JP4947144B2 - Power amplification control device - Google Patents

Description

  The present invention relates to a power amplification control device that compensates for distortion generated in a power amplifier.

  In wireless communication such as a mobile communication system, high-speed and large-capacity transmission by digitalization has been adopted, and wireless broadband is becoming a reality. Conventional wireless communication uses a fixed multi-level phase modulation method, linearizes the amplification characteristics of the power amplifier on the transmission side to suppress nonlinear distortion, reduces adjacent channel leakage power, and uses an amplifier with poor linearity. Distortion compensation was performed in order to improve power efficiency.

  However, in recent years, further improvements in power amplifier efficiency, expansion of the frequency band used, and wireless communication technology using various multi-level phase modulation schemes have been considered, and sufficient characteristics for diversified wireless communication, The effect is no longer obtained.

  FIG. 1 is a block diagram showing an example of a conventional power amplification control device. This apparatus is provided in a base station of a mobile communication system, for example.

  In the figure, a transmission signal generator 1 outputs a serial digital data string, and a serial / parallel converter (S / P) 2 converts the digital data string into a parallel string of I and Q signals.

  The distortion compensator 3 has one type of LUT (Look up Table) that is referred to by the amplitude of the I signal and the Q signal and the time variation of the amplitude. The distortion compensator 3 uses the compensation data read from the LUT and the I and Q signals fed back from the A / D converter 13 to use the DPD (Digital Pre) of the I and Q signals supplied from the parallel converter 2. -Distortion) processing. Thus, the distortion-compensated I signal and Q signal are converted into analog signals by the D / A converter 4 and supplied to the quadrature modulator 5.

  The quadrature modulator 5 multiplies the supplied I signal and Q signal by the reference carrier wave from the oscillator 6 and the 90 ° phase-shifted carrier wave and adds them, and outputs the result. The frequency converter 7 mixes the quadrature modulation signal and the local oscillation signal, converts the signal to a radio frequency, and supplies it to a power amplifier (PA) 8. The power amplifier 8 amplifies the radio frequency signal and transmits it from an antenna (antenna) 9.

  A directional coupler 10 provided between the power amplifier 8 and the antenna 9 branches a part of the radio frequency signal and supplies it to the frequency converter 11. The frequency converter 11 converts the radio frequency signal into a quadrature modulation signal, and the quadrature detector 12 performs quadrature demodulation of the baseband signal by multiplying by using the reference carrier wave from the oscillator 6 and the 90 ° phase shift carrier wave, Converts to analog I signal and Q signal. The A / D converter 13 performs analog / digital conversion of the analog I signal and the Q signal and supplies the analog I signal and the Q signal to the distortion compensator 3.

  When the transmission signal is transmitted at a high output in the configuration without the distortion compensator 3, the input / output characteristics of the power amplifier 8 are non-linear, and therefore nonlinear distortion occurs due to the non-linear characteristics. For this reason, the spectrum of the amplification channel spreads, and radio waves leak to the adjacent channels, and the ACLR (Adjacent Channel Leakage power Ratio) deteriorates.

  Therefore, the distortion compensator 3 performs digital predistortion processing, performs distortion compensation of transmission power, and compensates the transmission signal so as to obtain high output and good characteristics.

  In Patent Document 1, when the input signal level is detected and the signal level is low, the power amplifier is bias-controlled so as to satisfy the distortion condition generated by the amplifier, thereby reducing the power consumption. It is described.

  Patent Document 2 describes that the bias value of the power amplifier is optimized and reduced in accordance with the number of multi-values and different maximum transmission power by switching the modulation method or changing the common amplified wave number. Yes.

Further, Patent Document 3 describes that the bias value is adaptively controlled by extracting the distortion component included in the FB signal from the transmission carrier instead of extracting the modulation information on the input side. .
JP 2003-258563 A JP 2001-244828 A JP 2001-160718 A

  The conventional apparatus can operate effectively in wireless communication to which one kind of multi-level phase modulation method such as 16QAM is applied.

  However, in wireless communication to which various multilevel phase modulation methods such as QPSK, 16QAM, and 64QAM are applied, such as WiMAX (Worldwide Interoperability for Microwave Access), it is extremely difficult to increase the efficiency of the power amplifier. In addition, it is difficult to sufficiently cope with wireless communication using half duplex communication / full duplex communication such as TDD (Time Division Duplex) / FDD (Frequency Division Duplex), and sufficient characteristics and There was a problem that the effect could not be obtained.

