Distortion compensation device, transmission signal generation method in distortion compensation device, transmission signal generation program in distortion compensation device, and recording medium

Abstract

This distortion compensation device is disposed between a transmission signal generation unit (1) and a high-frequency power amplifier (4). The distortion compensation device is provided with: a low-regrowth transmission signal generation unit (21) to which a transmission signal from the transmission signal generation unit (1) and an operation status signal of the high-frequency power amplifier (4) are input, and which generates, from the input transmission signal according to the input operation status signal, a low-regrowth transmission signal in which spectrum regrowth, in which power outside a frequency band in a transmission signal output from the high-frequency power amplifier (4) increases when the high-frequency power amplifier (4) operates with low back-off, is suppressed; and a distortion compensation unit (22) that imparts distortion that compensates for a distortion component generated in the high-frequency power amplifier (4) to the low-regrowth transmission signal generated by the low-regrowth transmission signal generation unit (21) to generate a distortion-compensated low-regrowth transmission signal.

Description

Distortion compensation device, transmission signal generation method in distortion compensation device, transmission signal generation program in distortion compensation device, and recording medium

[0001] This disclosure relates to a distortion compensation device for reducing distortion components generated in a high-frequency power amplifier in a microwave wireless transmitter, a transmission signal generation method in the distortion compensation device, a transmission signal generation program in the distortion compensation device, and a recording medium.

[0002] Patent Document 1 describes a nonlinear distortion compensation method for reducing distortion components generated in a high-frequency power amplifier in a microwave radio device. The microwave radio device described in Patent Document 1 has a modulation unit, a transmission unit, a high-frequency power amplifier, a reception unit, and a demodulation unit, and a digital filter is provided on the input side of the modulation unit. The digital filter is controlled by a control unit using the demodulated signal from the demodulation unit to minimize intersymbol interference caused by fluctuations in the operating conditions of the high-frequency power amplifier, and a distortion that compensates for the nonlinear distortion components generated in the high-frequency power amplifier is applied to the modulation unit in advance.

[0003] Japanese Patent Application Publication No. 4-290321

[0004] A nonlinear distortion compensation method for reducing distortion components generated in a high-frequency power amplifier in a microwave radio device operates the high-frequency power amplifier so that its input / output characteristics become the ideal input / output characteristics shown in Figure 18, within the overall input / output characteristics of the radio transmitter in the microwave radio device. In Figure 18, the horizontal axis represents the input power Pin of the transmission signal input to the high-frequency power amplifier, and the vertical axis represents the output power Pout of the transmission signal output from the high-frequency power amplifier. Psat represents the saturation power of the high-frequency power amplifier, and Pin,s represents the input power when the output power Pout is at saturation power.

[0005] In the operation of a high-frequency power amplifier, the output power Pout of the transmitted signal increases linearly with respect to the input power Pin of the transmitted signal until it reaches the saturation power Psat. When the input power Pin of the transmitted signal exceeds the input power Pin,s at saturation power, the output power Pout of the transmitted signal becomes constant at the saturation power Psat. The phase characteristics of a high-frequency power amplifier are always constant.

[0006] By the way, when a high-frequency power amplifier is operated with a backoff setting (hereinafter referred to as low backoff) where the operating point is set to be smaller than the peak-to-average power ratio (PAPR) of the transmitted signal, there are cases where the input power Pin of the transmitted signal input to the high-frequency power amplifier exceeds the input power Pin,s at saturation power.

[0007] The nonlinear distortion compensation method shown in Patent Document 1 can reduce the backoff amount of the high-frequency power amplifier, and moreover, when operating at low backoff, if the input power Pin is less than or equal to the input power Pin,s at saturation power, the input / output characteristics of the high-frequency power amplifier are linear. However, in the nonlinear distortion compensation method shown in Patent Document 1, when the input power Pin exceeds the input power Pin,s at saturation power, the output power Pout of the transmitted signal becomes the saturation power Psat, which causes the transmitted signal output from the high-frequency power amplifier to clip, and the power outside the frequency band of the transmitted signal increases, resulting in a problem of large spectral regrowth (hereinafter referred to as regrowth).

[0008] This disclosure has been made in view of the above-mentioned points, and aims to provide a distortion compensation device for a microwave radio transmitter that can suppress the occurrence of regrowth in the transmitted signal output from the high-frequency power amplifier, even when the high-frequency power amplifier in the microwave radio transmitter is operated with a backoff amount smaller than the peak power to average power ratio.

[0009] The distortion compensation device according to this disclosure is a distortion compensation device disposed between a transmission signal generation unit and a high-frequency power amplifier, comprising: a low-regrowth transmission signal generation unit that receives a transmission signal from the transmission signal generation unit and an operating status signal of the high-frequency power amplifier as inputs, and generates a low-regrowth transmission signal that suppresses spectrum regrowth, in which out-of-band power increases in the transmission signal output from the high-frequency power amplifier when the high-frequency power amplifier is operating at low backoff, based on the input transmission signal and the input operating status signal; and a distortion compensation unit that generates a distortion-compensated low-regrowth transmission signal by adding distortion to the low-regrowth transmission signal generated by the low-regrowth transmission signal generation unit to compensate for distortion components generated in the high-frequency power amplifier.

[0010] According to this disclosure, an amplified transmission signal with low regrowth can be obtained in the transmission signal output from a high-frequency power amplifier in a microwave radio transmitter.

[0011] This is a block diagram showing an example configuration of a microwave radio transmitter equipped with a distortion compensation device according to Embodiment 1. This is a block diagram showing an example configuration of the low-regrowth transmission signal generation unit in the distortion compensation device according to Embodiment 1. This is a diagram showing the results of an investigation into the input / output characteristics from the distortion compensation device to the power amplifier in a microwave radio transmitter equipped with a distortion compensation device according to Embodiment 1. This is a diagram showing the results of an investigation into the relationship between the output power and the frequency of the output signal of the power amplifier in a microwave radio transmitter equipped with a distortion compensation device according to Embodiment 1. This is a diagram showing an example of the hardware configuration of the distortion compensation device according to Embodiment 1. This is a flowchart showing an example of the operation of the distortion compensation device according to Embodiment 1. This is a flowchart showing an example of the operation of the low-regrowth transmission signal generation unit in the distortion compensation device according to Embodiment 1. This is a block diagram showing an example configuration of a microwave radio transmitter equipped with a distortion compensation device according to Embodiment 2. This is a block diagram showing an example of the configuration of a microwave radio transmitter equipped with a distortion compensation device according to Embodiment 3. This is a diagram showing an example of an address corresponding to the parameters of the transmission signal average power Pave and backoff amount Pbo generated by the address generation unit 21Bc of the low-regrowth transmission signal generation unit in the distortion compensation device according to Embodiment 3. This is a flowchart showing an example of the operation of the low-regrowth transmission signal generation unit in the distortion compensation device according to Embodiment 3. This is a block diagram showing an example configuration of a microwave radio transmitter equipped with a distortion compensation device according to Embodiment 4. This is a block diagram showing an example configuration of the training data generation unit in the distortion compensation device according to Embodiment 4. This is a flowchart showing an example of operation of the low-regrowth transmission signal generation unit in the distortion compensation device according to Embodiment 4. This is a block diagram showing an example configuration of a microwave radio transmitter equipped with a distortion compensation device according to Embodiment 5. This is a block diagram showing an example configuration of the training data generation unit in the distortion compensation device according to Embodiment 5. This is a flowchart showing an example of operation of the low-regrowth transmission signal generation unit in the distortion compensation device according to Embodiment 5. This is a diagram showing the ideal input / output characteristics of a high-frequency power amplifier in a microwave radio device.

[0012] Embodiment 1. A microwave radio transmitter equipped with the distortion compensation device according to Embodiment 1 will be described with reference to Figures 1 to 7. As shown in Figure 1, the microwave radio transmitter comprises a transmission signal generation unit 1, a distortion compensation device 2 according to Embodiment 1, a digital-to-analog converter (DAC) 3, a high-frequency power amplifier (hereinafter simply referred to as a power amplifier) ​​4, and an antenna 5. The distortion compensation device 2 according to Embodiment 1 is arranged between the transmission signal generation unit 1 and the power amplifier 4 in the microwave radio transmitter.

[0013] The transmission signal generation unit 1 generates and outputs a transmission signal consisting of a digital signal to be transmitted by a microwave radio transmitter. The transmission signal is, for example, a radio frequency (RF) signal. However, if a frequency converter that converts an intermediate frequency (IF) baseband signal to an RF signal is provided before the power amplifier, the transmission signal may be an IF baseband signal.

[0014] The distortion compensation device 2 according to Embodiment 1 comprises a low-regrowth transmission signal generation unit 21 and a distortion compensation unit 22. The low-regrowth transmission signal generation unit 21 receives the transmission signal from the transmission signal generation unit 1 and the operating status signal of the power amplifier 4 as input. The input transmission signal is converted by the input operating status signal into a transmission signal (hereinafter referred to as a low-regrowth transmission signal) that suppresses spectral regrowth (hereinafter referred to as regrowth), which is an increase in power outside the frequency band in the transmission signal, when the power amplifier 4 is operating at low backoff. The low-regrowth transmission signal is generated by converting the input transmission signal into a transmission signal (hereinafter referred to as a low-regrowth transmission signal) that suppresses spectral regrowth (hereinafter referred to as regrowth), which is an increase in power outside the frequency band in the transmission signal.

[0015] In Embodiment 1, the operating status signal is backoff information consisting of a digital signal indicating the backoff amount (value) of the power amplifier 4. In Embodiment 1, the low regrowth transmission signal generation unit 21 generates a low regrowth transmission signal from the transmission signal generation unit 1 and the digital signal indicating the backoff amount of the power amplifier 4.

[0016] The backoff amount indicating the operating status signal may be acquired externally, acquired experimentally, or pre-set in accordance with the power amplifier 4. The acquired or set backoff amount may be stored in a memory means and read out by a read command signal from the low-regrowth transmission signal generation unit 21.

