JP6070820B2 - Communication apparatus and peak suppression method thereof - Google Patents

Description

  The present invention relates to a communication apparatus and a peak suppression method thereof, for example, a communication apparatus that transmits a signal obtained by combining a plurality of baseband signals belonging to different frequency bands, and a peak suppression method thereof.

  In recent years, in wireless communication systems, countermeasures have been demanded as data traffic increases. In order to communicate a large amount of data at high speed, the frequency bandwidth to be used may be expanded, but the frequency band allocated to each communication carrier is limited. Thus, it is considered to use a plurality of frequency bands. However, in general, a separate device is required for each frequency band, and installation space is tight. Therefore, in order to reduce the size of the apparatus, research and development of dual band antennas and dual band common amplifiers corresponding to a plurality of RF (Radio Frequency) frequency bands are being promoted.

  Communication standards used in such devices include LTE (Long Term Evolution) and WiMAX (Worldwide Interoperability for Microwave Access). In these communication systems, an OFDM (Orthogonal Frequency-Division Multiplexing) system is used as a modulation system. OFDM is a type of multi-carrier modulation scheme that modulates data with subcarriers orthogonal to each other, and is widely used because high frequency utilization efficiency is obtained. An OFDM signal is a superposition of subcarrier signals having independent phases, and may have a very high peak power depending on the combination of phases. When such a signal is input to the amplifier, sufficient linearity is required in the input / output characteristics. If there is not sufficient linearity, nonlinear distortion occurs and the signal level outside the transmission frequency band increases. In order to ensure sufficient linearity, it is necessary to lower the operating point of the amplifier and ensure sufficient back-off against the saturated output power, but this is a problem that reduces the power efficiency of the amplifier. There is.

  Therefore, clipping processing for suppressing peak power may be performed. For peak suppression (Crest Factor Reduction, CFR), for example, Patent Documents 1 to 3 propose various methods.

  Patent Document 1 discloses a technique for performing subtraction with a peak amplitude using a compensation signal having an impulsive property generated based on the peak amplitude. Thereby, in patent document 1, a peak component is reduced, suppressing signal quality degradation which arises at the time of peak component reduction small.

  In Patent Document 2, a transmitter that suppresses peak power of a transmission signal includes a plurality of peak suppression signal generation means, peak suppression signal synthesis means, and subtraction means. In Patent Document 2, a plurality of peak suppression signal generation means generate a peak suppression signal for suppressing the peak voltage of the transmission signal, and a peak suppression signal synthesis means generates a peak generated by the plurality of peak suppression signal generation means. A technique is disclosed in which a suppression signal is combined, and a subtracting unit subtracts a combined signal obtained by a peak suppression signal combining unit from a transmission signal. Thereby, in patent document 2, the peak electric power which generate | occur | produces in a transmission signal is suppressed effectively.

  In Patent Document 3, a plurality of OFDM signals are generated, a baseband peak suppression unit suppresses each OFDM signal based on these signals, and an IF conversion unit converts each OFDM signal subjected to peak suppression to an intermediate frequency. The intermediate frequency peak suppression means suppresses each of the intermediate frequency signals based on these signals, the combining means combines the peak-suppressed signals having a plurality of intermediate frequencies, and the amplification means Amplifies the combined signal. Further, in Patent Document 3, the baseband peak suppressing means suppresses the peak value by combining the absolute value of each OFDM signal as a predicted peak value, and the intermediate frequency peak suppressing means combines a plurality of intermediate frequency signals. Peak suppression is performed using the absolute value of the result as a predicted peak value. That is, in Patent Document 3, when a multicarrier signal is transmitted by the OFDM method, peak suppression processing is performed on a baseband signal based on a combined result of absolute values of a plurality of OFDM signals (baseband signals). Peak suppression is effectively performed by performing peak suppression processing on an intermediate frequency signal based on the absolute value of the combined result of a plurality of OFDM signals (intermediate frequency signals).

  Here, in Patent Documents 1 and 2, the frequency band of a signal included in a transmission signal (for example, an RF signal) is limited to one, and an RF signal modulated with a carrier wave in a different frequency band is synthesized and output. In case there is a problem. More specifically, in the case of an apparatus that commonly amplifies RF signals modulated with carriers of different frequency bands, the common amplifier receives an RF signal obtained by combining the OFDM signals modulated with carriers of different frequency bands. . At the time of this signal synthesis, there arises a problem that the phases of two different frequency carriers coincide with each other and the peak is reproduced. In this regard, in Patent Document 3, the peak suppression process is also performed on the intermediate frequency signal, thereby preventing the peak of the combined signal from being reproduced.

JP 2004-179813 A JP 2008-47959 A JP 2008-294519 A

  However, in the technique described in Patent Document 3, a plurality of OFDM signals having different intermediate frequencies are combined and then frequency conversion to an RF signal is performed. For this reason, the technique described in Patent Document 3 has a problem in that peak suppression cannot be performed on an RF signal obtained by synthesizing a plurality of OFDM signals modulated by carrier waves in frequency bands that are far apart as the frequency allocation is different.

  The present invention has been made to solve the above-described problem, and a communication apparatus and a peak capable of performing peak suppression even on an RF signal obtained by combining a plurality of OFDM signals modulated by carriers of different frequency bands. The purpose is to provide a suppression method.

