Signal processing device, signal processing method and program

Abstract

A signal processing apparatus (100) according to an embodiment is provided with: a distortion compensating means (101) that performs a distortion compensating process for compensating for non-linear distortion with respect to at least one of a plurality of input signals, and that outputs a signal obtained by the distortion compensating process; a plurality of amplifiers (102) that amplify a plurality of input signals including the signal output from the distortion compensating means (101), and that output output signals; a calculation means (103) which, during a calibration operation of the signal processing apparatus (100) in which a calibration signal is used as the plurality of input signals and input to the plurality of amplifiers (102), calculates, for each input signal, a comparison result for at least one of the phase, amplitude, and intensity of the input signal and an output signal corresponding to the input signal; and a control means (104) for controlling whether, on the basis of the calculated comparison result, the distortion compensating means (101) should perform the distortion compensating process on the calibration signal.

Description

[Technical field]

[0001] The present invention relates to a signal processing apparatus, a signal processing method and a non-transitory computer readable medium. [Background technology]

[0002] Wireless communication technologies such as 5G (5th Generation) are evolving. In this technology field, compensating for distortions present in signals is important to ensure accurate transmission of signal content.

[0003] For example, Patent Document 1 discloses an antenna device equipped with a distortion compensation unit that compensates for distortion caused by multiple amplifiers. A detection unit of the antenna device detects, for example, AM (Amplitude Modulation)-AM distortion or AM-PM (Phase Modulation) distortion as the distortion characteristics of the power amplifier. The distortion compensation unit performs distortion compensation for the multiple amplifiers based on the detection result.

[0004] Patent Document 2 describes that a DPD (Digital Pre-Distortion) module and a nonlinear adjustment module of a correction device compensate for the nonlinearity of multiple power amplifiers. The DPD module uniformly compensates for the nonlinearity of multiple power amplifiers based on DPD parameters. The nonlinear adjustment module compensates for the nonlinearity of the power amplifiers that is not compensated for by the DPD module based on analog nonlinear correction parameters.

[0005] Also, Patent Document 3 discloses a dual channel remote radio head unit in which a digital logic circuit generates a predistortion compensation signal suitable for each power amplifier. Furthermore, Patent Document 4 discloses an RF power amplifier system in which an error between an input signal to a power amplifier 110 and an output signal of the power amplifier 110 is minimized by a predistorter. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JP 2020-136772 A [Patent Document 2] Special Publication No. 2020-526150 [Patent Document 3] Special Publication No. 2013-515424 [Patent Document 4] Special Publication No. 2010-519862 Summary of the Invention [Problem to be solved by the invention]

[0007] In a wireless communication system, a DPD compensation unit is provided in front of an amplifier to suppress nonlinear distortion generated by the amplifier and expand the linear range of the amplifier's output signal. However, depending on the amplifier, a memory effect may occur in the input / output characteristics. In this situation, when a calibration signal is input to the amplifier during a calibration operation for wireless communication settings, the calibration signal amplified by the amplifier and output reflects the memory effect. Therefore, there is a possibility that accurate calibration cannot be performed.

[0008] An object of the present disclosure is to provide a signal processing device, a signal processing method, and a non-transitory computer-readable medium to enable accurate calibration. [Means for solving the problem]

[0009] A signal processing device according to one aspect of the present embodiment includes a distortion compensation means that performs distortion compensation processing to compensate for nonlinear distortion on one or more of a plurality of input signals and outputs a signal that has been subjected to distortion compensation processing; a plurality of amplifiers that amplify the plurality of input signals including the signal output by the distortion compensation means and output them as output signals; a calculation means that calculates, for each input signal, a comparison result of at least one of the phase, amplitude and intensity between the input signal and an output signal corresponding to the input signal during a calibration operation of the device in which a calibration signal is used as a plurality of input signals and input to the plurality of amplifiers; and a control means that controls whether or not the distortion compensation means performs distortion compensation processing on the calibration signal based on the comparison result calculated by the calculation means.

[0010] A signal processing method according to one aspect of the present embodiment performs distortion compensation processing to compensate for nonlinear distortion on one or more of a plurality of input signals, outputs the signal that has been subjected to distortion compensation processing, and a plurality of amplifiers amplify the plurality of input signals including the signal that has been subjected to distortion compensation processing and output them as output signals.During a calibration operation of the device in which a calibration signal is used as the plurality of input signals and is input to the plurality of amplifiers, a comparison result of at least any of the phase, amplitude, and intensity between the input signal and an output signal corresponding to the input signal is calculated for each input signal, and based on the calculated comparison result, controls whether or not to perform distortion compensation processing on the calibration signal.

[0011] A non-transitory computer-readable medium according to one aspect of the present embodiment has stored therein a program that causes a computer to execute the following operations: performing distortion compensation processing to compensate for nonlinear distortion on one or more input signals among a plurality of input signals; outputting the signal that has been subjected to distortion compensation processing; a plurality of amplifiers amplifying the plurality of input signals including the signal that has been subjected to distortion compensation processing and outputting them as output signals; during a calibration operation of the device in which a calibration signal is used as a plurality of input signals and input to a plurality of amplifiers, calculating, for each input signal, a comparison result of at least one of the phase, amplitude, and intensity between the input signal and an output signal corresponding to the input signal; and controlling whether or not to perform distortion compensation processing on the calibration signal based on the calculated comparison result. Effect of the Invention

[0012] According to the present disclosure, it is possible to provide a signal processing device, a signal processing method, and a non-transitory computer-readable medium for enabling accurate calibration. [Brief description of the drawings]

[0013] [Figure 1] FIG. 1 is a block diagram showing an example of a wireless communication device according to a related art. [Diagram 2] FIG. 1 is a block diagram showing an example of a BB unit according to a related art. [Diagram 3] FIG. 1 is a block diagram showing an example of an FE unit according to a related art. [Figure 4] 1 is a graph showing an example of a power level of a transmitter in a wireless communication device according to a related art. [Diagram 5] FIG. 13 is a diagram illustrating an example of a frequency arrangement of DL calibration signals for each transmitter according to the related art. [Figure 6A] FIG. 1 is a diagram showing an example of an arrangement of antennas according to a related art; [Figure 6B] 1 is a graph showing an example of AM-AM input / output characteristics of a transmission amplifier according to a related art. [Figure 7A]1 is a graph showing an example of a phase difference between each signal channel according to the related art. [Figure 7B] 1 is a graph showing an example of an angular spectrum of a horizontal radiation pattern when a radio signal is output in accordance with data beamforming according to a related art. [Figure 8] 1 is a block diagram showing an example of a signal processing device according to a first embodiment; [Figure 9A] 5 is a flowchart showing an example of processing by the signal processing device according to the first embodiment. [Figure 9B] 5 is a flowchart showing an example of processing by the signal processing device according to the first embodiment. [Figure 10] FIG. 11 is a block diagram showing an example of a wireless communication device according to a second embodiment. [Figure 11] FIG. 11 is a block diagram showing an example of a BB unit according to a second embodiment. [Figure 12] FIG. 11 is a block diagram showing an example of an FE unit according to a second embodiment. [Figure 13A] 11 is a flowchart illustrating an example of a process performed by the wireless communication device according to the second embodiment. [Figure 13B] 11 is a flowchart illustrating an example of detailed processing performed by the wireless communication device according to the second embodiment. [Figure 14] FIG. 2 is a block diagram showing an example of a hardware configuration of an apparatus according to each embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] First, the related art of the present application will be described. Below, an embodiment of a wireless communication device using TDD (Time Division Duplex) as a communication method and MIMO (Multi User-Multi Input Multi Output) for wireless transmission and reception will be described. In addition, in order to achieve high frequency utilization efficiency, this wireless communication device uses digital beamforming technology.

[0015] FIG. 1 is a block diagram showing an example of a wireless communication device 10 according to the related art. The wireless communication device 10 is equipped with a massive element AAS (Active Antenna System) for 5G, and is a device provided in, for example, a base station. As shown in FIG. 1, the wireless communication device 10 includes a BF-BB (Beamforming-Baseband) unit 20 and an AAS unit 30. Here, the AAS unit 30 includes an optical transceiver 31, a TRX-BB unit 32, a front-end unit 33, 32 antennas 34, a wireless transmission unit (though 32 antennas and transceivers are given as an example in this embodiment, cases where the arrangement and number are other than the same number are also included within the scope of the disclosure), a distributor / synthesizer 35, a SW (Switch) 36, a CAL-TRX (calibration transceiver) 37, and a control unit (not shown) that controls each of these units. Note that, in the following, an uplink (UL) refers to a communication path from a UE (User Equipment: terminal) (not shown) to the wireless communication device 10, and a downlink (DL) refers to a communication path from the wireless communication device 10 to the UE.

[0016] The BF-BB unit 20 is a baseband unit having a function of generating a beamforming signal. The BF-BB unit 20 stores a preset receiving system characteristic [CAL-RX (fixed)] inside. The BF-BB unit 20 also stores the characteristic TX#n*[CAL-RX] of each signal channel acquired by the operation of the TRX-BB unit 32 when the wireless communication device 10 is started and periodically, and updates it every time a new value is acquired. The BF-BB unit 20 uses these values ​​to output a communication signal for communication to the AAS unit 30, thereby performing communication in the DL direction. Details of this process will be described later.

[0017] Next, a description will be given of each component of the AAS unit 30. The optical transceiver 31 performs photoelectric conversion of signals (eg, multi-layer signals) transmitted and received between the BF-BB unit 20 and the TRX-BB unit 32, and the reverse conversion.

