WIRELESS COMMUNICATION APPARATUS AND WIRELESS COMMUNICATION METHOD

A wireless communication apparatus according to the present disclosure includes: a crest factor reduction (CFR) circuit; a digital pre-distortion (DPD) circuit; at least one memory configured to store instructions; and at least one processor configured to execute the instructions to determine frequency arrangement of a synthesized time signal of a plurality of component carriers (CCs) acquired by synthesizing time signals of each of the plurality of CCs being input to the CFR circuit, and control the CFR circuit, based on the determined frequency arrangement of the synthesized time signal of the plurality of CCs.

INCORPORATION BY REFERENCE

This application is based upon and claims the benefit of priority from Japanese patent application No. 2022-183944, filed on Nov. 17, 2022, the disclosure of which is incorporated herein in its entirety by reference.

TECHNICAL FIELD

The present disclosure relates to a wireless communication apparatus and a wireless communication method.

BACKGROUND ART

A transmission amplifier (AMP) is mounted on a radio unit (RU) being an active antenna system (AAS) or the like. However, there is a concern that communication quality such as adjacent channel leakage ratio/error vector magnitude (ACLR/EVM) deteriorates due to nonlinear distortion properties such as amplitude modulation (AM)-AM/AM-phase modulation (PM) of the transmission AMP.

Therefore, in the RU, a digital pre-distortion (DPD) circuit is configured to linearize the nonlinear distortion properties of the transmission AMP and thereby improve ACLR/EVM. However, in the RU, a crest factor reduction (CFR) circuit is a key fundamental technological element in order to further improve ACLR/EVM by the DPD circuit. The CFR circuit is disclosed in, for example, Published Japanese Translation of PCT International Publication for Patent Application No. 2020-523833.

Hereinafter, an RU according to a related art is described. Note that the following description and drawings are omitted or simplified as appropriate for clarity of description. In the following drawings, the same element is denoted by the same reference numeral, and redundant description is omitted as necessary. Further, specific numerical values and the like described below are merely examples for facilitating understanding of the present disclosure, and are not limited thereto.

FIG.1is a diagram illustrating a configuration example of an RU10according to the related art. InFIG.1, a unidirectional arrow briefly indicates a direction of flow of a certain signal (data), and does not exclude bidirectionality (the same applies toFIGS.3and23described later).

As illustrated inFIG.1, the RU10according to the related art includes an optical transceiver11, an enhanced common public radio interface (eCPRI) unit12, a low-physical layer (LPHY) unit13, a plurality of carrier digital up converters (CDUCs)14, a plurality of adders15, a digital baseband unit16, a TRX-frontend unit17, and a plurality of antennas18.

The LPHY unit13receives a data stream to be transmitted from a distributed unit (DU)20to each terminal of a plurality of radio access network (RAN) sharing operators via the optical transceiver11and the eCPRI unit12. Herein, the data stream is composed of a plurality of component carriers (CCs). Specifically, a plurality of CC signals including a plurality of CCs are input to the LPHY unit13for each frequency.

The LPHY unit13includes an inverse fast Fourier transform (IFFT) unit (not illustrated). The IFFT unit converts a plurality of CC signals being input for each frequency into a time signal for each CC, and outputs the time signal for each CC to each of the plurality of CDUCs14.

The plurality of CDUCs14are provided in association with each of a plurality of transceivers (TRXs)171, which is described later, in the TRX-frontend unit17.

It is assumed that the RU10illustrated inFIG.1is able to support up to eight CCs. Therefore, each CDUC14includes eight DUC slices provided in association with the eight CCs.

Each of the DUC slices includes a channel filter141, a numerically controlled oscillator (NCO)142, and a multiplier143. The DUC slice uses the channel filter141and extracts the time signal of the associated CC from among the time signal of each CC of the associated TRX171. Then, the DUC slice uses the NCO142and the multiplier143and arranges the time signal of the associated CC on a digital baseband (DBB) frequency axis.

The plurality of adders15are provided in association with the plurality of TRXs171, which are described later.

Each of the adders15synthesizes the time signal of each of the CCs of the associated TRX171being arranged on the DBB frequency axis, and outputs the synthesized time signal to the digital baseband unit16as a synthesized time signal of a plurality of CCs of the associated TRX171.

FIG.2is a diagram illustrating an example of frequency arrangement of a synthesized time signal of a plurality of CCs. In the synthesized time signal of a plurality of CCs illustrated inFIG.2, three CCs are non-contiguously arranged. Hereinafter, such a state is appropriately referred to as a 3CC non-contiguous state. The frequency arrangement of the 3CC non-contiguous state is similar to a DBB spectrum employed in the United Kingdom. Hereinafter, a state in which two CCs are contiguously arranged is appropriately referred to as a 2CC contiguous state. The frequency arrangement of the 2CC contiguous state is almost equivalent to the frequency arrangement employed in Germany. Further, hereinafter, a state in which two CCs are non-contiguously arranged is appropriately referred to as a 2CC non-contiguous state.

