according to the first embodiment. [Figure 5] FIG. 1 is a diagram illustrating distortion compensation when switching modulation methods according to the prior art. [Figure 6] FIG. 4 is a diagram illustrating distortion compensation when switching modulation methods in the first embodiment. [Figure 7] FIG. 10 is a diagram illustrating MER characteristics when switching between modulation schemes according to the prior art and the first embodiment. [Figure 8] FIG. 4 is a diagram illustrating distortion compensation when switching modulation methods in the first embodiment. [Figure 9] FIG. 10 is a diagram illustrating MER characteristics when switching between modulation schemes according to the prior art and the first embodiment. [Figure 10] FIG. 10 is a diagram illustrating the transmission signal level of a non-constant envelope modulated signal according to the second embodiment. [Figure 11] FIG. 10 is a diagram illustrating mapping of a constant envelope modulated signal according to the second embodiment. [Figure 12] FIG. 1 is a diagram illustrating distortion compensation when switching modulation methods according to the prior art. [Figure 13] FIG. 4 is a diagram illustrating distortion compensation when switching modulation methods in the first embodiment. [Figure 14] FIG. 10 is a diagram illustrating distortion compensation when switching modulation schemes in the second embodiment. [Figure 15] FIG. 10 is a diagram showing MER characteristics when switching between modulation schemes according to the prior art and the first and second embodiments. [Figure 16] FIG. 10 is a diagram showing MER characteristics when switching between modulation schemes according to the prior art and the first and second embodiments. [Figure 17] FIG. 4 is a diagram illustrating weighting coefficients when switching modulation schemes in the first embodiment. [Figure 18] FIG. 10 is a diagram illustrating weighting coefficients when switching modulation schemes in the second embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0024]

[0023] The following embodiments of the present disclosure will be described with reference to the accompanying drawings. The embodiments described below are examples of implementation of the present disclosure, and the present disclosure is not limited to the following embodiments.

[0025] (Configuration of the transmission / reception system of the present disclosure) The configuration of a transmission / reception system according to the present disclosure is shown in Fig. 1. The procedure of the transmission / reception process according to the present disclosure is shown in Fig. 2. The transmission / reception system S is applied to wireless or wired communication and includes a transmission device T and a reception device R. The transmission device T includes a modulator 1 and an amplifier 2. The reception device R includes an equalizer 3, a demodulator 4, and a switch 5. To cause the modulator 1 to execute step S1, a transmission program for step S1 can be installed in a computer.

[0026] Transmitting device T switches between a constant envelope modulated signal and a non-constant envelope modulated signal for transmission. Modulator 1 switches between generating a constant envelope modulated signal and a non-constant envelope modulated signal (step S1). Amplifier 2 amplifies the constant envelope modulated signal and the non-constant envelope modulated signal (step S2).

[0027] Receiver R switches between constant envelope modulated signals and non-constant envelope modulated signals for reception. Equalizer 3 compensates for non-linear distortion in the constant envelope modulated signals and non-constant envelope modulated signals (step S3). Demodulator 4 switches between the constant envelope modulated signals and non-constant envelope modulated signals for demodulation (step S4). Switch 5 outputs a known signal such as a pilot signal as a reference signal (described later) during the acquisition process, and outputs a hard decision value of demodulator 4 during the data transmission process.

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

[0029] The first-order equalization filter 31 receives the input signal y 1、n As the modulated signal and the additive noise x n +z n(See 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 calculates the input signal y 2、n The cube of the modulated signal and the additive noise |x n +z n | 2 (x n +z n ) (see the second equation in Equation 1).

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[0030] The first-order equalization filter 31 and the third-order equalization filter 34 may be implemented by a finite impulse response (FIR) filter or the like. n may be sampled at the symbol timing of the eye pattern aperture point, or may be oversampled at a sampling frequency P times the symbol timing. n AWGN (Additive White Gaussian Noise) or the like may be assumed.