  One aspect of a communication apparatus according to the present invention performs peak suppression processing on a first baseband signal and a second baseband signal, and outputs a third baseband signal and a fourth baseband signal. A peak suppressor, a first digital-to-analog converter that converts the third baseband signal into an analog signal, a second digital-to-analog converter that converts the fourth baseband signal into an analog signal, and A first frequency converter for converting a frequency of the third baseband signal output from the first digital-analog converter into a frequency of a first carrier wave and outputting a first transmission signal; The frequency of the fourth baseband signal output from the digital-to-analog converter is converted to the frequency of the second carrier belonging to a frequency band different from the first carrier, and the second A second frequency converter for outputting a transmission signal, a combiner for combining the first transmission signal and the second transmission signal and outputting a third transmission signal, and the third transmission signal. An amplifier that amplifies and outputs an output signal, and the peak suppressor includes a phase of the first carrier wave in a combined signal of the first baseband signal and the second baseband signal. The power of the combined signal when the phase of the second carrier coincides is calculated as a maximum power value, and a first suppression signal having a value other than zero when the maximum power value is greater than a power threshold, 2, a third baseband signal is generated by reflecting the first suppression signal in the first baseband signal, and the second suppression signal is generated in the second baseband signal. The fourth baseband signal reflecting the signal is generated. To.

  The peak suppression method according to the present invention performs peak suppression processing on the first baseband signal and the second baseband signal, and outputs a third baseband signal and a fourth baseband signal. A first digital-to-analog converter that converts the third baseband signal into an analog signal, a second digital-to-analog converter that converts the fourth baseband signal into an analog signal, and the first A first frequency converter for converting the frequency of the first baseband signal output from the digital-analog converter to a frequency of a first carrier wave and outputting a first transmission signal; and the second digital signal The frequency of the second baseband signal output from the analog converter is converted to the frequency of the second carrier belonging to a frequency band different from the first carrier, and the second A second frequency converter that outputs a transmission signal, a combiner that combines the first transmission signal and the second transmission signal and outputs a third transmission signal, and the third transmission signal. An amplifier that amplifies and outputs an output signal, the peak suppression method in a communication device, wherein, in the peak suppression unit, of the combined signal of the first baseband signal and the second baseband signal, The power of the combined signal when the phase of the first carrier wave matches the phase of the second carrier wave is calculated as a maximum power value, and the first base when the maximum power value is larger than the power threshold value A first suppression signal for reducing the power of the band signal and a second suppression signal for reducing the second baseband signal are calculated, and the first suppression signal is reflected in the first baseband signal. Said third base van Generates a signal, the reflecting the second suppression signal to generate the fourth baseband signal to the second baseband signal.

  According to the communication apparatus and the peak suppression method of the present invention, peak suppression can be performed even on an output signal obtained by combining a plurality of OFDM signals modulated by carrier waves having different frequencies.

1 is a block diagram of a communication device according to a first exemplary embodiment. FIG. 3 is a block diagram of a peak suppressor according to the first embodiment. FIG. 3 is a schematic diagram illustrating a frequency band of a baseband signal handled in the communication apparatus according to the first embodiment. 6 is a graph showing a complementary cumulative distribution function of an output signal of the communication device according to the first exemplary embodiment; It is a graph which shows the complementary cumulative distribution function of an output signal at the time of performing the conventional peak suppression process. FIG. 3 is a block diagram of a communication device according to a second exemplary embodiment. FIG. 6 is a block diagram of a communication apparatus according to a third embodiment. FIG. 6 is a block diagram of a communication apparatus according to a fourth embodiment. FIG. 10 is a block diagram of a peak suppressor according to a fourth embodiment.

Embodiment 1
Embodiments of the present invention will be described below with reference to the drawings. The communication apparatus according to the first embodiment is capable of outputting a synthesized signal obtained by synthesizing a baseband signal that is modulated by a carrier wave having a frequency that is far away from the frequency allocation. Therefore, when a transmission signal (for example, an OFDM signal) obtained by modulating a baseband signal with a carrier wave having such a large frequency is combined to output a combined signal (for example, an RF signal), the conventional peak suppression method The reason why the peak suppression could not be sufficiently performed will be described in detail.

  For example, in the conventional peak suppression methods described in Patent Documents 1 to 3, peak power is determined for a digital signal and clipping processing is performed. Even a synthesized signal obtained by synthesizing a plurality of OFDM signals can use a conventional peak suppression method as long as the frequencies of the OFDM signals are adjacent to each other at a frequency that can be expressed as a single digital signal.

  However, a utilization form using carrier waves in a frequency band that is far away from each other, such as generating an RF signal by combining an OFDM signal in the 800 MHz band and an OFDM signal in the 2.6 GHz band, is conceivable. In such a combination of OFDM signals, a sampling frequency of several GHz is required to represent a single digital signal, and it is substantially difficult to realize the sampling process. Moreover, in patent document 3, the synthesis | combination of OFDM signal is performed in the intermediate frequency of a frequency lower than RF signal, and the peak is suppressed in the said intermediate frequency band. However, since the intermediate frequency is processed with a digital signal, in Patent Document 3, only an OFDM signal adjacent at a frequency close to a level that can be expressed as a single digital signal is targeted for peak suppression.

  Here, when a conventional peak suppression method is used for a synthesized signal obtained by synthesizing OFDM signals in frequency bands that are far apart, the following method can be considered. First, clipping processing using a conventional peak suppression method is individually performed on the baseband signal of the OFDM signal before synthesis. An RF signal including OFDM signals in a plurality of frequency bands can be obtained by combining these after up-converting them to the carrier frequency. However, the peak power to average power ratio (PAPR) of the RF signal obtained in this way is the peak power to average power ratio of a single OFDM signal that has been subjected to peak suppression processing before synthesis. There is an increasing problem. The reason why the PAPR increases in this way is that when combining OFDM signals of different frequency bands, the peak power of the RF signal at the time when the phases match between the carriers of different frequencies increases. This is because there is no means for suppressing in the conventional peak suppressing method. Therefore, one of the features of the communication apparatus according to the first embodiment is to provide means and a method for suppressing the peak power of a combined signal obtained by combining signals modulated by carriers in different frequency bands.