The digital baseband unit16includes a plurality of CFR circuits161and a plurality of DPD circuits162.

The plurality of CFR circuits161and the plurality of DPD circuits162are each provided in association with the plurality of TRXs171to be described later.

Each of the CFR circuits161performs soft clipping processing of suppressing a peak of the synthesized time signal of the plurality of CCs of the associated TRX171. Specifically, the CFR circuit161suppresses the peak of the synthesized time signal of the plurality of CCs in such a way as to be equal to or lower than a saturation (Psat) level of a transmission AMP172to be described later, which is provided in a subsequent stage of the associated TRX171.

The synthesized time signal of the plurality of CCs to which a nonlinear distortion is applied by the transmission AMP172(to be described later) provided in a subsequent stage of the associated TRX171is fed back to each of the DPD circuits162. Then, each DPD circuit162successively forms AM/PM having an inverse property to the nonlinearity of the transmission AMP172as a DPD weight in such a way that the fed back synthesized time signal of the plurality of CCs asymptotically approximates the synthesized time signal of the plurality of CCs after output from the CFR circuit161(before input to the DPD circuit162). Then, each DPD circuit162multiplies the formed DPD weight by the synthesized time signal of the plurality of CCs after output from the CFR circuit161. When the synthesized time signal of the plurality of CCs acquired by this multiplication passes through the transmission AMP172, nonlinear distortions such as AM/PM distortions of the transmission AMP172are cancelled out, and nonlinear distortions in a vicinity of the maximal rated transmission power (root mean square (RMS)) level are linearized.

The TRX-frontend unit17includes a plurality of the TRXs171, a plurality of the transmission AMPs172, a plurality of reception AMPs173, a plurality of couplers174, a plurality of switches175, and a plurality of band pass filters (BPFs)176.

The plurality of transmission AMPs172, the plurality of reception AMPs173, the plurality of couplers174, the plurality of switches175, and the plurality of BPFs176are each provided in association with each of the plurality of TRXs171.

The synthesized time signal of the plurality of CCs is subjected to RMS level matching in the TRX171, amplified in the transmission AMP172, passed through a predetermined frequency band in the BPF176, and then output to an associated antenna18and transmitted to user equipment (UE: terminal).

In addition, the synthesized time signal of the plurality of CCs to which the nonlinear distortion is applied in the transmission AMP172is fed back by the coupler174to the associated DPD circuit162.

Meanwhile, a signal received from the UE by the associated antenna18is amplified by the reception AMP173and output to the TRX171.

The switch175is a switch for switching between transmission and reception.

Note that, inFIG.1, only a configuration related to transmission is illustrated as a configuration between the LPHY unit13and the digital baseband unit16, and a configuration related to reception is omitted.

FIG.3is a diagram illustrating an example of a waveform of the synthesized time signal of the plurality of CCs after an input stage of the CFR circuit161, in the RU10illustrated inFIG.1.

InFIG.3, a waveform W1indicates a waveform of the synthesized time signal of the plurality of CCs before input from the CFR circuit161.

The CFR circuit161performs soft clipping processing of suppressing a peak of the waveform W1in such a way as to be equal to or lower than a saturation (Psat) level of the transmission AMP172. As a result, a waveform W2is acquired.

The TRX171performs level matching of the RMS level of the waveform W2with another TRX171. As a result, a waveform W3is acquired.

The transmission AMP172amplifies the waveform W3. At this time, the nonlinear distortion of the transmission AMP172is applied to the waveform W3. As a result, a waveform W4is acquired. The linearity of a region to which the nonlinear distortion of the waveform W4is applied is improved by the DPD circuit162.

Thus, it is necessary to ensure the following relationship:

For this purpose, it is important that the CFR circuit161always maintains magnitude relationship between the level of the peak of the input signal of the transmission AMP172and the level of the Psat (saturation output) of the transmission AMP172.

Therefore, a main objective of the CFR circuit161is the following two items.

Hard clipping at the Psat of the transmission AMP172may cause occurrence of significant higher-order nonlinear distortion. The objective (1) is to avoid improvement of distortion compensation by the DPD circuit162from becoming impossible in such a case.

In a case where an efficiency-oriented Doherty AMP is adopted as the transmission AMP172, current consumption increases when an inadvertent peak is applied. The objective (2) is to avoid exceeding allowable power consumption and heat dissipation amount of the RU10due to the increase in the current consumption in such a case.

However, a location of the RU10may be changed. For example, when the location of the RU10is changed from Germany to the United Kingdom, frequency arrangement of the synthesized time signal of the plurality of CCs is switched or changed from the 2CC contiguous state to the 3CC non-contiguous state.

When the frequency arrangement of the synthesized time signal of the plurality of CCs is switched or changed from the 2CC contiguous state to the 2CC non-contiguous state or the 3CC non-contiguous state, a frequency of occurrence of a peak time of the synthesized time signal of the plurality of CCs and a half width of the peak time change.

Therefore, a first technical problem to be solved by the present disclosure is to autonomously set the CFR circuit161to an optimum setting according to a change in the frequency arrangement of the synthesized time signal of the plurality of CCs. Hereinafter, the first technical problem of the present disclosure is described in detail.

