Wireless communication device and distortion compensation method

Abstract

To compensate nonlinear distortion generated in a power amplifier that amplifies signals of a plurality of different frequency bands.SOLUTION: A radio communication device comprises: a plurality of antenna elements; a phase shifter that forms beams corresponding to first band data and second band data having different frequency bands; a power amplifier that amplifies the first band data and the second band data; and a processor. The processor calculates a distortion compensation signal that compensates nonlinear distortion in the first band data and the second band data using a first distortion compensation coefficient, and performs processing to calculate an out-of-band compensation signal that compensates out-of-signal band nonlinear distortion of the first band data and the second band data using a second distortion compensation coefficient, and the power amplifier amplifies a signal in which the out-of-band compensation signal is synthesized with the distortion compensation signal.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a wireless communication device and a distortion compensation method. [Background technology]

[0002] Generally, a wireless communication device such as a base station device is provided with a power amplifier that amplifies the power of a transmission signal. In the wireless communication device, in order to improve power efficiency, the power amplifier may be operated near a saturation region where the output power is saturated with respect to the input power. When the power amplifier is operated near the saturation region, nonlinear distortion occurring in the power amplifier increases. Therefore, in order to suppress this nonlinear distortion and satisfy standards such as ACLR (Adjacent Channel Leakage Ratio) and SEM (Spectrum Emission Mask), the wireless communication device may perform distortion compensation to compensate for the nonlinear distortion.

[0003] Specifically, one of the distortion compensation methods is Digital Pre-Distortion (DPD). When distortion compensation is performed by DPD, a distortion compensation coefficient having an inverse characteristic of the nonlinear distortion generated in the power amplifier is multiplied in advance by a transmission signal before input to the power amplifier. This DPD processing improves the linearity of the output of the power amplifier and suppresses nonlinear distortion. In DPD, the output signal of the power amplifier is fed back, and a distortion compensation coefficient is found or adaptively updated using a LUT (Look Up Table) or a series, etc.

[0004] Incidentally, some wireless communication devices are equipped with an array antenna and perform beamforming to form a beam directed in a desired direction. Such wireless communication devices have a plurality of power amplifiers corresponding to the antenna elements in order to amplify the transmission signals branched to the plurality of antenna elements. It has been considered to collectively compensate for nonlinear distortions occurring in the plurality of power amplifiers by DPD. That is, DPD processing is performed to multiply the transmission signals before being branched to the plurality of antenna elements by a distortion compensation coefficient that suppresses nonlinear distortion in the direction of the beam. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2018-33109 A [Patent Document 2] JP 2019-154024 A [Non-patent literature]

[0006] [Non-Patent Document 1] Lei Ding et al., "Concurrent dual-band digital predistortion", 2012 IEEE / MTT-S International Microwave Symposium Digest, June 2012 Summary of the Invention [Problem to be solved by the invention]

[0007] However, the above-mentioned DPD has a problem that nonlinear distortion occurring in a power amplifier that amplifies multiple signals with different frequency bands may not be sufficiently compensated for. That is, in recent years, a wireless communication device may transmit and receive signals of multiple operators, and when the frequency bands of the signals of these operators are different, the power amplifier of the wireless communication device may amplify multiple signals with different frequency bands.

[0008] In such a case, if DPD processing is performed independently for each signal with a different frequency band, it is possible to suppress the nonlinear distortion in each signal band to a certain degree. However, since signals with different frequency bands are amplified by the same power amplifier, it is not easy to feed back the output signal of this power amplifier and independently update the distortion compensation coefficient for each signal with the different frequency band. Furthermore, since signals with different frequency bands are amplified by the same power amplifier, nonlinear distortion occurs outside each signal band, and this nonlinear distortion outside the band may degrade the signal quality.

[0009] These problems can be solved by using a filter such as a bandpass filter when the frequency bands of the respective signals are sufficiently apart compared with the signal bandwidth. Specifically, as shown in FIG. 6(a), for example, a case will be described in which the center frequency of the first signal 11 is 26 GHz, the center frequency of the second signal 12 is 28 GHz, and these center frequencies are separated by, for example, about 5 times the signal bandwidth. In this way, when the frequency bands of the first signal 11 and the second signal 12 are sufficiently apart, the signal components of each frequency band can be separated by a filter from the output signal of the power amplifier that amplifies these signals. Therefore, it is possible to update the distortion compensation coefficients independently for each of the first signal 11 and the second signal 12.

[0010] Furthermore, when the frequency bands of the first signal 11 and the second signal 12 are sufficiently apart, the nonlinear distortion 13 outside the signal band also occurs at a frequency sufficiently apart from the signal band. Therefore, it is possible to remove the nonlinear distortion outside the band from the output signal of the power amplifier by using, for example, a bandpass filter having a passband 15.

[0011] On the other hand, for example, as shown in Fig. 6(b), consider a case where the center frequency of the first signal 21 is 27.6 GHz, the center frequency of the second signal 22 is 28.0 GHz, and these center frequencies are only as far apart as the signal bandwidth. When the frequency bands of the first signal 21 and the second signal 22 are close to each other in this way, it is difficult to separate the signal components of each frequency band by using a filter from the output signal of the power amplifier that amplifies these signals. For this reason, it is difficult to update the distortion compensation coefficients independently for each of the first signal 21 and the second signal 22, and accurate distortion compensation is not performed.