  FIG. 1 shows a block diagram of a communication apparatus 1 according to the first embodiment. As shown in FIG. 1, the communication apparatus 1 according to the first embodiment includes a first OFDM baseband signal generation unit 10, a second OFDM baseband signal generation unit 20, digital analog converters 11 and 21, an up-converter. 12, 22, a peak suppression unit 30, a distortion correction unit 31, a combiner 35, an amplifier 36, and a directional coupler 37.

  The first OFDM baseband signal generation unit 10 outputs a first baseband signal TxBB11. The second OFDM baseband signal generation unit 20 outputs a second baseband signal TxBB21. The first OFDM baseband signal generation unit 10 and the second OFDM baseband signal generation unit 20 are arithmetic devices such as a processor that generates data to be transmitted to the communication partner of the communication device 1, for example.

  The peak suppression unit 30 performs peak suppression processing on the first baseband signal TxBB11 and the second baseband signal TxBB21, and outputs a third baseband signal TxBB12 and a fourth baseband signal TxBB22. More specifically, the peak suppressor 30 matches the phase of the first carrier and the phase of the second carrier in the combined signal of the first baseband signal TxBB11 and the second baseband signal TxBB12. The power of the combined signal at the time is calculated as the maximum power value, and when the maximum power value is larger than the power threshold, a first suppression signal and a second suppression signal having values other than zero are generated, and the first base A third baseband signal TxBB12 is generated by reflecting the value of the first suppression signal in the band signal TxBB11, and a fourth baseband signal in which the value of the second suppression signal is reflected in the second baseband signal TxBB21 TxBB22 is generated. A more detailed description of the peak suppressor 30 will be described later.

  The distortion correction unit 31 is provided after the peak suppression unit 30 and compares the third baseband signal TxBB12 and the fourth baseband signal TxBB22 with an output signal (for example, an RF signal Txout) to generate an RF signal. A distortion amount of Txout is calculated, and distortion compensation processing is performed on the third baseband signal and the fourth baseband signal so as to reduce the distortion amount.

  The distortion correction unit 31 includes a predistortion unit 32, a first delay unit (for example, a delay unit 33), and a second delay unit (for example, a delay unit 34). The predistortion unit 32 calculates the distortion amount of the RF signal Txout, and multiplies the third baseband signal TxBB12 and the fourth baseband signal TxBB22 by a distortion compensation coefficient generated according to the magnitude of the distortion amount. The third baseband signal TxBB13 and the fourth baseband signal TxBB23 are output. The predistortion unit 32 also includes a first delay setting value DL1 and a second delay setting value having values corresponding to the difference in delay amount from the input of the predistortion unit 32 to the amplifier 36 of two OFDM signals. DL2 is output. In other words, the predistortion unit 32 receives the first baseband signal and the second baseband signal between the two baseband signals after the third transmission signal reaches the amplifier 36 after the first baseband signal and the second baseband signal are input to the predistortion unit 32. 1st delay setting value DL1 and 2nd delay setting value DL2 which have a value according to the difference of the amount of delay which arises in 2 are output. In FIG. 1, the baseband signals before the processing with the distortion compensation coefficient are labeled with TxBB12 and TxBB22, and the baseband signals after the processing with the distortion compensation coefficient are performed with TxBB13 and TxBB23. A reference is attached. In the following description, the codes of TxBB12 and TxBB22 are used for the baseband signal before the processing using the distortion compensation coefficient, and the codes of TxBB13 and TxBB23 are used for the baseband signal after the processing using the distortion compensation coefficient. Is used.

  The delay unit 33 delays the third baseband signal TxBB13 according to the first delay setting value DL1. The delay unit 34 delays the fourth baseband signal in accordance with the second delay setting value.

  The digital-analog converter 11 converts the third baseband signal TxBB13 into an analog signal. The digital-analog converter 21 converts the fourth baseband signal TxBB23 into an analog signal. The up converter 12 is a first frequency converter. The up-converter 12 converts the frequency of the third baseband signal TxBB13 output from the first digital-analog converter 11 into the frequency of a first carrier wave (for example, a first local signal) and performs first transmission. Output a signal. The up converter 22 is a second frequency converter. The up-converter 22 sets the frequency of the fourth baseband signal TxBB 23 output from the second digital-analog converter 21 to a second carrier (for example, a second local signal) belonging to a frequency band different from the first carrier. ) To output a second transmission signal.

  The combiner 35 combines the first transmission signal and the second transmission signal, and outputs a third transmission signal. The amplifier 36 amplifies the third transmission signal and outputs a signal (for example, an RF signal Txout). The directional coupler 37 outputs a small part of the RF signal Txout transmitted to the antenna to the distortion correction unit 31 as a feedback signal.

  Next, the peak suppression unit 30 and the distortion correction unit 31 that are one of the features of the communication device 1 according to the first embodiment will be described in detail. First, the peak suppression unit 30 will be described in detail. A detailed block diagram of the peak suppressor 30 is shown in FIG.