[0018] The TRX-BB unit 32 mediates communication signals transmitted and received between the optical transceiver 31 and the front-end unit 33. During DL calibration operation, the TRX-BB unit 32 generates a DL calibration signal (hereinafter referred to as DL-CAL signal), which is an IQ signal, and outputs it to the CAL-TRX 37 via the front-end unit 33, the distributor / synthesizer 35, and the SW 36. During UL calibration operation, the TRX-BB unit 32 generates a UL-CAL signal (hereinafter referred to as UL-CAL signal), which is an IQ signal, and outputs it directly to the CAL-TRX 37. In this way, the TRX-BB unit 32 functions as a transceiver baseband unit.

[0019] The TRX-BB unit 32 is a unit that mediates communication signals transmitted and received between the optical transceiver 31 and the front-end unit 33, and includes 32 BB units 40#0-#31. Hereinafter, the BB units 40#0-#31 will be collectively referred to as BB unit 40.

[0020] 2 is a block diagram of the BB unit 40. The BB unit 40 includes a CFR processing unit 41 and a DPD processing unit 42. Each of the BB units 40#0 to #31 has the same configuration as that shown in FIG.

[0021] The CFR processing unit 41 limits the peak level of the IQ signal (multiple layer signal) output from the BF-BB unit 20 and input via the optical transceiver 31 by a CFR threshold (a threshold for suppressing the maximum peak component). Specifically, the CFR processing unit 41 suppresses, among the amplitude components in the input multi-layer signal, signal amplitude components that exceed the peak level set by the CFR threshold to the peak level set by the CFR threshold, and outputs the suppressed signal to the DPD processing unit 42.

[0022] The reason why the CFR processing unit 41 suppresses the peak level is as follows. If the peak level is not suppressed, a transmission signal having a high peak level may be output to the transmission amplifier downstream of the CFR processing unit 41. In that case, hard clipping occurs at the saturation output level of the transmission amplifier, generating nonlinear distortion components of high-order intermodulation, and the DPD processing unit 42 may not be able to sufficiently compensate for this nonlinear distortion component. To avoid this state, the CFR processing unit 41 limits the peak level of the transmission signal input to the transmission amplifier, and adjusts the transmission signal so that the output level of the transmission amplifier does not exceed the saturation level.

[0023] The DPD processor 42 is provided between each CFR processor 41 and each TRX 51. The DPD processor 42 compares the IQ signal (multi-layer signal) output from the CFR processor 41 with the IR signal (multi-layer signal) that is output from the transmission amplifier 52 (transmission power amplifier) ​​and then returned via the directional coupler 53 and the FB (Feedback) path and that has nonlinear distortion added based on the nonlinearity of the transmission amplifier 52. The DPD processor 42 performs compensation by applying a weighting that inversely corrects the nonlinearity to the input signal in order to compensate for nonlinear distortion in the input / output characteristics of AM-AM and AM-PM that occurs in the transmission amplifier 52 through this comparison. The IR signal is represented as a signal FB in FIGS. 2 and 3.

[0024] The DPD processor 42 performs DPD compensation processing to compensate the amplitude and phase of the IQ signal for wireless communication output from the CFR processor 41 based on a DPD compensation coefficient that represents the inverse characteristic of the input / output characteristic of the downstream transmitting amplifier 52, and outputs the signal that has been subjected to the DPD compensation processing as a TR signal to the FE (Front End) unit 50. By providing a DPD processor 42 for each TRX 51, it is possible to perform DPD compensation processing based on the characteristics of each TRX 51. This DPD compensation processing is performed to suppress nonlinear distortion radiation and improve the DL SINR (Signal to Interference plus Noise Ratio) performance. The DPD compensation processing can also improve the EVM (Error Vector Magnitude) and ACLR (Adjacent Channel Leakage Ratio) of the transmitting amplifier 52.

[0025] The TRX-BB unit 32 executes a DL or UL calibration operation when the wireless communication device 10 is started and periodically to determine and store a calibration weight (hereinafter, referred to as a CAL weight) for DL ​​or UL. This DL / UL-CAL weight is a value for correcting the variation in amplitude and phase of each TX or RX described later, and is determined by a DL / UL calibration operation based on a DL / UL-CAL signal. When the wireless communication device 10 transmits a spatially multiplexed signal consisting of multiple layers by data beamforming, the radio wave beam outputted by the wireless communication device 10 to a UE with which the wireless communication device 10 communicates may cause interference with a UE (other UE) with which the wireless communication device 10 does not communicate, so it is preferable to reduce the interference. Therefore, when the wireless communication device 10 forms a beam pattern for transmitting data in the direction of a certain UE and radiates the beam, a null is formed in the direction of the other UE as the pattern of the radiated beam. DL calibration is performed to ensure a desired angle and depth of the null.

[0026] When performing DL calibration, the TRX-BB unit 32 generates a DL-CAL signal and transmits it to the CAL-TRX 37 via the front-end unit 33, the distributor / synthesizer 35, and the SW 36. The CAL-TRX 37 outputs the DL-CAL signal that has passed through its interior to the TRX-BB unit 32. The TRX-BB unit 32 measures the difference in amplitude and phase between the original DL-CAL signal and the DL-CAL signal received by the CAL-TRX 37, and determines the DL-CAL weight to be applied to each signal channel in order to inversely correct the difference.

[0027] Moreover, when the TRX-BB unit 32 executes UL calibration, it generates a UL-CAL signal and inputs it to the CAL-TRX 37. The CAL-TRX 37 inputs the UL-CAL signal that has passed through the inside of the CAL network to the receiver RX of the TRX 51 via the SW 36 and the distributor / synthesizer 35. The receiver RX inputs the UL-CAL signal to the TRX-BB unit 32. The TRX-BB unit 32 measures the difference in amplitude and phase between the original UL-CAL signal and the UL-CAL signal transmitted by the CAL-TRX 37, and determines the UL-CAL weight to be applied to the receiver RX of each TRX 51 to inversely correct the difference. In this way, the TRX-BB unit 32 functions as a transceiver baseband unit. In addition, in Figs. 1 and 2, the DL / UL-CAL signal, which is an IQ signal transmitted and received between the TRX-BB unit 32 (DPD processing unit 42) and the CAL-TRX 37, is indicated as DL / UL-CAL IQ.

[0028] 1, the description of the AAS section 30 will continue. The front-end section 33 includes 32 FE units 50#0-#31. The FE units 50#0-#31 will be collectively referred to as FE unit 50 below.

[0029] Fig. 3 is a block diagram of the FE unit 50. The FE unit 50 includes a TRX 51, a transmission amplifier (transmission power amplifier) ​​52, a directional coupler (COUPLER) 53, a SW 54, and a reception amplifier (reception power amplifier) ​​55. Each of the FE units 50#0 to #31 has the same configuration as that shown in Fig. 3.

[0030] The TRX 51 is a transceiver, and includes a transmitter TX and a receiver RX, not shown. The transmitter TX converts an IQ signal received from the TRX-BB unit 32 into an RF signal, and outputs the RF signal to the antenna 34 or the CAL-TRX 37. When the wireless communication device 10 transmits a wireless signal, the transmitter TX outputs the RF signal to the antenna 34, and when performing DL calibration, the transmitter TX outputs a DL-CAL signal (RF signal) to the CAL-TRX 37 via the distributor / synthesizer 35.

[0031] Furthermore, the receiver TX converts an RF signal received from the antenna 34 or CAL-TRX 37 into an IQ signal and outputs it to the TRX-BB unit 32. When the wireless communication device 10 receives a wireless signal from the UE, the TRX 51 receives the RF signal from the antenna 34. When UL calibration is performed, the TRX 51 receives a UL-CAL signal (RF signal) from the CAL-TRX 37 via the distributor / synthesizer 35. Then, the TRX 51 converts the received UL-CAL signal into a UL-CAL signal (IQ signal) and outputs the converted UL-CAL signal to the BF-BB unit 20 via the TRX-BB unit 32.

[0032] Furthermore, the TRX 51 has an FB path that outputs the signal FB output from the directional coupler 53 to the DPD processing unit 42 described above.

[0033] Each transmitting amplifier 52 is disposed between each antenna 34 and a TRX 51 provided corresponding to each antenna 34. The transmitting amplifier 52 amplifies the RF signal (a signal for wireless communication or a DL-CAL signal) output from the TRX 51, and outputs the amplified signal to the directional coupler 53.

[0034] Each directional coupler 53 is a coupler provided between each transmitting amplifier 52 and each antenna 34. The directional coupler 53 outputs the RF signal output from each transmitting amplifier 52 to the antenna 34, and also outputs the RF signal to the corresponding TRX 51 via the FB path. The TRX 51 outputs the output RF signal to the DPD processing unit 42 via the FB path, and the DPD processing unit 42 receives the output RF signal and performs the above-mentioned processing.

[0035] The SW54 is a switch that switches a signal to be input or output to the TRX51 based on a control signal from the control unit of the AAS unit 30. That is, under the control of the AAS unit 30, the connection destination of the front-end unit 33 is switched.

[0036] Specifically, when the wireless communication device 10 is performing wireless communication, in each of the signal channels #0 to #31, the front-end unit 33 is connected to the antenna 34, and the SW54 is controlled so as not to connect the front-end unit 33 to the CAL-TRX 37. As a result, during data transmission, an RF signal is output from the TRX51 to the antenna 34, while during data reception, the SW54 causes the TRX51 to output an RF signal from the antenna 34.