[0012] Furthermore, when the frequency bands of the first signal 21 and the second signal 22 are close to each other, nonlinear distortion 23 outside the signal band may occur at a frequency that overlaps with the signal band, making it difficult to remove the nonlinear distortion outside the band from the output signal of the power amplifier by using a filter.

[0013] As described above, particularly when the frequency bands of multiple signals are close to each other, it is difficult to perform effective DPD processing on each signal, and nonlinear distortion that occurs in the power amplifier that amplifies these signals is not adequately compensated for.

[0014] The disclosed technology has been developed in consideration of the above points, and aims to provide a wireless communication device and a distortion compensation method that can compensate for nonlinear distortion that occurs in a power amplifier that amplifies multiple signals of different frequency bands. [Means for solving the problem]

[0015] In one aspect, a wireless communication device disclosed in the present application has a plurality of antenna elements, a phase shifter that assigns weights for each antenna element to first band data and second band data having different frequency bands and forms beams corresponding to the first band data and the second band data, a power amplifier provided for each antenna element and that amplifies the first band data and the second band data, and a processor that compensates for nonlinear distortion occurring in the first band data and the second band data in the power amplifier, wherein the processor executes a process of calculating a distortion compensation signal from the first band data and the second band data using a first distortion compensation coefficient to compensate for nonlinear distortion within the signal band of the first band data and the second band data, and calculating an out-of-band compensation signal from the first band data and the second band data using a second distortion compensation coefficient to compensate for nonlinear distortion outside the signal band of the first band data and the second band data, and the power amplifier amplifies a signal obtained by combining the out-of-band compensation signal with the distortion compensation signal. Effect of the Invention

[0016] According to one aspect of the wireless communication device and distortion compensation method disclosed in the present application, it is possible to compensate for nonlinear distortion that occurs in a power amplifier that amplifies signals in a plurality of different frequency bands. [Brief description of the drawings]

[0017] [Figure 1] FIG. 1 is a diagram illustrating an example of the configuration of a wireless communication system. [Diagram 2] FIG. 2 is a block diagram showing a configuration of an RU according to an embodiment. [Diagram 3] FIG. 3 is a flow diagram illustrating a distortion compensation method. [Figure 4] FIG. 4 is a flow diagram showing a coefficient updating method. [Diagram 5] FIG. 5 is a block diagram showing a modified example of the RU. [Figure 6] FIG. 6 is a diagram showing a specific example of frequency allocation. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] Hereinafter, an embodiment of a wireless communication device and a distortion compensation method disclosed in the present application will be described in detail with reference to the drawings. Note that the present invention is not limited to this embodiment.

[0019] Fig. 1 is a diagram showing an example of the configuration of a wireless communication system according to an embodiment. As shown in Fig. 1, the wireless communication system includes a CU (Central Unit) / DU (Distributed Unit) 10, a RU (Radio Unit) 100, and a UE (User Equipment) 20.

[0020] The CU / DU 10 connects to a core network (not shown) and performs baseband processing on data transmitted to the UE 20 and data received from the UE 20. Specifically, the two CU / DU 10 connect to the core networks of the respective operators, perform baseband processing on data from each operator having a different frequency band, and transmit the data to the RU 100. For example, one CU / DU 10 performs baseband processing on first band data, and the other CU / DU 10 performs baseband processing on second band data having a different frequency band from the first band data.

[0021] The first band data and the second band data may be data of different operators transmitted from different CU / DUs 10, or may be data of the same operator transmitted from one CU / DU 10. The CU / DU 10 may be configured as one device with the CU and DU integrated, or may be configured as multiple devices with the CU and DU provided separately. The CU / DU 10 and the RU 100 function as base station devices of a wireless communication system.

[0022] The RU 100 performs RF (Radio Frequency) processing on data to be transmitted to the UE 20 and data received from the UE 20. Specifically, the RU 100 receives first band data and second band data having different frequency bands from the CU / DU 10, performs RF processing on the first band data and second band data, and transmits the data to the UE 20.

[0023] The RU 100 has an array antenna made up of multiple antenna elements, and forms beams corresponding to the first band data and the second band data, respectively, to perform wireless communication with the UE 20. At this time, the RU 100 performs distortion compensation to compensate for nonlinear distortion in a power amplifier that amplifies the first band data and the second band data. That is, the RU 100 performs distortion compensation to compensate for nonlinear distortion within the signal band of the first band data and the second band data, and also performs distortion compensation to compensate for nonlinear distortion outside the signal band of the first band data and the second band data. The configuration of the RU 100 will be described in detail later.

[0024] The UE 20 is a terminal device that performs wireless communication with the RU 100. That is, the UE 20 receives wireless signals from the RU 100 and transmits wireless signals to the RU 100.