FIG.4is a diagram illustrating an example of frequency arrangement of a synthesized time signal of a plurality of CCs in a 2CC contiguous state.FIG.5is a diagram illustrating an example of a frequency spectrum of the synthesized time signal of the plurality of CCs in the 2CC contiguous state illustrated inFIG.4.FIG.6is a diagram illustrating an example of a peak phase of the synthesized time signal of the plurality of CCs in the 2CC contiguous state illustrated inFIG.4.

Meanwhile,FIG.7is a diagram illustrating an example of frequency arrangement of a synthesized time signal of a plurality of CCs in a 3CC non-contiguous state.FIG.8is a diagram illustrating an example of a frequency spectrum of the synthesized time signal of the plurality of CCs in a 2CC non-contiguous state similar to the 3CC non-contiguous state illustrated inFIG.7.FIG.9is a diagram illustrating an example of a peak phase of the synthesized time signal of the plurality of CCs in the 2CC non-contiguous state similar to the 3CC non-contiguous state illustrated inFIG.7.

As illustrated inFIGS.6and9, in a case of frequency arrangement in the 2CC non-contiguous state, a frequency of occurrence of a peak time is increased and a half width of the peak time is decreased, as compared with a case of the frequency arrangement in the 2CC contiguous state. Therefore, it can be said that, as the frequency interval between CCs increases, the occurrence frequency of the peak time increases and the half width of the peak time decreases.

This phenomenon corresponds to an increase in a beat frequency of an AM modulation component of the synthesized time signal of the plurality of CCs as the frequency interval between CCs increases, that is, an increase in the occurrence frequency of the peak time and a decrease in the half width of the peak time. In other words, this phenomenon is a phenomenon in which, when the beat frequency of the AM modulation component of the synthesized time signal of the plurality of CCs increases, a peak having a decreased half width of a peak time appears at a high frequency regarding time.

FIG.10is a diagram illustrating an example of distribution of peaks of the synthesized time signal of the plurality of CCs in each of the 2CC contiguous state and the 3CC non-contiguous state.FIG.11is a diagram illustrating an example of distribution of peak distances of the synthesized time signal of the plurality of CCs in each of the 2CC contiguous state and a 3CC non-contiguous state. The Peak distance indicates a distance between an occurrence position of the peak and an occurrence position of a previous peak.

As illustrated inFIGS.10and11, the frequency arrangement in the 3CC non-contiguous state is higher in the occurrence frequency of peaks and extension of peak than in the frequency arrangement in the 2CC contiguous state.

FIG.12is a diagram illustrating an example of a peak phase before and after the CFR processing by the CFR circuit161is performed once on a synthesized time signal of a plurality of CCs having certain frequency arrangement.

As illustrated inFIG.12, there may be a peak that is not suppressed by performing the CFR processing only once. Such a peak is suppressed by the CFR processing to be performed next.

Therefore, the CFR circuit161performs CFR iteration of cyclically performing the CFR processing. In the CFR iteration, a time waveform group after the CFR processing is performed is stored in a first-in first-out (FIFO), and then the CFR processing is performed again. In this manner, the CFR circuit161performs the CFR processing in a cyclic manner.

FIG.13is a diagram illustrating an example of a peak level distribution after the CFR processing is performed twice on the synthesized time signal of the plurality of CCs in each of the 2CC contiguous state and the 3CC non-contiguous state.

As illustrated inFIG.13, in the synthesized time signal of the plurality of CCs in the 2CC contiguous state, two times of the CFR processing completely suppress the peaks. However, in the synthesized time signal of the plurality of CCs in the 3CC non-contiguous state, peaks may remain even when the CFR processing is performed twice. In such a case, since a frequency of occurrence of the peak time is higher in the synthesized time signal of the plurality of CCs in the 3CC non-contiguous state than in the synthesized time signal of the plurality of CCs in the 2CC contiguous state, it is considered that peaks tend to remain even when the number of times of the CFR iteration is increased.

As described above, when a plurality of CCs are arranged in a non-contiguous manner as in the frequency arrangement in the 3CC non-contiguous state, in other words, when the frequency interval among CCs is wide, the frequency of occurrence of the peak time is increased and the half width of the peak time is reduced.

Therefore, when a plurality of CCs are arranged in a non-contiguous manner, a degree of suppression of peak components increases as the number of times of the CFR iteration is increased and a CFR threshold is set to be lowered. However, on the other hand, since the synthesized time signal of the plurality of CCs itself is excessively lost, communication quality of the EVM or the like is deteriorated. This point relates to a second technical problem to be described later of the present disclosure.

Herein, a configuration example of the CFR circuit161is described.

FIG.14is a diagram illustrating a configuration example of the CFR circuit161.

As illustrated inFIG.14, the CFR circuit161includes a switch1611, a converter1612, a peak detector1613, a basic impulse signal generator1614, an inverse impulse generator1615, a delay FIFO1616, an adder1617, and an iteration determiner1618.