[0031] As will be described later, the weighting coefficient calculation unit 32 calculates a weighting coefficient vector w1 of the primary equalization filter 31 (see the first equation of Equation 2, where 0, 1, . . . , M1-1 indicate tap numbers). The weighting coefficient calculation unit 35 calculates a weighting coefficient vector w2 of the third-order equalization filter 34 (see 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 is a filter that calculates a weighting coefficient vector w1 and an input signal vector y 1、n The dot product w1 between T y 1、n(See the first equation in Equation 3 and the first term on the right side of Equation 4.) The third-order equalization filter 34 calculates the weighting coefficient vector w2 and the input signal vector y 2、n The dot product w2 between T y 2、n (See the second equation in Equation 3 and the second term on the right side of Equation 4.) The adder 36 calculates the inner product w1 T y 1、n and the inner product w2 T y 2、n The sum x between n ^ (see Equation 4).

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[0033] The demodulator 4 outputs the sum x n ^ and demodulate the hard decision value x n-m The switch 5 outputs the reference signal x n-m In the acquisition process, the known signal x such as the pilot signal n-m In the data transmission process, the demodulator 4 outputs the hard decision value x n-m The subtractor 37 outputs the sum x n ^ and the reference signal x n-m The error value e between n (see Equation 5).

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[0034] In the present disclosure, when the first-order equalization filter 31 and the third-order equalization filter 34 are not applied with a roll-off filter (ROF), the first-order equalization filter 31 and the third-order equalization filter 34 are applied with a roll-off filter (ROF) of w 1、m and w 2、m is non-zero. Here, when m=0, the reference signal x n-m When m=1, the reference signal x n-mAs a modified example, when applying the ROF, the first-order equalization filter 31 and the third-order equalization filter 34 use a value of w at a plurality of m, for example, at the center tap of the ROF. 1、m and w 2、m may be non-zero.

[0035] The weighting coefficient calculation unit 32 calculates the error value e n The expected value of the square of E[|e n | 2 ], the weighting coefficient vector w1 of the first-order equalization filter 31 is ^ (See the first term on the left side of Equation 6.) The weighting coefficient calculation unit 35 calculates the error value e n The expected value of the square of E[|e n | 2 ], the weighting coefficient vector w2 of the third-order equalization filter 34 is ^ (See the second term on the left side of Equation 6.)

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[0036] In the present disclosure, the weighting coefficient calculation units 32 and 35 calculate the weighting coefficient vector w1 according to the MMSE (Minimum Mean Square Error) standard. ^ , w2 ^ As the Wiener solution w1 ^ , w2 ^ As a modified example, the weighting coefficient calculation units 32 and 35 calculate the weighting coefficient vector w1 according to the LMS (Least Mean Square) criterion or the RLS (Recursive Least Square) criterion. ^ , w2 ^ That is, the weighting coefficient calculation units 32 and 35 may calculate the error value e n The squared value of |e n | 2 The weight coefficient vector w1 is ^ , w2 ^ can be calculated.

[0037] Weighting coefficient vector w1 of the first-order equalization filter 31 ^ is expressed as in Equation 7. The weighting coefficient vector w2 of the third-order equalization filter 34 ^ is expressed as in Equation 8. Here, the modulated signal x n The nonlinear distortion of is extremely small, and the additive noise z n is assumed to be AWGN.

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[0038] In Equations 7 and 8, P 11 , P 12 , P 22 , r1, and r2 are expressed as in Equations 10 and 11. Here, P x is the modulated signal power, and P z is the additive noise power (see Equation 9). And, E[|x| α ](α≧2) is the modulating signal x n is the expectation of the α-th power of E[|z| 2 ] is the additive noise z n is the expected value of the square of (see Equations 9 to 11).

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[0039] Incidentally, when the receiving device R switches between receiving a constant envelope modulated signal and a non-constant envelope modulated signal, if the equalizer 3 included in the receiving device R can equally adjust the weighting coefficient vectors w1, w2 of the first-order equalization filter 31 and the third-order equalization filter 34 (or, as a variant, the weighting coefficient vectors of a third-order or higher equalization filter), it is possible to suppress a sudden deterioration in characteristics such as the error rate of the received bits.

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

[0041] In this way, when switching the modulation scheme from a constant envelope modulated signal to a non-constant envelope modulated signal, it is possible to suppress a sudden deterioration in characteristics such as the error rate of the received bits. Furthermore, since it is not necessarily necessary to perform equalization processing after performing error correction, it is possible to suppress an increase in the system delay of the entire receiving device R and the amount of calculation per demodulated symbol.

