JPS63121326A - Transmitter - Google Patents

Abstract

PURPOSE:To stably control a transmitter by previously changing a communication signal waveform to transmit to an amplifier in order to compensate the nonlinearity of the amplifier and keeping the balance of a modulator and demodulator. CONSTITUTION:Signals 100-r and 100-theta inputted from input terminals 51 and 52 are transformed 120 into orthogonal coordinates, with the complex signal to which a strain is added in expressed in polar coordinate by a pre-strain addition circuit 110, and D/A converted 130. The amplifier 145 which receives the output controls a gain in order to equalize the mean power of the signals 141-I and 141-Q and transmits the signal 146 to an adder 160. In the adder the signals 141-I and 141-Q are added to be amplified 170 as the complex signals and the output, a part of which is transmitted to the amplifier 245, is outputted from a terminal 53 and the effective value of based signal is calculated in an effective value calculating device 250 so as to control the gain of the amplifier 245 with the signal 251 in proportion to the difference between the mean powers of both signals. And the signal obtained by A/D converting 230 and coordinate converting 220 the output from the amplifier 245, controls the circuit 110.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention is a method for pre-preparing a communication signal waveform in order to compensate for the nonlinearity of an amplifier in a transmitter that employs a modulation method that uses the amplitude and phase of a carrier wave as information. The present invention relates to a modulation device that deforms and sends the deformed signal to an amplifier, and particularly relates to a modulation device that performs stability control by balancing conversion loss in a modulator/demodulator.

(Prior Art) In recent years, as radio wave resources have become scarce, channels in wireless communications have become narrower in order to make more effective use of frequencies. If the channel bandwidth becomes narrower,
A linear modulation method is preferable to a nonlinear modulation method such as FM, which has a wide band. This applies regardless of digital transmission or analog transmission. In the linear modulation method, problems arise such as deterioration of the transmission spectrum and deterioration of reception characteristics due to nonlinearity of the amplifier.

As shown in Figure 9, the input/output nonlinear characteristics of a normal amplifier include an output amplitude saturation characteristic called AM-AM conversion, and an A
There is a change in the output phase depending on the input amplitude called M-PM conversion. When the input amplitude is sufficiently small from the saturation point, the amplitude characteristic is linear and there is no change in phase. However, as the input amplitude approaches the saturation point, the output amplitude becomes saturated and the output phase begins to rotate. As a result, the transmission spectrum deteriorates and the reception characteristics deteriorate.
(d) shows the influence of such a nonlinear amplifier on a signal using 16-value QAM as an example. FIG. 7(a) shows the signal point distribution in the phase plane of the transmission signal as it should be,
FIG. 7(b) shows the transmission spectrum distribution at that time. Figure 7(C) shows the distribution of signal points in the phase plane of the amplifier output when the operating point is close to the saturation level.The signal points in Figure 7(C) are the same as those in Figure 7(a). It is distorted compared to the signal point. In the transmission spectrum at this time, as shown in FIG. 7(d), odd-numbered intermodulation components such as third and fifth orders appear, causing interference with adjacent channels. Furthermore, when the signal point shown in FIG. 7(a) is sent to the receiver, errors occur due to small noise, and the reception characteristics deteriorate.

In order to prevent deterioration of transmit spectrum characteristics and reception characteristics,
It is necessary to compensate for such nonlinearity of the amplifier. Conventionally, as a means for digital transmission that compensates for such nonlinearity and also compensates for time changes in amplifier characteristics,
FIG. 6 is a block diagram of a first conventional adaptive modulation device, which is described in Japanese Patent Application No. 56-204120 entitled "Adaptive Modulation Device." Transmission data sequences are input in parallel from the input terminal 600. The diagonal lines on the connections in FIG. 6 indicate a plurality of connections.
(Ran d ora＾ccess Hen+ory
) l and the second memory, read-only
Memory 620+ROM (Read Only He+
nory)l address. 7th in ROM620
The original signal point arrangement as shown in Figure (a) is stored as a complex number value, and the contents of the RAM 610 are also stored as a complex number value after the nonlinear amplifier output is distorted to the correct signal point. The output of the RAM 610 is converted into an analog signal by a digital-to-analog converter 630, band-limited by a band-limiting filter 635, and quadrature-modulated by a modulator 640, and output to terminal 6.
01 to the nonlinear amplifier. RAM 610
In order to adaptively convert the contents of the signal, the signal is input from the output terminal 602 of the nonlinear amplifier and demodulated by the demodulator 660 using the output of the oscillator 651. The signal demodulated by the IM modulator 660 is converted into a complex digital signal by an analog-to-digital converter 670. This demodulated complex digital signal is subtracted from the original signal read from the ROM 620 in a subtraction circuit 680, and the result is multiplied by a constant coefficient in a correction amount generation diagram 9690 (in order to quickly converge the RAM value, is a value sufficiently lower than 1), RA
Addition circuit 691 adds the output read from M 610. If the demodulated value is larger than the original value from ROM 820, the contents of RAM 610 are controlled to be smaller, and if the demodulated value is smaller than the original value from ROM 620, the contents of RAM 610 are controlled to be smaller. The contents of 610 are controlled to be enlarged. By doing this, even if the input/output characteristics of the nonlinear amplifier change, the output of the nonlinear amplifier, that is, the input signal from the terminal 602, will always have the correct signal point arrangement as shown in Figure 7(a). Yoyo R
The content of AM 610 can be controlled.