[0017] The low-regrowth transmission signal generation unit 21 receives the transmission signal from the transmission signal generation unit 1 and the backoff amount Pbo (dB) indicated by the operating status signal of the power amplifier 4 as input. The transmission signal from the transmission signal generation unit 1 is saturated (clipped) near the power (Pave + Pbo (dBm)) which is the sum of the average transmission signal power Pave (dBm) of the transmission signal from the transmission signal generation unit 1 and the backoff amount Pbo (dBm) indicated by the operating status signal of the power amplifier 4. The power amplifier 4 exhibits ideal input / output characteristics, that is, the output power increases linearly with respect to the input power up to the saturation power, and then remains constant at the saturation power. The unit converts the transmission signal output from the power amplifier 4 into a low-regrowth transmission signal in which regrowth is suppressed, thereby generating a low-regrowth transmission signal.

[0018] In other words, the low-regrowth transmission signal is the transmission signal from the transmission signal generation unit 1 that has been clipped at (Pave + Pbo (dBm)). As a result, the peak power of the transmission signal from the transmission signal generation unit 1 is clipped at (Pave + Pbo).

[0019] By making the transmission signal from the transmission signal generation unit 1 a low-regrowth transmission signal, as a result, in the power amplifier 4, the output power Pout in the transmission signal increases nonlinearly with respect to the input power Pin, and moreover, the power amplifier 4 exhibits an input / output characteristic in which the slope up to the saturation power is small compared to the slope up to the saturation power in an input / output characteristic where the output power is linear with respect to the input power. In other words, the low-regrowth transmission signal is a signal that, compared to the input / output characteristic of an ideal power amplifier 4 where the output power is linear with respect to the input power, exhibits an input / output characteristic in which the output power changes gradually with respect to the input power near the saturation power.

[0020] As shown in Figure 2, the low-regrowth transmission signal generation unit 21 includes a first fast Fourier transform (FFT) unit 211, a peak cut unit 212, a second fast Fourier transform (FFT) unit 213, a regrowth suppression unit 214, and an inverse fast Fourier transform (IFFT) unit 215.

[0021] The first FFT unit 211 performs a Fourier transform on the transmission signal from the transmission signal generation unit 1 to generate a frequency spectrum X1(f). In X1(f), f represents the frequency of the transmission signal. The peak cut unit 212 clips the power of the transmission signal from the transmission signal generation unit 1 at a power of (Pave + Pbo (dBm) = Psat). That is, the peak cut unit 212 receives the transmission signal from the transmission signal generation unit 1 and generates a transmission signal in which the power component of the input transmission signal that exceeds (Pave + Pbo) is converted to a power of (Pave + Pbo).

[0022] In other words, the peak cut unit 212 generates a transmission signal from the transmission signal generation unit 1 that has its peak power clipped to (Pave + Pbo) so that if the input power Pin of the transmission signal input to the power amplifier 4 exceeds the power of (Pave + Pbo) (Pin > (Pave + Pbo)), the input power Pin of the transmission signal is clipped to the power of (Pave + Pbo).

[0023] In the first embodiment, the peak cut unit 212 performs a conversion similar to the input / output characteristics of an ideal power amplifier shown in Figure 18, and therefore the threshold value for the clipped power of the transmitted signal from the transmitted signal generation unit 1 is set to (Pave + Pbo). However, it is not necessarily required to be (Pave + Pbo), and the threshold value for the clipped power may be adjusted to maximize the effect of regrowth reduction.

[0024] The second FFT unit 213 performs a Fourier transform on the transmitted signal generated by the peak cut unit 212 to generate a frequency spectrum X2(f). In X2(f), f represents the frequency of the transmitted signal.

[0025] The regrowth suppression unit 214 receives the frequency spectrum X1(f) generated by the first FFT unit 211 and the frequency spectrum X2(f) generated by the second FFT unit 213, and generates a frequency spectrum X3(f) by replacing the frequency spectrum X2(f) generated by the second FFT unit 213 that has a large regrowth frequency component with a frequency spectrum that has a small regrowth frequency component.

[0026] In other words, the regrowth suppression unit 214 replaces the regrowth frequency component of the frequency spectrum X2(f) generated by the second FFT unit 213 with the frequency spectrum X1(f) generated by the first FFT unit 211. In short, as can be expressed by equation (1) below, the regrowth suppression unit 214 selects the frequency spectrum X1(f) generated by the first FFT unit 211 for the frequency component of the transmitted signal at the set regrowth frequency f, and selects the frequency spectrum X2(f) generated by the second FFT unit 213 for the other frequency components, i.e., frequency components other than the regrowth frequency f, to generate the frequency spectrum X3(f).

[0027]

[0028] In Embodiment 1, the regrowth suppression unit 214 selected the frequency spectrum X1(f) generated by the first FFT unit 211 for the set regrowth frequency f. However, other methods are acceptable as long as the magnitude of the regrowth frequency components can be reduced. For example, the frequency spectrum generated by multiplying the frequency spectrum X2(f) generated by the second FFT unit 213 for the set regrowth frequency f by a positive number less than 1, α (0 < α < 1), may be selected.

[0029] ​In other words, the regrowth suppression unit 214 selects a frequency spectrum obtained by multiplying the frequency spectrum X2(f) generated by the second FFT unit 213 by α for the set regrowth frequency f, and for other frequencies f, it selects the frequency spectrum X2(f) generated by the second FFT unit 213 to generate a frequency spectrum X3(f). In this case, the first FFT unit 211 becomes unnecessary. The IFFT unit 215 converts the frequency spectrum X3(f) generated by the regrowth suppression unit 214 into a time waveform using an inverse Fourier transform to generate a low-regrowth transmission signal.

[0030] The distortion compensation unit 22 receives the low-regrowth transmission signal generated by the low-regrowth transmission signal generation unit 21, and applies distortion to the low-regrowth transmission signal to compensate for the nonlinear distortion component generated in the power amplifier 4, thereby generating a distortion-compensated low-regrowth transmission signal. The distortion compensation unit 22 includes a digital filter unit 22a and a distortion compensation coefficient storage unit 22b.

[0031] The digital filter section 22a is composed of a Pre Distorter (PD, hereinafter referred to as the PD section). The PD section 22a receives the low-regrowth transmission signal generated by the low-regrowth transmission signal generation section 21 and the distortion compensation coefficient from the distortion compensation coefficient storage section 22b, and applies the distortion compensation coefficient to the low-regrowth transmission signal to generate a distortion-compensated low-regrowth transmission signal.

[0032] The distortion-compensated low-regrowth transmission signal generated by the PD unit 22a is a signal to which distortion is added to compensate for the distortion component generated by the power amplifier 4 to the low-regrowth transmission signal generated by the low-regrowth transmission signal generation unit 21. Therefore, the distortion added by the PD unit 22a and the distortion generated by the power amplifier 4 cancel each other out.

[0033] As a result, the waveforms of the transmission signal input to the PD unit 22a and the transmission signal output from the power amplifier 4 match. The distortion compensation coefficient storage unit 22b stores distortion compensation coefficients for controlling the distortion that the PD unit 22a imposes on the low-regrowth transmission signal.

[0034] The digital-to-analog converter 3 converts the distortion-compensated transmission signal for low ring loss output from the distortion compensation unit 22 into an analog signal. The power amplifier 4 amplifies the power of the distortion-compensated transmission signal for low ring loss from the digital-to-analog converter 3.

[0035] In the power amplifier 4, the investigation results of the input-output characteristics of the output power Pout of the amplified transmission signal with respect to the input power Pin of the transmission signal input to the distortion compensation device 2 are shown by the solid line E in FIG. 3. In FIG. 3, the horizontal axis represents the input power Pin of the transmission signal input to the distortion compensation device 2, the vertical axis represents the output power Pout of the transmission signal output from the power amplifier 4, and Psat represents the saturation power of the power amplifier 4.

[0036] The broken line R shows the input-output characteristics of a comparative example in the case where the low ring loss transmission signal generation unit 21 in the distortion compensation device 2 is not provided, the transmission signal from the transmission signal generation unit 1 is distortion-compensated by the distortion compensation unit 22 in the distortion compensation device 2, converted into a digital signal by the digital-to-analog converter 3, and input to the power amplifier 4.

[0037] As is clear from FIG. 3, by using the low ring loss transmission signal generation unit 21 to make the transmission signal from the transmission signal generation unit 1 a transmission signal for low ring loss, in the power amplifier 4, the output power Pout with respect to the input power Pin in the transmission signal indicated by the solid line E increases non-linearly.

[0038] Furthermore, in the power amplifier 4, the slope of the output power Pout with respect to the input power Pin up to the saturation power in the input-output characteristics indicated by the broken line R where the output power Pout is linear with respect to the input power Pin, and the slope of the output power Pout with respect to the input power Pin in the transmission signal indicated by the solid line E in the assumed range including the input power at the saturation power are small, showing so-called gently changing input-output characteristics.

[0039] Also, in the power amplifier 4, the investigation results of the characteristics of the output power Pout of the amplified transmission signal with respect to the frequency f of the distortion-compensated transmission signal for low jitter are shown by the solid line E in FIG. 4. In FIG. 4, the horizontal axis represents the frequency f of the transmission signal output from the power amplifier 4, and the vertical axis represents the output power Pout of the transmission signal output from the power amplifier 4. The broken line R shows the characteristics according to a comparative example when the transmission signal from the transmission signal generation unit 1 is distortion-compensated by the distortion compensation unit 22 without providing the low jitter transmission signal generation unit 21 in the distortion compensation device 2, converted into a digital signal by the digital-to-analog converter 3, and input to the power amplifier 4.

[0040] As is clear from FIG. 4, by using the low jitter transmission signal generation unit 21 to convert the transmission signal from the transmission signal generation unit 1 into a low jitter transmission signal, the output power Pout with respect to the frequency f in the transmission signal (low jitter transmission signal) shown by the solid line E is lower than the output power Pout with respect to the frequency f in the transmission signal shown by the broken line R outside the frequency band of the transmission signal, suppressing the generation of jitter.

[0041] The antenna 5 receives the transmission signal amplified by the power amplifier 4 for the distortion-compensated low jitter transmission signal and radiates it into space as a transmission radio wave.

[0042] The distortion compensation device 2 may be realized by dedicated hardware, but in Embodiment 1, it is realized by software, firmware, or a combination of software and firmware. FIG. 5 shows the hardware configuration of a computer when the distortion compensation device 2 is realized by software or firmware.