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

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[0043] In the constant envelope modulated signal x, the weighting coefficient w of the third-order equalization filter 34 is 2、m ^ is expressed as Equation 13 based on Equations 8 to 12. In the upper left column of FIG. 3, the weighting coefficient w 2、m ^ approaches 0 when the signal-to-noise ratio CNR is low, approaches -0.5 when the signal-to-noise ratio CNR is high, and can take on values ​​less than 0 and greater than -0.5 when the signal-to-noise ratio CNR is within the expected range of -10 to 30 dB.

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[0044] That is, in Equation 8, it is assumed that the nonlinear distortion of the constant envelope modulated signal x is extremely small. However, the weighting coefficient w of the third-order equalization filter 34 2、m ^ can take on non-zero values.

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

[0046] In the case of a non-constant envelope modulated signal x (in FIG. 3, a 16QAM signal, a 32APSK signal, or a 64QAM signal), the weighting coefficient w of the third-order equalization filter 34 is 2、m ^ is expressed in a different form from Equation 13 based on Equations 8 to 11. In the upper right column, lower left column, and lower right column of FIG. 3, the weighting coefficient w 2、m ^ approaches 0 when the signal-to-noise ratio CNR is low or high, and can take a value less than 0 and greater than about -0.1 when the signal-to-noise ratio CNR is within the expected range of -10 to 30 dB, but never as small as -0.5.

[0047] That is, in Equation 8, the weighting coefficient w of the third-order equalization filter 34 is set in accordance with the assumption that the nonlinear distortion of the non-constant envelope modulated signal x is extremely small. 2、m ^ can be said to take on a value of almost zero.

[0048] Therefore, in the prior art, when the receiving device R switches between receiving a constant envelope modulated signal and a non-constant envelope modulated signal, the equalizer 3 included in the receiving device R adjusts the weighting coefficient vector w2 of the third-order equalization filter 34 (or, as a variant, the weighting coefficient vector of a third-order or higher equalization filter) to a different value, making it impossible to suppress a sudden deterioration in characteristics such as the error rate of the received bits.

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

[0050] Then, when the receiving device R receives a constant envelope modulated signal that has been determined to have small nonlinear distortion, the equalizer 3 provided in the receiving device R can adjust the weighting coefficient vector w2 of the third-order equalization filter 34 (or, as a variant, the weighting coefficient vector of a third-order or higher equalization filter) to 0.

[0051] In the constant envelope modulated signal x (QPSK signal in FIG. 4), the weighting coefficient w of the third-order equalization filter 34 is 2、m ^ is adjusted to 0 (see the first equation of Equation 14). Therefore, the expected value E[|x| 4 ] is adjusted as shown in the second equation of Equation 14. Then, the weighting coefficient w 1、m ^ is adjusted as in the third equation of Equation 14.

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[0052] In the left column of Fig. 4, one envelope level in the constant envelope modulated signal x (QPSK signal) before mapping is s. In the right column of Fig. 4, two envelope levels in the constant envelope modulated signal x (QPSK signal) after mapping are s1 and s2, and the occurrence frequencies of 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| 2 ] is the modulated signal power P x The expected value E[|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 Fig. 4, occurrence frequencies p1 and p2 of mapping to two envelope levels s1 and s2 are known quantities, and the two envelope levels s1 and s2 are unknown quantities, and it can be calculated as in Equation 17. As a modified example, it can be calculated in the same way as Equation 17, with one of the two envelope levels s1 and s2 being a known quantity, and the occurrence frequencies p1 and p2 of mapping to the two envelope levels s1 and s2 and the other of the two envelope levels s1 and s2 being unknown quantities. However, when the inner envelope level s1 is a known quantity, 0≦s1<√P x If the outer envelope level s2 is a known quantity, then √(2P x )≦s2. Also, p1≧p2.

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[0055] In order to determine that constant envelope modulated signal x has small nonlinear distortion, receiving device R may refer to the backoff condition of the transmission signal level using a frame header or the like (the smaller the backoff, the smaller the nonlinear distortion is determined to be), or may refer to the modulation order of constant envelope modulated signal x (the lower the modulation order, the smaller the nonlinear distortion is determined to be). Furthermore, modulator 1 included in 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] In this way, when receiving device R receives a constant envelope modulated signal that has been determined to have small nonlinear distortion, modulator 1 provided in transmitting device T maps the constant envelope modulated signal to multiple envelope levels with a predetermined occurrence frequency, and therefore equalizer 3 provided in receiving device R can adjust the weighting coefficients of third-order or higher equalization filters to 0, as described above.