  As shown in FIG. 2, the peak suppressor 30 includes a tone signal generator 41, filters 42 and 43, and subtractors 44 and 45.

  The tone signal generation unit 41 combines the first transmission signal generated from the first baseband signal TxBB11 and the second transmission signal generated from the second baseband signal TxBB21. Based on the maximum power of the signal, a first suppression signal (for example, the first impulse signal I1) and a second suppression signal (for example, the second impulse signal I2) are output. More specifically, the tone signal generation unit 41 includes a phase coincidence power calculation unit 51, a threshold power calculation unit 52, a power determination unit 53, an impulse signal generator 54, and a zero signal generator 55.

When the phase coincidence power calculation unit 51 matches the phase of the first local signal and the phase of the second local signal in the combined signal of the first baseband signal TxBB11 and the second baseband signal TxBB21. Is calculated as the maximum power value Pmax. The maximum power value Pmax can be expressed by equation (1). Note that t in the expression (1) indicates the time when the signal is sampled.

ここで、（４）式のクリッピング係数Ｃは、例えば、７ｄＢ程度の値が設定される。このクリッピング係数Ｃが小さいほどピーク電力対平均電力比ＰＡＰＲを低く抑えることができることから、増幅器３６にとっては、歪み特性及び電力効率の観点から好ましい。しかし、クリッピング係数Ｃを小さく設定すると、変調精度ＥＶＭ（Error Vector Magnitude）が劣化するため、クリッピング係数Ｃはピーク電力対平均電力比と変調精度ＥＶＭとのトレードオフ関係を鑑みて適切な値に設定されることが好ましい。また、クリッピング係数Ｃは、平均電力Ｐｍｅａｎ或いは第１のベースバンド信号ＴｘＢＢ１１と第２のベースバンド信号ＴｘＢＢ２１それぞれの電力レベルに応じて可変させても良い。The threshold power calculation unit 52 calculates an average power value in a predetermined period of a combined signal obtained by combining the first baseband signal TxBB11 and the second baseband signal TxBB21, and a clipping coefficient C set in advance for the average power value. To calculate the power threshold value Pth. The power threshold value Pth can be calculated from the following equations (2) to (4). Note that TxBB (t) in equation (2) is the sum of the powers of the two baseband signals at time t. Pmean in the equation (3) is an average power during a predetermined period n.

Here, for example, a value of about 7 dB is set as the clipping coefficient C in the equation (4). The smaller the clipping coefficient C is, the lower the peak power-to-average power ratio PAPR is. Therefore, the amplifier 36 is preferable from the viewpoint of distortion characteristics and power efficiency. However, since the modulation accuracy EVM (Error Vector Magnitude) deteriorates when the clipping coefficient C is set small, the clipping coefficient C is set to an appropriate value in consideration of the trade-off relationship between the peak power to average power ratio and the modulation accuracy EVM. It is preferred that Further, the clipping coefficient C may be varied according to the average power Pmean or the power levels of the first baseband signal TxBB11 and the second baseband signal TxBB21.

  The power determination unit 53 compares the maximum power value Pmax and the power threshold Pth, and switches between the first enable signal EN1 and the second enable signal EN2 to be enabled. Specifically, if the maximum power value Pmax is larger than the power threshold value Pth, the power determination unit 53 enables the first enable signal EN1 and disables the second enable signal EN2. Thereby, when the maximum power value Pmax is larger than the power threshold value Pth, the impulse signal generator 54 is in an operating state and the zero signal generator 55 is in a stopped state. On the other hand, when the maximum power value Pmax is equal to or smaller than the power threshold value Pth, the power determination unit 53 disables the first enable signal EN1 and enables the second enable signal EN2. Thereby, when the maximum power value Pmax is equal to or less than the power threshold value Pth, the impulse signal generator 54 is stopped and the zero signal generator 55 is activated.

  The impulse signal generator 54 generates impulse signals (for example, the first impulse signal I1 and the second impulse signal I2) having magnitudes calculated based on the maximum power value Pmax, the power threshold value Pth, and the weighting factors a1 and a2. Generate. The first impulse signal I1 is applied to the first baseband signal TxBB11, and the second impulse signal I2 is applied to the second baseband signal TxBB21.

Here, a method of calculating the impulse signal output from the impulse signal generator 54 will be described. The first impulse signal I1 and the second impulse signal I2 can be calculated by the equations (5) and (6). Note that the weighting factors a1 and a2 are stored in advance in a storage unit (not shown) such as a nonvolatile memory.

The zero signal generator 55 generates a zero signal whose value is zero. The zero signal is an impulse signal having a value of zero, and the zero signal generator 55 according to the first embodiment generates a first impulse signal I1 and a second impulse signal I2 having a value of zero. That is, the first impulse signal I1 and the second impulse signal I2 output from the zero signal generator 55 are expressed by the equations (7) and (8).

  The filter 42 outputs the first impulse signal I1 in which the level of the out-of-band signal is attenuated to the subtractor 44 as a first suppression signal. The filter 43 outputs the second impulse signal I2 in which the level of the out-of-band signal is attenuated to the subtracter 45 as a second suppression signal. In FIG. 2, the impulse signals input to the filters 42 and 43 and the output impulse signals are the same with respect to necessary signal components, and thus the same reference numerals are given to these signals.

The subtractor 44 is a first subtracter, and generates a third baseband signal TxBB12 by subtracting a first suppression signal (for example, the first impulse signal I1) from the first baseband signal TxBB11. To do. That is, the third baseband signal TxBB12 is expressed by the equation (9).