[0043] The distortion compensation device 2 includes a CPU (Central Processing Unit) 20A, a large-capacity semiconductor memory (RAM: Random Access Memory) 20B, a storage device (ROM: Read only memory) such as a hard disk device or an SSD device which is a non-volatile recording device, an input interface unit 20D, an output interface unit 20E, and a signal path (bus) 20F.

[0044] The CPU 20A controls and manages the RAM 20B, ROM 20C, input interface unit 20D, and output interface unit 20E. The CPU 20A loads the program stored in ROM 20C into RAM 20B, and the CPU 20A executes various processes based on the program loaded into RAM. The signal path 20F is a bus that interconnects the CPU 20A, RAM 20B, ROM 20C, input interface unit 20D, and output interface unit 20E.

[0045] The transmission signal from the transmission signal generation unit 1 is first taken into the RAM 20B via the input interface unit 20D. When backoff information, which is an operating status signal, is acquired from an external source, it is first taken into the RAM 20B via the input interface unit 20D. If the backoff information is pre-set to correspond to the power amplifier 4, it is stored in the ROM 20C.

[0046] The functions of the low-regrowth transmission signal generation unit 21 are executed by a program stored in ROM 20C, CPU 20A, and RAM 20B. The functions of the PD unit 22a are executed by a program stored in ROM 20C, CPU 20A, and RAM 20B. The distortion compensation coefficient storage unit 22b corresponds to either ROM 20C or RAM 20B and stores distortion compensation coefficients for controlling the distortion that ROM 20C or RAM 20B imposes on the low-regrowth transmission signal. The distortion-compensated low-regrowth transmission signal obtained is executed by the program stored in ROM 20C, CPU 20A, and RAM 20B and output to the digital-to-analog converter 3 via the output interface unit 20E.

[0047] Next, the operation of the distortion compensation device 2 according to Embodiment 1 will be explained with reference to Figure 6. In step ST1, the low-regrowth transmission signal generation unit 21 acquires an operating status signal, which is backoff information consisting of a digital signal indicating the backoff amount of the power amplifier 4. Step ST1 is a step for acquiring backoff information.

[0048] In step ST2, the low-regrowth transmission signal generation unit 21 uses the backoff amount of the power amplifier 4 to clip the transmission signal from the transmission signal generation unit 1 to the power (Pave + Pbo) which is the sum of the average power Pave of the transmission signal from the transmission signal generation unit 1 and the backoff amount Pbo of the power amplifier 4. This generates a low-regrowth transmission signal in which regrowth, which is an increase in out-of-band power in the transmission signal output from the power amplifier 4 during low-backoff operation, is suppressed. Step ST2 is a step for generating a low-regrowth transmission signal.

[0049] In step ST3, the PD unit 22a reads a distortion compensation coefficient from the distortion compensation coefficient storage unit 22b that represents the distortion that compensates for the nonlinear distortion component generated in the power amplifier 4, and applies the distortion compensation coefficient to the low-regrowth transmission signal to generate a distortion-compensated low-regrowth transmission signal. The distortion-compensated low-regrowth transmission signal generated in step ST3 is output to the digital-to-analog converter 3. Step ST3 is a step for generating a distortion-compensated low-regrowth transmission signal. In this way, the distortion compensation device 2 generates a distortion-compensated low-regrowth transmission signal from the transmission signal generation unit 1.

[0050] The step of generating a low-regrowth transmission signal by the low-regrowth transmission signal generation unit 21 in step ST2 will be explained with reference to Figure 7. In step ST21, the first FFT unit 211 performs a Fourier transform on the transmission signal from the transmission signal generation unit 1 to generate a frequency spectrum X1(f). Step ST21 is the step of generating the frequency spectrum X1(f).

[0051] In step ST22, the peak cut unit 212 clips any power component of the transmitted signal that exceeds the sum of the average power Pave of the transmitted signal and the back-off amount Pbo of the power amplifier 4 (Pave + Pbo) to a power of (Pave + Pbo), thereby generating a clipped transmitted signal. Step ST22 is a step of clipping the power of the transmitted signal.

[0052] In step ST23, the second FFT unit 213 performs a Fourier transform on the transmitted signal clipped by the peak cut unit 212 to generate a frequency spectrum X2(f). Step ST23 is the step for generating the frequency spectrum X2(f). Steps ST21, ST22, and ST23 are performed at the same time. That is, in step ST24, the timing at which the regrowth suppression unit 214 receives the frequency spectrum X1(f) and the timing at which it receives the frequency spectrum X2(f) are synchronized with the timing of the transmitted signal from the transmitted signal generation unit 1.

[0053] In step ST24, the regrowth suppression unit 214 replaces the frequency spectrum X2(f) generated by the second FFT unit 213 in which the regrowth frequency component is large with the frequency spectrum X1(f) generated by the first FFT unit 211, thereby generating the frequency spectrum X3(f) shown by equation (1) above. Step ST24 is a step in which the frequency spectrum X3(f) is generated.

[0054] In step ST25, the IFFT unit 215 performs an inverse Fourier transform on the frequency spectrum X3(f) generated by the regrowth suppression unit 214 to generate a low-regrowth transmission signal. Step ST25 is a step for generating a low-regrowth transmission signal.

[0055] In the distortion compensation device that generates a distortion-compensated low-regrowth transmission signal by steps ST1 to ST3, the transmission signal generation method is performed by the CPU 20A executing processing according to a program stored in ROM 20C. Specifically, the program stored in ROM 20C includes a procedure for generating a low-regrowth transmission signal in which spectral regrowth, an increase in out-of-band power in the transmission signal output from the high-frequency power amplifier when the high-frequency power amplifier is operating at low backoff, is suppressed by using the transmission signal from the transmission signal generation unit and the operating status signal of the high-frequency power amplifier; and a procedure for generating a distortion-compensated low-regrowth transmission signal by adding distortion to the low-regrowth transmission signal to compensate for the distortion component generated in the high-frequency power amplifier.

[0056] The distortion compensation device 2 according to Embodiment 1 includes a low-regrowth transmission signal generation unit 21 that generates a low-regrowth transmission signal that suppresses regrowth, which is an increase in out-of-band power in the transmission signal output from the power amplifier 4 when the power amplifier 4 is operating at low backoff, by using the transmission signal generation unit 1 and the operating status signal of the power amplifier 4. As a result, an amplified transmission signal with low regrowth can be obtained in the transmission signal output from the power amplifier 4.

[0057] Furthermore, the distortion compensation device 2 according to Embodiment 1 can generate a distortion-compensated low-regrowth transmission signal using software via a computer, thus simplifying the device configuration and design.

[0058] For example, one could consider a configuration in which the low-regrowth transmission signal generation unit 21 in the distortion compensation device 2 is omitted, and the frequency component of the regrowth frequency in the transmission signal output from the power amplifier 4 is removed using a bandpass filter. However, it is difficult to achieve the ideal characteristics of removing the frequency component of the regrowth frequency using a bandpass filter, and moreover, it is necessary to use a bandpass filter that corresponds to the frequency of the transmission signal from the transmission signal generation unit 1.

[0059] In contrast, the distortion compensation device 2 according to Embodiment 1 simplifies the device configuration and simplifies the design because the low-regrowth transmission signal generation unit 21, which generates the low-regrowth transmission signal, can be created using software via a computer.

[0060] Embodiment 2. A microwave wireless transmitter equipped with a distortion compensation device 2A according to Embodiment 2 will be described with reference to Figure 8. The distortion compensation device 2A according to Embodiment 2 is modified from the distortion compensation device 2 according to Embodiment 1 to learn and update the distortion compensation coefficients stored in the distortion compensation coefficient storage unit 22b that are supplied to the PD unit 22a in the distortion compensation unit 22, based on the transmitted signal amplified by the power amplifier 4. In Figure 8, the same reference numerals as in Figure 1 indicate the same or equivalent parts.

[0061] The microwave radio transmitter equipped with the distortion compensation device 2A according to Embodiment 2 comprises a transmission signal generation unit 1, the distortion compensation device 2A according to Embodiment 2, a digital-to-analog converter 3, a power amplifier 4, and an antenna 5. The transmission signal generation unit 1, the digital-to-analog converter 3, the power amplifier 4, and the antenna 5 are the same as those of the microwave radio transmitter equipped with the distortion compensation device 2 according to Embodiment 1, so their description will be omitted, and the distortion compensation device 2A according to Embodiment 2 will be described in detail.

[0062] The distortion compensation device 2A according to Embodiment 2 includes a low-regrowth transmission signal generation unit 21, a distortion compensation unit 22, an analog-to-digital converter (ADC) 23, and a distortion compensation coefficient learning unit 24. The low-regrowth transmission signal generation unit 21 and the distortion compensation unit 22 are the same as those of the distortion compensation device 2 according to Embodiment 1, so their description is omitted.

[0063] The distortion compensation device 2A according to Embodiment 2 is configured to update the distortion compensation coefficients stored in the distortion compensation coefficient storage unit 22b according to the learning results (output) of the distortion compensation coefficient learning unit 24. The ADC 23 receives a portion of the transmission signal amplified by the power amplifier 4 as input, converts it into a digital signal, and outputs an amplified transmission signal consisting of digital signals. The distortion compensation coefficient learning unit 24 learns distortion compensation coefficients for controlling the distortion applied to the PD unit 22a based on the amplified transmission signal from the analog-to-digital converter 23.

[0064] The distortion compensation coefficient learning unit 24 provides the learning model with at least one of the signals—the amplified transmission signal from the analog-to-digital converter 23 and the low-regrowth transmission signal provided to the PD unit 22a, or the distortion-compensated low-regrowth transmission signal generated by the PD unit 22a—as learning data to determine the distortion compensation coefficient. The learning method used in the distortion compensation coefficient learning unit 24 is a generally known learning method such as the LS (Least Square) method, LMS (Least Mean Square) method, or RLS (Recursive Least Square) method.

[0065] The hardware configuration of the strain compensation device 2A according to Embodiment 2 is the same as that of the strain compensation device 2 according to Embodiment 1, and is realized by the hardware configuration shown in Figure 5. Learning in the strain compensation coefficient learning unit 24 is performed by the CPU 20A executing processing according to the program stored in the ROM 20C.

[0066] In other words, the program stored in ROM20C includes a procedure for learning at least one of the signals—the transmission signal amplified by the power amplifier and the low-regrowth transmission signal applied to the digital filter section, or the distortion-compensated low-regrowth transmission signal generated by the digital filter section—as learning data, and for determining the distortion compensation coefficient.