The CFR circuit161receives a synthesized time signal of a plurality of CCs as complex signals from an associated adder15.

The switch1611outputs either the synthesized time signal of the plurality of CCs being input from the adder15or a synthesized time signal of a plurality of CCs being input from the iteration determiner1618after several CFR processing are performed.

The converter1612converts a complex signal HQ being output as a synthesized time signal of a plurality of CCs from the switch1611, into a power level 1{circumflex over ( )}2+Q{circumflex over ( )}2, and outputs the converted result.

The peak detector1613detects a peak being equal to or larger than the CFR threshold of the synthesized time signal of the plurality of CCs, based on the output of the converter1612, and extracts and outputs a level c exceeding a time position1and the CFR threshold for each of the detected peaks.

The basic impulse signal generator1614generates a basic impulse signal.

The inverse impulse generator1615generates and outputs an inverse impulse for suppressing peaks of the synthesized time signal of the plurality of CCs, based on the basic impulse signal generated by the basic impulse signal generator1614. A detailed operation of the inverse impulse generator1615is described later.

The delay FIFO1616delays the synthesized time signal of the plurality of CCs being output from the switch1611, and performs timing matching when the inverse impulse is added by the adder1617in the subsequent stage.

The adder1617performs CFR processing of adding the inverse impulse being output from the inverse impulse generator1615at a peak position of the synthesized time signal of the plurality of CCs being output from the delay FIFO1616. Thus, peak suppression of the synthesized time signal of the plurality of CCs is achieved.

The iteration determiner1618determines whether to perform the CFR processing again. For example, the iteration determiner1618determines that the CFR processing is to be performed again when the number of times of performing the CFR processing has not reached the number of times of the CFR iteration being set in the CFR circuit161. When performing the CFR processing again, the iteration determiner1618inputs the synthesized time signal of the plurality of CCs being output from the adder1617, to the switch1611. Meanwhile, when the CFR processing is not to be performed again, the iteration determiner1618outputs the synthesized time signal of the plurality of CCs being output from the adder1617, to the associated DPD circuit162in the subsequent stage.

Herein, a detailed operation of the inverse impulse generator1615is described.

First, the inverse impulse generator1615calculates a correction amplitude (error magnitude vector) c being a peak suppression amount. The correction amplitude c corresponds to the peak level c extracted by the peak detector1613.

Next, the inverse impulse generator1615generates an inverse impulse base signal, based on the basic impulse signal generated by the basic impulse signal generator1614and the correction amplitude E. An example of the inverse impulse base signal is illustrated inFIG.15.

Next, the inverse impulse generator1615generates an inverse impulse by passing the inverse impulse base signal through a CFR filter (correction pulse filter) having a passband according to the frequency arrangement of the synthesized time signal of the plurality of CCs. By this processing, a frequency component of the inverse impulse may be adjusted to the frequency arrangement of the synthesized time signal of the plurality of CCs. Therefore, it is possible to prevent a wideband spread spectrum due to the inverse impulse from leaking out of a region where the CC is arranged. This processing corresponds to multiplication and mixing as time domain processing, and corresponds to convolution integration as frequency domain processing. An example of such processing is illustrated inFIG.16. An example of an inverse impulse generated by such processing is illustrated inFIG.17.

Thereafter, the inverse impulse generator1615adds the inverse impulse to the adder1617at the peak position of the synthesized time signal of the plurality of CCs. As a result, the peak of the synthesized time signal of the plurality of CCs is suppressed.FIG.18illustrates an example in which a peak of the synthesized time signal of the plurality of CCs is suppressed.

Next, a second technical problem to be solved by the present disclosure is described.

As described above, when a plurality of CCs are arranged in a non-contiguous state, a degree of suppression of peak components increases as the number of times of the CFR iteration increases. However, on the other hand, since the synthesized time signal of the plurality of CCs itself is excessively lost, communication quality such as EVM is deteriorated.

Therefore, when the CFR threshold is not increased while power backoff is being performed, a problem that communication quality such as EVM cannot be maintained and secured occurs. Herein, the power backoff indicates lowering the maximum rated transmission power (RMS) level and thereby ensuring a backoff between Psat of the transmission AMP172and RMS. However, when the CFR threshold is set excessively high, Psat becomes equal to or less than the CFR threshold, and saturation of a transmission system is predominantly determined by Psat. In such a case, hard clipping by Psat always occurs, leading to a large amount of high-order nonlinear distortion being generated. Therefore, nonlinear distortion compensation by the DPD circuit162becomes difficult. Therefore, careful attention needs to be paid to inadvertently increasing the CFR threshold.

FIG.19is a diagram illustrating an example of a peak-to-average power ratio/complementary cumulative distribution function (PAPR/CCDF) property when CFR is inactivated of the synthesized time signal of the plurality of CCs in each of a 2CC contiguous state and a 3CC non-contiguous state.FIG.20is a diagram illustrating an example of a PAPR/CCDF property when CFR is activated of the synthesized time signal of the plurality of CCs in each of the 2CC contiguous state and the 3CC non-contiguous state.FIG.21is an enlarged view of an x-region illustrated inFIG.20. InFIGS.20and21, the CFR threshold is 8.5 dB.