  The present invention has been made in view of the above points, and it is possible to improve the efficiency of a power amplifier by various multi-level phase modulation schemes, and to provide a power amplification control apparatus that can cope with time-division simultaneous transmission / reception. Purpose.

To this end, the power amplifier control device of the present invention compensates for the distortion generated by the power amplifier when the radio transmission with power amplification have rows of a plurality of types of multi-level phase modulation at the transmission digital data sequence A power amplification control device having compensation means, a table unit having a plurality of types of tables storing compensation data in advance corresponding to the type of the multi-level phase modulation, and a multi-level in symbol units from the transmission digital data sequence Detection means for detecting multi-level phase modulation information indicating the type of phase modulation; and table switching means for selecting one of a plurality of types of tables in the table unit based on the multi-level phase modulation information detected by the detection means; And reading compensation data from the selected table to compensate for distortion generated in the power amplifier, and the table switching means includes multi-level phase modulation information. One of the time to indicate that the type of multi-level phase modulation is present different bursts in the symbol, select the most multilevel a phase modulation multilevel phase modulation table.

  According to such a power amplification control device, it is possible to increase the efficiency of the power amplifier by various multi-level phase modulation methods, and it is possible to cope with time division simultaneous transmission / reception.

It is a block block diagram of an example of the conventional power amplification control apparatus. It is a block block diagram of one Embodiment of the power amplification control apparatus of this invention. It is a figure which shows one Embodiment of a WiMAX frame format. It is a figure which shows the relationship between the multi-value phase modulation in a symbol unit, a gate voltage, and a transmission output.

Explanation of symbols

DESCRIPTION OF SYMBOLS 21 Transmission signal generator 22 Serial / parallel converter 23 DLMAP detection part 24 Address generation part 25 DPD process part 26,27,28 Switching part 30 D / A converter 31 Quadrature modulator 32 Oscillator 33,41 Frequency converter 34 Power Amplifier 35 Gate control unit 36 Directional coupler 37 Antenna 42 Quadrature detector 43 A / D converter 231 Modulation estimation unit 251 LUT unit 252 Distortion compensation unit

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

<Configuration of power amplification control device>
FIG. 2 shows a block diagram of an embodiment of the power amplification control device of the present invention. This apparatus is provided in a base station of a mobile communication system, for example.

  In the figure, a transmission signal generator 21 sends out a serial data string of, for example, a WiMAX (Worldwide Interoperability for Microwave Access) frame. The serial / parallel converter (S / P) 22 converts the serial data string into a parallel data string of I and Q signals.

  The DLMAP detection unit 23 detects multi-level phase modulation information of transmission signals and DLMAP (Down Link Map) information which is time ratio information from the parallel data sequence, and performs switching control of each of the switching units 26, 27, 28 to perform DPD. The LUT (Look up Table) of the processing unit 25 is switched. The address generation unit 24 generates a LUT (Look Up Table) reference address of the DPD processing unit 25 from the parallel data strings of the I signal and the Q signal.

  The DPD processing unit 25 includes an LUT unit 251 having a plurality of LUTs corresponding to various multi-level phase modulation schemes, and a distortion compensation unit 252, and the distortion compensation unit 252 is read from one LTU of the LUT unit 251. Using the compensation data and the I and Q signals fed back from the switching unit 28, DPD processing (digital predistortion) of the I and Q signals supplied from the switching unit 26 is performed.

  The D / A converter 30 performs digital / analog conversion of the I and Q signals subjected to the DPD process. The quadrature modulator 31 performs quadrature modulation that multiplies the analog I signal and Q signal by the reference carrier wave from the oscillator 32 and the 90 ° phase-shifted carrier wave and adds them to each other to convert the signal to a baseband signal.

  The frequency converter 33 mixes the quadrature modulation signal and the local oscillation signal and converts them to a radio frequency. The power amplifier (PA) 34 performs power amplification of the radio frequency signal. The gate control unit 35 performs gain control of the power amplifier 34 by changing the gate voltage of the power amplifier 34 based on the multilevel phase modulation information from the DLMAP detection unit 23. The power-amplified radio frequency signal output from the power amplifier 34 is radiated from an antenna (antenna) 37 into the air.

