JP2005130051A - Method and apparatus transmission power control - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a transmission power control means capable of reducing the load of a distortion correcting circuit in digital processing, and coping with transmission power control by a comparatively inexpensive DSP. <P>SOLUTION: The symbol (VM_I_SYM/VM_Q_SYM) of an input digital signal (VM_I/VM_Q), before distortion correction, and the symbol (VD_I_SYM/VD_Q_SYM) of an input digital signal (VD_I/VD_Q) after distortion correction are extracted, and an operation of VD_I_SYM^2+VD_Q_SYM^2 and VD_I_SYM^2+VD_Q_SYM^2 from the extracted symbols to obtain power VM_P and VD_P in the symbols, and the difference between VM_P-VD_P is calculated, to obtain the difference in power. A multiplying factor, corresponding to this difference in power, is set in a multiplier 10, and a signal obtained by multiplying a multiplying factor set in the input digital signal (VD_I/VD_Q), after the distortion correction by the set multiplying factor, is outputted as a digital signal for demodulation. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a transmission power control method and apparatus in a digital modulation radio communication system.

  In a digital modulation type radio communication system, it is required to output stable transmission power. For this reason, the transmission power in such a digital radio system is determined within a guaranteed temperature range. However, semiconductors that gain gains such as operational amplifiers, FETs, transistors, etc. inevitably vary depending on temperature conditions, so a control circuit for controlling the power to be constant is mounted.

  On the other hand, a base station in a digital wireless system is provided with a device that performs high power transmission, and a transmission amplifier for obtaining a large gain is used to transmit large power. Gain fluctuation due to waveform distortion, environmental change, and secular change will occur. Since both have legal restrictions, control is usually performed regardless of analog or digital means.

  For example, in Patent Document 1, a control signal that compensates for a non-linear distortion (AM-AM conversion distortion, AM-PM conversion distortion) component generated by a subsequent high-frequency transmission power amplifier is written to Ich and Qch input digital signals. A digital filter having a ROM, and feeding back a part of the output of the high-frequency power amplifier to the digital filter as a control signal, and reading out the ROM according to the feedback information. A predistortion type transmission apparatus configured to output a signal that compensates for nonlinear distortion occurring in a certain region within a dynamic range is described.

  The distortion correction circuit may be performed by an analog circuit such as a Cartesian loop or may be performed digitally by a DSP (digital signal processor) such as a predistorter. I have to.

  FIG. 5 is a block diagram showing an example of a transmission apparatus equipped with a DSP (digital signal processor) such as a conventional predistorter and mounted with a circuit for correcting distortion by digital processing.

  In FIG. 5, the data to be transmitted is input to the QPSK mapping unit (51) to generate a MAP_I / MAP_Q signal, and the signal VM_I / VM_Q is generated after waveform shaping by the filter (52). This signal is input to the distortion correction circuit (53). Feedback data FB_I / FB_Q distorted by the amplifier (56) is also input to the distortion correction circuit (53), and the distortion of the amplifier (56) is compared by comparing the reference VM_I / VM_Q with the distorted FB_I / FB_Q. Analyze and apply inverse distortion to compensate for distortion in amplifier (56). The output is VD_I / VD_Q.

  The VM_I / VM_Q signal output from the filter (52) is a reference signal without distortion. In contrast, the signal distorted by the amplifier (56) is extracted as an FB_I / FB_Q signal by the coupler (58), the quadrature demodulator (59), and the AD converter (60). These signals are input to the distortion correction circuit (53).

  The distortion correction circuit (53) has the configuration shown in FIG. 3, and the distortion of the amplifier (56) is analyzed by accurately comparing VM_I / VM_Q and FB_I / FB_Q. FB_I / FB_Q is an analog circuit. And an absolute delay such as a conversion time of an AD converter or the like occurs. Therefore, the delay circuit (31) delays VM_I / VM_Q to adjust the phase to FB_I / FB_Q. The table address calculation unit (32) calculates the power of the VM_I / VM_Q signal data at that time, and assigns the table numbers divided into the tables corresponding to the power as shown in FIG.