[0025] Fig. 2 is a block diagram showing the configuration of RU 100 according to one embodiment. RU 100 shown in Fig. 2 includes wired interface unit (hereinafter abbreviated as "wired IF unit") 110, processor 120, memory 130, D / A (Digital / Analog) converters (hereinafter abbreviated as "D / A") 141-144, A / D (Analog / Digital) converter (hereinafter abbreviated as "A / D") 145, up-converters 151-154, down-converter 155, phase shifters (PS) 161-168, combiners 171-176, power amplifiers 181 and 182, and a switching unit 190.

[0026] The wired IF unit 110 is wiredly connected to the CU / DU 10, and receives first band data and second band data having different frequency bands from the CU / DU 10. Then, the wired IF unit 110 outputs the first band data and second band data to the processor 120. In addition, the wired IF unit 110 transmits a reception signal received from the UE 20 to the CU / DU 10.

[0027] The processor 120 includes, for example, a central processing unit (CPU), a field programmable gate array (FPGA), or a digital signal processor (DSP), and generally controls the entire RU 100. Specifically, the processor 120 includes a first band DPD processing unit 121, a second band DPD processing unit 122, a first out-of-band DPD processing unit 123, a second out-of-band DPD processing unit 124, a phase conversion unit 125, and a coefficient update unit 126.

[0028] The first band DPD processing unit 121 uses the first band data and the second band data to calculate a distortion compensation signal that suppresses nonlinear distortion occurring within the signal band of the first band data. Specifically, the first band DPD processing unit 121 multiplies the first band data and the second band data by a distortion compensation coefficient to calculate a distortion compensation signal for suppressing nonlinear distortion occurring within the signal band of the first band data in the power amplifiers 181 and 182. The first band DPD processing unit 121 calculates a distortion compensation signal y in1 Calculate.

number

[0029] In equation (1), K is the maximum order of nonlinear distortion, N is the memory depth, and a 2k+1,n,i is a complex distortion compensation coefficient.

[0030] The second band DPD processing unit 122 uses the first band data and the second band data to calculate a distortion compensation signal that suppresses nonlinear distortion occurring within the signal band of the second band data. Specifically, the second band DPD processing unit 122 multiplies the first band data and the second band data by a distortion compensation coefficient to calculate a distortion compensation signal for suppressing nonlinear distortion occurring within the signal band of the second band data in the power amplifiers 181 and 182. The second band DPD processing unit 122 calculates a distortion compensation signal y in2 Calculate.

number

[0031] In this way, the first-band DPD processor 121 and the second-band DPD processor 122 use the same distortion compensation coefficient a 2k+1,n,i and the distortion compensation signal y in1 , y in2 Calculate.

[0032] The first out-of-band DPD processing unit 123 uses the first band data and the second band data to calculate a distortion compensation signal (hereinafter referred to as the "out-of-band compensation signal") that suppresses nonlinear distortion occurring outside the signal band of the first band data. Specifically, the first out-of-band DPD processing unit 123 multiplies the first band data and the second band data by a distortion compensation coefficient to calculate an out-of-band compensation signal for suppressing nonlinear distortion occurring outside the signal band of the first band data in the power amplifiers 181, 182. For example, when suppressing third-order distortion outside the signal band, the first out-of-band DPD processing unit 123 calculates the out-of-band compensation signal y from the first band data x1(t) and the second band data x2(t) at discrete times t using the following equation (3): out1 Calculate.

number

[0033] In equation (3), K is the order of nonlinear distortion, N is the memory depth, and b2k+1,n,i is a complex distortion compensation coefficient, and * indicates the complex conjugate.

[0034] The second out-of-band DPD processing unit 124 uses the first band data and the second band data to calculate an out-of-band compensation signal that suppresses nonlinear distortion occurring outside the signal band of the second band data. Specifically, the second out-of-band DPD processing unit 124 multiplies the first band data and the second band data by a distortion compensation coefficient to calculate an out-of-band compensation signal for suppressing nonlinear distortion occurring outside the signal band of the second band data in the power amplifiers 181 and 182. For example, when suppressing third-order distortion outside the signal band, the second out-of-band DPD processing unit 124 calculates an out-of-band compensation signal y out2 Calculate.

number

[0035] In this way, the first out-of-band DPD processor 123 and the second out-of-band DPD processor 124 use the same distortion compensation coefficient b 2k+1,n,i and the out-of-band compensation signal y out1 , y out2 Hereinafter, the distortion compensation coefficient for calculating the out-of-band compensation signal is referred to as the "out-of-band compensation coefficient."

[0036] The phase conversion unit 125 converts and synthesizes the phases of the first-band data and the second-band data, which are reference signals during the update of the distortion compensation coefficient and the out-of-band compensation coefficient, and outputs the obtained reference signal to the coefficient update unit 126. Specifically, the phase conversion unit 125 assigns weights corresponding to the power amplifier to which the output signal of the power amplifiers 181 and 182 is fed back to the first-band data and the second-band data, synthesizes the first-band data and the second-band data with their phases converted, and outputs them to the coefficient update unit 126. When the output signal of the power amplifier 181 is fed back, the phase conversion unit 125 assigns the same weight as PS161 to the first-band data, assigns the same weight as PS162 to the second-band data, and synthesizes the first-band data and the second-band data with their phases converted. Also, when the output signal of the power amplifier 182 is fed back, the phase conversion unit 125 assigns the same weight as PS163 to the first-band data, assigns the same weight as PS164 to the second-band data, and synthesizes the first-band data and the second-band data with their phases converted.