  A directional coupler 36 provided between the power amplifier 34 and the antenna 37 branches a part of the radio frequency signal output from the power amplifier 34 and supplies it to the frequency converter 41. The frequency converter 41 mixes the radio frequency signal and the local oscillation signal and converts them into an orthogonal modulation signal.

  The quadrature detector 42 performs quadrature demodulation of the baseband signal by multiplication using the reference carrier wave from the oscillator 32 and the 90 ° phase-shifted carrier wave, and converts it into analog I signal and Q signal. The A / D converter 43 performs analog / digital conversion of the analog I signal and Q signal, and supplies the analog I signal and Q signal to the distortion compensation unit 252 in the DPD processing unit 25 from the switching unit 28.

<Detailed operation of each part>
Next, the detailed operation of each unit will be described.

  The DLMAP detection unit 23 extracts DLMAP information from the parallel data string, and detects multi-level phase modulation information in symbol units and the time ratio between downlink and uplink in frame time units.

  By the way, when the DLMAP detection unit 23 cannot read the set value from the DLMAP information, the modulation estimation unit 231 built in the DLMAP detection unit 23 performs the discrete fast Fourier transform of the baseband signal output from the quadrature modulator 31. Then, the amplitude of the subcarrier is detected in each symbol, and the used multilevel phase modulation scheme is estimated.

  The transmission frame format in WiMAX wireless communication is defined by IEEE 802.16d and IEEE 802.16e, and DLMAP information is included in the symbol data of the second symbol. This information includes a downlink burst profile, and the DLMAP information can know the time ratio between the downlink and the uplink of the transmission signal and the details thereof.

<WiMAX frame format>
FIG. 3 shows an embodiment of a frame format for WiMAX (Worldwide Interoperability for Microwave Access) wireless communication. In the figure, the horizontal axis represents time, and the vertical axis represents carriers (subchannels).

  A preamble that is a synchronization pattern is arranged in the first symbol k of the downlink (DL), DLMAP information is arranged in the second symbol k + 1, and a plurality of downlink bursts are arranged in the subsequent 3rd symbol k + 2 to 16th symbol k + 15 Has been. In the uplink (UL), a plurality of uplink bursts are arranged from the 18th symbol k + 17 to the 27th symbol k + 26.

  In the present embodiment, multilevel phase modulation information in symbol data units is determined based on DLMAP information, and the digital I signal and Q signal are supplied by switching to an LUT corresponding to the multilevel phase modulation information in symbol units.

  The address generation unit 24 generates a reference address for the LUT. The address generation unit 24 generates an address using the amplitudes of the conventional I and Q signals and their temporal changes as variables, and then adds the phase change information as a variable to generate the addresses. Do.

  The LUT unit 251 of the DPD processing unit 25 has an LUT in each of the pre-frame stage and the post-frame stage corresponding to the elapsed time from the start of downlink transmission for each of multilevel phase modulation such as QPSK, 16QAM, and 64QAM. Each LUT uses the amplitude of the I signal and Q signal, the time change of the amplitude of the I signal and Q signal (amplitude change information), and the time change of the phase of the I signal and Q signal (phase change information) as variables. It is a three-dimensional table. Further, a plurality of LUTs provided for each of the pre-frame and post-frame for each of the multi-level phase modulations are provided with a first working surface and a second spare surface.

  Compensation data corresponding to the input I-signal, Q-signal amplitude, amplitude change over time, and phase change over time is read out from the LUT switched according to the multi-level phase modulation information and the preceding and following stages of the frame. The distortion compensation unit 252 is supplied.

  The distortion compensation unit 252 obtains a difference between the I signal and Q signal supplied from the switching unit 26 and the I signal and Q signal supplied from the switching unit 28, and the I signal and Q signal supplied from the switching unit 26 The I signal from the switching unit 26 is obtained by multiplying the compensation data read out from the LUT switched according to the multi-level phase modulation information and the preceding and following stages of the frame by the compensation coefficient generated so as to minimize the difference. , Q signals are compensated and supplied to the switching unit 27, and the contents of the LUT are updated so as to constantly correct the difference. The distortion compensation unit 252 multiplies the compensation data to perform DPD processing of the I signal and Q signal from the switching unit 26 and performs distortion compensation processing including peak suppression processing according to each multi-level phase modulation method. . This processing enables optimum distortion compensation in symbol data units.