As illustrated inFIG.19, when CFR is inactivated, that is, when peak suppression is not performed by the CFR processing, it can be seen that there is no difference in CCDF between the 2CC contiguous state and the 3CC non-contiguous state.

Meanwhile, as illustrated inFIGS.20and21, when CFR is activated, that is, when peak suppression is performed by the CFR processing, PAPR in a vicinity of the CFR threshold becomes 0.2 dB smaller in the case of the 3CC non-contiguous state than in the case of the 2CC contiguous state. Therefore, in the case of the 3CC non-contiguous state, peaks are suppressed by the CFR processing as compared with the case of the 2CC contiguous state. In other words, in the case of the 3CC non-contiguous state, when peak suppression by the CFR processing is thoroughly performed, a signal purity is deteriorated by 0.2 dB as compared with the case of the 2CC contiguous state. Therefore, in the case of the 3CC non-contiguous state, deterioration of the EVM is noticeably caused by the CFR.

Therefore, in the case of the 3CC non-contiguous state, in order to achieve an EVM being equivalent to the EVM in the case of the 2CC contiguous state, the related art requires the CFR circuit161to increase power backoff and decrease a level of the maximum rated transmission power (RMS). However, the EVM (=downlink (DL) signal to interference plus noise ratio (SINR)) can be finally secured at the expense of lowering the transmission equivalent isotropically radiated power (EIRP). However, a decrease in transmission EIRP leads to a reduction in DL coverage.

FIG.22is a diagram illustrating an example of a PAPR/EVM property of the synthesized time signal of the plurality of CCs for each of a 2CC contiguous state and a 3CC non-contiguous state.

As illustrated inFIG.22, in the case of the 3CC non-contiguous state, the (CFR threshold) vs. (EVM property) is deteriorated as compared with the case of the 2CC contiguous state. As an example, it can be seen that, in order to acquire EVM 2% (5G NR-TM3. 1a: 256 quadrature amplitude modulation (QAM) EVM Core Spec 3.5%, Test Tolerance: +1% added test specification is 4.5% or less) in the case of the 3CC non-contiguous state, power backoff of 0.6 dB is required.

Therefore, the technical problem of the present disclosure is summarized as follows.

First Technical Problem

The first technical problem is to autonomously set the CFR circuit161to an optimum setting according to a change in the frequency arrangement of the synthesized time signal of the plurality of CCs.

Second Technical Problem

In a case where a frequency interval between the CCs is widened by changing the frequency arrangement of the synthesized time signal of the plurality of CCs from the 2CC contiguous state to the 3CC non-contiguous state or the like, when peak suppression by the CFR processing is completed, the synthesized time signal of the plurality of CCs is lost, and communication quality such as EVM deteriorates. Therefore, the second technical problem is to avoid deterioration of communication quality such as EVM due to excessive peak suppression by CFR in a case where the frequency interval between CCs is widened.

SUMMARY

An example object of the present disclosure is to provide a wireless communication apparatus and a wireless communication method that are able to contribute to solution of any of the technical problems described above.

In a first example aspect, a wireless communication apparatus includes:a crest factor reduction (CFR) circuit;a digital pre-distortion (DPD) circuit;at least one memory configured to store instructions; andat least one processor configured to execute the instructions todetermine frequency arrangement of a synthesized time signal of a plurality of component carriers (CCs) acquired by synthesizing time signals of each of the plurality of CCs being input to the CFR circuit, andcontrol the CFR circuit, based on the determined frequency arrangement of the synthesized time signal of the plurality of CCs.

In a second example aspect, a wireless communication method to be executed by a wireless communication apparatus including a crest factor reduction (CFR) circuit and a digital pre-distortion (DPD) circuit includes:determining frequency arrangement of a synthesized time signal of a plurality of component carriers (CCs) acquired by synthesizing time signals of each of the plurality of CCs being input to the CFR circuit; andcontrolling the CFR circuit, based on the determined frequency arrangement of the synthesized time signal of the plurality of CCs.

EXAMPLE EMBODIMENT

Hereinafter, example embodiments of the present disclosure are described with reference to the drawings.

First Example Embodiment

FIG.23is a diagram illustrating a configuration example of an RU10A according to the first example embodiment.

As illustrated inFIG.23, the RU10A according to the first example embodiment differs from the RU10according to the related art illustrated inFIG.1in that frequency arrangement determination unit131and a CFR control unit163are added.

The frequency arrangement determination unit131is provided in an LPHY unit13, and determines the frequency arrangement of a synthesized time signal of a plurality of CCs being input to a CFR circuit161.

As described above, the LPHY unit13includes an IFFT unit (not illustrated) that converts a plurality of CC signals input for each frequency into a time signal for each CC. In the preceding stage of the IFFT unit, a plurality of CC signals for each frequency are in a state before being synthesized.