The subtracter 45 is a second subtracter, and generates a fourth baseband signal TxBB22 by subtracting a second suppression signal (for example, the second impulse signal I2) from the second baseband signal TxBB21. To do. That is, the fourth baseband signal TxBB22 is expressed by equation (10).

  Substituting Equations (5) and (6) into Equations (9) and (10) above, the third baseband signal TxBB12 and the fourth baseband signal TxBB22 are converted into the first baseband signal TxBB11 and The term of the second baseband signal TxBB21 is eliminated. That is, the third baseband signal TxBB12 and the fourth baseband signal TxBB22 are signals that are clipped with the power threshold value Pth on the basis of the power maximum value Pmax. As described above, the peak suppression unit 30 sets the maximum power when the first baseband signal TxBB11 and the second baseband signal TxBB21 are combined after being up-converted with the respective local signals to the power threshold Pth or less. Next, peak suppression processing is performed on the baseband signal.

  Here, the effect of the peak suppression processing by the peak suppression unit 30 will be described. Therefore, first, an example of the frequency band of the first transmission signal generated from the first baseband signal TxBB11 and the second transmission signal generated from the second baseband signal TxBB21 in the communication device 1 is provided. A diagram for explanation is shown in FIG. As shown in FIG. 3, in the communication apparatus 1, an OFDM signal whose center frequency fc1 belongs to the 800 MHz band is generated as the first transmission signal, and an OFDM signal whose center frequency fc2 belongs to the 2.6 GHz band as the second transmission signal. And the first and second transmission signals are combined to generate a third transmission signal.

  FIG. 4 is a graph showing the complementary cumulative distribution function CCDF when the first transmission signal and the second transmission signal in the frequency band shown in FIG. 3 are combined in the communication apparatus 1 according to the first embodiment. . In the example shown in FIG. 4, the RF signal output from the amplifier 36 is indicated by Txout. In addition, the first transmission signal is OFDM1 and the second transmission signal is OFDM2. In addition, as a comparison target, an AWGN (Additive White Gaussian Noise) CCDF is shown.

  As shown in FIG. 4, by using the communication apparatus 1 according to the first embodiment, the CCDF of the RF signal Txout obtained by synthesizing the first transmission signal OFDM1 and the second transmission signal OFDM2 is greatly reduced compared to AWGN. You can see that

  On the other hand, FIG. 5 shows a graph showing the complementary cumulative distribution function CCDF when the peak suppression process is performed using the conventional peak suppression method as a comparative example with the output characteristics of the communication apparatus 1 according to the first embodiment. Here, the conventional peak suppression method is a method of performing synthesis processing and up-conversion processing after performing peak suppression processing only on each local signal.

  As shown in FIG. 5, in the conventional peak suppression method, CCDF is suppressed for individual OFDM signals. However, the CCDF of the RF signal Txout generated after combining these signals is less suppressed than the individual OFDM signal. That is, by using the communication device 1 according to the first embodiment, it is possible to efficiently suppress the peak power as compared with the communication device to which the conventional peak suppression method is applied.

Next, the distortion correction unit 31 will be described in detail. First, the influence of the delay time difference on the distortion characteristics due to the difference in the transmission path will be described. When there is no delay time difference between the two transmission paths from the output of the peak suppressor 30 to the amplifier 36, the RF signal Txout fed back to the predistortion unit 32 is a carrier wave applied in the upconverters 12 and 22. If the influence is ignored, it can be expressed by equation (11).

On the other hand, for example, when the fourth baseband signal TxBB22 has a delay by a delay time difference Δt compared to the third baseband signal TxBB12, the RF signal Txout is expressed by Expression (12).

  In the communication apparatus 1 according to the first embodiment, peak suppression is appropriately performed by combining the third baseband signal TxBB12 and the fourth baseband signal TxBB22 in a state expressed by the equation (11). However, when the RF signal Txout is in a state expressed by the equation (12), peak suppression is not performed correctly, and there is a problem that the peak power to average power ratio PAPR increases.

  Therefore, in the communication device 1 according to the first embodiment, the above problem is solved by using the distortion correction unit 31. The distortion correction unit 31 first compares the RF signal Txout with the third baseband signal TxBB12 and the fourth baseband signal TxBB22 output from the peak suppression unit 30 in the predistortion unit 32, and the RF signal Txout. The amount of distortion is calculated. Then, the predistortion unit 32 performs distortion compensation calculation by multiplying the third baseband signal TxBB12 and the fourth baseband signal TxBB22 by a distortion compensation coefficient generated according to the magnitude of the calculated distortion amount. In FIG. 1, TxBB13 and TxBB23 are attached as codes of the third baseband signal TxBB12 and the fourth baseband signal TxBB22 after the distortion compensation calculation.

  The predistortion unit 32 obtains a delay amount in the process of comparing the third baseband signal TxBB12 and the fourth baseband signal TxBB22 with the RF signal Txout, and has a value corresponding to the difference. 1 delay setting value DL1 and 2nd delay setting value DL2 are calculated.

  In the distortion correction unit 31, the subtractor 44 delays the third baseband signal TxBB12 according to the first delay setting value DL1, and the subtractor 45 delays the fourth baseband signal TxBB12 according to the second delay setting value DL2. The baseband signal TxBB22 is delayed. For example, when the third baseband signal TxBB12 is delayed by Δt compared to the fourth baseband signal TxBB22, a zero delay amount is set as the first delay setting value DL1, and the second delay setting value is set. A delay amount Δt is set as DL2. As a result, when the third baseband signal TxBB12 and the fourth baseband signal TxBB22 arrive at the synthesizer 35, the delay time difference between the signals becomes zero. That is, by eliminating the delay difference between the two signals, the signals are combined with a phase difference of zero, and the peak is appropriately suppressed.