[0037] On the other hand, when the wireless communication device 10 performs DL / UL calibration, the SW54 is controlled so that, in each of the signal channels #0 to #31, the front-end unit 33 and the CAL-TRX37 are connected and the front-end unit 33 and the antenna 34 are not connected. In other words, the TRX51 and the distributor / synthesizer 35 are connected, while the connection between the antenna 34 and the TRX51 is released. When the wireless communication device 10 performs DL calibration, the DL-CAL signal output from the transmitting amplifier 52 is input to the distributor / synthesizer 35. When the wireless communication device 10 performs UL calibration, the UL-CAL signal output from the distributor / synthesizer 35 is input to the receiving amplifier 55.

[0038] The wireless communication device 10 prevents the DL / UL-CAL signal processed by each TRX 51 from being affected by interference from other systems by controlling each SW 54. That is, since the DL / UL-CAL signal processed by each TRX 51 does not contain an interference component, the AAS unit 30 can accurately determine the CAL weight to be applied to each TRX 51. Furthermore, when the DL / UL calibration is completed, the control unit of the AAS unit 30 controls each SW 54 so that each TRX 51 and each antenna 34 are connected.

[0039] Each receiving amplifier 55 amplifies an input RF signal (a signal for wireless communication or a UL-CAL signal) and outputs the amplified signal to the corresponding TRX 51.

[0040] Returning to Fig. 1, the AAS unit 30 will be described further. The antenna 34 is an antenna provided corresponding to each TRX 51, each transmitting amplifier 52, and each receiving amplifier 55. The antenna 34 transmits polarized waves having mutually orthogonal polarizations of +45 degrees and -45 degrees. jointly There are four antennas with eight sets of eight, for a total of 32 antennas, but each antenna element has two polarized waves. jointly Since the number of antennas is 64, each antenna 34 is equivalent to 64 antennas. Each antenna 34 wirelessly transmits the RF signal received from each FE unit 50 to one or more UEs. Note that at least one of a filter and a duplexer may be provided in front of each antenna 34 as appropriate.

[0041] When wireless communication device 10 performs DL calibration, distributor / synthesizer 35 combines the DL-CAL signals output from each SW 54, and outputs the combined DL-CAL signal to SW 36. When wireless communication device 10 performs UL calibration, distributor / synthesizer 35 distributes the UL-CAL signal output from SW 36, and outputs the distributed UL-CAL signal to each SW 54.

[0042] SW36 is a switch that switches the signal direction. When the wireless communication device 10 performs DL calibration, SW36 outputs the DL-CAL signal output from the distribution combiner 35 to SW36. Also, when the wireless communication device 10 performs UL calibration, SW36 outputs the UL-CAL signal output from SW36 to the distribution combiner 35.

[0043] When the wireless communication device 10 performs DL calibration, CAL-TRX37 converts the DL-CAL signal (RF signal) output from SW36 into a DL-CAL signal (IQ signal). Then, the converted DL-CAL signal is output to the TRX-BB unit 32.

[0044] Also, when the wireless communication device 10 performs UL calibration, CAL-TRX37 converts the UL-CAL signal (IQ signal) output from the TRX-BB unit 32 into a UL-CAL signal (RF signal), and outputs the converted UL-CAL signal to SW36. Note that CAL-TRX37 may be provided with a transmitter and a receiver, similar to TRX51.

[0045] Hereinafter, the DL calibration operation and UL calibration operation of the wireless communication device 10 will be described. During the calibration operations shown below, each DPD processing unit 42 is turned off and does not perform DPD compensation processing.

[0046] First, the DL calibration operation will be described. First, the TRX-BB unit 32 outputs a preset DL-CAL signal (IQ signal) to the front-end unit 33. Each TRX 51 (transmitter TX) in the front-end unit 33 converts the DL-CAL signal (IQ signal) into a DL-CAL signal (RF signal). The DL-CAL signal (RF signal) converted by each TRX 51 is output to the distribution combiner 35 via the transmission amplifier 52 and SW 54, and is combined by the distribution combiner 35. The DL-CAL signal combined by the distribution combiner 35 is input to the CAL-TRX 37 via SW 36. The AAS unit 30 may output the DL-CAL signal by dividing the timing for each signal channel.

[0047] The CAL-TRX 37 converts the received DL-CAL signal (RF signal) into a DL-CAL signal (IQ signal) and outputs it to the TRX-BB unit 32. The DL-CAL signal sent from the CAL-TRX 37 is in a state in which the DL-CAL signals sent from each TRX 51#n are combined by frequency multiplexing. Therefore, the TRX-BB unit 32 separates the DL-CAL signal sent from the CAL-TRX 37 into frequencies by FFT (Fast Fourier Transform), extracts the DL-CAL signal for each of the signal channels #0 to #31, and calculates the DL-CAL weight.

[0048] Specifically, the TRX-BB unit 32 learns the variations in the amplitude and phase of the DL-CAL signal for each signal channel by measuring the difference in amplitude and phase between the DL-CAL signal transmitted for each signal channel and the original (i.e., before transmission) DL-CAL signal. The TRX-BB unit 32 calculates the DL-CAL weight of each TRX 51#n based on the learning result.

[0049] Here, the DL-CAL weight of each TRX51#n is the product of the transmission system characteristics (amplitude and phase characteristics) [TX#n] of TRX51#n and the reception system characteristics (amplitude and phase characteristics) [CAL-RX] of CAL-TRX37, as expressed in the following equation 1.

number

[0050] This completes the DL calibration learning. The BF-BB unit 20 stores this DL-CAL weight internally. Thereafter, during normal DL wireless communication, the BF-BB unit 20 outputs to each TRX 51 a DL signal weighted by the above-mentioned DL-CAL weight for that TRX 51.

[0051] Next, an example of DL operation of the AAS unit 30 will be described. The BF-BB unit 20 generates a BF signal (IQ signal) in an internal circuit. Then, the generated BF signal is corrected with the above-mentioned DL-CAL weight for each of the signal channels #0 to #31, and then output to the TRX-BB unit 32 via the optical transceiver 31.

[0052] Note that the optical transceiver 31 may not be provided between the BF-BB unit 20 and the TRX-BB unit 32, and the BF-BB unit 20 and the TRX-BB unit 32 may be directly connected to each other. In this case, the BF-BB unit 20 is connected to an external distribution unit (DU) via an optical transceiver.

[0053] Specifically, the BF-BB unit 20 multiplies the BF signal by a fraction whose denominator is the DL-CAL weight and whose numerator is the fixed receiving system characteristic [CAL-RX (fixed)] of the CAL-TRX 37. The corrected BF signal is expressed by the following formula 2. Note that [CAL-RX (fixed)] is stored in advance in a storage unit (not shown) of the BF-BB unit 20.

number

[0054] The corrected BF signal is converted from an IQ signal to an RF signal by each TRX 51#n of the TRX-BB unit 32 and sent out, amplified by each transmission amplifier 52#n, and output from the front-end unit 33. The BF signal output from the front-end unit 33 passes through each TRX 51#n, and is therefore expressed by the following Equation 3.

number

[0055] Furthermore, when Equation 3 is simplified by deleting [TX#n], it can be expressed as Equation 4 below.

number

[0056] In formula 4, if [CAL-RX(fixed)]=[CAL-RX], the BF signal is in an ideal state, and the BF signal in the ideal state is transmitted from each antenna 34#n. Note that, in order for [CAL-RX(fixed)]=[CAL-RX], the stability of CAL-RX is important.

[0057] By performing the above operations, it is possible to compensate for the variations in amplitude and phase characteristics of each transmitter TX#n. This DL calibration operation makes it possible to set with high precision the angle and depth of nulls formed in the direction of other UEs when transmitting spatially multiplexed radio signals of multiple layers by data beamforming. In addition, it is possible to suppress the occurrence of nonlinear distortion radiation caused by third-order intermodulation distortion in each spatial direction.

[0058] Note that the update of the DL-CAL weights shown above may be performed between the transmission of a wireless signal by fan beamforming (with a beam pattern shape equivalent to omni-directional broad beamforming) and the transmission of a wireless signal by data beamforming, as described later. Alternatively, the update of the DL-CAL weights may be performed periodically. As yet another example, the wireless communication device 10 may update the DL-CAL weights triggered by the sensor of the wireless communication device 10 detecting an environmental change (e.g., a temperature change) or a change in the signal over time. The update period in this case is, for example, a period of one minute or more.

[0059] Next, the UL calibration operation will be described. The TRX-BB unit 32 outputs a preset UL-CAL signal (IQ signal) directly to the CAL-TRX 37. The CAL-TRX 37 converts the UL-CAL signal (IQ signal) into a UL-CAL signal (RF signal). The UL-CAL signal (RF signal) converted by the CAL-TRX 37 is output to the distribution combiner 35 via the SW 36 and distributed by the distribution combiner 35. The UL-CAL signal distributed by the distribution combiner 35 is output to each TRX 51 via each SW 54 and the receiving amplifier 55. Each TRX 51 converts the UL-CAL signal (RF signal) into a UL-CAL signal (IQ signal) and outputs it to the TRX-BB unit 32.

[0060] The TRX-BB unit 32 measures the difference in amplitude and phase between the UL-CAL signal of the UL-CAL signal received by each TRX 51 and the original UL-CAL signal, and learns the variation in amplitude and phase of the UL-CAL signal. The TRX-BB unit 32 calculates the UL-CAL weights of each TRX 51 based on the learning result.