  For example, in the case of having a table as shown in FIG. 4, when the power calculated from VM_I / VM_Q is calculated in the time sequence, the first result of power (VM_P) is “21”, so the table number is “ 2 "is added. Since the next power is “10”, the table number is “2”, and the next is “5”, so the table number is “1”.

  On the other hand, the error calculation processing unit (33) compares VM_I / VM_Q and FB_I / FB_Q to calculate an error, and stores this error in each number group of the table number calculated by the table address calculation unit (32). To do. The error averaging processor 34 averages the errors stored in each table number. The distortion of the amplifier usually has an AM-AM characteristic and an AM-PM characteristic, and this error average is a combination of the AM-AM characteristic and the AM-PM characteristic.

  The inverse distortion characteristics are calculated by the AM-AM characteristics LUT (Look Up Table) calculating section (35-1) and the AM-PM characteristics LUT (Look Up Table) calculating section (35-2). The fact that the LUT is a characteristic for each table number means a characteristic for the magnitude of power. The inverse distortion of the amplifier is output by performing a complex operation on the LUT with VM_I / VM_Q by the complex operation unit (6).

JP-A-4-290321

  In the AM-AM characteristic of the amplifier, as shown in FIG. 6A, the gain is constant until the time when there is an input. The AM-AM characteristic LUT for distortion correction has the opposite characteristic to that of FIG. 6-1, as shown in FIG. If the amplifier increases or decreases in gain due to temperature change or aging, the AM-AM characteristic LUT of the distortion correction circuit also moves up and down in the same manner. If the gain of the amplifier fluctuates by one half or one third, the AM-AM characteristic LUT also doubles or triples. For this reason, VD_I / VD_Q is doubled and tripled for output.

  As described above, the distortion correction usually has a certain level of power control capability. However, when the power control is performed only by digital processing of the distortion correction circuit, the gain of the amplifier is 1/2, 1/3. Then, it is necessary to have a margin of 2 or 3 in the calculation of digital processing, and an expensive DSP is required.

  Further, when processing is performed digitally, if the gain of the amplifier fluctuates, there is a possibility that overflow occurs due to the limitation of the bit width. Therefore, it is necessary to design the number of bits for digital processing such as a DSP with a margin corresponding to the gain fluctuation of the amplifier, and there is a problem that the performance cannot be used to the limit. If there is a margin in the bit width to prevent overflow, the calculation accuracy cannot be improved for the number of bits, and there is a demerit such as an increase in hardware price.

  In view of the above problems, an object of the present invention is to organically combine a distortion correction circuit and a transmission power control circuit in digital processing, thereby reducing the load on the distortion correction circuit in digital processing and making it a relatively inexpensive DSP. It is another object of the present invention to provide a novel transmission power control means that can cope with transmission power control with respect to gain variation of an amplifier.

  The transmission power control method of the present invention converts a modulation digital signal into an analog signal, generates a modulated wave using the converted analog signal, amplifies the generated modulated wave, and transmits it from an antenna. And demodulating the power-amplified modulated wave, analyzing the distortion of the power-amplified signal by comparing feedback data obtained by converting the demodulated analog signal into digital data, and an input digital signal, In the transmission power control method for generating the modulation digital signal by multiplying the input digital signal by a reverse distortion for correcting the distortion of the power amplified signal based on the analysis result, Calculate the power difference between the input digital signal before correction and the input digital signal after distortion correction, and set a multiplication factor according to the power difference, And outputs a signal obtained by multiplying a multiplying factor that is the set input digital signal after uncorrected as a digital signal for the modulation.

  In other words, in the present invention, the transmission power is controlled by analyzing the gain of the current amplifier based on the digitally processed distortion-corrected transmission data and adding the gain to the corrected transmission data separately. Therefore, the power after distortion correction can always be a constant value (a value almost equal to the power of the digital signal recorded before distortion correction), and the DSP's calculation ability can always be maximized. .