[0057] In the right column of Figure 4, when generating a constant envelope modulated signal x, the modulator 1 performs only phase modulation without performing amplitude modulation, regardless of the multiple envelope levels s, or performs both amplitude modulation and phase modulation in accordance with the multiple envelope levels s.

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

[0059] In this way, the modulator 1 provided in the transmitting device T maps the constant envelope modulated signal to a plurality of envelope levels at a predetermined occurrence frequency, and can perform only phase modulation without performing amplitude modulation as the original constant envelope modulated signal, or can perform both amplitude modulation and phase modulation according to the plurality of envelope levels.

[0060] Distortion compensation when switching modulation schemes in the conventional technology and the first embodiment is shown in Figures 5 and 6, respectively. MER (Modulation Error Ratio) characteristics when switching modulation schemes in the conventional technology and the first embodiment are shown in Figure 7. In Figures 5 to 7, there is no nonlinear distortion, CNR = 25 dB, and the modulation scheme 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 an ideal QPSK signal and a post-distortion compensation QPSK signal, respectively. The lower left and lower right columns of Figures 5 and 6 show the constellations of an ideal 64QAM signal and a post-distortion compensation 64QAM signal, respectively.

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

[0062] In the first embodiment (see FIGS. 6 and 7), in the distortion-compensated QPSK signal, the signal points are not distorted in the amplitude direction, so the deviation characteristic MER of the signal points from the ideal point is sufficient, and the weighting 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 weighting 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 distorted in either the amplitude direction or the phase direction, and the deviation characteristic MER of the signal points from the ideal point does not change.

[0063] FIG. 8 shows distortion compensation when switching modulation schemes in the first embodiment. FIG. 9 shows MER characteristics when switching modulation schemes in the conventional technology and the first embodiment. In FIG. 8, there is slight 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 FIG. 8 show ideal constellations of a QPSK signal after distortion and after distortion compensation, respectively. The lower left, lower middle, and lower right columns of FIG. 8 show ideal constellations of a 64QAM signal after distortion and after distortion compensation, respectively.

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

[0065] In the first embodiment (see FIGS. 8 and 9), in the distortion-compensated QPSK signal, the signal points are not distorted in the amplitude direction, so the deviation characteristic MER of the signal points from the ideal point is sufficient, and the weighting 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 weighting 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 distorted in the amplitude direction or the phase direction, and the deviation characteristic MER of the signal points from the ideal point does not change. However, in FIGS. 8 and 9, unlike FIGS. 5 to 7, there is some nonlinear distortion, so the deviation characteristic MER of the signal points from the ideal point changes slightly before and after switching the modulation scheme.

[0066] (Mapping of constant envelope modulated signal in the second embodiment) The transmission signal levels of the non-constant envelope modulated signal of the second embodiment are shown in Figure 10. The mapping of the constant envelope modulated signal of the second embodiment is shown in Figure 11. The modulator 1 provided in the transmitting device T maps the constant envelope modulated signal to a plurality of envelope levels s, regardless of the presence or absence of nonlinear distortion, and adjusts the occurrence frequency p of the mapping to the plurality of envelope levels s (step S1).

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

[0068] When there is no nonlinear distortion, the weighting coefficient w of the third-order equalization filter 34 2、m ^ is expressed by Equations 8 to 11. Here, for a constant envelope modulated signal and a non-constant envelope modulated signal, among the terms of Equations 8 to 11, the modulated signal power P x are adjusted to be equal (see the first equation in Equation 18), and the signal-to-noise ratio CNR is automatically equal (see the second equation in Equation 18).

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[0069] Therefore, in the constant envelope modulated signal and the non-constant envelope modulated signal, among the terms of Equations 8 to 11, the expected value E[|x| 4 ] are adjusted equally, and the expected value E[|x| 6 ] are adjusted equally, (weighting coefficient w 1、m ^ Of course, the weighting coefficient w of the third-order equalization filter 34 2、m ^ should also be adjusted equally (see Equation 19).

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[0070] When nonlinear distortion is present, the weighting coefficient vector w2 of the third-order equalization filter 34 becomes more complicated than those in equations 8 to 11. However, for a constant envelope modulated signal and a non-constant envelope modulated signal, among the terms in the weighting coefficient equations, the modulated signal power P x are adjusted to be equal (see the first equation in Equation 18), and the signal-to-noise ratio CNR is automatically equal (see the second equation in Equation 18).