Therefore, the frequency arrangement determination unit131determines the presence or absence of a plurality of CCs on the basis of the frequency spectrum of the plurality of CC signals in the preceding stage of the IFFT unit.

Further, each of a plurality of CDUCs14includes a plurality of (eight inFIG.23) DUC slices, and each DUC slice uses an NCO142and a multiplier143to arrange the CC time signals on a DBB frequency axis. At this time, the frequency arrangement determination unit131outputs NCO control information for controlling the NCO142to each CDUC14. Each CDUC14controls the NCO142, based on the NCO control information, and arranges the CC time signal on the DBB frequency axis.

Thus, the frequency arrangement determination unit131holds the NCO control information.

Therefore, the frequency arrangement determination unit131determines the frequency arrangement of the synthesized time signal of the plurality of CCs, based on the presence or absence of the plurality of CCs determined in the preceding stage of the IFFT unit and the NCO control information. Specifically, the frequency arrangement determination unit131determines the number of CCs, the frequency interval between CCs, and the like as the frequency arrangement of the synthesized time signal of the plurality of CCs. Therefore, the frequency arrangement determination unit131may determine whether the frequency arrangement of the synthesized time signal of the plurality of CCs is in a 2CC contiguous state, a 2CC non-contiguous state, or a 3CC non-contiguous state.

The CFR control unit163is provided in a digital baseband unit16, and controls the CFR circuit161, based on the frequency arrangement of the synthesized time signal of the plurality of CCs determined by the frequency arrangement determination unit131.

As described above, an inverse impulse generator1615in the CFR circuit161uses a CFR Filter (correction pulse filter) to generate the inverse impulse. At this time, the passband of the CFR filter needs to conform to the frequency arrangement of the synthesized time signal of the plurality of CCs being input to the CFR circuit161.

Therefore, in the first example embodiment, in order to generate such an inverse impulse frequency spectrum that only allows a plurality of CCs having different passbands and different frequency arrangement from one another to pass through, the inverse impulse generator1615selects, from among a plurality of CFR filters, a CFR filter having a passband according to the frequency arrangement determined by the frequency arrangement determination unit131. The inverse impulse generator1615generates an inverse impulse by passing an inverse impulse base signal through the CFR filter selected by the CFR control unit163.

Therefore, even when the frequency arrangement of the synthesized time signal of the plurality of CCs is changed, the CFR circuit161is able to be autonomously set to an optimum setting according to the change in the frequency arrangement.

This contributes to solving the above-described first technical problem. Next, a method that may contribute to solving the above-described second technical problem is described.

As described above, when the frequency arrangement of the synthesized time signal of the plurality of CCs is switched/changed from the 2CC contiguous state to the 2CC non-contiguous state or the 3CC non-contiguous state, the frequency of occurrence of the peak time is increased and the half width of the peak time is decreased in the synthesized time signal of the plurality of CCs.

Therefore, when a plurality of CCs are arranged in a non-contiguous manner, the degree of suppression of peak components increases when the number of times of the CFR iteration is increased. However, on the other hand, since the synthesized time signal of the plurality of CCs are excessively lost, the communication quality such as the EVM or the like is deteriorated.

Further, as described above, an iteration determiner1618in the CFR circuit161determines whether to perform CFR processing again according to whether the number of times of performing the CFR processing has reached the number of times of the CFR iteration being set in the CFR circuit161.

Therefore, when the frequency arrangement determination unit131determines that the frequency interval between the CCs is large, such as when the frequency arrangement of the synthesized time signal of the plurality of CCs is in the 2CC non-contiguous state or the 3CC non-contiguous state, the CFR control unit163reduces the number of times of the CFR iteration to be set in the CFR circuit161. That is, the CFR control unit163performs control such that the number of times of the CFR iteration decreases as the frequency interval between the CCs increases. When the frequency arrangement of the synthesized time signal of the plurality of CCs includes three or more CCs, the frequency interval between the CCs being used for determining the number of times of the CFR iteration may be either the largest or the smallest.

Therefore, excessive loss of the synthesized time signal of the plurality of CCs is avoided, and thus it is possible to maintain the communication quality such as the EVM or the like.

This contributes to solving the above-described second technical problem.

Next, another method that may contribute to solving the above-described second technical problem is described.

As described above, when the frequency arrangement of the synthesized time signal of the plurality of CCs is switched/changed from the 2CC contiguous state to the 2CC non-contiguous state or the 3CC non-contiguous state, the frequency of the occurrence of the peak time is increased and the half width of the peak time is decreased in the synthesized time signal of the plurality of CCs.

Therefore, when a plurality of CCs are arranged in a non-contiguous manner, the degree of suppression of the peak components increases if the CFR thresholds are lowered. However, on the other hand, since the synthesized time signal of the plurality of CCs are excessively lost, the communication quality such as the EVM is deteriorated.

Further, as described above, the inverse impulse generator1615in the CFR circuit161calculates the correction amplitude (error magnitude vector) c, being the peak suppression amount, and generates the inverse impulse, based on the calculated correction amplitude E.