[0067] The distortion compensation device 2A according to Embodiment 2 has the same effects as the distortion compensation device 2 according to Embodiment 1. In addition, by learning the distortion compensation coefficient using the amplified transmission signal from the analog-to-digital converter 23 and the low-regrowth transmission signal provided to the PD unit 22a or the distortion-compensated low-regrowth transmission signal generated by the PD unit 22a, it is possible to set an appropriate value for the distortion compensation coefficient provided to the PD unit 22a.

[0068] Embodiment 3. A microwave radio transmitter equipped with the distortion compensation device 2B according to Embodiment 3 will be described with reference to Figures 9 to 11. As shown in Figure 9, the microwave radio transmitter comprises a transmission signal generation unit 1, the distortion compensation device 2B according to Embodiment 3, a digital-to-analog converter 3, a high-frequency power amplifier 4, and an antenna 5.

[0069] The microwave radio transmitter equipped with the strain compensation device 2B according to Embodiment 3 differs from the microwave radio transmitter equipped with the strain compensation device 2 according to Embodiment 1 in that the strain compensation device 2B is present, but all other aspects are the same. Therefore, the explanation will focus on the strain compensation device 2B. In Figure 9, the same reference numerals as in Figure 1 indicate the same or corresponding parts.

[0070] In the distortion compensation device 2 according to Embodiment 1, the low-regrowth transmission signal generation unit 21 generates a low-regrowth transmission signal by clipping the transmission signal from the transmission signal generation unit 1 with a power that is the sum of the average power of the transmission signal from the transmission signal generation unit 1 and the backoff amount of the power amplifier 4.

[0071] In contrast, the distortion compensation device 2B according to Embodiment 3 generates a low-regrowth signal in the low-regrowth transmission signal generation unit 21B by processing step by step using a model (hereinafter referred to as the low-regrowth model) that provides input / output characteristics that reduce regrowth when the power amplifier 4 is operating at low backoff, using a low-regrowth transmission signal. That is, the low-regrowth model is a model that represents the low-regrowth transmission signal in relation to the transmission signal from the transmission signal generation unit 1.

[0072] The low-regrowth model is, for example, a differentiable model, that is, a model in which the input / output characteristics of the low-regrowth transmission signal with respect to the transmission signal (input power) from the transmission signal generation unit 1 are differentiable. In Embodiment 3, the low-regrowth model uses a behavior model for the power amplifier 4 that can generate the low-regrowth transmission signal with simple processing. The behavior model used for the power amplifier 4 is a behavior model method consisting of at least one of the following: a lookup table method, a polynomial method, or a neural network method.

[0073] The distortion compensation device 2B according to Embodiment 3 comprises a low-regrowth transmission signal generation unit 21B and a distortion compensation unit 22. The distortion compensation unit 22 is the same as the distortion compensation unit 22 in the distortion compensation device 2 according to Embodiment 1, so its description is omitted.

[0074] The low-regrowth transmission signal generation unit 21B converts the input transmission signal from the transmission signal generation unit 1 into a low-regrowth transmission signal using a low-regrowth model corresponding to the peak power to average power ratio PAPR and the backoff amount Pbo of the power amplifier 4 in the transmission signal from the transmission signal generation unit 1, thereby generating a low-regrowth transmission signal. The low-regrowth transmission signal generation unit 21B includes a transmission signal conversion unit 21Ba, a low-regrowth model storage unit 21Bb, and an address generation unit 21Bc.

[0075] The transmission signal conversion unit 21Ba receives the transmission signal from the transmission signal generation unit 1, reads out the behavior model stored in the low-regrowth model storage unit 21Bb corresponding to the address generated by the address generation unit 21Bc, converts the transmission signal from the transmission signal generation unit 1 that was input using the read-out behavior model into a low-regrowth transmission signal, and generates a low-regrowth transmission signal.

[0076] In the case of a microwave radio transmitter in which the peak power to average power ratio and the backoff amount of the power amplifier 4 in the transmitted signal from the transmitting signal generation unit 1 do not change, the transmitting signal conversion unit 21Ba receives the transmitted signal from the transmitting signal generation unit 1 as input, reads out the behavior model stored in the low-regrowth model storage unit 21Bb, converts the transmitted signal from the transmitting signal generation unit 1 that was input using the read-out behavior model into a low-regrowth transmitted signal, and generates a low-regrowth transmitted signal.

[0077] The low-regrowth model storage unit 21Bb stores a low-regrowth model for generating a low-regrowth transmission signal when the power amplifier 4 is operating at low backoff. The low-regrowth model storage unit 21Bb stores multiple behavior models associated with addresses generated by the address generation unit 21Bc.

[0078] If the behavior model stored in the low-regrowth model storage unit 21Bb is a lookup table type, the lookup table is stored, and the transmission signal conversion unit 21Ba reads the lookup table. If it is a polynomial type, the coefficients of the polynomial type are stored, and the transmission signal conversion unit 21Ba reads the coefficients of the polynomial type. If it is a neural network type, the coefficients of the neural network are stored, and the transmission signal conversion unit 21Ba reads the coefficients of the neural network.

[0079] The multiple behavior models associated with an address may, for example, be behavior models that have been confirmed in advance through simulation to have low regrowth in a microwave radio transmitter, or they may be behavior models that reproduce the input / output characteristics of other power amplifiers with low regrowth.

[0080] In the case of a microwave wireless transmitter in which the peak power to average power ratio of the transmitted signal from the transmitting signal generation unit 1 and the backoff amount of the power amplifier 4 do not change, the behavior model stored in the low-regrowth model storage unit 21Bb is one behavior model under the conditions of the peak power to average power ratio of the transmitted signal from the transmitting signal generation unit 1 and the backoff amount of the power amplifier 4.

[0081] The address generation unit 21Bc receives the transmission signal from the transmission signal generation unit 1 and backoff information indicating the backoff amount of the power amplifier 4, and generates an address corresponding to the parameters of the peak power to average power ratio PAPR in the transmission signal from the transmission signal generation unit 1 and the backoff amount Pbo of the power amplifier 4. An example of an address is shown in Figure 10. When the peak power to average power ratio PAPR in the transmission signal from the transmission signal generation unit 1 is 0 to 3 [dB] and the backoff amount Pbo is 0 to 1 [dB], the address is set to 1; when the backoff amount Pbo is 1 to 2 [dB], the address is set to 2; and when the backoff amount Pbo is 2 to 3 [dB], the address is set to 3.

[0082] Furthermore, when the peak power to average power ratio PAPR of the transmitted signal from the transmitted signal generation unit 1 is 3 to 4 [dB] and the backoff amount Pbo is 0 to 1 [dB], the address is set to 4; when the backoff amount Pbo is 1 to 2 [dB], the address is set to 5; when the backoff amount Pbo is 2 to 3 [dB], the address is set to 6; and when the backoff amount Pbo is 3 to 4 [dB], the address is set to 7.

[0083] The address generation unit 21Bc sequentially generates addresses corresponding to the parameters of the peak power to average power ratio PAPR and the backoff amount Pbo. In the case of a microwave radio transmitter in which the peak power to average power ratio and the backoff amount of the power amplifier 4 in the transmitted signal from the transmission signal generation unit 1 do not change, the address generation unit 21Bc is not necessary.

[0084] The hardware configuration of the distortion compensation device 2B according to Embodiment 3 is the same as the hardware configuration of the distortion compensation device 2 according to Embodiment 1, and is realized by the hardware configuration shown in Figure 5.

[0085] Next, the step of generating a low-regrowth transmission signal by the low-regrowth transmission signal generation unit 21B in the distortion compensation device 2B according to Embodiment 3 will be explained with reference to Figure 11. In step ST21B, the address generation unit 21Bc generates addresses corresponding to the peak power to average power ratio PAPR and the backoff amount parameters of the power amplifier 4 in the transmission signal from the transmission signal generation unit 1, based on the address table shown in Figure 10. Step ST21B is the step of generating addresses.

[0086] In step ST22B, the transmission signal conversion unit 21Ba reads out the behavior model, which is a low-regrowth model, stored in the low-regrowth model storage unit 21Bb corresponding to the address generated by the address generation unit 21Bc, and converts the transmission signal from the transmission signal generation unit 1 input to a low-regrowth transmission signal using the read-out behavior model. Step ST22B is a step in which a low-regrowth transmission signal is generated. The steps after the step in which the low-regrowth transmission signal is generated are the same as step ST3 of the distortion compensation device 2 according to Embodiment 1.

[0087] The method for generating a low-regrowth transmission signal in a distortion compensation device that generates a distortion-compensated low-regrowth transmission signal by steps ST1, ST21B, ST22B, and ST3 is performed by the CPU 20A executing processing according to a program stored in ROM 20C. Specifically, the program stored in ROM 20C includes a procedure for generating addresses corresponding to the peak power to average power ratio PAPR and the backoff amount parameter of the power amplifier in the transmission signal from the transmission signal generation unit; a procedure for reading a behavior model which is a low-regrowth model corresponding to the generated address, converting the transmission signal from the transmission signal generation unit input by the read behavior model into a low-regrowth transmission signal to generate a low-regrowth transmission signal; and a procedure for generating a distortion-compensated low-regrowth transmission signal by adding distortion to the low-regrowth transmission signal to compensate for the distortion component generated in the high-frequency power amplifier.

[0088] Further explanation of an example using a polynomial model as a low-regrowth model The low-regrowth transmission signal generation unit 21B uses a low-regrowth model represented by the following equation (2), which corresponds to the peak power to average power ratio PAPR in the transmission signal from the transmission signal generation unit 1 and Pbo, which corresponds to the back-off amount of the power amplifier 4. It converts the input transmission signal x(n) from the transmission signal generation unit 1 into a low-regrowth transmission signal y(n) and generates a low-regrowth transmission signal y(n).

[0089]

[0090] In equation (2) above, x(n) is the transmission signal input to the transmission signal conversion unit 21Ba from the transmission signal generation unit 1, and y(n) is the low-regrowth transmission signal generated by the transmission signal conversion unit 21Ba. ｋ (k = 0, 1, ..., K-1) represents the coefficient of the polynomial, n is a variable that identifies the transmitted signal, and k represents the degree of the polynomial (0, 1, ..., K-1).