  Here, when a plurality of bursts having different multilevel phase modulations are mixed in one symbol data, it is difficult to deal with all the multilevel phase modulations in one symbol data due to factors such as an increase in the number of combinations. Therefore, the most multilevel phase modulation information is assigned to the symbol data. This allocation is performed by the DLMAP detection unit 23. For example, when there is a 16QAM burst and a 64QAM burst in one symbol data, a distortion compensation process including a peak suppression process is performed using a 64QAM LUT.

  This is because by giving priority to the most multi-level phase modulation information in one symbol data, it becomes possible to perform extremely good and large-capacity transmission to a relay station, a terminal, or the like that is a reception destination.

  In this embodiment, each LUT corresponding to the above-described multilevel phase modulation information is a frame in which the elapsed time from the start of downlink transmission is short (first to mth symbols, m is an integer of about 3 to 5, for example). The configuration is divided into a pre-stage LUT and a post-frame LUT after that (m-th to n-th symbols, n is the last symbol number of the downlink). In accordance with the elapsed time from the start of downlink transmission of the frame, the LUT (front frame / back frame) combined with the multi-level phase modulation method is instantaneously switched to perform distortion compensation processing including peak suppression processing.

  This is because the preamble of the first symbol of the downlink is at a higher level than the other symbols of the downlink, so that the peak suppression control is performed between the symbol at the preceding stage of the frame near the preamble and the latter stage of the other frames. This is to cope with different compensation data.

  When performing half-duplex communication / full-duplex communication such as TDD / FDD, imperfections peculiar to TDD occur in the transmission-side analog unit at the start of transmission. This imperfection is mainly caused by the transient response of the power supply system of the power amplifier 34. Since the power supply system of the power amplifier (PA) cannot follow the current fluctuation due to the transient response of the power supply system, immediately after starting transmission. Will be distorted.

  The pre-frame LUT is an LUT corresponding to the transient response time, and mainly includes an overshoot correction element. The post-frame LUT is an LUT corresponding to the time after the transient response is stabilized. By using the LUT having these two time elements, it is possible to configure the LUT unit 251 corresponding to the multi-level phase modulation method and corresponding to the time response.

  The address generator 24 generates an address by adding phase change information to the amplitude and amplitude change information of the I signal and Q signal, and adds an element of phase change information to the three-dimensional LUT. Therefore, it is possible to adapt to signals having different frequency components without switching the LUT.

  Further, the LUT unit 251 has a two-surface configuration to avoid table destruction due to a device failure, and the first surface is used as an active LUT and the second surface is used as a spare LUT. As described above, the distortion compensation unit 252 obtains a difference between the I signal and Q signal supplied from the switching unit 26 and the I signal and Q signal supplied from the switching unit 28, and minimizes the difference. The contents of the LUT (LUT corresponding to the multi-level phase modulation information and the elapsed time from the start of downlink transmission) of the working LUT on the first surface are constantly updated.

  Further, the distortion compensation unit 252 periodically copies the contents (previous value) of the first side active LUT to the second side spare LUT and updates the second side spare LUT.

  With such a configuration, it is possible to suppress unnecessary wave transmission output by switching to the second-side spare LUT when the table on the first-side active LUT is destroyed due to a failure.

  Note that if table destruction occurs in a conventional one-surface LUT, it is necessary to initialize the LUT, and a transient unnecessary wave transmission signal is output until the table update converges. With the two-plane configuration according to the present invention, even when a table breaks down, it is possible to suppress unnecessary waves due to table breaking and transient unnecessary wave transmission until table convergence by switching to the backup surface instantly. It is. Moreover, since the table update is performed from the LUT (previous value) on the second surface, the convergence time of the table update on the first surface can be shortened, and the transient unnecessary wave transmission output until the table generation is completed can also be reduced. .

  Next, the gate control unit 35 sets the gate voltage of the power amplifier 34 based on the multilevel phase modulation information in units of symbols from the DLMAP detection unit 23 and the time ratio between the downlink and the uplink in units of frame time. By changing the gain, the gain of the power amplifier 34 is controlled.

  FIG. 4 shows the relationship among multilevel phase modulation, gate voltage, and transmission output in symbol units. For the WiMAX frame shown in FIG. 4 (A), the DLMAP information represents the multi-level phase modulation of each symbol of the downlink burst shown in FIG. 4 (B). The LUT is switched according to the multilevel phase modulation information shown. In FIG. 4B, the fifth symbol indicates that there is a 64QAM burst and a 16QAM burst, and in FIG. 4C, the fifth symbol is switched to 64QAM, which is the most multilevel phase modulation information. ing.