[0061] This completes the UL calibration operation. The BF-BB unit 20 stores this UL-CAL weight internally. Thereafter, during normal UL wireless communication, the BF-BB unit 20 outputs to each TRX 51 a UL signal weighted by the above-mentioned UL-CAL weight for that TRX 51.

[0062] <Calibration execution timing> Next, the timing of DL and UL calibration execution will be described. As described above, the wireless communication device 10 is a wireless communication device compatible with the TDD mode (TDD communication method). The TDD mode is a communication method in which the same frequency is used in uplink and downlink (UL / DL) and DL communication and DL communication and UL communication are switched over time for transmission and reception. A DL subframe is transmitted for DL ​​communication, and a UL subframe is transmitted for UL communication. In addition, at the timing of switching from DL communication to UL communication, a special subframe is transmitted. The special subframe is a subframe composed of a DwPTS (Downlink Pilot Time Slot), an UpPTS (Uplink Pilot Time Slot), and a GP (Guard Period). The DwPTS is a field reserved for DL ​​communication, the UpPTS is a field reserved for UL communication, and the GP is a field in which neither DL communication nor UL communication is performed.

[0063] In the wireless communication device 10, during a GP (Guard Period) time period in which neither DL communication nor UL communication is performed, the transmitter TX and the receiver RX in the TRX 51 are exclusively in an OFF / ON state. The wireless communication device 10 performs at least one of DL calibration and UL calibration during the GP time period of the special subframe, for example.

[0064] <Transmitter power level when performing calibration> FIG. 4 shows the power level of the transmitter TX at each timing of DL and UL timing. The horizontal axis of FIG. 4 shows time, and the vertical axis shows power level. A solid line L1 in FIG. 4 shows the transition of the transmission power level of the transmitter TX of the wireless communication device 10. It can be seen from FIG. 4 that the transmission power level, which was an off power level in the initial transmitter off section, becomes an on power level in the transmitter on section after passing through a transmitter transition section, and then becomes an off power level in the transmitter off section after passing through another transmitter transition section. In FIG. 4, the time section marked UL transmission indicates the time section of UL communication. Also, the time section marked DL transmission indicates the time section of DL communication. Also, the time section marked GP or UL transmission indicates the time section of GP or UL communication.

[0065] The wireless communication device 10 performs DL calibration or UL calibration in the time interval (transmitter transition interval) of the GP of the special subframe. This time interval is included in the interval of the uplink-downlink frame timing. In the GP, (a) the time interval in which the transmitter TX transitions from OFF to ON state and (b) the time interval in which the transmitter TX transitions from ON to OFF state are, for example, 10 μs. The wireless communication device 10 can perform the above-mentioned DL calibration or UL calibration in at least one of the intervals (a) and (b). That is, in this example, the output time of the DL / UL-CAL signal may be within 10 μs. In addition, the main purpose of the calibration is to unify the frequency characteristics of the amplitude and phase in the linear region between the 32 TRXs. Therefore, it is important to reduce the power of the DL / UL-CAL signal to a level that can ensure a required SNR (Signal-to-Noise Ratio) below the maximum rating so that the DL / UL-CAL signal is not subjected to nonlinear degradation. In this manner, the DL-CAL weight is calculated periodically in the time interval of the GP and stored inside the BF-BB unit 20.

[0066] <Regarding the frequency arrangement of DL-CAL signals> Furthermore, an example of the frequency arrangement of DL-CAL signals with orthogonal frequencies for each TRX#n will be described. Here, as shown in FIG. 1, an example of the frequency arrangement of DL-CAL signals for each transmitter TX#n when 32 TRX#n are provided will be described.

[0067] Referring to FIG. 5, an example of the frequency arrangement of DL-CAL signals for each transmitter TX#n will be described. FIG. 5 illustrates the frequency arrangement of DL-CAL signals for each transmitter TX#n.

[0068] In FIG. 5, in the frequency arrangement of the DL-CAL signal of one transmitter TX#n, the subcarriers used for transmitting the DL-CAL signal are arranged at intervals of X [MHz]. And between adjacent transmitters TX#n, the frequency arrangement of the DL-CAL signal is shifted by Y [MHz] in the frequency direction. Note that fs0 [MHz] is the reference frequency.

[0069] Here, in the example shown in FIG. 5, it is necessary to satisfy the following two frequency arrangement conditions A1 and A2. Frequency arrangement condition A1: X [MHz]> Y [MHz] × (number of transmitters TX#n - 1) holds. Frequency arrangement condition A2: Within the range of the signal bandwidth, from the frequency “sc0 = fs0 [MHz]” of the lowest subcarrier sc0 of the DL-CAL signal for transmitter TX#1 to the frequency “sck = fsc0 + 31Y + kX [MHz]” of the highest subcarrier sck of the DL-CAL signal for transmitter TX#31 is included.

[0070] Next, problems associated with the related art will be described. Fig. 6A shows an example of the arrangement of antennas 34#0 to #31 in the related art. Eight antennas 34 are arranged in four rows, and antennas 34 in the same row in Fig. 6A output the same wireless signal. For example, four antennas belonging to each of (a1), (a2), (b1), (b2), (c1), (c2), (d1), and (d2) in Fig. 6A output the same wireless signal. Therefore, the radio wave strength of the four antennas in these rows is approximately the same.

[0071] The antennas 34#0-#31 can transmit radio signals by, for example, fan beamforming and data beamforming. Here, the transmission of radio signals by fan beamforming means transmitting radio signals of approximately constant intensity in front of the wireless communication device 10 and in a range of a predetermined angle in the horizontal direction from the front, and is used for broadcast data transmission, for example. In contrast, the transmission of radio signals by data beamforming means transmitting radio signals of high intensity in front of the wireless communication device 10 and in a certain angle direction in the horizontal direction, while forming a null in the direction of another UE and transmitting a radio signal of low intensity. This method of transmitting radio signals is used for data communication with a specific UE.

[0072] When the antennas 34#0 to 31 transmit radio signals by fan beam forming, for example, (a1) and (a2) output radio signals of the maximum rating, and (b1) and (b2), (c1) and (c2), and (d1) and (d2) output radio signals of increasing radio field strength in this order. That is, the strength of the output radio signals decreases from the center of the antenna shown in FIG. 6A to the outside. As an example, the BF-BB unit 20 outputs input signals of up to -14 dBFS (average) to the transmission amplifiers 52 corresponding to (a1) and (a2), and outputs input signals of up to -24 dBFS (average) to the transmission amplifiers 52 corresponding to (b1) and (b2).

[0073] The phases of the input signals to the transmitting amplifier 52 corresponding to (a1), (a2), (c1), and (c2) are the same, and the phases of the input signals to the transmitting amplifier 52 corresponding to (b1), (b2), (d1), and (d2) are inverted from the phases of the input signals to the transmitting amplifier 52 corresponding to (a1), (a2), (c1), and (c2).

[0074] FIG. 6B is a graph showing an example of the AM-AM input / output characteristics of the transmitting amplifier 52 corresponding to the antennas 34 of (a1), (a2), (b1), and (b2) of FIG. 6A. The horizontal axis of FIG. 6B is the amplitude of the input signal, and the vertical axis of FIG. 6B is the amplitude of the output signal. The input / output characteristics of the transmitting amplifier 52 corresponding to (a1) and (a2) are shown in (a) of FIG. 6B, and the input / output characteristics of the transmitting amplifier 52 corresponding to (b1) and (b2) are shown in (b) of FIG. 6B. The ideal input / output characteristics of the transmitting amplifier 52 are linear and shown in (e) of FIG. 6B. The input / output characteristics (a) and (b) of the transmitting amplifier 52 are not compensated for by the DPD processors 42. Also, consider a case where a memory effect (a phenomenon in which the AM-AM characteristics and the AM-PM characteristics change depending on the input / output levels that passed through the transmitting amplifier in the past time period and are held for a certain period of time) occurs in the AM-AM characteristics and the AM-PM characteristics of the transmitting amplifier 52. In this case, when a signal of −37 dBFS (average) is input as a DL-CAL signal to the transmission amplifier 52, the points indicating the corresponding output signals in the input / output characteristics (a) and (b) are (c) and (d).

[0075] 6B, the input / output characteristics (a) and (b) have nonlinearity that deviates from the ideal input / output characteristics. In particular, the input / output characteristic (a) has a larger nonlinearity than the input / output characteristic (b). A DL-CAL signal having a small amplitude (intensity) is input to each transmission amplifier 52.

[0076] Similarly to the AM-AM input / output characteristics, the phase difference between the input signal and output signal of the transmission amplifier 52 (AM-PM input / output characteristics) also has a significant difference when compared with ideal input / output characteristics (characteristics in which the phase difference is 0). The differences increase in the order of (a1) and (a2), (b1) and (b2), (c1) and (c2), and (d1) and (d2).

[0077] The distortion due to the above-mentioned nonlinearity is essentially eliminated by changing the input signal to the transmission amplifier 52. However, when the transmission amplifier 52 is a Doherty amplifier (e.g., a gallium nitride amplifier), a memory effect may occur in the AM-AM input / output characteristics and the AM-PM input / output characteristics. In this case, even if the input signal has changed, the transmission amplifier 52 outputs an output signal based on the input / output characteristics related to the input signal before the change for a certain period of time due to the memory effect occurring in the transmission amplifier 52 itself.