[0071] Therefore, for constant envelope modulated signals and non-constant envelope modulated signals, among the terms in the weighting coefficient formula, the expected value E[|x| 4 ] are adjusted equally, and the expected value E[|x| 6 ] are adjusted equally, it is considered that the weight coefficient vector w2 of the third-order equalization filter 34 (as well as the weight coefficient vector w1 of the first-order equalization filter 31) is also adjusted equally (see Equation 19).

[0072] 12 to 18 actually show that even when there is nonlinear distortion, if Equation 19 holds, the deviation characteristic MER of the signal point from the ideal point does not change before and after switching the modulation scheme. Therefore, even when there is nonlinear distortion, if Equation 19 holds, it is empirically known that the weighting coefficient vector w2 of the third-order equalization filter 34 (as well as the weighting coefficient vector w1 of the first-order equalization filter 31) will be equal before and after switching the modulation scheme.

[0073] In the left or right column of Figure 10, in a non-constant envelope modulated signal x (16QAM signal or 32APSK signal), the three envelope levels are s1, s2, and s3, and the occurrence 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 FIG. 10, the expected value E[|x| 4 ] is expressed by the first equation of Equation 20, and is the expectation value E[|x| 6 ] is expressed by the second equation of Equation 20. Here, γk is the k-th envelope level s relative to the first envelope level s1. k As a first step, the calculation of Equation 20 is performed on a non-constant envelope modulated signal x (16QAM signal or 32APSK signal).

number

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

[0076] In the right column of Fig. 11, the expected value E[|x| 4 ] is expressed by the first equation of Equation 20, and is the expected value E[|x| 6 ] is expressed by the second equation of Equation 20. Here, γ2 is the ratio of the second envelope level s2 to the first envelope level s1. As a 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] Note that receiving device R can apply the second embodiment regardless of whether the nonlinear distortion of constant envelope modulated signal x is small or large, in contrast to the first embodiment which can be applied only when the nonlinear distortion of constant envelope modulated signal x is small. Furthermore, modulator 1 included in transmitting device T may map the constant envelope modulated signal to three or more envelope levels s, and may adjust the frequency p of occurrence of mapping to three or more envelope levels s.

[0078] In this way, when the receiving device R switches between receiving a constant envelope modulated signal and a non-constant envelope modulated signal, the modulator 1 provided in the transmitting device T adjusts the expected value of the α-th power value of the transmission signal level (where α is a natural number equal to or greater than 2 depending on the order of the equalization filter) to be equal, and therefore the equalizer 3 provided in the receiving device R can adjust the weighting coefficients of the equalization filter to be equal, as described above.

[0079] In the right column of Figure 11, when generating a constant envelope modulated signal x, the modulator 1 performs only phase modulation without performing amplitude modulation, regardless of the multiple envelope levels s, or performs both amplitude modulation and phase modulation in accordance with the multiple envelope levels s.

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

[0081] In this way, the modulator 1 provided in the transmitting device T maps the constant envelope modulated signal to a plurality of envelope levels at a predetermined occurrence frequency, and can perform only phase modulation without performing amplitude modulation as the original constant envelope modulated signal, or can perform both amplitude modulation and phase modulation according to the plurality of envelope levels.

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

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

[0084] In the first embodiment (see FIGS. 13, 15, and 16), in the distortion-compensated QPSK signal, the signal points are not distorted in the amplitude direction, so the MER, the deviation characteristic of the signal points from the ideal point, is sufficient, and the weighting 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 weighting 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 distorted in the amplitude direction or the phase direction, and the MER, the deviation characteristic of the signal points from the ideal point, does not change. However, in FIG. 13, unlike FIG. 6, there is some nonlinear distortion, so the MER, the deviation characteristic of the signal points from the ideal point, changes slightly before and after switching the modulation scheme.