  In accordance with the multi-level phase modulation shown in FIG. 4C, the peak suppression threshold changes as shown in FIG. That is, the peak suppression threshold for BPSK of the first symbol is adB, the peak suppression threshold for QPSK of the second symbol is b dB (b ≧ a), and the peak suppression threshold for 16QAM of the third and nth symbols is c dB ( c> b), and the peak suppression threshold for 64QAM of the fourth and fifth symbols is d dB (d> c).

  FIG. 4E shows the gate voltage of the power amplifier 34 controlled by the gate control unit 35 in accordance with the change in the peak suppression threshold corresponding to the above multi-level phase modulation.

  In accordance with the change in the gate voltage shown in FIG. 4E, the average output power of the transmission power of the power amplifier 34 changes as shown by the broken line in FIG. Here, the higher the gate voltage, the higher the average output power of the transmission power. As a result, the maximum output power of the transmission power is controlled to be constant as shown by the solid line in FIG.

  In this way, by controlling the gate voltage of the power amplifier 34 according to the multilevel phase modulation information, the maximum output power of the transmission power can be made constant even if the multilevel phase modulation changes, and PAPR (Peak To Average Power Ratio (average power / instantaneous maximum power ratio) can be effectively used as the transmission capacity of the power amplifier 34. In addition, it is possible to correct the characteristics of the power amplifier 34 having different nonlinear distortions within a certain range by the above gain control.

  The gain control according to the multilevel phase modulation information is performed in symbol units, and at the same time, peak suppression processing is performed using the LUT according to the multilevel phase modulation information. By performing these two processes simultaneously, the operating point of the power amplifier 34 can be varied, and the power amplifier 34 can also output a multilevel phase modulation transmission signal with sufficient ACLR characteristics and EVM characteristics. It becomes possible. The EVM (Error Vector Magnet) is a ratio of the theoretical amplitude and phase of the carrier corresponding to the value of the digital data to the average of the actual amplitude and phase difference (modulation error) to the maximum carrier amplitude.

  In the above embodiment, the LUT unit 251 is used as an example of the table unit, the DLMAP detection unit 23 is used as an example of the detection unit, the switching units 26, 27, and 28 are used as an example of the selection unit and the table switching unit, The modulation estimation unit 231 is used as an example, and the gate control unit 35 is used as an example of gain control means.

Claims (6)

A power amplification control apparatus having compensation means for compensating for distortion generated in a power amplifier when performing wireless transmission by performing a plurality of types of multi-level phase modulation in a transmission digital data string,
A table unit having a plurality of types of tables in which compensation data is stored in advance corresponding to the types of the multi-level phase modulation;
Detecting means for detecting multilevel phase modulation information indicating the type of multilevel phase modulation in symbol units from the transmission digital data sequence;
Table switching means for selecting one of a plurality of types of tables in the table unit based on the multilevel phase modulation information detected by the detection means;
Read compensation data from the selected table to compensate for distortion generated in the power amplifier,
The table switching means selects the multi-level phase modulation table of the most multi-level phase modulation when the multi-level phase modulation information indicates that there are a plurality of bursts having different types of multi-level phase modulation in one symbol. A power amplification control device. The power amplification control device according to claim 1 ,
The said table part has a some table according to the elapsed time from the downlink transmission start of a flame | frame for every kind of multi-level phase modulation, The power amplification control apparatus characterized by the above-mentioned. In the power amplification control device according to claim 2 ,
The power amplification control apparatus according to claim 1, wherein the table unit has a two-surface configuration of an active table and a spare table. The power amplification control device according to any one of claims 1 to 3 ,
The plurality of types of tables in the table section are three-dimensional tables storing compensation data corresponding to the amplitude of the I signal and the Q signal obtained from the transmission digital data sequence, the temporal change in amplitude, and the temporal change in phase. A characteristic power amplification control device. The power amplification control device according to claim 4 , wherein
The power amplification control apparatus, wherein the compensation means performs distortion compensation including peak suppression by multiplying the I signal and Q signal by compensation data read from the three-dimensional table. The power amplification control device according to claim 1 ,
The detection means has an estimation means for estimating multi-level phase modulation information from a baseband signal obtained by multi-level phase modulation when multi-level phase modulation information cannot be detected from the transmission digital data sequence. Amplification control device.

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