  The transmission power control apparatus of the present invention includes a DA converter that converts a modulation digital signal into an analog signal, a modulator that generates a modulated wave using the converted analog signal, and power amplification of the modulated wave. A transmission power amplifier, a demodulator that demodulates a modulated wave transmitted from the transmission power amplifier, an AD converter that converts the analog signal demodulated by the demodulator into digital data and outputs it as feedback data, and an input Comparing the digital signal and the feedback data to analyze the distortion of the transmission power amplifier, and multiplying the input digital signal by the reverse distortion that compensates for the distortion of the transmission power amplifier. A transmission power control apparatus having a distortion correction circuit for generating a signal; and an input data input to the distortion correction circuit. A power difference detection means for detecting the power difference, and monitoring the power difference detected by the power difference detection means. Multiplier setting means for setting a multiplier according to the power difference, and the multiplier for the modulation digital signal inserted between the distortion correction circuit and the DA converter and output from the distortion correction circuit. A multiplier that multiplies the multiplier set by the setting means and outputs the product to the DA converter.

  In the present invention, power control of the amplifier is not performed for the distortion correction circuit by performing power control that reversely uses the power control function of the distortion correction circuit by providing another power control circuit without performing power control only by the distortion correction circuit. Can be.

  As a result, the AM-AM characteristic LUT (Look Up Table) is always constant regardless of the fluctuation of the amplifier, and overflow and underflow specific to the digital circuit due to the gain of the amplifier can be prevented. Further, since it is not necessary to design the number of bits for digital processing such as a DSP with a margin for the variation of the normal amplifier, the performance can be used to the limit.

  FIG. 1 is a block diagram showing an embodiment of the present invention, in which a transmission power control circuit configuration of QPSK modulation is shown as an example.

  In FIG. 1, data to be transmitted is input to a QPSK mapping unit (1) to generate a MAP_I / MAP_Q signal, and a signal VM_I / VM_Q is generated after waveform shaping by a filter (2). This signal is input to the distortion correction circuit (3).

  Feedback data FB_I / FB_Q signals distorted by the amplifier (14) are also input to the distortion correction circuit (3), and the distortion of the amplifier (14) is compared by comparing the reference VM_I / VM_Q with the distorted FB_I / FB_Q. And an inverse distortion that compensates for the distortion of the amplifier (14) is applied. The output is VD_I / VD_Q.

  The constellation in the QPSK modulation has a coordinate arrangement as shown in FIG. 2, and the power is always constant in the symbol in the QPSK modulation. Using this, the symbol extraction unit (4) extracts VM_I / VM_Q and VM_I_SYM / VM_Q_SYM and VD_I_SYM / VD_Q_SYM which are VD_I / VD_Q symbols.

  The power detection unit (5) calculates VD_I_SYM ^ 2 + VD_Q_SYM ^ 2 and VD_I_SYM ^ 2 + VD_Q_SYM ^ 2 to obtain VM_P and VD_P which are powers in the symbol. The difference calculation unit (6) calculates VM_P-VD_P to obtain POW_DET. Further, the average unit (7) takes the average of POW_DET, and the monitoring unit (8) monitors whether the power is within the specified range. Here, if the power is not specified, the multiplication factor calculation unit (9) determines how much multiplication factor the multiplier (10) has.

  The multiplier (10) multiplies VD_I / VD_Q by the multiplier determined by the multiplier calculation unit (9) with respect to VD_I / VD_Q, respectively, performs digital / analog conversion by the DA converter (11), and performs DA_I / DA_Q. Is output. The DA_I / DA_Q is input to the quadrature modulator (12), and the quadrature modulator (12) performs quadrature modulation on the transmission frequency output from the oscillator (13). This quadrature modulation signal is input to the amplifier (14), amplified to the desired transmission power, and transmitted by the antenna (15).