[0037] The coefficient update unit 126 updates the distortion compensation coefficient used by the first-band DPD processing unit 121 and the second-band DPD processing unit 122, and the out-of-band compensation coefficient used by the first out-of-band DPD processing unit 123 and the second out-of-band DPD processing unit 124. Specifically, the coefficient update unit 126 updates the basic coefficient using, for example, the LMS (Least Mean Square) algorithm so that the error between the reference signal output from the phase conversion unit 125 and the feedback signal fed back from the switching unit 190 becomes small. Then, the coefficient update unit 126 calculates the distortion compensation coefficient and the out-of-band compensation coefficient from the updated basic coefficient. The coefficient update unit 126 calculates the error err(t) between the feedback signal (hereinafter abbreviated as "FB signal") y m fed back from the m-th (0 < m ≤ M) power amplifier among the M (M is an integer of 2 or more) power amplifiers and the reference signal subjected to phase conversion corresponding to the m-th power amplifier by the following formula (5). err(t)=(x1(t)e jφ1m +x2(t)e jφ2m )-y m(5)

[0038] In equation (5), j is the imaginary unit, φ 1m is the weight given to the first band data input to the mth power amplifier, φ 2m is the weight given to the second band data input to the mth power amplifier. In other words, (x1(t)e jφ1m + x2(t)e jφ2m ) is a reference signal obtained by phase conversion section 125 combining the first band data and the second band data after phase conversion.

[0039] Then, the coefficient update unit 126 updates the base coefficient c by, for example, the following equation (6) so that the error err(t) becomes small. 2k+1,n Update. c 2k+1,n (g+1)=c 2k+1,n (g)+μ·err(t)·{x1(tn)+x2(tn)} * ·|x1(tn)+x2(tn)| 2k (6)

[0040] In the formula (6), g indicates the generation of the base coefficient, and μ is the step size. 2k+1,n When updating, the updated base coefficient c 2k+1,n The distortion compensation coefficient a is calculated by the following equations (7) and (8). 2k+1,n,i and the out-of-band compensation coefficient b 2k+1,n,i Calculate.

number

[0041] The coefficient update unit 126 outputs the updated distortion compensation coefficients to the first band DPD processing unit 121 and the second band DPD processing unit 122, and outputs the updated out-of-band compensation coefficients to the first out-of-band DPD processing unit 123 and the second out-of-band DPD processing unit 124.

[0042] The memory 130 includes, for example, a random access memory (RAM) or a read only memory (ROM), and stores information used in processing by the processor 120.

[0043] The D / A 141 performs D / A conversion on the distortion compensation signal calculated by the first band DPD processing unit 121. Similarly, the D / A 142 performs D / A conversion on the distortion compensation signal calculated by the second band DPD processing unit 122. The D / A 143 performs D / A conversion on the out-of-band compensation signal calculated by the first out-of-band DPD processing unit 123. Similarly, the D / A 144 performs D / A conversion on the out-of-band compensation signal calculated by the second out-of-band DPD processing unit 124.

[0044] The A / D 145 A / D converts the FB signals fed back from the power amplifiers 181 and 182 , and outputs the digital FB signals to the coefficient update unit 126 .

[0045] The upconverter 151 upconverts the distortion-compensated signal that has been D / A converted by the D / A 141, and converts it into a radio frequency signal. Similarly, the upconverter 152 upconverts the distortion-compensated signal that has been D / A converted by the D / A 142, and converts it into a radio frequency signal. The upconverter 153 upconverts the out-of-band compensation signal that has been D / A converted by the D / A 143, and converts it into a radio frequency signal. Similarly, the upconverter 154 upconverts the out-of-band compensation signal that has been D / A converted by the D / A 144, and converts it into a radio frequency signal.

[0046] The downconverter 155 downconverts the FB signals fed back from the power amplifiers 181 and 182, and converts them into signals of baseband frequency.

[0047] PS161, 163 impart weights (hereinafter referred to as "beam forming weights") for forming a beam for transmitting first band data in a desired direction to the distortion-compensated signal upconverted by upconverter 151. PS162, 164 impart beam forming weights for transmitting second band data in a desired direction to the distortion-compensated signal upconverted by upconverter 152. PS161, 162 impart beam forming weights to the distortion-compensated signal amplified by power amplifier 181. On the other hand, PS163, 164 impart beam forming weights to the distortion-compensated signal amplified by power amplifier 182.