[0091] Furthermore, as is clear from equation (2) above, the low-regrowth model represented by equation (2) above is a differentiable model; that is, the input / output characteristics shown by the low-regrowth transmission signal y(n) with respect to the transmission signal x(n) from the transmission signal generation unit 1 are differentiable.

[0092] The transmission signal conversion unit 21Ba in the low-regrowth transmission signal generation unit 21B converts the coefficient a of the polynomial in equation (2) above, which represents the low-regrowth model stored in the low-regrowth model storage unit 21Bb corresponding to the address generated by the address generation unit 21Bc. ｋ The data is read, and the transmission signal x(n) input from the transmission signal generation unit 1 is converted into a low-regrowth transmission signal y(n) using the above equation (2), thereby generating a low-regrowth transmission signal y(n).

[0093] In the low-regrowth transmission signal generation unit 21B, the low-regrowth model storage unit 21Bb stores the coefficient a of the polynomial in equation (2) above, which represents the low-regrowth model associated with the address generated by the address generation unit 21Bc. ｋ The low-regrowth model storage unit 21Bb stores the peak power to average power ratio PAPR in the transmitted signal from the transmitted signal generation unit 1 and the coefficient a of the polynomial in equation (2) above, which corresponds to the back-off amount Pbo of the power amplifier 4. ｋ Remember this.

[0094] The address generation unit 21Bc receives the transmission signal from the transmission signal generation unit 1 and backoff information indicating the backoff amount of the power amplifier 4, and generates an address corresponding to the parameters of the peak power to average power ratio PAPR and the backoff amount Pbo of the power amplifier 4 in the transmission signal from the transmission signal generation unit 1, as shown in Figure 10.

[0095] In the case of a microwave radio transmitter in which the peak power to average power ratio of the transmitted signal from the transmitting signal generation unit 1 and the backoff amount of the power amplifier 4 do not change, the coefficient a of the polynomial in equation (2) above, which represents the low-regrowth model stored in the low-regrowth model storage unit 21Bb, is shown. ｋThe coefficient a of one of the polynomials in equation (2) above, or one of the polynomials in equation (2) above, under the conditions of the peak power to average power ratio in the transmitted signal from the transmitting signal generation unit 1 and the back-off amount of the power amplifier 4. ｋ Therefore, in this case, the address generation unit 21Bc is unnecessary.

[0096] The distortion compensation device 2B according to Embodiment 3, like the distortion compensation device 2 according to Embodiment 1, can obtain an amplified transmission signal with low regrowth in the transmission signal output from the power amplifier 4, and has the effect of simplifying the device configuration and simplifying the design.

[0097] Furthermore, since the distortion compensation device 2B according to Embodiment 3 uses a low-regrowth model, the signal processing for generating the low-regrowth transmission signal becomes simpler. In particular, if the polynomial model shown in equation (2) above is used as the low-regrowth model, the signal processing for generating the low-regrowth transmission signal y(n) becomes even simpler.

[0098] Furthermore, in contrast to a configuration in which the frequency component of the regrowth frequency in the transmitted signal output from the power amplifier 4 is removed using a bandpass filter, the low-regrowth transmitted signal generation unit 21B, which generates a low-regrowth transmitted signal using a low-regrowth model, can be software-generated by a computer, thus simplifying the device configuration and simplifying the design.

[0099] As the distortion compensation device 2B according to Embodiment 3, similar to the distortion compensation device 2A according to Embodiment 2, the distortion compensation coefficients stored in the distortion compensation coefficient storage unit 22b that are supplied to the PD unit 22a in the distortion compensation unit 22 may be learned and updated based on the transmitted signal amplified by the power amplifier 4, using an analog-to-digital converter 23 and a distortion compensation coefficient learning unit 24.

[0100] Embodiment 4. A microwave radio transmitter equipped with the distortion compensation device 2C according to Embodiment 4 will be described with reference to Figures 12 to 14. As shown in Figure 12, the microwave radio transmitter comprises a transmission signal generation unit 1, the distortion compensation device 2C according to Embodiment 4, a digital-to-analog converter 3, a high-frequency power amplifier 4, and an antenna 5.

[0101] The strain compensation device 2C according to Embodiment 4 differs from the strain compensation device 2B according to Embodiment 3 in that it has an added function for learning a low-regrowth model; otherwise, it is the same. Therefore, the following description will focus on the added function for learning a low-regrowth model. In Figure 12, the same reference numerals as in Figure 9 indicate the same or corresponding parts.

[0102] The distortion compensation device 2C according to Embodiment 4 comprises a low-regrowth transmission signal generation unit 21C and a distortion compensation unit 22. The low-regrowth transmission signal generation unit 21C includes a transmission signal conversion unit 21Ba, a low-regrowth model storage unit 21Bb, an address generation unit 21Bc, a training data generation unit 21Ca, and a model learning unit 21Cb.

[0103] The transmission signal conversion unit 21Ba, the low-regrowth model storage unit 21Bb, the address generation unit 21Bc, and the distortion compensation unit 22 are the same as those in the distortion compensation device 2B according to Embodiment 3, so their description is omitted.

[0104] The training data generation unit 21Ca receives the transmission signal from the transmission signal generation unit 1 and backoff information indicating the backoff amount, which is an operating status signal of the power amplifier 4. It generates training data in which the regrowth is small in the transmission signal output from the power amplifier 4 when the power amplifier 4 is operating at a low backoff setting.

[0105] The training data generated by the training data generation unit 21Ca corresponds to the low-regrowth transmission signal corresponding to the low-regrowth model. The training data generated by the training data generation unit 21Ca is associated with addresses corresponding to parameters such as the peak power to average power ratio PAPR and the backoff amount Pbo of the power amplifier 4 in the transmission signal from the transmission signal generation unit 1, as shown in Figure 10.

[0106] As shown in Figure 13, the training data generation unit 21Ca includes a first fast Fourier transform (FFT) unit 21C1, a peak cut unit 21C2, a second fast Fourier transform (FFT) unit 21C3, a regrowth suppression unit 21C4, and an inverse fast Fourier transform (IFFT) unit 21C5. The first FFT unit 21C1 performs a Fourier transform on the transmission signal from the transmission signal generation unit 1 to generate a frequency spectrum X1(f).

[0107] The peak cut unit 21C2 clips the power of the transmission signal from the transmission signal generation unit 1 at a power of (Pave + Pbo (dBm) = Psat). Although (Pave + Pbo) is set as the threshold power for clipping, it is not necessarily required to be (Pave + Pbo), and the threshold power for clipping may be adjusted to maximize the effect of regrowth reduction.

[0108] The second FFT unit 21C3 performs a Fourier transform on the transmitted signal generated by the peak cut unit 21C2 to generate a frequency spectrum X2(f). The regrowth suppression unit 21C4 receives the frequency spectrum X1(f) generated by the first FFT unit 21C1 and the frequency spectrum X2(f) generated by the second FFT unit 21C3, and generates a frequency spectrum X3(f) by replacing the frequency spectrum X2(f) generated by the second FFT unit 21C3 that has a large regrowth frequency component with a frequency spectrum that has a small regrowth frequency component.

[0109] As the regrowth suppression unit 21C4, for example, it may select a frequency spectrum generated by multiplying the frequency spectrum X2(f) generated by the second FFT unit 213 by a positive number less than 1, α (0 < α < 1), with respect to the set regrowth frequency f. In this case, the first FFT unit 21C1 becomes unnecessary. The IFFT unit 21C5 converts the frequency spectrum X3(f) generated by the regrowth suppression unit 21C4 into a time waveform using an inverse Fourier transform and generates training data.

[0110] The model learning unit 21Cb receives the transmission signal from the transmission signal generation unit 1, receives the training data generated by the training data generation unit 21Ca, and learns the low-regrowth model stored in the low-regrowth model storage unit 21Bb. At this time, the low-regrowth model learned and generated by the model learning unit 21Cb is configured such that the error between the model learning unit 21Cb and the training data generated by the training data generation unit 21Ca is minimized for each address generated by the address generation unit 21Bc.

[0111] Since the training data generated by the training data generation unit 21Ca is associated with addresses, the low-regrowth model generated by the model learning unit 21Cb is also associated with addresses. The learning method for the low-regrowth model used by the training data generation unit 21Ca is a generally known learning method such as the LS method, LMS method, or RLS method.

[0112] The low-regrowth model generated by the model learning unit 21Cb, or the table or coefficients for reproducing the low-regrowth model, is stored in the low-regrowth model storage unit 21Bb. That is, the low-regrowth model stored in the low-regrowth model storage unit 21Bb, or the table or coefficients for reproducing the low-regrowth model, is updated with the low-regrowth model generated by the model learning unit 21Cb, or the table or coefficients for reproducing the low-regrowth model.

[0113] The training of the low-regrowth model by the training data generation unit 21Ca may be performed in real time or may be pre-trained. If the model is pre-trained by the model training unit 21Cb, the low-regrowth model generated by the model training unit 21Cb, or a table or coefficients for reproducing the said low-regrowth model, is stored in the low-regrowth model storage unit 21Bb.

[0114] The hardware configuration of the distortion compensation device 2C according to Embodiment 4 is the same as the hardware configuration of the distortion compensation device 2 according to Embodiment 1, and is realized by the hardware configuration shown in Figure 5.

[0115] Next, the step of generating a learned low-regrowth transmission signal in the low-regrowth transmission signal generation step by the low-regrowth transmission signal generation unit 21C in the distortion compensation device 2C according to Embodiment 4 will be explained with reference to Figure 14.

[0116] In step ST23C, the training data generation unit 21Ca receives the transmission signal from the transmission signal generation unit 1 and backoff information indicating the backoff amount, which is an operating status signal of the power amplifier 4. The unit generates training data indicating a low-regrowth transmission signal, which reduces regrowth in the transmission signal output from the power amplifier 4 when the power amplifier 4 is operating at low backoff. The training data generated by the training data generation unit 21Ca is associated with the address generated by the address generation unit 21Bc. Step ST23C is a step in which training data is generated.

[0117] In step ST24C, the model learning unit 21Cb receives the transmission signal from the transmission signal generation unit 1, receives the training data generated by the training data generation unit 21Ca, and learns a low-regrowth model for each address generated by the address generation unit 21Bc using a learning method such as the LS method, LMS method, or RLS method.