[0078] In particular, when the wireless communication device 10 transmits a wireless signal by fan beamforming, performs DL calibration, and then transmits a wireless signal by data beamforming, the following problem occurs. When transmitting a wireless signal by fan beamforming, the output of the transmitting amplifier 52 varies in strength from the maximum rated output to a low signal strength. Note that distortion due to the nonlinearity of each transmitting amplifier 52 at this stage is compensated for by the corresponding DPD processor 42.

[0079] When DL calibration is performed after the wireless communication device 10 transmits (radiates) the radio signal by this data beamforming, the output level of the DL-CAL signal output by the BF-BB unit 20 is approximately the same between each transmitter, unlike the case of fan beamforming. However, due to the memory effect of the transmitting amplifier 52, when passing through each transmitting amplifier 52, the characteristics of AM-AM and AM-PM determined by the input / output characteristics during fan beamforming affect the DL-CAL signal output from each transmitter.

[0080] As an example, a signal with an average level of -37 dBFS is assumed as the DL-CAL signal. Note that 0 dBFS corresponds to the full scale: maximum output level of the transmission DAC (Digital Analog Converter). As described above, when the DL-CAL signal is input to the transmission amplifier 52 in a state where the memory effect occurs, the points indicating the output signals corresponding to the input / output characteristics (a) and (b) in FIG. 6B are (c) and (d), and a gain difference occurs compared to the ideal input / output characteristics. In addition, during the DL calibration operation using the DL-CAL signal, it is assumed that the wireless communication device 10 learns the frequency characteristics of the amplitude and phase of each transmitter in a linear region without nonlinearity, and unifies and corrects the difference between each frequency characteristic. Therefore, since the DPD processing unit 42 is off, the distortion due to the nonlinearity of each transmission amplifier 52 is not compensated for by the corresponding DPD processing unit 42. Therefore, during the DL calibration operation, the DL-CAL weight is set so as to compensate for the difference in amplitude and phase between each transmitter caused by this memory effect.

[0081] When the wireless communication device 10 transmits a radio signal by data beamforming in the next data slot, the output of each transmitting amplifier 52 is at the maximum rating for transmitting data to the UE. That is, the radio signal output by the BF-BB unit 20 has substantially the same amplitude for each signal channel. Also, when the radio signal by data beamforming is transmitted, each DPD processing unit 42 is turned on, so that each DPD processing unit 42 attempts to compensate for distortion caused by the nonlinearity of the corresponding transmitting amplifier 52.

[0082] However, as described above, the DL-CAL weights that were set in the previous DL calibration reflect the history of fan beamforming. Therefore, the output signals of each transmitting amplifier 52 should have substantially the same amplitude, but due to unnecessary DL-CAL weights, the amplitudes of the output signals of each transmitting amplifier 52 are different. In addition, a phase difference that should not exist in reality is generated in each transmitting amplifier 52. In this way, over-compensation or under-compensation occurs in the amplitude and phase of the wireless signal by data beamforming. This phenomenon continues until the DL-CAL weights are updated.

[0083] FIG. 7A is a graph showing an example of the phase difference of each signal channel. The horizontal axis of the graph in FIG. 7A indicates the number of the transmitting amplifier 52, and the vertical axis of the graph indicates the phase difference amount from the transmitting amplifiers 52#3, #4, #11, and #12 (corresponding to (a1) and (a2) in FIG. 6). FIG. 7A shows the phase shift amount between the radio signals of the data beamforming output from each transmitting amplifier 52 when transmitting a radio signal in a state in which correction by unnecessary DL-CAL weight is performed by the above-mentioned process in the configuration of the antenna 34 shown in FIG. 6A. Note that while FIG. 7A shows the phase difference amount from the transmitting amplifiers 52#0 to #15, the phase difference amount from the transmitting amplifiers 52#16 to #31 (phase difference amount from the transmitting amplifiers 52#19, #20, #27, and #28) is also shown in the same graph as FIG. 7A.

[0084] 7A shows a case where, statistically, within a range of ±3σ where σ is the standard deviation, when the memory effect exists, the phase difference between each transmitter is a maximum of 11.6 degrees pp (phase-phase) in (1), a maximum of 23.1 degrees pp in (2), and a maximum of 34.6 degrees pp in (3). The effect of this phase difference on data beamforming was verified by the following calculation. As can be understood by referring to FIG. 7A, the phase difference amount of the transmitting amplifier 52 corresponding to the antennas 34 of (d1) and (d2) in FIG. 6A is the largest, and the phase difference amount becomes smaller as the transmitting amplifiers 52 corresponding to (c1) and (c2), and the transmitting amplifiers 52 corresponding to (b1) and (b2) are arranged.

[0085] Fig. 7B is a graph showing an example of an angular spectrum of a horizontal radiation pattern when a radio signal related to data beamforming is output. The horizontal axis of the graph in Fig. 7B indicates the horizontal (left-right) angle from the front of the wireless communication device 10, and the vertical axis of the graph indicates a normalized radiation power level when the output signal from the front of the wireless communication device 10 is used as a reference. (1) to (3) in Fig. 7B are graphs showing angular spectra when there are phase differences of (1) to (3) in Fig. 7A, and (0) in Fig. 7B indicates the original angular spectrum without unnecessary DL-CAL weight.

[0086] As can be understood by referring to FIG. 7B, the depth of the null point closest to the front of the wireless communication device 10 (first null depth) is 46 dB in (0), 27 dB in (1), 21 dB in (2), and 17 dB in (3). That is, the larger the phase difference, the shallower the null depth. That is, the DL SINR in the direction of each UE during spatial multiplexing signal transmission is degraded by this shallow null (meaning interference waves in beamforming to other UEs). The null depth determines the MU-MIMO performance of the wireless communication device 10. Therefore, the throughput of the cell when the wireless communication device 10 functions as a base station does not improve, and communication quality is degraded.

[0087] The present disclosure shows a configuration capable of suppressing SINR degradation so that, when there is a memory effect in the nonlinear characteristics of an amplifier, the memory effect degrades the accuracy of calibration, thereby preventing SINR degradation of signals to each terminal during spatial multiplexing signal transmission. As a specific example, even in a case where a wireless communication device transmits a wireless signal by fan beamforming, performs DL calibration, and then transmits a wireless signal by data beamforming, the present disclosure can suppress degradation of wireless communication quality due to data beamforming.

[0088] First embodiment Hereinafter, a first embodiment of the present disclosure will be described with reference to the drawings. Fig. 8 is a block diagram showing a signal processing device according to the first embodiment. The signal processing device 100 is a device for processing an electric signal, and can be applied to, for example, a wireless communication device in a communication system, but is not limited thereto.

[0089] The signal processing device 100 includes distortion compensation units 101#1 to #n, amplifiers 102#1 to #n, a calculation unit 103, and a control unit 104. Each component will be described below. Note that n is an arbitrary number equal to or greater than 2, and the distortion compensation units 101#1 to #n will be collectively referred to as distortion compensation units 101, and the amplifiers 102#1 to #n will be collectively referred to as amplifiers 102.

[0090] The distortion compensation units 101#1-#n perform distortion compensation processing to compensate for nonlinear distortion on the input signals IN#1-#n, respectively, and output the signals that have been subjected to distortion compensation processing to the corresponding amplifiers 102#1-#n. This distortion compensation processing suppresses nonlinear distortion in the signal output by the amplifier 102. The distortion compensation unit 101 can be switched under the control of the control unit 104 between an ON state in which distortion compensation processing is performed, and an OFF state in which distortion compensation processing is not performed and the input signal is output as is as an output signal.

[0091] The distortion compensation unit 101 executes, for example, DPD compensation processing as the distortion compensation processing. When the DPD compensation processing is executed, DPD compensation coefficients related to amplitude and phase are stored inside the distortion compensation unit 101. The DPD compensation coefficients are weights for compensating for nonlinear AM / PM components of the amplifier 102, and the distortion compensation unit 101 selects appropriate DPD compensation coefficients related to amplitude and phase based on the characteristics of the input signal IN. The distortion compensation unit 101 executes DPD compensation processing on the input signal IN using the selected DPD compensation coefficient. For example, the distortion compensation unit 101 stores an LUT (lookup table) in which the amplitude or (I, Q) value of the input signal IN is associated with the DPD compensation coefficient corresponding to the value. The distortion compensation unit 101 determines the value of the input signal IN, and refers to the LUT based on the value to select an appropriate DPD compensation coefficient and executes the DPD compensation processing. The distortion compensation unit 101 appropriately updates the DPD compensation coefficients related to amplitude and phase.

[0092] The amplifier 102#1 is an amplifier that amplifies the signal output from the distortion compensation unit 101#1 and outputs it as an output signal OUT#1. Similarly, the amplifiers 102#2,...,#n amplify the signals output from the distortion compensation units 101#2...,#n, respectively, and output them as output signals OUT#2...,#n. Any type of amplifier can be used as the amplifier 102.

[0093] The calculation unit 103 calculates a comparison result of at least one of the phase, amplitude, and intensity between the input signal IN and the output signal OUT corresponding to the input signal IN for each signal channel #1 to #n. This process is at least executed during a calibration operation of the signal processing device 100 in which a calibration signal is used as a plurality of input signals IN#1 to #n and input to the amplifiers 102#1 to #n. The calibration operation may be, for example, a DL calibration operation or a UL calibration operation in a wireless communication device described in the related art mentioned above, but is not limited to these. In this example, the calibration signal is a signal of approximately the same level for the input signals IN#1 to #n.