[0048] The PSs 165 and 167 assign weights (hereinafter referred to as "out-of-band weights") according to the beam direction of the first band data for suppressing nonlinear distortion outside the signal band to the out-of-band compensation signal upconverted by the upconverter 153. The PSs 166 and 168 assign out-of-band weights according to the beam direction of the second band data for suppressing nonlinear distortion outside the signal band to the out-of-band compensation signal upconverted by the upconverter 154. For example, the beam forming weights that the PSs 161 to 164 assign to the distortion compensation signals are each φ 11 , φ 21 , φ 12 , φ 22 Then, the PS165 uses out-of-band weighting (2φ 11 -φ 21 ) is added to the out-of-band compensation signal. Similarly, PS166 to PS168 also add out-of-band weights (2φ 21 -φ 11 ), (2φ 12 -φ 22 ), (2φ 22 -φ 12 ) to the out-of-band compensation signal.

[0049] The PSs 165 and 166 provide out-of-band weighting to the out-of-band compensation signal amplified by the power amplifier 181. On the other hand, the PSs 167 and 168 provide out-of-band weighting to the out-of-band compensation signal amplified by the power amplifier 182.

[0050] The combiner 171 combines distortion compensation signals to which beam forming weights have been assigned by PSs 161 and 162. Similarly, the combiner 172 combines distortion compensation signals to which beam forming weights have been assigned by PSs 163 and 164. Furthermore, the combiner 173 combines out-of-band compensation signals to which out-of-band weights have been assigned by PSs 165 and 166. Similarly, the combiner 174 combines out-of-band compensation signals to which out-of-band weights have been assigned by PSs 167 and 168.

[0051] The combiner 175 combines the out-of-band compensation signal output from the combiner 173 with the distortion compensation signal amplified by the power amplifier 181. For this reason, the combiner 175 outputs to the power amplifier 181 a signal that suppresses nonlinear distortion occurring within and outside the signal bands of the first band data and the second band data.

[0052] The combiner 176 combines the out-of-band compensation signal output from the combiner 174 with the distortion compensation signal amplified by the power amplifier 182. For this reason, the combiner 176 outputs to the power amplifier 182 a signal that suppresses nonlinear distortion occurring within and outside the signal bands of the first band data and second band data.

[0053] Power amplifier 181 amplifies the signal output from combiner 175 and transmits it via an antenna element. Power amplifier 182 amplifies the signal output from combiner 176 and transmits it via an antenna element. In addition, the signals output from power amplifiers 181 and 182 are fed back to switching unit 190.

[0054] The switching unit 190 switches between the signals output from the power amplifiers 181 and 182 and outputs the signals as feedback signals to the down converter 155. That is, the switching unit 190 outputs the signal output from the power amplifier 181 as an FB signal to the down converter 155, and after a predetermined time has elapsed, outputs the signal output from the power amplifier 182 as an FB signal to the down converter 155. After that, after a predetermined time has elapsed, the switching unit 190 again outputs the signal output from the power amplifier 181 as an FB signal to the down converter 155. Note that, although the case where RU 100 has two power amplifiers 181 and 182 has been described here, if RU 100 has M power amplifiers, the switching unit 190 outputs the signals output from the M power amplifiers as FB signals to the down converter 155, switching between them for a predetermined time each.

[0055] Next, a distortion compensation method using the RU 100 configured as above will be described with reference to the flowchart shown in FIG.

[0056] When a signal is wirelessly transmitted from RU 100, beam forming weights are set in PSs 161 to 164 (step S101). Specifically, beam forming weights corresponding to a beam for transmitting first band data are set in PSs 161 and 163, and beam forming weights corresponding to a beam for transmitting second band data are set in PSs 162 and 164. Here, for example, a beam forming weight φ 11 is set, and the beam forming weight φ 21 is set, and the beam forming weight φ 12 is set, and the beam forming weight φ 22 is set.

[0057] When the beam forming weights are set, the out-of-band weights corresponding to the beam forming weights are set to PS165 to 168 (step S102). That is, the out-of-band weights for suppressing nonlinear distortion outside the signal band of the first band data are set to PS165 and 167, and the out-of-band weights for suppressing nonlinear distortion outside the signal band of the second band data are set to PS166 and 168. For example, when suppressing third-order distortion outside the signal band of the first and second band data, an out-of-band weight (2φ 11 -φ 21 ) is set, and out-of-band wait (2φ 21 -φ 11 ) is set, and out-of-band wait (2φ 12 -φ 22 ) is set, and out-of-band wait (2φ 22 -φ 12 ) is set.

[0058] Then, when the wired IF unit 110 receives the first band data and the second band data, the first band DPD processing unit 121 and the second band DPD processing unit 122 execute DPD processing, and calculate a distortion compensation signal that suppresses nonlinear distortion in the signal bands of the first band data and the second band data (step S103). That is, the first band DPD processing unit 121 calculates a distortion compensation signal that compensates for nonlinear distortion in the signal band of the first band data by the above formula (1), and the second band DPD processing unit 122 calculates a distortion compensation signal that compensates for nonlinear distortion in the signal band of the second band data by the above formula (2). The distortion compensation coefficient used in calculating the distortion compensation signal is updated by the coefficient update unit 126. The update of the distortion compensation coefficient will be described in detail later.