Therefore, when the frequency arrangement determination unit131determines that the frequency interval between the CCs is large, such as when the frequency arrangement of the synthesized time signal of the plurality of CCs is in a 2CC non-contiguous state or a 3CC non-contiguous state, the CFR control unit163controls the CFR circuit161in such a way that the correction amplitude c as the inverse impulse becomes small. At this time, the CFR control unit163sets the correction amplitude c to be smaller as the frequency interval between the CCs is larger.

Specifically, the inverse impulse generator1615in the CFR circuit161multiplies the correction amplitude c by a weight, and generates an inverse impulse, based on the acquired correction amplitude ε′.

When the frequency arrangement determination unit131determines that the frequency interval between the CCs is large, the CFR control unit163performs control in such a way that the weight being set in the inverse impulse generator1615becomes small. At this time, the CFR control unit163makes the inverse impulse correction smaller as the frequency interval between the CCs is larger. When the frequency arrangement of the synthesized time signal of the plurality of CCs includes three or more CCs, the frequency interval between the CCs being used for determining the weight may be either the largest or the smallest.

FIG.24is a diagram illustrating an example of an inverse impulse base signal being generated by the CFR circuit161according to the first example embodiment.FIG.25is a diagram illustrating an example of processing of generating, in the CFR circuit161according to the first example embodiment, an inverse impulse by passing an inverse impulse base signal through a CFR filter having a passband according to the frequency arrangement of the synthesized time signal of a plurality of CCs.FIG.26is a diagram illustrating an example in which a peak of the synthesized time signal of the plurality of CCs is suppressed in the CFR circuit161according to the first example embodiment.

As illustrated inFIGS.24,25, and26, in the first example embodiment, it can be seen that the peak suppression amount is reduced from an amount corresponding to c to an amount corresponding to C.

Therefore, excessive loss of the synthesized time signal of the plurality of CCs is avoided, and thus it is possible to maintain the communication quality such as the EVM.

This contributes to solving the above-described second technical problem.

As described above, according to the first example embodiment, the frequency arrangement determination unit131determines the frequency arrangement of the synthesized time signal of the plurality of CCs being input to the CFR circuit161. The CFR control unit163controls the CFR circuit161, based on the frequency arrangement of the synthesized time signal of the plurality of CCs determined by the frequency arrangement determination unit131. Specifically, the CFR control unit163selects a CFR filter having a passband according to the frequency arrangement determined by the frequency arrangement determination unit131. The inverse impulse generator1615in the CFR circuit161generates an inverse impulse by using the CFR filter selected by the CFR controller163.

Therefore, even when the frequency arrangement of the synthesized time signal of the plurality of CCs is changed, the CFR circuit161can be autonomously set to an optimum setting according to the change of the frequency arrangement.

This contributes to solving the above-described first technical problem.

Therefore, even if trade or the like of a frequency band is frequently performed in the U.S. and Europe after the RU10A is arranged, the CFR circuit161is autonomously set to an optimum setting by the RU10A alone. Therefore, it is possible to acquire an effect that a setting change by the RU10A is required neither locally nor remotely.

Further, according to the first example embodiment, when the frequency arrangement determination unit131determines that the frequency interval between the CCs is large, the CFR control unit163reduces the number of times of the CFR iteration in the CFR circuit161or reduces the correction amplitude being the peak suppression amount in the CFR circuit161. Therefore, excessive loss of the synthesized time signal of the plurality of CCs is avoided, and thus it is possible to maintain the communication quality such as the EVM.

This contributes to solving the above-described second technical problem.

This eliminates the need to satisfy the EVM standard by increasing power backoff and reducing the level of the maximum rated transmission power (RMS), that is, EIRP, implicitly. Therefore, it is possible to secure the EVM required for each DL QAM (that is, DL SINR) without sacrificing the transmission EIRP. In addition, DL-SINR/EVM can be secured without lowering the EIRPs from the low-order to high-order QAMs (QPSK/16QAM/64QAM/256QAM/1024QAM). Therefore, even when a plurality of CCs are arranged in a non-contiguous manner over a wide band, reduction in DL coverage can be avoided and DL coverage can be maintained.

Second Example Embodiment

The second example embodiment corresponds to an example embodiment in which the first example embodiment described above is put into a higher-level concept.

FIG.27is a diagram illustrating a configuration example of a wireless communication apparatus10B according to the second example embodiment.

As illustrated inFIG.27, the wireless communication apparatus10B according to the second example embodiment includes a CFR circuit101, a determination unit102, a control unit103, and a DPD circuit104.

The wireless communication apparatus10B corresponds to the RU10A according to the first example embodiment described above.

The CFR circuit101corresponds to the CFR circuit161according to the first example embodiment described above.

The DPD circuit104corresponds to the DPD circuit162according to the first example embodiment described above.

The determination unit102determines frequency arrangement of a synthesized time signal of a plurality of CCs being input to the CFR circuit101. The synthesized time signal of the plurality of CCs is a signal acquired by synthesizing time signals for each of a plurality of CCs. The determination unit102corresponds to the frequency arrangement determination unit131according to the first example embodiment described above.