[0094] The calculation unit 103 can calculate, for example, at least one of a phase difference, an amplitude ratio, and an intensity ratio between an input signal IN and an output signal OUT corresponding to the input signal IN for each signal channel #1 to #n. As an example, the calculation unit 103 calculates a phase difference by subtracting an output signal corresponding to the input signal from the input signal. The calculation unit 103 also calculates an amplitude ratio by dividing an input signal by an output signal corresponding to the input signal. The calculation unit 103 also calculates an intensity ratio by dividing a square of an input signal by a square of an output signal corresponding to the input signal. Among the phase difference, the amplitude ratio, and the intensity ratio, the phase difference is considered to be most sensitive to the deterioration of DL SINR during data beamforming in the determination by the control unit 104 described later, but the amplitude ratio and the intensity ratio can also be used as a determination factor. Such a comparison result is calculated to determine whether or not there is a memory effect in the distortion compensation units 101#1 to #n.

[0095] Based on the comparison result calculated by the calculation unit 103, the control unit 104 controls whether the distortion compensation unit 101 performs distortion compensation processing by controlling the on / off of the distortion compensation units 101#1 to #n during the calibration operation.

[0096] As described above, the calibration signal has approximately the same level for the input signals IN#1 to #n. In contrast, the input and output levels of the input signals #1 to #n when going back beyond the calibration signal section are different from each other. Furthermore, if there is a memory effect in the nonlinearity of the amplifier, different AM-AM and AM-PM characteristics are maintained for each signal channel. As a result, in the subsequent calibration section, the calibration signal passes through each amplifier 102 having different AM-AM and AM-PM characteristics, and a difference occurs in the frequency characteristics of the amplitude or phase between the signal channels. For example, when each amplifier is connected to a transmitter, a difference occurs in the frequency characteristics of the amplitude or phase between the transmitters.

[0097] Therefore, by comparing the phase difference and the like in each signal channel #1 to #n when the calibration signal is output to the amplifiers 102 #1 to #n, it is possible to determine whether or not the memory effect of the amplifier 102 is at a significant level. If there is a significant memory effect, the influence of the previous input signal is large, and the difference based on the comparison result will be a large value. In contrast, if there is no significant memory effect, the influence of the previous input signal is 0 or small, and the difference based on the comparison result will be 0 or a small value.

[0098] 9A is a flowchart showing the process executed by the signal processing device 100 when a normal input signal, not a calibration signal, is input to each amplifier 102. First, the distortion compensation units 101#1-#n perform distortion compensation processing on the multiple input signals IN#1-#n, and output the signals that have been subjected to the distortion compensation processing to the corresponding amplifier 102 (step S11). The amplifiers 102#1-#n amplify the signals output from the distortion compensation units 101#1-#n, respectively, and output them as output signals OUT#1-#n (step S12).

[0099] The above-mentioned normal input signal is, for example, a signal (communication signal) related to wireless transmission or reception in a wireless communication device. In this case, the SINR of the communication signal can be improved by performing distortion compensation processing.

[0100] Fig. 9B is a flowchart showing the processing executed by the signal processing device 100 when calibration signals are input as input signals IN#1-#n to the amplifiers 102. Note that since the signal processing device 100 is not in a state where it executes normal processing based on normal input signals, in the initial state of the flow shown in Fig. 9B, the distortion compensation units 101#1-#n are off.

[0101] First, the calibration signals are input to the amplifiers 102#1 to #n as the input signals IN#1 to #n. The amplifiers 102#1 to #n each amplify and output the calibration signal (step S13).

[0102] In this example, the calculation unit 103 calculates the phase difference between the input signals IN#1-#n and the output signals OUT#1-#n corresponding to the input signals IN#1-#n, respectively (step S14). However, as described above, the calculation unit 103 may calculate other types of phase, amplitude, and intensity comparison results. The control unit 104 controls whether or not to perform distortion compensation processing on the calibration signal of each signal channel by controlling the on / off of the distortion compensation units 101#1-#n based on the phase difference comparison results calculated by the calculation unit 103 (step S15).

[0103] As described above, the control unit 104 of the signal processing device 100 controls whether or not to cause the distortion compensation unit 101 to execute distortion compensation processing, based on the comparison result calculated by the calculation unit 103. Therefore, the control unit 104 can accurately determine that a memory effect remains in the amplifier 102, and cause the distortion compensation unit 101 to execute distortion compensation processing. Therefore, the signal processing device 100 can learn about the difference in the frequency characteristics of the amplitude or phase between the signal channels by using the calibration signal. As a result, the difference in the frequency characteristics is corrected, enabling accurate calibration.

[0104] Specifically, when the calculation unit 103 calculates the phase difference between the input signal IN#1 and the output signal OUT#1, between the input signal IN#2 and the output signal OUT#2, ..., and between the input signal IN#n and the output signal OUT#n, the control unit 104 may determine whether or not a predetermined condition exists where a difference between the phase differences is equal to or greater than a first threshold value set in advance. When the calculation unit 103 calculates the amplitude ratio, the control unit 104 may determine whether or not a predetermined condition exists where a difference between the amplitude ratios is equal to or greater than a second threshold value set in advance. When the calculation unit 103 calculates the intensity ratio, the control unit 104 may determine whether or not a predetermined condition exists where a difference between the intensity ratios is equal to or greater than a third threshold value set in advance.

[0105] The calculation unit 103 may also calculate a plurality of the n phase differences, the n amplitude ratios, and the n intensity ratios. For example, when the calculation unit 103 calculates the phase difference and the amplitude ratio, the control unit 104 may determine whether or not a predetermined condition exists in which at least one of the difference between the phase differences that is equal to or greater than a first threshold value and the difference between the amplitude ratios that is equal to or greater than a second threshold value exists. The same determination can be performed even when the calculation unit 103 calculates the phase difference and the intensity ratio, when the calculation unit 103 calculates the amplitude ratio and the intensity ratio, or when the calculation unit 103 calculates the phase difference, the amplitude ratio, and the intensity ratio. That is, the control unit 104 determines whether or not at least one of the difference between the phase differences, the difference between the amplitude ratios, and the difference between the intensity ratios exists in a difference that is equal to or greater than a predetermined threshold value.

[0106] When the above-mentioned predetermined conditions are satisfied, the control unit 104 controls the distortion compensation units 101#1 to #n to be turned on and to execute distortion compensation processing for the calibration signal. As a result, even if the amplifier 102 has a memory effect of nonlinear characteristics based on a past input signal, the control unit 104 treats the amplitude or phase fluctuation caused by the memory effect of the calibration signal as a correction target, and controls the input signal so as not to be overcompensated. Specifically, the control unit 104 corrects the nonlinearity of the amplifier 102 in a short period of time in the distortion compensation unit 101 when learning the frequency characteristics of the calibration signal. As a result, the control unit 104 can accurately determine the amplitude or phase error between each signal channel, correct the error, and make the output signal of the amplifier 102 uniform.

[0107] Furthermore, when the above-mentioned predetermined condition is not satisfied, the control unit 104 can control the distortion compensation units 101#1 to 101#n to be turned off so as not to execute the distortion compensation process. This can prevent the CAL signal from being subjected to an unnecessary signal change due to the distortion compensation process when it is determined that there is no significant memory effect. This can prevent the calibration from becoming inaccurate.

[0108] In the above process, the control unit 104 may specify the maximum phase difference and the minimum phase difference among the calculated n phase differences, calculate the difference between the two, and determine whether the difference is equal to or greater than the first threshold. In this way, the control unit 104 uses the maximum and minimum values ​​of the calculated values ​​for comparison, so that the control unit 104 does not need to perform comparison processing for all values, and therefore can perform the comparison processing more quickly. This process can also be performed for the amplitude ratio and the intensity ratio in the same way.

[0109] The calibration signals may not be completely identical in phase or amplitude in each of the signal channels #1 to #n. In this case, the threshold value used for the determination in the control unit 104 is set to a value that allows reliable detection of the memory effect of the amplifier 102, taking into consideration the difference in the original phase or amplitude of the calibration signals in each signal channel.

[0110] In the above description, a distortion compensation unit 101 is provided for each of the signal channels #1 to #n. However, there may be a signal channel in which an amplifier 102 is provided but no distortion compensation unit 101 is provided. Also, one unit of distortion compensation unit 101 may perform distortion compensation processing on a plurality of signal channels and output the signals that have been subjected to distortion compensation processing to a plurality of amplifiers 102. Even with such a circuit configuration, it is possible to configure a wireless communication circuit by connecting a wireless communication transmitter to the rear stage of each amplifier 102.

[0111] Furthermore, the distortion compensation unit 101 may perform distortion compensation using a method other than DPD compensation. For example, feed-forward distortion compensation (open loop compensation) may be performed. In addition, AI (Artificial Intelligence) and deep learning technology may be applied to the distortion compensation unit 101, and the maximum likelihood compensation coefficient used for distortion compensation may be determined by having the distortion compensation unit learn and store a large amount of nonlinear distortion compensation results.

[0112] Embodiment 2 Hereinafter, a second embodiment of the present disclosure will be described with reference to the drawings. In the second embodiment, the signal processing shown in the first embodiment will be described with a detailed concrete example.

[0113] 10 is a block diagram showing a wireless communication device 200 according to a second embodiment. The wireless communication device 200 is a specific application example of the signal processing device 100. Note that the wireless communication device 200 is a partial modification of the wireless communication device 10 according to the related art described above. Parts denoted by the same reference numerals as those in the wireless communication device 10 have the same configuration as the corresponding parts in the wireless communication device 10 and execute the same processes, and therefore description thereof will be omitted as appropriate.