[0059] Furthermore, the first out-of-band DPD processing unit 123 and the second out-of-band DPD processing unit 124 execute DPD processing, and calculate an out-of-band compensation signal that suppresses nonlinear distortion outside the signal band of the first band data and the second band data (step S104). That is, the first out-of-band DPD processing unit 123 calculates an out-of-band compensation signal that compensates for third-order distortion outside the signal band of the first band data by the above equation (3), and the second out-of-band DPD processing unit 124 calculates an out-of-band compensation signal that compensates for third-order distortion outside the signal band of the second band data by the above equation (4). The out-of-band compensation coefficient used in calculating the out-of-band compensation signal is updated by the coefficient update unit 126. The update of the out-of-band compensation coefficient will be described in detail later.

[0060] Then, the distortion compensation signals and the out-of-band compensation signals are D / A converted by the D / As 141 to 144, respectively (step S105), and are upconverted by the upconverters 151 to 154, respectively (step S106). Weights are assigned by the PSs 161 to 168 to the distortion compensation signals and the out-of-band compensation signals upconverted to radio frequencies (step S107).

[0061] Specifically, the PSs 161 and 163 apply a beam forming weight φ to a distortion compensation signal that compensates for nonlinear distortion within the signal band of the first band data. 11 , φ 12 is added, and the PS 162 and 164 add a beam forming weight φ to the distortion compensation signal that compensates for the nonlinear distortion in the signal band of the second band data. 21 , φ 22 In addition, the PS 165 and 167 add an out-of-band weight (2φ 11 -φ 21 ), (2φ 12 -φ 22 ) is added to the out-of-band compensation signal that compensates for the third-order distortion outside the signal band of the second band data by the PS 166 and 168. 21 -φ 11 ), (2φ 22 -φ 12 ) will be granted.

[0062] The distortion compensation signal and the out-of-band compensation signal to which the beam forming weight or the out-of-band weight is assigned are combined by combiners 171 to 174 for each signal amplified by the same power amplifiers 181 and 182. That is, the distortion compensation signal and the out-of-band compensation signal amplified by the power amplifier 181 are combined by combiners 171 and 173, respectively, and the distortion compensation signal and the out-of-band compensation signal amplified by the power amplifier 182 are combined by combiners 172 and 174, respectively.

[0063] Then, the distortion compensation signals amplified by the power amplifiers 181 and 182 are combined with the corresponding out-of-band compensation signals (step S108). That is, the distortion compensation signal amplified by the power amplifier 181 is combined with the out-of-band compensation signal output from the combiner 173 by the combiner 175, and the distortion compensation signal amplified by the power amplifier 182 is combined with the out-of-band compensation signal output from the combiner 174 by the combiner 176.

[0064] As a result, signals that suppress nonlinear distortion within the signal bands of the first and second band data and third-order distortion outside the signal bands are input to the power amplifiers 181 and 182. These signals are amplified by the power amplifiers 181 and 182 (step S109). At this time, in the power amplifiers 181 and 182, nonlinear distortion within the signal bands of the first and second band data occurs, and nonlinear distortion outside the signal band occurs due to the amplification of signals with different frequency bands. In this embodiment, a signal obtained by combining the distortion compensation signal with the out-of-band compensation signal is input to the power amplifiers 181 and 182, so that nonlinear distortion within and outside the signal bands generated in the power amplifiers 181 and 182 is suppressed. That is, it is possible to compensate for nonlinear distortion generated in the power amplifiers 181 and 182 that amplify a plurality of signals with different frequency bands.

[0065] The signals amplified by the power amplifiers 181 and 182 are transmitted from the corresponding antenna elements, respectively (step S110). Since beamforming weights are applied to the signals transmitted from the respective antenna elements, the first-band data and the second-band data are transmitted as beams formed in desired directions, respectively.

[0066] Next, a coefficient update method using the RU100 according to the present embodiment will be described with reference to the flowchart shown in FIG. 4. In the coefficient update method described below, the distortion compensation coefficients used by the first-band DPD processing unit 121 and the second-band DPD processing unit 122 and the out-of-band compensation coefficients used by the out-of-band DPD processing unit 123 and the second out-of-band DPD processing unit 124 are updated.

[0067] First, the coefficient update unit 126 initializes the basic coefficients that are the basis for calculating the distortion compensation coefficients and the out-of-band compensation coefficients (step S201). Specifically, the basic coefficient c shown in the above equation (6) is initialized to 0 for all k (0 ≦ k < K) and n (0 ≦ n < N). Then, the switching unit 190 initializes the FB signal to be fed back (step S202). That is, the signal output from the m-th (m = 1) power amplifier among the M (here, M = 2) power amplifiers 181 and 182 is set to be output to the downconverter 155 as the FB signal. As a result, the signals to which the beamforming weights φ, φ are applied to the first-band data and the second-band data in PS161 to 164 are fed back as the FB signal from the switching unit 190. The FB signal is downconverted and A / D converted and input to the coefficient update unit 126. 2k+1,n On the other hand, the phase conversion unit 125 performs phase conversion on the first-band data and the second-band data serving as reference signals (step S203). That is, a weight equivalent to the beamforming weight φ is applied to the first-band data, and a beamforming weight φ is applied to the second-band data. 1m 、φ 2m is applied, and the signal to which the beamforming weight φ is applied to the second-band data is fed back as the FB signal from the switching unit 190. The FB signal is downconverted and A / D converted and input to the coefficient update unit 126.