[0085] In the second embodiment (see FIGS. 14, 15, and 16), in the distortion-compensated QPSK signal, the signal points are not distorted in the amplitude direction, so the signal point deviation characteristic MER from the ideal point is sufficient, and the weighting 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 weighting 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 distorted in either the amplitude direction or the phase direction, and the signal point deviation characteristic MER from the ideal point does not change. Furthermore, in FIG. 14, unlike FIG. 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 Fig. 15, after switching the modulation scheme in the first embodiment, the weighting coefficient vector w2 of the third-order equalization filter 34 is fixed to 0, so the deviation characteristic MER of the signal point from the ideal point remains almost unchanged from immediately after switching the modulation scheme to after switching the modulation scheme. In Fig. 16, after switching the modulation scheme in the first embodiment, the weighting coefficient vector w2 of the third-order equalization filter 34 is updated from 0, so the deviation characteristic MER of the signal point from the ideal point converges to the same extent as in the second embodiment from immediately after switching the modulation scheme to after switching the modulation scheme.

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

[0088] In the first embodiment (see FIG. 17), the weighting coefficient |w of the primary equalization filter 31 changes from immediately before the modulation scheme is switched, through immediately after the modulation scheme is switched, to the time when the weighting coefficient converges. 1、m | remains almost unchanged, but the weighting coefficient |w 2、m | converges to a small value. Here, since there is some nonlinear distortion, the weighting coefficient |w of the third-order equalization filter 34 2、m | is non-zero at multiple m and at the center tap of the ROF.

[0089] In the second embodiment (see FIG. 18), the weighting coefficient |w of the primary equalization filter 31 changes from immediately before the modulation scheme is switched, through immediately after the modulation scheme is switched, to the time when the weighting coefficient converges. 1、m | has hardly changed, and the weighting coefficient |w 2、m In the first embodiment (see FIG. 17), the weighting coefficient |w of the third-order equalization filter 34 is almost unchanged compared to the second embodiment (see FIG. 18) when the weighting coefficients converge. 2、m | converges to the same extent.

[0090] 12 to 18, it has been actually shown that even when there is nonlinear distortion, if Equation 19 holds, the deviation characteristic MER of the signal point from the ideal point does not change before and after switching the modulation method. Furthermore, it has been empirically found that even when there is nonlinear distortion, if Equation 19 holds, the weighting coefficient vector w2 of the third-order equalization filter 34 (as well as the weighting coefficient vector w1 of the first-order equalization filter 31) will be equal before and after switching the modulation method. [Industrial Applicability]

[0091] The transmitting device and transmitting program disclosed herein can compensate for nonlinear distortion in a modulated signal by switching the modulation method from a constant envelope modulated signal to a non-constant envelope modulated signal, while suppressing an increase in the system delay of the entire receiving device and the amount of calculation per demodulated symbol, while suppressing a sudden deterioration in characteristics such as the error rate of received bits. [Explanation of symbols]

[0092] S: Transmitting and receiving system T: Transmitter R: Receiver 1: Modulator 2: Amplifier 3: Equalizer 4: Demodulator 5: Switch 31:1st order equalization filter 32: Weighting coefficient calculation unit 33:3rd power calculation section 34: 3rd order equalization filter 35: Weighting coefficient calculation unit 36: Adder 37: Subtractor

Claims

1. A transmitting device that selectively transmits a constant envelope modulated signal and a non-constant envelope modulated signal to a receiving device that selectively receives the constant envelope modulated signal and a non-constant envelope modulated signal, the transmitting device comprising: a modulator that switches between generating the constant envelope modulated signal and the non-constant envelope modulated signal; an amplifier that amplifies the constant envelope modulated signal and the non-constant envelope modulated 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 a plurality of envelope levels and adjusts the frequency of occurrence of mapping to the plurality of envelope levels so that a non-linear equalizer included in the receiving device equally adjusts weighting coefficients of an equalization filter. A transmitting device applicable to wireless or wired communication.

2. When the receiving device receives the constant envelope modulated signal and the non-constant envelope modulated signal by switching between them, 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 as to equally adjust the expected values ​​of the α-th power values ​​of the transmission signal levels (where α is a natural number equal to or greater than 2).

2. The transmitting device according to claim 1, wherein:

3. When the receiving device receives the constant envelope modulated signal 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 included in the receiving device adjusts the weighting coefficient of the equalization filter of third order or higher to 0.

3. The transmitting device according to claim 1 or 2.

4. The modulator performs only phase modulation without amplitude modulation when generating the constant envelope modulated signal, regardless of the plurality of envelope levels.

2. The transmitting device according to claim 1, wherein:

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

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