[0114] The wireless communication device 200 includes a BF-BB unit 20 and an AAS unit 30. Here, the AAS unit 30 includes an optical transceiver 31, a TRX-BB unit 60, a front-end unit 61, 32 antennas 34, a distributor / synthesizer 35, a SW 36, a CAL-TRX 37, and a BB control unit 62.

[0115] The TRX-BB unit 60 functions as a transceiver baseband unit, and includes 32 BB units 70#0 to 70#31. Hereinafter, the BB units 70#0 to 70#31 will be collectively referred to as the BB unit 70.

[0116] 11 is a block diagram of the BB unit 70. The BB unit 40 includes a CFR processing unit 41, a DPD processing unit 71, a DPD control unit 72, and an ORX 73. Each of the BB units 70#0 to #31 has the same configuration as that shown in FIG.

[0117] The DPD processing unit 71 is a unit corresponding to the distortion compensation unit 101 described in the first embodiment, and performs the following processing in addition to the processing performed by the DPD processing unit 42 according to the related art. The DPD processing unit 71 can be switched between an ON state in which DPD compensation processing is performed and an OFF state in which the input signal is output as is without performing DPD compensation processing, by a control signal DPD_SW output by the DPD control unit 72. Furthermore, DPD compensation coefficients are stored inside the DPD processing unit 71, and the DPD processing unit 71 selects an appropriate DPD compensation coefficient based on the characteristics of the input signal and performs DPD compensation processing on the input signal. The DPD compensation coefficients are weights for compensating for nonlinear AM / PM components of the transmission amplifier 52, and the DPD processing unit 71 selects appropriate DPD compensation coefficients related to amplitude and phase based on the characteristics of the input signal IN and performs DPD compensation processing on the input signal IN. Details of the DPD compensation coefficients are as described in the first embodiment.

[0118] The DPD control unit 72 is a unit corresponding to the calculation unit 103 described in the first embodiment, and receives the input signal IN output by the CFR processing unit 41 and the output signal FB. The output signal FB is a signal that is a feedback of the output signal output by the transmission amplifier 52 on the same channel as the BB unit 70. The DPD control unit 72 calculates the phase difference and amplitude ratio between the input signal IN and the output signal FB. The DPD control unit 72 outputs data of the calculated phase difference and amplitude ratio to the BB control unit 62.

[0119] Furthermore, the DPD control unit 72 receives a control signal CTRL from the BB control unit 62, and outputs a control signal DPD_SW that switches the DPD processing unit 71 on and off based on the control signal CTRL.

[0120] The ORX 73 is a receiver, and transfers an output signal FB output from a directional coupler 53 (described later) to the DPD control unit 72 .

[0121] 12 is a block diagram of the FE unit 80. The FE unit 50 includes a TRX 51, a transmitting amplifier 52, a directional coupler 81, a SW 54, and a receiving amplifier 55. Each of the FE units 80#0 to #31 has the same configuration as that shown in FIG.

[0122] The directional coupler 81 has the following functions in addition to the functions of the directional coupler 53 according to the related art. The directional coupler 81 outputs the RF signal output by the transmission amplifier 52 as an output signal FB to the DPD control unit 72 via the ORX 73.

[0123] Returning to Fig. 10, the BB control unit 62 will be described. The BB control unit 62 is a unit corresponding to the control unit 104 described in the first embodiment, and receives the data of the phase difference and the amplitude ratio output by the DPD control unit 72 of each signal channel. Then, the BB control unit 62 specifies the maximum phase difference and the minimum phase difference of the calculated 32 phase differences, calculates the difference between the two, and judges whether the difference is equal to or greater than a first threshold. Also, the BB control unit 62 specifies the maximum amplitude ratio and the minimum amplitude ratio of the calculated 32 amplitude ratios, calculates the difference between the two, and judges whether the difference is equal to or greater than a second threshold.

[0124] When the difference between the maximum phase difference and the minimum phase difference is equal to or greater than the first threshold, or when the difference between the maximum amplitude ratio and the minimum amplitude ratio is equal to or greater than the second threshold, the BB control unit 62 outputs control signals CTRL#0-#31 to each DPD control unit 72 to turn on the DPD processing unit 71. On the other hand, when the difference between the maximum phase difference and the minimum phase difference is less than the first threshold and the difference between the maximum amplitude ratio and the minimum amplitude ratio is less than the second threshold, the BB control unit 62 does not output control signals CTRL#0-#31. Therefore, each DPD processing unit 71 does not turn on and remains off.

[0125] 13A is a flowchart showing signal processing executed by wireless communication device 200. The signal processing executed will be described below.

[0126] First, the wireless communication device 200 transmits a wireless signal by fan beamforming (step S21). Specifically, as described in the related art, the BF-BB unit 20 generates a BF signal using DL-CAL weights previously generated and stored in the BF-BB unit 20, and outputs the BF signal to the AAS unit 30.

[0127] Next, the wireless communication device 200 performs DL calibration (step S22). This process will be described in detail later. In step S22, the BF-BB unit 20 can update the DL-CAL weight.

[0128] Then, the wireless communication device 200 transmits a wireless signal by data beamforming (step S23). The DL calibration set in step S22 enables the wireless communication device 200 to perform wireless communication by data beamforming with a null point set with high accuracy. Note that in steps S21 and S23, each DPD processing unit 71 is set to an ON state under the control of the BB control unit 62. Other details of the signal processing in steps S21 and S23 are as described in the related art.

[0129] 13B is a flowchart showing details of the signal processing executed in step S22. The details of the processing will be described below.

[0130] First, the TRX-BB unit 60 outputs a DL-CAL signal to the front-end unit 61 (step S31). The DL-CAL signal is amplified and output by the transmission amplifier 52 of the FE unit 80 of each transmitter. The directional coupler 81 outputs the output signal FB of the transmission amplifier 52 to the DPD control unit 72 via the ORX 73. At this stage, each DPD processing unit 71 is set to the off state.

[0131] The DPD control unit 72 of each transmitter calculates the phase difference and amplitude ratio between the output signal FB and the input signal IN, which is the DL-CAL signal output from the CFR processing unit 41 (step S32). The DPD control unit 72 outputs the calculated phase difference and amplitude ratio data to the BB control unit 62.

[0132] The BB control unit 62 identifies the maximum and minimum phase differences from the calculated phase differences of each transmitter (32 transmitters) and calculates the difference between the two. Also, the BB control unit 62 identifies the maximum and minimum amplitude ratios from the calculated amplitude ratios of each transmitter and calculates the difference between the two (step S33).

[0133] The BB control unit 62 determines whether or not the difference between the maximum phase difference and the minimum phase difference is less than a first threshold value and the difference between the maximum amplitude ratio and the minimum amplitude ratio is less than a second threshold value (step S34).

[0134] As described in the related art, the radio signal by fan beam forming is a signal with different amplitude and phase in each transmitter. When the radio communication device 200 outputs this radio signal, differences occur in the AM-AM and AM-PM characteristics due to the nonlinear memory effect in the transmission amplifiers between the transmitters. On the other hand, for the DL-CAL signal, it is important to prevent over-compensation or under-compensation of the DL-CAL signal due to the differences in the AM-AM and AM-PM characteristics. Therefore, if there is no significant memory effect in the transmission amplifier 52, even after the radio signal by fan beam forming is output, the AM-AM and AM-PM characteristics between the transmitters are uniquely determined depending on the same level of DL-CAL signal level. Therefore, the influence on the DL-CAL signal is small. On the other hand, if there is a significant memory effect, the influence of the signal by the previous fan beam forming is reflected, and the difference between the phase differences and the like becomes a large value. The BB control unit 62 judges the presence or absence of such a significant memory effect in step S34.

[0135] If the difference between the maximum phase difference and the minimum phase difference is less than the first threshold value and the difference between the maximum amplitude ratio and the minimum amplitude ratio is less than the second threshold value (Yes in step S34), the BB control unit 62 does not output the control signals CTRL#0 to #31 and controls each DPD processing unit 71 to remain off (step S35).

[0136] On the other hand, when at least either the difference between the maximum phase difference and the minimum phase difference is equal to or greater than the first threshold value or the difference between the maximum amplitude ratio and the minimum amplitude ratio is equal to or greater than the second threshold value (No in step S34), the BB control unit 62 performs the following process: The BB control unit 62 outputs control signals CTRL#0 to #31 for turning on the DPD processing units 71 to each DPD control unit 72 (step S36).

[0137] After setting the DPD processor 71 to on or off as described above, the wireless communication device 200 sets the DL-CAL weight by the DL calibration operation shown in the related art. At this time, even if a significant memory effect occurs in the transmission amplifier 52, the memory effect is compensated for by the DPD processor 71, so that the null point in wireless communication in the next data beamforming can be set with high accuracy.

[0138] When no significant memory effect occurs in the transmission amplifier 52, even if the CAL weight is set without performing the DPD compensation process in the DL calibration operation, it is considered that the accuracy of the null point in the wireless communication in the next data beamforming is sufficiently guaranteed. In addition, in general, the update period of the DPD compensation coefficient in the DPD processing unit 71 is not synchronized with or is not the same as the update period of the DL-CAL. Therefore, when the DPD processing unit 71 is turned on, it is considered that the amplitude and phase of the output DL-CAL signal change due to the DL-CAL signal being DPD-compensated with the DPD compensation coefficient determined at the time of wireless signal transmission by fan beamforming. As a result, the CAL weight calculated when the DPD compensation is turned on may have a lower accuracy of the null point than the CAL weight calculated when the DPD processing unit 71 is turned off. Therefore, in this case, the wireless communication device 200 turns off the DPD processing unit 71. In this way, in the second embodiment, by switching on and off the DPD compensation process during the calibration operation, it is possible to autonomously achieve both the DPD compensation process that compensates for the nonlinearity of the amplifier and the calibration operation that determines the MU-MIMO performance (the performance of MIMO spatial multiplexing).