[0068] On the other hand, the phase conversion unit 125 performs phase conversion on the first-band data and the second-band data serving as reference signals (step S203). That is, a weight equivalent to the beamforming weight φ is applied to the first-band data, and a beamforming weight φ is applied to the second-band data. 1m is applied to the first-band data, and a weight equivalent to the beamforming weight φ is applied to the second-band data. 2mEqual weights are assigned, and these first-band data and second-band data are combined. The reference signal obtained by the combination is input to the coefficient update unit 126.

[0069] Then, the coefficient update unit 126 calculates the error between the FB signal and the reference signal (step S204). That is, the coefficient update unit 126 performs the operation of the above formula (5). The error calculated by the above formula (5) is 0 if there is no non-linear distortion in the power amplifiers 181 and 182. Therefore, for example, the LMS algorithm is used by the coefficient update unit 126 to update the basic coefficient c so as to reduce the error. 2k+1,n That is, as in the above formula (6), the current basic coefficient c 2k+1,n (g) to the next-generation basic coefficient c 2k+1,n (g + 1) is calculated for all k (0 ≦ k < K) and n (0 ≦ n < N).

[0070] When the basic coefficient c 2k+1,n is updated, the coefficient update unit 126 calculates the distortion compensation coefficient a 2k+1,n based on this basic coefficient c (step S206). Also, the coefficient update unit 126 calculates the out-of-band compensation coefficient b 2k+1,n,i based on the basic coefficient c (step S207). That is, according to the above formulas (7) and (8), the distortion compensation coefficient a 2k+1,n and the out-of-band compensation coefficient b 2k+1,n,i are calculated from the basic coefficient c 2k+1,n for each k and n. 2k+1,n,i and the out-of-band compensation coefficient b 2k+1,n,i are calculated.

[0071] The update of the basic coefficient c 2k+1,n , the distortion compensation coefficient a 2k+1,n,i and the out-of-band compensation coefficient b 2k+1,n,iWhen the calculation of is repeated for a predetermined time, the switching unit 190 switches the FB signal (step S208). That is, the signal output from the m-th (m=m+1) power amplifier among the M (here, M=2) power amplifiers 181, 182 is switched to be output to the down converter 155 as the FB signal. At this time, it is determined whether or not switching has been completed for the signals output from all M power amplifiers 181, 182 and m exceeds M (step S209). Then, if switching has not been completed for the m-th power amplifier and m is equal to or smaller than M (step S209No), the process is repeated from step S203 using the FB signal from the m-th power amplifier. On the other hand, if switching has been completed for the signals output from all M power amplifiers 181, 182 and m exceeds M (step S209Yes), the coefficient update is terminated. Note that if m exceeds M (step S209Yes), the process may be repeated from step S202 where m is initialized to 1 again.

[0072] In this way, the basic coefficients are updated so as to reduce the error between the reference signal and the FB signal, and the distortion compensation coefficients and out-of-band compensation coefficients are calculated from the basic coefficients, so that it is possible to obtain distortion compensation coefficients and out-of-band compensation coefficients that suppress nonlinear distortion inside and outside the signal band that occurs in each power amplifier.

[0073] As described above, according to this embodiment, an out-of-band compensation signal that compensates for nonlinear distortion outside the signal band of the first band data and the second band data, which have different frequency bands, is combined with a distortion compensation signal that compensates for nonlinear distortion within the signal band of the first band data and the second band data. The combined signal is then amplified and transmitted by a power amplifier provided in each of the multiple antenna elements. As a result, nonlinear distortion inside and outside the signal band can be efficiently suppressed regardless of the frequency bands of the first band data and the second band data, and nonlinear distortion occurring in a power amplifier that amplifies signals of multiple frequency bands with different frequency bands can be compensated for.

[0074] In the above embodiment, a beamforming weight is applied to the distortion compensation signal, and then the out-of-band compensation signal is combined with the distortion compensation signal. However, it is also possible to combine the out-of-band compensation signal with the distortion compensation signal, and then apply a beamforming weight to the combined signal. The configuration of RU 100 in such a case is shown in Fig. 5. In Fig. 5, the same reference numerals are used for the same parts as in Fig. 2, and D / As 141-144, A / D 145, up-converters 151-154, and down-converter 155 are not shown.

[0075] 5, an out-of-band weight corresponding to a beam forming weight is assigned to an out-of-band compensation signal that compensates for nonlinear distortion outside the signal band of the first band data by PSs 201 and 202. Also, an out-of-band weight corresponding to a beam forming weight is assigned to an out-of-band compensation signal that compensates for nonlinear distortion outside the signal band of the second band data by PSs 203 and 204.

[0076] The distortion compensation signal that compensates for nonlinear distortion within the signal band of the first band data is combined with an out-of-band compensation signal that compensates for nonlinear distortion outside the signal band of the first band data by combiners 211 and 212. Moreover, the distortion compensation signal that compensates for nonlinear distortion within the signal band of the second band data is combined with an out-of-band compensation signal that compensates for nonlinear distortion outside the signal band of the second band data by combiners 213 and 214.