  If the delay time between the two transmission paths for transmitting the baseband is known in advance, the delay time can be set in advance in the delay units 33 and 34 without using the predistortion unit 32. This eliminates the need to use the predistortion unit 32.

  From the above description, the communication apparatus 1 according to the first embodiment generates two transmission signals by converting the frequency of the two baseband signals into the frequency band of the RF signal by the up-converters 12 and 13, and generates two transmission signals. Is synthesized by the synthesizer 35 to generate an RF signal Txout, whereby an RF signal Txout including a transmission signal in a frequency band far away can be generated.

  In addition, the communication device 1 according to the first embodiment uses the peak suppression unit 30 to base the maximum power value Pmax of the transmission signal at the time when the phases of two carrier waves (local signals) used for baseband signal modulation match. The peak suppression process is performed on the baseband signal so that the maximum power value Pmax is calculated from the band signal and does not exceed the power threshold value Pth. Thereby, the communication apparatus 1 according to the first embodiment can reduce the peak power of the RF signal Txout and suppress the peak power to average power ratio PAPR.

  Further, the communication device 1 according to the first embodiment calculates the threshold power Pth from the average power value of the RF signal Txout generated from the baseband signal. Thereby, the communication apparatus 1 according to the first embodiment can adaptively change the power threshold Pth with respect to the change in the baseband signal sequence.

  In addition, the communication device 1 according to the first embodiment uses the distortion correction unit 31 to achieve a high peak suppression effect even when there is a difference in delay time between a plurality of transmission paths that transmit baseband signals. Can be maintained.

Embodiment 2
In the second embodiment, a communication device 2 that is another form of the communication device 1 according to the first embodiment will be described. FIG. 6 shows a block diagram of the communication device 2 according to the second embodiment. In the description of the second embodiment, the same components as those described in the first embodiment are denoted by the same reference numerals as those used in the first embodiment, and description thereof is omitted.

  As illustrated in FIG. 6, the communication device 2 according to the first embodiment is obtained by deleting the distortion correction unit 31 from the communication device 1 according to the first embodiment. That is, the communication device 2 according to the second embodiment is the same as the communication device 1 according to the first embodiment, in which the delay times of the delay unit 33 and the delay unit 34 of the distortion correction unit 31 are both zero.

  If there is no delay time difference between the transmission path of the third baseband signal TxBB12 and the transmission path of the fourth baseband signal TxBB22, or if it is negligible, the distortion correction unit 31 is not mounted. The communication device 2 according to the second embodiment may be used. Thereby, since the distortion correction unit 31 can be deleted, the communication device 2 can reduce the circuit area as compared with the communication device 1.

Embodiment 3
In the third embodiment, another form of the communication device 1 according to the first embodiment will be described. FIG. 7 shows a block diagram of the communication device 3 according to the third embodiment. In the description of the third embodiment, the same components as those described in the first embodiment are denoted by the same reference numerals as those used in the first embodiment, and description thereof is omitted.

  As illustrated in FIG. 7, the communication device 3 according to the third embodiment is obtained by deleting the distortion correction unit 31 from the communication device 1 according to the first embodiment and replacing the peak suppression unit 30 with a peak suppression unit 60. is there.

  The peak suppression unit 60 includes a first peak suppression unit 61 and a second peak suppression unit 62. The first peak suppressing unit 61 and the second peak suppressing unit 62 are connected in multiple stages. The first peak suppressor 61 and the second peak suppressor 62 have the same configuration as that of the peak suppressor 30, respectively. However, the first peak suppressor 61 and the second peak suppressor 62 are based on different values of the clipping coefficient and the weighting coefficient. A second suppression signal is generated. Note that the clipping coefficient and the weighting coefficient may have the same value in the first peak suppressing unit 61 and the second peak suppressing unit 62.

  As described above, since the peak suppression unit is connected in multiple stages, it is possible to suppress the peak power while suppressing the excessive subtraction in the clipping process, and thus it is possible to suppress the deterioration of the modulation accuracy EVM.

Embodiment 4
In the fourth embodiment, another form of the communication device 1 according to the first embodiment will be described. FIG. 8 shows a block diagram of the communication device 4 according to the fourth embodiment. In the description of the fourth embodiment, the same components as those described in the first embodiment are denoted by the same reference numerals as those used in the first embodiment, and description thereof is omitted.

  As illustrated in FIG. 8, the communication device 4 according to the fourth embodiment is obtained by deleting the distortion correction unit 31 from the communication device 1 according to the first embodiment and replacing the peak suppression unit 30 with a peak suppression unit 70. is there.

  The peak suppression unit 70 includes a clipping processing unit 71 and filters 42 and 43. The clipping processing unit 71 generates the third baseband signal TxBB12 and the fourth baseband signal TxBB22 having the same peak suppression effect without performing the subtraction processing used in the peak suppression unit 30 of the first embodiment. A detailed block diagram of the clipping processing unit 71 is shown in FIG. In FIG. 9, filters 42 and 43 associated with the clipping processing unit 71 are also illustrated.

  As illustrated in FIG. 9, the clipping processing unit 71 includes a phase coincidence power calculation unit 51, a threshold power calculation unit 52, a power determination unit 53, a signal level suppression unit 72, and a signal passage unit 73. Here, since the phase coincidence power calculation unit 51, the threshold power calculation unit 52, and the power determination unit 53 have been described in the first embodiment, description thereof is omitted here.