[0139] In the wireless communication device 10, a calibration operation is performed after a signal for wireless transmission by fan beamforming is output, and then a signal for wireless transmission by beamforming is output. Therefore, the wireless communication device 10 can improve the quality of the signal in beamforming.

[0140] The transmission amplifier 52 can be of various types, but may be, for example, a Doherty amplifier. The Doherty amplifier is an amplifier for high frequencies, and as an example, a GaN (gallium nitride) Doherty amplifier is used because it can output large power and is highly efficient and capable of reducing power consumption. Although such a GaN Doherty amplifier is effective in reducing power consumption, as described above, a memory effect may occur in the AM-AM input / output characteristics and the AM-PM input / output characteristics. However, in the second embodiment, the inconvenience caused by this memory effect can be eliminated.

[0141] Moreover, in wireless communication device 200 that performs wireless communication, it is possible to perform both DPD compensation processing and calibration operation, thereby further improving the quality of wireless communication.

[0142] The present disclosure is not limited to the above-described embodiments, and can be modified as appropriate without departing from the spirit of the present disclosure. For example, the number of transmitters in the second embodiment does not need to be limited to 32. Also, instead of the fan beam radio signal in the second embodiment, other wide-angle radiation radio signals (for example, those intended to radiate radio signals in all directions) may be used.

[0143] The wireless communication schemes to which the technology of the present disclosure can be applied are not limited to those described in the related art and the second embodiment.

[0144] In the above-mentioned embodiment, this disclosure has been described as a hardware configuration, but this disclosure is not limited to this. This disclosure can also be realized by making a processor in a computer execute a computer program to perform the processes (steps) of the device described in the above-mentioned embodiment.

[0145] 14 is a block diagram showing an example of a hardware configuration of an information processing device (signal processing device) for executing the processes of the above-described embodiments. Referring to FIG. 14, the information processing device 90 includes a signal processing circuit 91, a processor 92, and a memory 93.

[0146] The signal processing circuit 91 is a circuit for processing signals in accordance with the control of the processor 92. The signal processing circuit 91 may include a communication circuit for receiving a signal from a transmitting device.

[0147] The processor 92 performs the processing of the device described in the above embodiment by reading and executing software (computer programs) from the memory 93. As an example of the processor 92, one of a CPU (Central Processing Unit), an MPU (Micro Processing Unit), an FPGA (Field-Programmable Gate Array), a DSP (Demand-Side Platform), and an ASIC (Application Specific Integrated Circuit) may be used, or a plurality of them may be used in parallel.

[0148] The memory 93 is configured by a combination of volatile memory and non-volatile memory. The memory 93 may include storage located away from the processor 92. In this case, the processor 92 may access the memory 93 via an I / O (Input / Output) interface (not shown).

[0149] 14, the memory 93 is used to store software modules. The processor 92 can perform the processes described in the above embodiments by reading and executing the software modules from the memory 93.

[0150] As described above, one or more processors included in each device in the above-mentioned embodiments execute one or more programs including instructions for causing a computer to execute the algorithms described with reference to the drawings. This process realizes the signal processing method described in each embodiment.

[0151] The program can be stored and provided to the computer using various types of non-transitory computer readable media. The non-transitory computer readable media includes various types of tangible storage media. Examples of the non-transitory computer readable media include magnetic recording media (e.g., flexible disks, magnetic tapes, hard disk drives), magneto-optical recording media (e.g., magneto-optical disks), CD-ROM (Read Only Memory), CD-R, CD-R / W, and semiconductor memory (e.g., mask ROM, PROM (Programmable ROM), EPROM (Erasable PROM), flash ROM, RAM (Random Access Memory)). The program may also be provided to the computer by various types of transitory computer readable media. Examples of the transitory computer readable media include electric signals, optical signals, and electromagnetic waves. The transitory computer readable media can provide the program to the computer via a wired communication path such as an electric wire and an optical fiber, or via a wireless communication path.

[0152] Although the present disclosure has been described above with reference to the embodiments, the present disclosure is not limited to the above. Various modifications that can be understood by a person skilled in the art can be made to the configuration and details of the present disclosure within the scope of the disclosure.

[0153] This application claims priority based on Japanese Patent Application No. 2020-217114, filed on December 25, 2020, the disclosure of which is incorporated herein in its entirety. [Explanation of symbols]

[0154] 10 Wireless communication devices 20 BF-BB section 30 AAS Department 31 Optical Transceiver 32 TRX-BB section 33 Front end 34 Antenna 35 Distribution combiner 36 SW 37 CAL-TRX 40 BB unit 41 CFR Processing Section 42 DPD Processing Unit 50 FE unit 51 TRX 52 Transmitting amplifier 53 Directional coupler 54 SW 55 Receiving amplifier 60 TRX-BB section 61 Front end 62 BB control section 70 BB unit 71 DPD Processing Unit 72 DPD control section 73 ORX 80 FE unit 81 Directional coupler 100 Signal processing device 101 Distortion compensation section 102 Amplifier 103 Calculation section 104 Control section 200 Wireless communication device

Claims

1. a distortion compensation unit that performs a distortion compensation process for compensating for nonlinear distortion on one or more of the input signals and outputs a signal that has been subjected to the distortion compensation process; a plurality of amplifiers that amplify the plurality of input signals including the signal output by the distortion compensation means and output the amplified signals as output signals; a calculation means for calculating, for each input signal, at least one of a phase difference, an amplitude ratio, and an intensity ratio between the input signal and the output signal corresponding to the input signal during a calibration operation of the device itself in which a calibration signal is used as the multiple input signals and is input to the multiple amplifiers; a control means for specifying a maximum value and a minimum value of any one of the comparison results of the phase difference, the amplitude ratio, and the intensity ratio calculated by the calculation means, determining whether a first difference between the maximum value and the minimum value is equal to or greater than a first threshold value, and controlling whether or not the distortion compensation means executes the distortion compensation process on the calibration signal based on the determination result; A signal processing device comprising:

2. The calculation means calculates, for each of the input signals, the phase difference and the amplitude ratio between the input signal and the output signal corresponding to the input signal; The control means determining whether a second difference, which is a difference between a maximum value and a minimum value of the phase difference, is equal to or greater than a second threshold value, and determining whether a third difference, which is a difference between a maximum value and a minimum value of the amplitude ratio, is equal to or greater than a third threshold value; When the second difference is equal to or greater than the second threshold value or when the third difference is equal to or greater than the third threshold value, the distortion compensation means is controlled to perform the distortion compensation process on the calibration signal; when the second difference is less than the second threshold value and the third difference is less than the third threshold value, the distortion compensation means is controlled not to perform the distortion compensation process on the calibration signal. The signal processing device according to claim 1 .

3. Before the calibration operation, a signal for wireless transmission of wide-angle radiation is input as the input signal to the plurality of amplifiers, and after the calibration operation, a signal for wireless transmission by data beamforming is input as the input signal to the plurality of amplifiers.

3. A signal processing device according to claim 1 or 2.

4. the plurality of amplifiers are Doherty amplifiers; A signal processing device according to any one of claims 1 to 3.

5. The signal processing device is a wireless communication device further comprising a wireless transmission means for wirelessly transmitting the output signals from the plurality of amplifiers. A signal processing device according to any one of claims 1 to 4.

6. performing distortion compensation processing for compensating for nonlinear distortion on one or more of the input signals among the plurality of input signals, and outputting the signal subjected to the distortion compensation processing; a plurality of amplifiers amplify the plurality of input signals including the signal that has been subjected to the distortion compensation processing, and output the amplified signals as output signals; During a calibration operation of a signal processing device in which a calibration signal is used as the plurality of input signals and input to the plurality of amplifiers, at least one of a phase difference, an amplitude ratio, and an intensity ratio between the input signal and the output signal corresponding to the input signal is calculated for each of the input signals; a maximum value and a minimum value are identified for any one of the calculated numerical values ​​of the comparison result of the phase difference, the amplitude ratio, and the intensity ratio, and a determination is made as to whether a first difference between the maximum value and the minimum value is equal to or greater than a first threshold value, and based on the determination result, a control is made as to whether or not to execute the distortion compensation process on the calibration signal. A signal processing method executed by a signal processing device.

7. performing distortion compensation processing for compensating for nonlinear distortion on one or more of the input signals among the plurality of input signals, and outputting the signal subjected to the distortion compensation processing; a plurality of amplifiers amplify the plurality of input signals including the signal that has been subjected to the distortion compensation processing, and output the amplified signals as output signals; During a calibration operation of a signal processing device in which a calibration signal is used as the plurality of input signals and input to the plurality of amplifiers, at least one of a phase difference, an amplitude ratio, and an intensity ratio between the input signal and the output signal corresponding to the input signal is calculated for each of the input signals; a maximum value and a minimum value are identified for any one of the calculated numerical values ​​of the comparison result of the phase difference, the amplitude ratio, and the intensity ratio, and a determination is made as to whether a first difference between the maximum value and the minimum value is equal to or greater than a first threshold value, and based on the determination result, a control is made as to whether or not to execute the distortion compensation process on the calibration signal. A program that causes a signal processing device to execute the above.

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