[0077] Then, the beamforming weights are applied by PS221 to PS224 to the combined signal in which the out-of-band compensation signal is combined with the distortion compensation signal. That is, the beamforming weight φ 11 is added, and the beam forming weight φ 12 is added, and the beam forming weight φ 21 is added, and the beam forming weight φ 22 When such beamforming weights are applied, the above-mentioned PSs 201 to 204 each apply an out-of-band weight (φ 11 -φ21 ), (φ 12 -φ 22 ), (φ 21 -φ 11 ), (φ 22 -φ 12 ) is added.

[0078] When the beam forming weights are applied to the combined signals, the signals amplified by the power amplifiers 181 are combined by the combiner 231, and the signals amplified by the power amplifiers 182 are combined by the combiner 232.

[0079] In this way, it is possible to compensate for nonlinear distortion inside and outside the signal band of the first band data and the second band data by synthesizing an out-of-band compensation signal with the distortion compensation signal before applying a beam forming weight to the distortion compensation signal and then applying a beam forming weight to the combined signal.

[0080] In the above embodiment, the third-order distortion is compensated as the nonlinear distortion outside the signal band of the first band data and the second band data, but the nonlinear distortion outside the signal band is not limited to the third-order distortion. For example, higher-order fifth-order distortion, seventh-order distortion, etc. may be suppressed by the out-of-band compensation signal. In such a case, the calculation formula for the out-of-band compensation signal (the above formulas (3) and (4)) and the out-of-band weight are appropriately adjusted according to the order of the nonlinear distortion to be suppressed. [Explanation of symbols]

[0081] 110 Wired IF section 120 processors 121 1st band DPD processing unit 122 Second band DPD processing unit 123 First out-of-band DPD processing unit 124 Second out-of-band DPD processing unit 125 Phase conversion section 126 Coefficient update unit 130 Memory 141~144 D / A 145 A / D 151~154 Upconverter 155 Down Converter 161~168, 201~204, 221~224 Phase shifter 171~176, 211~214, 231, 232 Synthesizer 181, 182 Power amplifier 190 Switching section

Claims

1. A plurality of antenna elements; a phase shifter that assigns a weight for each antenna element to each of first band data and second band data having different frequency bands, and forms a beam corresponding to the first band data and the second band data; a power amplifier provided for each antenna element, the power amplifier amplifying the first band data and the second band data; a processor that compensates for nonlinear distortion occurring in the first band data and the second band data in the power amplifier, The processor, calculating, from the first band data and the second band data, a distortion compensation signal that compensates for nonlinear distortion within a signal band of the first band data and the second band data, using a first distortion compensation coefficient; An out-of-band compensation signal that compensates for nonlinear distortion outside the signal band of the first band data and the second band data is calculated from the first band data and the second band data using a second distortion compensation coefficient. Execute the process, The power amplifier is A signal obtained by combining the distortion compensation signal with the out-of-band compensation signal is amplified.

23. A wireless communication device comprising:

2. The processor, The first distortion compensation coefficient and the second distortion compensation coefficient are updated based on a feedback signal fed back from the power amplifier and the first band data and the second band data.

2. The wireless communication device of claim 1, further comprising: a processor configured to:

3. The updating process includes: performing the same phase conversion as that performed by the phase shifter on the first band data and the second band data; Calculating an error between a reference signal obtained by the phase conversion and the feedback signal; Update the base coefficients so that the calculated error is reduced. Calculating the first distortion compensation coefficient and the second distortion compensation coefficient based on the updated basic coefficient 3. The wireless communication device of claim 2, further comprising a processing unit.

4. A switching unit that switches the signals output from the power amplifiers for each antenna element at predetermined intervals and feeds the signals back to the processor.

3. The wireless communication device according to claim 2, further comprising:

5. an out-of-band phase shifter that assigns an out-of-band weight to the out-of-band compensation signal, the out-of-band weight corresponding to the weight assigned to the distortion compensation signal by the phase shifter; 2. The wireless communication device according to claim 1, further comprising:

6. The process of calculating the out-of-band compensation signal includes the steps of: An out-of-band compensation signal is calculated to compensate for third-order distortion outside the signal band of the first band data and the second band data.

2. The wireless communication device according to claim 1.

7. A distortion compensation method executed by a wireless communication device having a plurality of antenna elements, a phase shifter that assigns weights for each antenna element to first band data and second band data having different frequency bands, and forms beams corresponding to the first band data and the second band data, and a power amplifier that is provided for each antenna element and amplifies the first band data and the second band data, calculating, from the first band data and the second band data, a distortion compensation signal that compensates for nonlinear distortion within a signal band of the first band data and the second band data, using a first distortion compensation coefficient; calculating an out-of-band compensation signal from the first band data and the second band data using a second distortion compensation coefficient to compensate for nonlinear distortion outside the signal band of the first band data and the second band data; combining the out-of-band compensation signal with the distortion compensation signal; The signal obtained by the synthesis is amplified by the power amplifier for each antenna element.

23. A distortion compensation method comprising the steps of:

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