[0118] The low-regrowth model, trained and generated by the model learning unit 21Cb, is either the low-regrowth model itself, or a table or coefficients for reproducing the said low-regrowth model. Step ST24C is the step for training the low-regrowth model.

[0119] The low-regrowth model learned in step ST24C is used as the low-regrowth model in step ST22B, which generates a low-regrowth transmission signal. Therefore, the low-regrowth model stored in the low-regrowth model storage unit 21Bb is updated with the low-regrowth model learned in step ST24C.

[0120] The steps of generating the low-regrowth transmission signal learned by the training data generation unit 21Ca and the model learning unit 21Cb in steps ST23C and ST24C are performed by the CPU 20A executing processing according to the program stored in ROM 20C. Specifically, the program stored in ROM 20C includes a procedure for generating training data that indicates a low-regrowth transmission signal in which spectral regrowth, where out-of-band power increases in the transmission signal output from the high-frequency power amplifier when the high-frequency power amplifier is operating at low backoff, is suppressed, based on the transmission signal from the transmission signal generation unit and the operating status signal of the high-frequency power amplifier, and a procedure for learning the transmission signal from the transmission signal generation unit and the training data as learning data to obtain a low-regrowth model.

[0121] The distortion compensation device 2C according to Embodiment 4, like the distortion compensation device 2B according to Embodiment 3, can obtain an amplified transmission signal with low regrowth in the transmission signal output from the power amplifier 4, simplifying the device configuration, simplifying the design, and simplifying the signal processing to generate a low-regrowth transmission signal.

[0122] Furthermore, the distortion compensation device 2C according to Embodiment 4 can learn a low regrowth model, thereby suppressing the degradation of the modulation accuracy of the transmitted signal output from the power amplifier 4 and obtaining a signal with less regrowth.

[0123] As the distortion compensation device 2C according to Embodiment 4, similar to the distortion compensation device 2A according to Embodiment 2, the distortion compensation coefficients stored in the distortion compensation coefficient storage unit 22b that are supplied to the PD unit 22a in the distortion compensation unit 22 may be learned and updated based on the transmitted signal amplified by the power amplifier 4, using an analog-to-digital converter 23 and a distortion compensation coefficient learning unit 24.

[0124] Embodiment 5. A microwave radio transmitter equipped with the distortion compensation device 2D according to Embodiment 5 will be described with reference to Figures 15 to 17. As shown in Figure 15, the microwave radio transmitter comprises a transmission signal generation unit 1, a distortion compensation device 2D according to Embodiment 5, a digital-to-analog converter 3, a high-frequency power amplifier 4, and an antenna 5. The distortion compensation device 2D according to Embodiment 5 differs from the distortion compensation device 2C according to Embodiment 4 in that the training data generation unit in the low-regrowth transmission signal generation unit is different, but other aspects are the same. Therefore, the training data generation unit will be the focus of the description below. In Figures 15 to 17, the same reference numerals as in Figures 12 to 14 indicate the same or corresponding parts.

[0125] As shown in Figure 15, the distortion compensation device 2D according to Embodiment 5 comprises a low-regrowth transmission signal generation unit 21D and a distortion compensation unit 22. The low-regrowth transmission signal generation unit 21D includes a transmission signal conversion unit 21Ba, a low-regrowth model storage unit 21Bb, an address generation unit 21Bc, a training data generation unit 21Da, and a model learning unit 21Cb.

[0126] The transmission signal conversion unit 21Ba, the low-regrowth model storage unit 21Bb, the address generation unit 21Bc, and the model learning unit 21Cb are the same as those in the distortion compensation device 2C according to Embodiment 4, so their description is omitted.

[0127] The training data generation unit 21Da is executed multiple times periodically, receiving the transmission signal from the transmission signal generation unit 1 and backoff information indicating the backoff amount, which is an operating status signal of the power amplifier 4. The unit periodically generates training data multiple times that reduces regrowth in the transmission signal output from the power amplifier 4 when the power amplifier 4 is operating at a low backoff setting.

[0128] The training data generated by the training data generation unit 21Da corresponds to the low-regrowth transmission signal corresponding to the low-regrowth model. The training data generated by the training data generation unit 21Da is linked to addresses corresponding to parameters such as the peak power to average power ratio PAPR and the backoff amount Pbo of the power amplifier 4 in the transmission signal from the transmission signal generation unit 1, as shown in Figure 10.

[0129] As shown in Figure 16, the training data generation unit 21Da includes a first fast Fourier transform (FFT) unit 21C1, a training data generation main unit 21D2, and a second transmission signal conversion unit 21D3. The first FFT unit 21C1 performs a Fourier transform on the transmission signal from the transmission signal generation unit 1 to generate a frequency spectrum X1(f).

[0130] The second transmission signal conversion unit 21D3 is executed multiple times periodically. The second transmission signal conversion unit 21D3 receives the transmission signal from the transmission signal generation unit 1 as input and the low-regrowth model learned by the model learning unit 21Cb, and uses the received low-regrowth model to convert the transmission signal from the transmission signal generation unit 1 that was input as input to a low-regrowth transmission signal, and generates it multiple times periodically as a low-regrowth transmission signal for learning.

[0131] The main training data generation unit 21D2 is executed multiple times periodically by the second transmission signal conversion unit 21D3, and is input to the low-regrowth transmission signal for learning and backoff information indicating the backoff amount of the power amplifier 4, which is generated by the second transmission signal conversion unit 21D3. The main training data generation unit 21D2 periodically generates multiple training data associated with addresses generated by the address generation unit 21Bc, which suppresses regrowth, an increase in out-of-band power in the transmission signal output from the power amplifier 4 when the power amplifier 4 is operating at low backoff, based on the input backoff information.

[0132] The main training data generation unit 21D2 includes a peak cut unit 21D22, a second fast Fourier transform (FFT) unit 21D23, a regrowth suppression unit 21C4, and an inverse fast Fourier transform (IFFT) unit 21C5. The peak cut unit 21D22 generates a training low-regrowth transmission signal in which power exceeding the threshold of the training low-regrowth transmission signal generated by the second transmission signal conversion unit 21D3 is clipped to a threshold. The power threshold for clipping is (Pave + Pbo). However, it does not necessarily have to be (Pave + Pbo), and the power threshold for clipping may be adjusted so as to maximize the effect of regrowth reduction.

[0133] The second FFT unit 21D23 performs a Fourier transform on the low-regrowth transmission signal for learning generated by the peak cut unit 21D22 to generate a frequency spectrum X2(f). The regrowth suppression unit 21C4 receives the frequency spectrum X1(f) generated by the first FFT unit 21C1 and the frequency spectrum X2(f) generated by the second FFT unit 21D23, and generates a frequency spectrum X3(f) by replacing the frequency spectrum X2(f) generated by the second FFT unit 21D23, in which the regrowth frequency component is large, with a frequency spectrum in which the regrowth frequency component is small.

[0134] As the regrowth suppression unit 21C4, for example, it may select a frequency spectrum generated by multiplying the frequency spectrum X2(f) generated by the second FFT unit 21D23 by a positive number less than 1, α (0 < α < 1), with respect to the set regrowth frequency f. In this case, the first FFT unit 21C1 becomes unnecessary. The frequency spectrum generated by the regrowth suppression unit is converted into a time waveform by an inverse Fourier transform to generate training data.

[0135] The model learning unit 21Cb performs learning each time the second transmission signal conversion unit 21D3 is executed periodically, and each time, the low-regrowth model stored in the low-regrowth model storage unit 21Bb is updated with the low-regrowth model learned by the model learning unit 21Cb.

[0136] The hardware configuration of the distortion compensation device 2D according to Embodiment 5 is the same as the hardware configuration of the distortion compensation device 2 according to Embodiment 1, and is realized by the hardware configuration shown in Figure 5.

[0137] Next, the step of generating a learned low-regrowth transmission signal in the low-regrowth transmission signal generation step by the low-regrowth transmission signal generation unit 21D in the distortion compensation device 2D according to Embodiment 5 will be explained with reference to Figure 17. The step of generating a learned low-regrowth transmission signal is performed multiple times periodically.

[0138] In step ST23D, the training data generation unit 21Da receives the transmission signal from the transmission signal generation unit 1 and backoff information indicating the backoff amount, which is an operating status signal of the power amplifier 4. The unit generates training data indicating a low-regrowth transmission signal, which reduces regrowth in the transmission signal output from the power amplifier 4 when the power amplifier 4 is operating at low backoff. The training data generated by the training data generation unit 21Ca is associated with the address generated by the address generation unit 21Bc. Step ST23D is a step in which training data is generated.

[0139] In step ST24D, the model learning unit 21Cb receives the transmission signal from the transmission signal generation unit 1, receives the training data generated by the training data generation unit 21Da, and learns a low-regrowth model for each address generated by the address generation unit 21Bc using a learning method such as the LS method, LMS method, or RLS method.

[0140] The low-regrowth model, trained and generated by the model learning unit 21Cb, is either the low-regrowth model itself, or a table or coefficients for reproducing the said low-regrowth model. Step ST24D is the step for training the low-regrowth model.

[0141] The low-regrowth model learned in step ST24D is used as the low-regrowth model in step ST22B, which generates a low-regrowth transmission signal. Therefore, the low-regrowth model stored in the low-regrowth model storage unit 21Bb is updated with the low-regrowth model learned in step ST24D.

[0142] Step ST23D, which generates training data, and Step ST24D, which trains a low-regrowth model, form a training loop, and the training loop of Steps ST23D and ST24D is repeated periodically. The number of times the loop is repeated periodically can be set based on the characteristics of the components of the microwave radio transmitter, particularly the power amplifier 4. For example, it can be set based on the amount of regrowth reduction in the transmitted signal output from the power amplifier 4.

[0143] The steps of generating the low-regrowth transmission signal learned by the training data generation unit 21Da and the model learning unit 21Cb in steps ST23D and ST24D are performed by the CPU 20A executing processing according to the program stored in ROM 20C. Specifically, the program stored in ROM 20C includes a procedure for generating training data that indicates a low-regrowth transmission signal in which spectral regrowth, where out-of-band power increases in the transmission signal output from the high-frequency power amplifier when the high-frequency power amplifier is operating at low backoff, is suppressed, based on the transmission signal from the transmission signal generation unit and the operating status signal of the high-frequency power amplifier, and a procedure for periodically repeating the process of learning the transmission signal from the transmission signal generation unit and the training data as learning data to obtain a low-regrowth model.