  Since the signal immediately before being input to the antenna (15) is distorted by the amplifier (14), a part of this transmission signal is extracted by the coupler 16 as a feedback signal. This feedback signal is input to the quadrature demodulator (17), quadrature demodulated at the transmission frequency output from the oscillator (13), and output as FB_I_A / FB_Q_A.

  This FB_I_A / FB_Q_A signal is analog / digital converted by an AD converter (17), and is input to the distortion correction circuit (3) as a digital feedback signal FB_I / FB_Q, and distortion analysis of the amplifier (14) is performed by the above operation.

  FIG. 3 is a block diagram showing an internal processing operation of the distortion correction circuit (3), and FIG. 4 is an operation explanatory diagram showing an example of power / table address conversion in the internal processing operation of the distortion correction circuit (3). . This distortion correction circuit itself is realized by a configuration similar to the conventional one. Hereinafter, the operation of the present embodiment will be described in detail with reference to FIGS.

  First, the distortion correction operation will be described.

  The VM_I / VM_Q signal output from the filter (2) is a reference signal without distortion. In contrast, the signal distorted by the amplifier (14) is extracted as an FB_I / FB_Q signal by the coupler (16), the quadrature demodulator (17), and the AD converter (18). These signals are input to the distortion correction circuit (3) shown in FIG.

  The distortion of the amplifier (14) is analyzed by accurately comparing VM_I / VM_Q and FB_I / FB_Q, but FB_I / FB_Q causes an absolute delay such as conversion time of an analog circuit and an AD converter. Therefore, the delay circuit (31) delays VM_I / VM_Q to adjust the phase to FB_I / FB_Q. The table address calculation unit (32) calculates the power of the VM_I / VM_Q signal data at that time, and assigns the table numbers divided into the tables corresponding to the power as shown in FIG.

  For example, in the case of having a table as shown in FIG. 4, when the power calculated from VM_I / VM_Q is calculated in the time sequence, the first result of power (VM_P) is “21”, so the table number is “ 2 "is added. Since the next power is “10”, the table number is “2”, and the next is “5”, so the table number is “1”.

  On the other hand, the error calculation processing unit (33) compares VM_I / VM_Q and FB_I / FB_Q to calculate an error, and stores this error in each number group of the table number calculated by the table address calculation unit (32). To do. The error averaging processor 34 averages the errors stored in each table number. The distortion of the amplifier usually has an AM-AM characteristic and an AM-PM characteristic, and this error average is a combination of the AM-AM characteristic and the AM-PM characteristic.

  The inverse distortion characteristics are calculated by the AM-AM characteristics LUT (Look Up Table) calculating section (35-1) and the AM-PM characteristics LUT (Look Up Table) calculating section (35-2). The fact that the LUT is a characteristic for each table number means a characteristic for the magnitude of power. The inverse distortion of the amplifier is output by performing a complex operation on the VM_I / VM_Q by the complex operation unit (6).

  In the present embodiment, a multiplier (10) that multiplies the distortion correction output VD_I / VD_Q output from the distortion correction circuit (3) by a multiplier specified by the multiplier calculation unit (9) and outputs the result. Accordingly, even if the gain of the amplifier varies due to temperature change or aging change, the distortion correction output VD_I / VD_Q output from the distortion correction circuit (3) is controlled so as not to fluctuate. It makes it possible to control the output.

  As a result, if the gain of the amplifier fluctuates by one half or one third, the AM-AM characteristic LUT need not be doubled or tripled. For this reason, the distortion correction circuit (3) The outputs VD_I / VD_Q need not be doubled or tripled. That is, the AM-AM characteristic LUT (Look Up Table) is always constant regardless of the fluctuation of the amplifier, and overflow and underflow specific to the digital circuit due to the gain of the amplifier can be prevented. Further, since it is not necessary to design the number of bits for digital processing such as a DSP with a margin for the variation of the normal amplifier, the performance can be used to the limit.

  Next, the power control operation of the present embodiment that exhibits the above-described effects will be described with reference to FIG.