  The signal level suppression unit 72 operates based on the first enable signal EN1 that is enabled when the maximum power value Pmax is larger than the power threshold value Pth. The signal level suppression unit 72 generates first and second suppression signals in the block, and uses the first and second suppression signals, the maximum power value Pmax, and the power threshold value Pth to generate the third suppression signal. A baseband signal TxBB12 and a fourth baseband signal TxBB22 are generated.

そして、信号レベル抑圧部７２は、第１の抑制信号Ｉ１と第２の抑制信号Ｉ２とを用いて第３のベースバンド信号ＴｘＢＢ１２及び第４のベースバンド信号ＴｘＢＢ２２を生成する。この第３のベースバンド信号ＴｘＢＢ１２は（１５）式で表され、第４のベースバンド信号ＴｘＢＢ２２は（１６）式で表される。

More specifically, the signal level suppression unit 72 generates a value expressed by the equation (13) as the first suppression signal I1, and generates a value expressed by the equation (14) as the second suppression signal I2. .

Then, the signal level suppression unit 72 generates the third baseband signal TxBB12 and the fourth baseband signal TxBB22 using the first suppression signal I1 and the second suppression signal I2. The third baseband signal TxBB12 is expressed by equation (15), and the fourth baseband signal TxBB22 is expressed by equation (16).

The signal passing unit 73 operates based on the second enable signal EN2 that is enabled when the maximum power value Pmax is less than or equal to the power threshold value Pth. The signal passing unit 73 outputs the input first baseband signal TxBB11 and second baseband signal TxBB21 as they are as the third baseband signal TxBB12 and the fourth baseband signal TxBB22. That is, the third baseband signal TxBB12 and the fourth baseband signal TxBB22 output from the signal passing unit 73 are expressed by Expressions (17) and (18).

  From the above description, in the fourth embodiment, the peak suppression unit 70 can output a signal equivalent to the signal output by the peak suppression unit 30. That is, also in the communication device 4 according to the fourth embodiment, a high peak suppression effect can be obtained with respect to the RF signal Txout including the transmission signal in a frequency band separated from the communication device 1 according to the first embodiment.

  Further, in the communication device 4 according to the fourth embodiment, since it is not necessary to perform subtraction processing in the peak suppression unit, the circuit scale and the processing time can be reduced compared to the communication device 1 according to the first embodiment. be able to.

  In the above embodiment, the description has been made with respect to an OFDM signal as a transmission signal. However, the present invention is not limited to OFDM modulation, and may be used in other modulation schemes such as W-CDMA and SD-FDMA. Can do. That is, by using the present invention, it is possible to generate a high-quality RF signal not only in multi-channel communication but also in multi-standard communication.

  Although the invention made by the present inventor has been specifically described based on the embodiments, the present invention is not limited to the embodiments already described, and various modifications can be made without departing from the scope of the invention. It goes without saying that it is possible.

  This application claims the priority on the basis of Japanese application Japanese Patent Application No. 2013-052873 for which it applied on March 15, 2013, and takes in those the indications of all here.

1-4 Communication device 10, 20 OFDM baseband signal generation unit 11, 21 Digital analog converter 12, 22 Up converter 30, 60, 61, 62, 70 Peak suppression unit 31 Distortion correction unit 32 Predistortion unit 33, 34 Delay Unit 35 synthesizer 36 amplifier 37 directional coupler 41 tone signal generation unit 42, 43 filter 44, 45 subtractor 51 phase coincidence power calculation unit 52 threshold power calculation unit 53 power determination unit 54 impulse signal generator 55 zero signal generation 71 Clipping processing unit 72 Signal level suppression unit 73 Signal passing unit TxBB11, TxBB12, TxBB13 Baseband signals TxBB21, TxBB22, TxBB23 Baseband signals DL1, DL2 Delay setting value Pmax Maximum power value Pth Power threshold value EN1, N1 enable signal I1, I2 impulse signal

Claims (12)