[0144] Further explanation of an example using a polynomial model as a low-regrowth model: The transmission signal conversion unit 21Ba in the low-regrowth transmission signal generation unit 21D is a low-regrowth model represented by equation (2) above. In this example, the coefficient a of the polynomial representing the low-regrowth model is... ｋ Using this method, the transmission signal x(n) from the input transmission signal generation unit 1 is converted into a low-regrowth transmission signal y(n), and the low-regrowth transmission signal y(n) is generated.

[0145] On the other hand, in the second transmission signal conversion unit 21D3 in the teacher data generation unit 21Da as well, using the low ring loss model represented by the above equation (2), the transmission signal x(n) from the input transmission signal generation unit 1 is converted into a transmission signal y(n) for low ring loss, and a transmission signal y(n) for low ring loss (for learning) is generated.

[0146] The second transmission signal conversion unit 21D3 gives coefficients so as to perform an identity conversion because the coefficients a ｋ of the polynomial are undetermined in the initial state. In this example, as shown in the following equation (3), when k is 0, the coefficient a ｋ of the polynomial is 1, and when k is other than 0, the coefficient a ｋ of the polynomial is 0, and the second transmission signal conversion unit 21D3 obtains the learning low ring loss transmission signal y(n) in the initial state from the transmission signal x(n) from the transmission signal generation unit 1 using the low ring loss model represented by the above equation (2).

[0147]

[0148] The learning low ring loss transmission signal in the initial state generated by the second transmission signal conversion unit 21D3 is generated as teacher data linked to the address generated by the address generation unit 21Bc by the teacher data generation main unit 21D2 having the peak cut unit 21D22, the second FFT unit 21D23, the ring loss suppression unit 21C4, and the IFFT unit 21C5 by the operation described above.

[0149] The model learning unit 21Cb learns based on the teacher data generated by the teacher data generation main unit 21D2 to generate a low ring loss model, and in this example, the coefficients a ｋ of the polynomial for representing the low ring loss model, and the generated coefficients a ｋ of the polynomial are stored in the low ring loss model storage unit 21Bb and used by the transmission signal conversion unit 21Ba. [[ID=2,3]]

[0150] After that, the second transmission signal conversion unit 21D3 uses the coefficients a ｋUsing the above equation (2), a low-regrowth transmission signal y(n) for learning is obtained from the transmission signal x(n) from the transmission signal generation unit 1, and the main training data generation unit 21D2 generates training data from the low-regrowth transmission signal y(n) for learning generated by the second transmission signal conversion unit 21D3. Based on the generated training data, the model learning unit 21Cb learns the coefficient a of the polynomial to represent the low-regrowth model. ｋ The coefficient a of the polynomial is generated and stored in the low-regrowth model storage unit 21Bb. ｋ It will be updated.

[0151] The second transmission signal conversion unit 21D3 generates a transmission signal for learning low-regrowth, the main training data generation unit 21D2 generates training data, and the model learning unit 21Cb generates the coefficient a of the polynomial representing the low-regrowth model. ｋ The generation of the polynomial coefficient a in the low-regrowth model storage unit 21Bb. ｋ The updates are performed repeatedly and periodically.

[0152] The distortion compensation device 2D according to Embodiment 5, like the distortion compensation device 2C according to Embodiment 4, can obtain an amplified transmission signal with low regrowth in the transmission signal output from the power amplifier 4, simplifying the device configuration, simplifying the design, and simplifying the signal processing for generating a low regrowth transmission signal.

[0153] Furthermore, the distortion compensation device 2D according to Embodiment 5, similar to the distortion compensation device 2C according to Embodiment 4, can learn a low-regrowth model, thereby suppressing the degradation of the modulation accuracy of the transmitted signal output from the power amplifier 4 and obtaining a signal with less regrowth. Moreover, the distortion compensation device 2D according to Embodiment 5 can improve the accuracy of the low-regrowth model by periodically generating training data multiple times and periodically learning the low-regrowth model multiple times. As a result, it can obtain an amplified transmitted signal with less regrowth in the transmitted signal output from the power amplifier 4.

[0154] As the distortion compensation device 2D according to Embodiment 5, similar to the distortion compensation device 2A according to Embodiment 2, the distortion compensation coefficients stored in the distortion compensation coefficient storage unit 22b that are supplied to the PD unit 22a in the distortion compensation unit 22 may be learned and updated based on the transmitted signal amplified by the power amplifier 4, using an analog-to-digital converter 23 and a distortion compensation coefficient learning unit 24.

[0155] Furthermore, it is possible to freely combine the embodiments, modify any component of each embodiment, or omit any component of each embodiment.

[0156] The distortion compensation device described herein is applicable to a distortion compensation device that reduces distortion components generated in a high-frequency power amplifier in a microwave radio transmitter having a high-frequency power amplifier.

[0157] 1 Transmit signal generation unit, 2, 2A-2D Distortion compensation device, 21, 21B-21D Low regrowth transmit signal generation unit, 211 First Fast Fourier Transform unit, 212 Peak cut unit, 213 Second Fast Fourier Transform unit, 214 Regrowth suppression unit, 215 Inverse Fast Fourier Transform unit, 21Ba Transmit signal conversion unit, 21Bb Low regrowth model storage unit, 21Bc Address generation unit, 21Ca, 21Da Training data generation unit, 21Cb Model learning unit, 21C1 First Fast Fourier Transform unit, 21C2 Peak cut unit, 21C3 Second Fast Fourier Transform unit, 21C5 Inverse Fast Fourier Transform unit, 21D3 Second transmit signal conversion unit, 22 Distortion compensation unit, 22a Digital filter unit, 22b Distortion compensation coefficient storage unit, 23 Analog-to-digital converter, 24 3. Distortion compensation coefficient learning unit, 4. Digital-to-analog converter, 5. High-frequency power amplifier, 6. Antenna.

Claims

1. A distortion compensation device disposed between a transmission signal generation unit and a high-frequency power amplifier, comprising: a low-regrowth transmission signal generation unit that receives a transmission signal from the transmission signal generation unit and an operating status signal of the high-frequency power amplifier as inputs, and generates a low-regrowth transmission signal that suppresses spectrum regrowth, which is an increase in out-of-band power in the transmission signal output from the high-frequency power amplifier when the high-frequency power amplifier is operating at low back-off; and a distortion compensation unit that generates a distortion-compensated low-regrowth transmission signal by adding distortion to the low-regrowth transmission signal generated by the low-regrowth transmission signal generation unit to compensate for distortion components generated in the high-frequency power amplifier.

2. The distortion compensation device according to claim 1, wherein the operating status signal of the high-frequency power amplifier is backoff information indicating the backoff amount of the high-frequency power amplifier.

3. The distortion compensation device according to claim 2, wherein the low-regrowth transmission signal generated by the low-regrowth transmission signal generation unit is a transmission signal obtained by clipping the transmission signal from the transmission signal generation unit with a power equal to the sum of the average power of the transmission signal in the transmission signal from the transmission signal generation unit and the backoff amount of the high-frequency power amplifier.

4. The distortion compensation device according to any one of claims 1 to 3, wherein the low-regrowth transmission signal generated by the low-regrowth transmission signal generation unit is a signal that has an input-output characteristic in which the slope in the assumed range including the saturation power is small with respect to the slope up to the saturation power of the high-frequency power amplifier in the input-output characteristic in which the output power increases linearly with respect to the input power.

5. The distortion compensation device according to any one of claims 1 to 4, wherein the low-regrowth transmission signal generation unit comprises: a peak cut unit that generates a transmission signal in which the power of the transmission signal from the transmission signal generation unit that exceeds a threshold is clipped to the threshold; a fast Fourier transform unit that performs a Fourier transform on the transmission signal generated by the peak cut unit and generates a frequency spectrum; a regrowth suppression unit that generates a frequency spectrum in which the magnitude of the regrowth frequency component of the frequency spectrum generated by the fast Fourier transform unit is replaced with a smaller value; and an inverse fast Fourier transform unit that converts the frequency spectrum generated by the regrowth suppression unit into a time waveform by an inverse Fourier transform and generates a low-regrowth transmission signal.

6. The distortion compensation device according to claim 5, wherein the threshold value clipped by the peak cut unit is the power of the sum of the average power of the transmitted signal in the transmitted signal from the transmitted signal generation unit and the backoff amount indicated by the operating status signal of the high-frequency power amplifier.

7. The distortion compensation device according to claim 5 or 6, wherein the magnitude of the regrowth frequency component to be replaced in the regrowth suppression unit is the regrowth frequency component of the frequency spectrum generated by performing a Fourier transform on the transmission signal from the transmission signal generation unit using a fast Fourier transform unit.

8. The distortion compensation device according to claim 5 or 6, wherein the frequency spectrum in which the magnitude of the regrowth frequency component to be replaced in the regrowth suppression unit is small is a frequency spectrum generated by multiplying the regrowth frequency component of the frequency spectrum generated by the fast Fourier transform unit by a positive number less than 1, namely α.

9. The distortion compensation device according to claim 1 or 2, wherein the low-regrowth transmission signal generation unit has differentiable input / output characteristics for the low-regrowth transmission signal generated by the low-regrowth transmission signal generation unit with respect to the transmission signal from the transmission signal generation unit.

10. The distortion compensation device according to claim 1 or 2, wherein the low-regrowth transmission signal generation unit converts the input transmission signal from the transmission signal generation unit into a low-regrowth transmission signal, and generates a low-regrowth transmission signal, using a low-regrowth model that represents a low-regrowth transmission signal for the transmission signal from the transmission signal generation unit, corresponding to the peak power to average power ratio in the transmission signal from the transmission signal generation unit and the backoff amount of the high-frequency power amplifier.

11. The distortion compensation device according to claim 10, wherein the low-regrowth model is a plurality of behavior models linked to addresses corresponding to the peak power to average power ratio in the transmitted signal from the transmitting signal generation unit and the backoff amount parameter of the high-frequency power amplifier.