  VD_I / VD_Q output from the distortion correction circuit (3) and VM_I / VM_Q output from the filter unit (2) are input to the symbol extraction unit (4). A symbol extraction unit (4) extracts a symbol, and a power detection unit (5) calculates VD_P and VM_P, which are respective powers of the symbol. The distortion corrected power VD_P and the reference power VM_P are input to the difference calculation unit (6) to obtain the difference between them to obtain the difference output POW_DET. The difference output POW_DET is input to the averaging unit (7) to take an average, and the average value is monitored by the monitoring unit (8).

  If the distortion-corrected power VD_P is larger, it can be determined that the gain of the transmission amplifier (14) is lowered. When the difference is opened to some extent in the monitoring unit (8), the multiplication factor calculation unit (9) slightly increases the power of VD_I / VD_Q output from the distortion correction circuit (3) by the multiplier (10). The multiplier of the multiplier (10) is changed from 1 time to 1.1 times, for example.

  Then, VD_I / VD_Q output from the distortion correction circuit (3) is increased by 1.1 times by the multiplier (10) and input to the DA converter (11). As a result, the feedback signal FB_I / FB_Q increases by 1.1 times, so that the distortion correction circuit (3) changes the AM-AM characteristic LUT so that it becomes 1 time, thereby lowering the level of VD_I / VD_Q.

  The symbol is extracted in the same manner, the power is calculated, and VD_P and VM_P are compared. If VD_P is still larger (the gain of the transmission amplifier (14) is lower), the multiplier of the multiplier (10) is changed from 1.1 times to 1.2 times. Then, since the feedback signal becomes 1.2 times, the distortion correction circuit (3) further lowers VD_I / VD_Q. In this way, transmission power control is performed by repeating until the difference between VD_P and VM_P falls within a certain range. At this time, the level of VD_I / VD_Q converges to be approximately the same as VM_I / VM_Q.

  On the other hand, if the distortion-corrected power VD_P is smaller, it can be determined that the gain of the transmission amplifier (14) is increased. When the difference is opened to some extent in the monitoring unit (8), the multiplication factor calculation unit (9) slightly reduces the power of VD_I / VD_Q output from the distortion correction circuit (3) by the multiplier (10). The multiplier is changed from 1 time to 0.9 times, for example.

  Then, VD_I / VD_Q output from the distortion correction circuit (3) is reduced 0.9 times by the multiplier (10) and input to the DA converter (11). As a result, the feedback signal FB_I / FB_Q decreases to 0.9 times, so that the distortion correction circuit (3) changes the AM-AM characteristic LUT so as to increase it to 1 and raises the level of VD_I / VD_Q.

  This value is similarly extracted, the power is calculated, and VD_P and VM_P are compared. If VD_P is still smaller, the multiplication factor is changed from 0.9 times to 0.8 times. Then, since the feedback signal becomes 0.8 times, the distortion correction circuit (3) increases VD_I / VD_Q. In this way, transmission power control is performed by repeating until the difference between VD_P and VM_P falls within a certain range. At this time, the level of VD_I / VD_Q converges to be approximately the same as VM_I / VM_Q.

  Therefore, the distortion correction circuit (3) does not move the AM-AM characteristic LUT as shown in FIG. 6-2 even if the gain of the amplifier fluctuates and the AM-AM characteristic of the amplifier shown in FIG. In other words, only the distortion correction operation is performed in a state where the AM-AM characteristic LUT position when the amplifier is normal (for example, an intermediate position in FIG. 6B) is substantially fixed.