Peak suppression means for performing peak suppression processing on the first baseband signal and the second baseband signal and outputting a third baseband signal and a fourth baseband signal;
First digital-to-analog conversion means for converting the third baseband signal into an analog signal;
Second digital-analog conversion means for converting the fourth baseband signal into an analog signal;
First frequency conversion means for converting a frequency of the third baseband signal output from the first digital-analog conversion means to a frequency of a first carrier wave and outputting a first transmission signal;
The frequency of the fourth baseband signal output from the second digital-analog conversion means is converted to the frequency of a second carrier belonging to a frequency band different from the first carrier, and the second transmission signal is converted. Second frequency converting means for outputting;
Combining means for combining the first transmission signal and the second transmission signal to output a third transmission signal;
Amplifying means for amplifying the third transmission signal and outputting an output signal;
Provided in a stage subsequent to the peak suppression means, and compares the third baseband signal and the fourth baseband signal with the output signal to calculate a distortion amount of the output signal, and calculates the distortion amount. Distortion correction means for performing distortion compensation processing on the third baseband signal and the fourth baseband signal so as to reduce ,
The peak suppression means includes
Of the combined signal of the first baseband signal and the second baseband signal, the power of the combined signal when the phase of the first carrier coincides with the phase of the second carrier is the maximum power value. As
Generating a first suppression signal and a second suppression signal having non-zero values when the maximum power value is greater than a power threshold;
Reflecting the value of the first suppression signal to the first baseband signal to generate the third baseband signal;
Generating the fourth baseband signal reflecting the value of the second suppression signal in the second baseband signal ;
The distortion correction means includes
The distortion amount of the output signal is calculated, the third baseband signal and the fourth baseband signal are multiplied by a distortion compensation coefficient generated according to the magnitude of the distortion amount, and the first The difference in delay amount generated between the two baseband signals from when the baseband signal and the second baseband signal are input to the distortion correction means until the third transmission signal reaches the amplification means. Predistortion means for outputting a first delay setting value and a second delay setting value having corresponding values;
First delay means for delaying the third baseband signal in accordance with the first delay setting value;
And a second delay means for delaying the fourth baseband signal in accordance with the second delay setting value . The peak suppression means includes
An average power value in a predetermined period of the synthesized signal obtained by synthesizing the first baseband signal and the second baseband signal is calculated, and the average power value is multiplied by a preset clipping coefficient to obtain the power The communication apparatus according to claim 1, wherein the threshold value is calculated. The peak suppression means includes
An impulse signal having a magnitude calculated based on the maximum power value, the power threshold, and the weighting factor as the first suppression signal and the second suppression signal when the maximum power value is larger than the power threshold. Impulse signal generating means for generating
The zero signal generation means for generating a zero signal having a value of zero as the first suppression signal and the second suppression signal when the maximum power value is equal to or less than the power threshold. Communication equipment. The peak suppression means includes
First subtracting means for subtracting the first suppression signal from the first baseband signal to generate the third baseband signal;
Second subtracting means for subtracting the second suppression signal from the second baseband signal to generate the fourth baseband signal;
The communication device according to claim 3, further comprising: The peak suppression means includes a first peak suppression means and a second peak suppression means,
4. The first peak suppression unit and the second peak suppression unit generate the first suppression signal and the second suppression signal based on the clipping coefficient and the weighting coefficient having different values. Or the communication apparatus of 4. Wherein the first carrier and the second carrier, the communication device according to any one of claims 1 to 5 having a frequency belonging to the frequency band in which the frequency allocation is different. Peak suppression means for performing peak suppression processing on the first baseband signal and the second baseband signal and outputting a third baseband signal and a fourth baseband signal;
First digital-to-analog conversion means for converting the third baseband signal into an analog signal;
Second digital-analog conversion means for converting the fourth baseband signal into an analog signal;
First frequency conversion means for converting a frequency of the first baseband signal output from the first digital-analog conversion means to a frequency of a first carrier wave and outputting a first transmission signal;
The frequency of the second baseband signal output from the second digital-analog conversion means is converted to the frequency of a second carrier belonging to a frequency band different from the first carrier, and the second transmission signal is converted. Second frequency converting means for outputting;
Combining means for combining the first transmission signal and the second transmission signal to output a third transmission signal;
Amplifying means for amplifying the third transmission signal and outputting an output signal;
The third baseband signal is calculated by comparing the third baseband signal and the fourth baseband signal with the output signal to calculate a distortion amount of the output signal, and to reduce the distortion amount. A distortion correction processing means for performing distortion compensation processing on a signal and the fourth baseband signal, and a peak suppression method in a communication apparatus,
In the peak suppression means,
Of the combined signal of the first baseband signal and the second baseband signal, the power of the combined signal when the phase of the first carrier coincides with the phase of the second carrier is set as the maximum power value. Calculate
Calculating a first suppression signal for reducing the power of the first baseband signal and a second suppression signal for reducing the second baseband signal when the maximum power value is greater than a power threshold;
Reflecting the first suppression signal to the first baseband signal to generate the third baseband signal;
Reflecting the second suppression signal to the second baseband signal to generate the fourth baseband signal ;
In the distortion correction process,
Calculating the amount of distortion of the output signal;
Multiplying the third baseband signal and the fourth baseband signal by a distortion compensation coefficient generated according to the magnitude of the distortion amount;
A delay amount generated between two baseband signals from when the first baseband signal and the second baseband signal are input to the distortion correction unit until the third transmission signal reaches the amplification unit. Output a first delay setting value and a second delay setting value according to the difference between
Delaying the third baseband signal according to the first delay setting value;
A peak suppression method for delaying the fourth baseband signal in accordance with the second delay setting value . In the peak suppression means,
An average power value in a predetermined period of the synthesized signal obtained by synthesizing the first baseband signal and the second baseband signal is calculated, and the average power value is multiplied by a preset clipping coefficient to obtain the power The peak suppression method according to claim 7 , wherein the threshold value is calculated. In the peak suppression means,
An impulse signal having a magnitude calculated based on the maximum power value, the power threshold, and the weighting factor as the first suppression signal and the second suppression signal when the maximum power value is larger than the power threshold. Produces
The peak suppression method according to claim 8 , wherein when the maximum power value is equal to or less than the power threshold, a zero signal having a value of zero is generated as the first suppression signal and the second suppression signal. In the peak suppression means,
Subtracting the first suppression signal from the first baseband signal to generate the third baseband signal;
The peak suppression method according to claim 9 , wherein the fourth baseband signal is generated by subtracting the second suppression signal from the second baseband signal. The peak suppression means performs a first peak suppression process and a second peak suppression process,
In the second peak suppression processing and the first peak suppression processing, claim 9 for generating and the clipping coefficient and said second suppression signal and said first suppression signal based on said weight coefficient for different values Or the peak suppression method of 10 . The peak suppression method according to any one of claims 7 to 11 , wherein the first carrier wave and the second carrier wave have frequencies belonging to frequency bands having different frequency assignments.

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