The control unit103controls the CFR circuit101, based on the frequency arrangement of the synthesized time signal of the plurality of CCs determined by the determination unit102. The control unit103corresponds to the CFR control unit163according to the first example embodiment described above.

FIG.28is a flowchart illustrating an example of a schematic operation flow of the wireless communication apparatus10B according to the second example embodiment.

As illustrated inFIG.28, the determination unit102determines the frequency arrangement of the synthesized time signal of the plurality of CCs being input to the CFR circuit101(step S11). The control unit103controls the CFR circuit101, based on the frequency arrangement of the synthesized time signal of the plurality of CCs determined by the determination unit102(step S12).

As described above, according to the second example embodiment, the determination unit102determines the frequency arrangement of the synthesized time signal of the plurality of CCs being input to the CFR circuit101, and the control unit103controls the CFR circuit101, based on the frequency arrangement of the synthesized time signal of the plurality of CCs determined by the determination unit102.

Therefore, even when the frequency arrangement of the synthesized time signal of the plurality of CCs is changed, the CFR circuit101can be autonomously set to an optimum setting according to the change of the frequency arrangement.

This contributes to solving the above-described first technical problem.

Specifically, the CFR circuit101may hold a plurality of filters having different passbands from one another. Further, the control unit103may select, from among the plurality of filters, a filter having a passband according to the frequency arrangement of the synthesized time signal of the plurality of CCs determined by the determination unit102. Further, the CFR circuit101may perform CFR processing for suppressing the peak of the synthesized time signal of the plurality of CCs by using the filter selected by the control unit103.

Further, the CFR circuit101may repeatedly perform the CFR processing. Further, the control unit103may control the number of repetitions of the CFR processing in the CFR circuit101, based on the frequency interval between the CCs in the frequency arrangement of the synthesized time signal of the plurality of CCs determined by the determination unit102. At this time, the control unit103may decrease the number of repetitions of the CFR processing in the CFR circuit101as the frequency interval between the CCs in the frequency arrangement of the synthesized time signal of the plurality of CCs determined by the determination unit102increases.

Further, the control unit103may control the correction amplitude being the suppression amount of the peak of the CFR processing in the CFR circuit101, based on the frequency interval between the CCs in the frequency arrangement of the synthesized time signal of the plurality of CCs determined by the determination unit102. At this time, the control unit103may decrease the correction amplitude in the CFR circuit101as the frequency interval between the CCs in the frequency arrangement of the synthesized time signal of the plurality of CCs determined by the determination unit102increases.

As described above, the control unit103controls the number of repetitions of the CFR processing and the correction amplitude in the CFR circuit101, based on the frequency interval between the CCs in the frequency arrangement of the synthesized time signal of the plurality of CCs. Therefore, excessive loss of the synthesized time signal of the plurality of CCs is avoided, and thus it is possible to maintain the communication quality such as the EVM.

This contributes to solving the above-described second technical problem.

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

For example, some functions of the wireless communication apparatus (including an RU) according to the present disclosure may be implemented by causing a processor such as a central processing unit (CPU) to execute a program.

FIG.29is a diagram illustrating an example of a hardware configuration of a computer90that implements some functions of the wireless communication apparatus according to the present disclosure.

As illustrated inFIG.29, the computer90includes a processor91and a memory92.

The processor91may be, for example, a microprocessor, a CPU, or a micro processing unit (MPU). The processor91may include a plurality of processors.

The memory92includes a combination of a volatile memory and a non-volatile memory. The memory92may include storage located away from the processor91. In such a case, the processor91may access the memory92via an input/output (I/O) interface (not illustrated).

A program is stored in the memory92. The program includes instructions (or software codes) for causing the computer90to perform some functions of the RU10A or the wireless communication apparatus10B according to the first or second example embodiment described above when the program is read into the computer90. The components in the RU10A or the wireless communication apparatus10B described above may be implemented by the processor91reading and executing a program stored in the memory92. In addition, the component having the storage function in the RU10A or the wireless communication apparatus10B described above may be implemented by the memory92. The above-described program can be stored and provided to a computer using any type of non-transitory computer readable media. Non-transitory computer readable media include any type of tangible storage media. Examples of non-transitory computer readable media include magnetic storage media (such as floppy disks, magnetic tapes, hard disk drives, etc.), optical magnetic storage media (e.g., magneto-optical disks), CD-ROM (compact disc read only memory), CD-R (compact disc recordable), CD-R/W (compact disc rewritable), and semiconductor memories (such as mask ROM, PROM (programmable ROM), EPROM (erasable PROM), flash ROM, RAM (random access memory), etc.). The program may be provided to a computer using any type of transitory computer readable media. Examples of transitory computer readable media include electric signals, optical signals, and electromagnetic waves. Transitory computer readable media can provide the program to a computer via a wired communication line (e.g., electric wires, and optical fibers) or a wireless communication line.

The first and second example embodiments can be combined as desirable by one of ordinary skill in the art.