It is a block diagram which shows embodiment of this invention. It is a figure which shows the constellation in QPSK modulation. It is a block diagram which shows an example of the distortion correction circuit comprised by the predistorter. It is a figure for demonstrating operation | movement of a distortion correction circuit. It is a block diagram which shows a prior art example. It is a figure for demonstrating distortion correction operation | movement.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Mapping circuit 2 Filter 3 Distortion correction circuit 4 Symbol extraction part 5 Power detection part 6 Difference calculation part 7 Averaging part 8 Monitoring part 9 Multiplication factor calculation part 10 Multiplier 11 DA converter 12 Orthogonal modulation part 13 Oscillator 14 Amplifier 15 Antenna 16 Coupler 17 Quadrature demodulator 18 AD converter 31 Delay circuit 32 Table address calculation unit 33 Error calculation processing unit 34 Error average processing unit 35-1 AM-AM LUT calculation unit 35-2 AM-PM LUT calculation unit 36 Complex calculation unit

Claims (4)

A digital signal for modulation is converted into an analog signal, a modulated wave is generated using the converted analog signal, the generated modulated wave is power amplified and transmitted from an antenna, and the power amplified modulation is performed. And analyzing the distortion of the power-amplified signal by comparing feedback data obtained by demodulating the wave and converting the demodulated analog signal into a digital signal with an input digital signal, and based on the analysis result, the input digital In a transmission power control method for generating the modulation digital signal by multiplying a signal with a reverse distortion for correcting the distortion of the power amplified signal,
The power difference between the input digital signal before distortion correction and the input digital signal after distortion correction is calculated, and a multiplier is set according to the power difference, and the set multiplier is set in the input digital signal after distortion correction. A transmission power control method characterized by outputting a signal multiplied by a digital signal for modulation.   Data to be transmitted is QPSK mapped, and the symbol (VM_I_SYM / VM_Q_SYM) of the input digital signal (VM_I / VM_Q) before distortion correction and the symbol (VD_I_SYM /) of the input digital signal (VD_I / VD_Q) after distortion correction. VD_Q_SYM) is extracted, and VD_I_SYM ^ 2 + VD_Q_SYM ^ 2 and VD_I_SYM ^ 2 + VD_Q_SYM ^ 2 are calculated based on the extracted symbols to obtain VM_P and VD_P which are powers of the symbols, and a difference VM_P−VD is calculated. The transmission power control method according to claim 1, wherein the power difference is obtained. A DA converter that converts a digital signal for modulation into an analog signal, a modulator that generates a modulated wave using the converted analog signal, a transmission power amplifier that amplifies the power of the modulated wave, and the transmission power amplifier Comparing a demodulator that demodulates a modulated wave to be transmitted, an AD converter that converts the analog signal demodulated by the demodulator into digital data and outputs it as feedback data, and an input digital signal and the feedback data A distortion correction circuit that analyzes the distortion of the transmission power amplifier and generates a digital signal for modulation by multiplying the input digital signal by a reverse distortion that compensates for the distortion of the transmission power amplifier. In the power control device,
Power difference detection means for calculating the power of each of the input digital signal input to the distortion correction circuit and the modulation digital signal output from the distortion correction circuit, and detecting the power difference;
The power difference detected by the power difference detection means is monitored, and a multiplier setting means for setting a multiplier according to the power difference is inserted between the distortion correction circuit and the DA converter, and the multiplier setting means A multiplier that multiplies the multiplication factor set in step 1 by the modulation digital signal output from the distortion correction circuit and outputs the signal to the DA converter;
A transmission power control apparatus comprising: Data to be transmitted is QPSK-mapped, and the power difference detection means receives each symbol (VM_I_SYM) from the input digital signal (VM_I / VM_Q) before distortion correction and the input digital signal (VD_I / VD_Q) after distortion correction. / VM_Q_SYM) and (VD_I_SYM / VD_Q_SYM), and VD_I_SYM ^ 2 + VD_Q_SYM ^ 2 and VD_I_SYM ^ 2 + VD_Q_SYM ^ 2 by calculating the power of V by V A power detection unit to be obtained, a difference calculation unit for calculating VM_P-VD_P from the power in the obtained symbol to obtain a power difference, and an averaging unit for averaging the obtained power differences. Transmission according to claim 3, characterized in that Force control apparatus.

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