12. The distortion compensation device according to claim 1 or 2, wherein the low-regrowth transmission signal generation unit is input to a transmission signal from the transmission signal generation unit and backoff information indicating the backoff amount of the high-frequency power amplifier, and generates an address corresponding to the peak power to average power ratio and the backoff amount parameters of the high-frequency power amplifier in the transmission signal from the transmission signal generation unit; a low-regrowth model storage unit stores a plurality of behavior models which are low-regrowth models associated with the address generated by the address generation unit; and a transmission signal conversion unit is input to a transmission signal from the transmission signal generation unit, reads out a behavior model stored in the low-regrowth model storage unit corresponding to the address generated by the address generation unit, converts the transmission signal from the transmission signal generation unit input to a low-regrowth transmission signal using the read-out behavior model, and generates a low-regrowth transmission signal.

13. The distortion compensation device according to claim 12, wherein the behavior model is a behavior model consisting of at least one of a lookup table method, a polynomial method, or a neural network method.

14. A distortion compensation device according to claim 12 or 13, further comprising: a teacher data generation unit that receives a transmission signal from the transmission signal generation unit and backoff information indicating the backoff amount of the high-frequency power amplifier, and which generates a plurality of teacher data associated with an address generated by the address generation unit, wherein the input transmission signal and the input backoff information suppress spectrum regrowth, in which out-of-band power increases in the transmission signal output from the high-frequency power amplifier when the high-frequency power amplifier is operating at low backoff; and a model learning unit that receives a transmission signal from the transmission signal generation unit, receives the teacher data generated by the teacher data generation unit, learns the low regrowth model stored in the low regrowth model storage unit, and updates the low regrowth model stored in the low regrowth model storage unit.

15. The distortion compensation device according to claim 1 or 2, wherein the low-regrowth transmission signal generation unit uses a low-regrowth model represented by the following equation (2), which corresponds to the peak power to average power ratio in the transmission signal from the transmission signal generation unit and the backoff amount of the high-frequency power amplifier, to convert the input transmission signal from the transmission signal generation unit into a low-regrowth transmission signal and generate a low-regrowth transmission signal. However, x(n) is the transmission signal input from the transmission signal generation unit to the low-regrowth transmission signal generation unit, and y(n) is the low-regrowth transmission signal generated by the low-regrowth transmission signal generation unit. ｋ k represents the coefficient of the polynomial, n is the variable that identifies the transmitted signal, and k is the degree of the polynomial.

16. The low-regrowth transmission signal generation unit includes: an address generation unit that receives a transmission signal from the transmission signal generation unit and backoff information indicating the backoff amount of the high-frequency power amplifier, and generates an address corresponding to the peak power to average power ratio and the backoff amount parameters of the high-frequency power amplifier in the transmission signal generation unit; a low-regrowth model storage unit that stores a plurality of low-regrowth models represented by the following equation (2) associated with the address generated by the address generation unit; and a transmission signal conversion unit that receives a transmission signal from the transmission signal generation unit, reads out a low-regrowth model stored in the low-regrowth model storage unit corresponding to the address generated by the address generation unit, converts the transmission signal from the transmission signal generation unit input using the read-out low-regrowth model into a low-regrowth transmission signal, and generates a low-regrowth transmission signal. A distortion compensation device according to claim 1 or 2, further comprising: a teacher data generation unit that receives a transmission signal from the transmission signal generation unit and backoff information indicating the backoff amount of the high-frequency power amplifier, and which generates a plurality of teacher data associated with an address generated by the address generation unit, wherein the input transmission signal and the input backoff information suppress spectrum regrowth, in which out-of-band power increases in the transmission signal output from the high-frequency power amplifier when the high-frequency power amplifier is operating at low backoff; and a model learning unit that receives a transmission signal from the transmission signal generation unit, receives the teacher data generated by the teacher data generation unit, learns the low regrowth model stored in the low regrowth model storage unit, and updates the low regrowth model stored in the low regrowth model storage unit. However, x(n) is the transmission signal input from the transmission signal generation unit to the low-regrowth transmission signal generation unit, and y(n) is the low-regrowth transmission signal generated by the low-regrowth transmission signal generation unit. ｋ k represents the coefficient of the polynomial, n is the variable that identifies the transmitted signal, and k is the degree of the polynomial.

17. The distortion compensation device according to claim 14 or claim 16, wherein the training data generation unit comprises: a peak cut unit that generates a transmission signal in which the power of the transmission signal from the transmission signal generation unit that exceeds a threshold is clipped to a threshold; a fast Fourier transform unit that performs a Fourier transform on the transmission signal generated by the peak cut unit and generates a frequency spectrum; a regrowth suppression unit that generates a frequency spectrum in which the magnitude of the regrowth frequency component of the frequency spectrum generated by the fast Fourier transform unit is replaced with a smaller value; and an inverse fast Fourier transform unit that converts the frequency spectrum generated by the regrowth suppression unit into a time waveform by an inverse Fourier transform and generates training data.

18. The distortion compensation device according to claim 14 or claim 16, comprising: a second transmission signal conversion unit that receives a transmission signal from the transmission signal generation unit as input, receives a low regrowth model learned by the model learning unit, converts the transmission signal from the transmission signal generation unit input by the received low regrowth model into a low regrowth transmission signal, and generates it as a learning low regrowth transmission signal; and a main unit for generating training low regrowth that receives the learning low regrowth transmission signal generated by the second transmission signal conversion unit and backoff information indicating the backoff amount of the high-frequency power amplifier as input, and generates a plurality of training data associated with addresses generated by the address generation unit, wherein the learning low regrowth transmission signal and the input backoff information suppress spectrum regrowth, in which out-of-band power increases in the transmission signal output from the high-frequency power amplifier when the high-frequency power amplifier is operating at low backoff.

19. The distortion compensation device according to claim 18, wherein the second transmission signal conversion unit is executed multiple times, and the main training data generation unit comprises: a peak cut unit that generates a learning low-regrowth transmission signal in which the power exceeding a threshold of the learning low-regrowth transmission signal generated by the second transmission signal conversion unit is clipped to a threshold; a fast Fourier transform unit that performs a Fourier transform on the learning low-regrowth transmission signal generated by the peak cut unit and generates a frequency spectrum; a regrowth suppression unit that generates a frequency spectrum in which the magnitude of the regrowth frequency component of the frequency spectrum generated by the fast Fourier transform unit is replaced with a smaller value; and an inverse fast Fourier transform unit that converts the frequency spectrum generated by the regrowth suppression unit into a time waveform by an inverse Fourier transform and generates training data.

20. The distortion compensation device according to any one of claims 17 to 19, wherein the threshold value clipped by the peak cut unit in the training data generation unit is the power of the sum of the average power of the transmitted signal in the transmitted signal from the transmitted signal generation unit and the backoff amount indicated by the operating status signal of the high-frequency power amplifier.

21. The distortion compensation device according to any one of claims 1 to 20, wherein the distortion compensation unit includes a distortion compensation coefficient storage unit that stores distortion that compensates for distortion components, and a digital filter unit that reads out the distortion that compensates for distortion components stored in the distortion compensation coefficient storage unit and applies the read-out distortion that compensates for distortion components to the low-regrowth transmission signal generated by the low-regrowth transmission signal generation unit to generate a distortion-compensated low-regrowth transmission signal, and a distortion compensation coefficient learning unit that learns at least one of the low-regrowth transmission signal generated by the low-regrowth transmission signal generation unit or the distortion-compensated low-regrowth transmission signal generated by the digital filter unit as learning data based on the transmission signal output from the high-frequency power amplifier and updates the distortion that compensates for distortion components stored in the distortion compensation coefficient storage unit.

22. A method for generating a transmission signal to a high-frequency power amplifier by converting a transmission signal from a transmission signal generation unit in a distortion compensation device disposed between a transmission signal generation unit and a high-frequency power amplifier, comprising: a step of generating a low-regrowth transmission signal in the distortion compensation device, using the transmission signal from the transmission signal generation unit and the operating status signal of the high-frequency power amplifier to generate a low-regrowth transmission signal in which spectral regrowth, an increase in out-of-band power in the transmission signal output from the high-frequency power amplifier when the high-frequency power amplifier is operating at low back-off; and a step of generating a distortion-compensated low-regrowth transmission signal by adding distortion to the low-regrowth transmission signal to compensate for distortion components generated in the high-frequency power amplifier.

23. The method for generating a transmission signal in a distortion compensation device according to claim 22, comprising: a step of generating a low-regrowth transmission signal, which is a step of generating a low-regrowth transmission signal by converting the transmission signal from the transmission signal generation unit into a low-regrowth transmission signal using a low-regrowth model; a step of the training data generation unit in the distortion compensation device generating learning data in which the transmission signal from the transmission signal generation unit is used with the operating status signal of the high-frequency power amplifier to suppress spectrum regrowth, which is an increase in out-of-band power in the transmission signal output from the high-frequency power amplifier when the high-frequency power amplifier is operating at low backoff; and a step of the model learning unit in the distortion compensation device learning a low-regrowth transmission signal using the transmission signal from the transmission signal generation unit and the learning data, and making the learned low-regrowth transmission signal the low-regrowth transmission signal used in the step of generating the low-regrowth transmission signal.

24. A transmission signal generation program that causes a computer to execute the following steps: a procedure for generating a low-regrowth transmission signal in which spectral regrowth, an increase in out-of-band power in the transmission signal output from the high-frequency power amplifier when the high-frequency power amplifier is operating at low backoff, is suppressed by using the transmission signal from the transmission signal generation unit and the operating status signal of the high-frequency power amplifier; and a procedure for generating a distortion-compensated low-regrowth transmission signal by adding distortion to the low-regrowth transmission signal to compensate for the distortion component generated in the high-frequency power amplifier.

25. A recording medium storing a program that causes a computer to execute the following steps: a procedure for generating a low-regrowth transmission signal in which spectral regrowth, an increase in out-of-band power in the transmission signal output from the high-frequency power amplifier when the high-frequency power amplifier is operating at low backoff, is suppressed by using the transmission signal from the transmission signal generation unit and the operating status signal of the high-frequency power amplifier; and a procedure for generating a distortion-compensated low-regrowth transmission signal by adding distortion to the low-regrowth transmission signal to compensate for distortion components generated in the high-frequency power amplifier.

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