However, although the first conventional method can prevent the deterioration of the reception characteristics, it cannot prevent the deterioration of the transmission spectrum. If it is shown as the solid line in FIG. 8(a), when it is subjected to distortion by the amplifier, it will become as shown in the broken line in FIG. 8(a). Such a change in the trajectory mimics the deterioration of the spectrum (, R
The AM 610 only outputs a signal point at each symbol point, and the output of the filter 635 is as shown in FIG. 8(b).

When distortion is further added to this, the result becomes as shown by the solid line in FIG. 8(C). However, the signal trajectory shown in Fig. 8 (e
) does not match the broken line, the transmission spectrum is not sufficiently improved. This is because the linear circuit shown in FIG. 6 only compensates for the linearity at the symbol point and does not compensate for the trajectory along the way.

Furthermore, if the configuration shown in FIG. 6 is adopted, it can only be applied to digital signal transmission.

Japanese Patent Application No. 60-057138 discloses a modulation device that can overcome these drawbacks and compensate for the nonlinearity of the amplifier so that the transmission spectrum does not deteriorate due to the nonlinearity of the amplifier. FIG. 3 is a block diagram of a second conventional example shown in Japanese Patent Application No. 60-057138 ``Modulation Apparatus''. The amplitude calculation circuit 310 calculates the amplitude of the input complex sample value signal series 311-I, 311-Q, and stores the calculated quantized amplitude value as an address from a rewritable memory (RAM>320) for nonlinear compensation. A complex expressed distortion 321° 322 is output.Signal 321.
322 and 311-I.

In response to the signal 311-Q, the signal generation circuit 325 generates signals 321-I and 321-Q with nonlinear distortion compensated for. Signals 321-I and 321-Q are supplied to the DA converter 3.
The signal becomes an analog signal at 30, is modulated by a quadrature modulator 340, and is input from an output terminal 304 to a nonlinear amplifier (not shown). A portion of the nonlinear amplifier is demodulated by a quadrature demodulator 345, and the demodulated signal is sampled by an AD converter 350. AD converter 350 output 351-1. 351-
Q is the input signal 311-1. 311-Q is input to the error detection circuit 360. The error detection circuit 360 output is input to the correction signal generation circuit 370 together with the RAM 320 output 321°322.

The contents of RAM 320 are adaptively controlled by the output of correction signal generation circuit 350. In Fig. 4, the signal generation circuit 1i
! RAM 320 showing a specific example of 3330 in a block diagram
Output 321. An example is shown in which 322 is expressed in polar coordinates. Input signal 311-1. 311-Q is converted by the coordinate conversion circuit 420 into a signal 421-r representing the amplitude of the output signal and a signal 421-θ representing the phase. Here, assuming that the signal 321 represents the amplitude of the distortion component and the signal 322 represents the phase of the distortion component, by adding the signal 321 and the signal 421-r in the adder circuit 430, the signal amplitude component with nonlinear compensation is obtained. Seek.

Further, by adding the signal 322 and the signal 421-θ in an adder circuit 435, the phase component of the signal with nonlinearity compensated for is determined. Therefore, in the coordinate converter I 425, the signals 321-I and 321-Q are obtained by converting the outputs of the adder circuits 430 and 435 into signals expressed in rectangular coordinates.

FIG. 5(a) shows the error detection circuit 340 in FIG.
5(b) shows a specific example of the correction signal generation circuit 350. FIG. 5(a) shows an example in which compensation distortion is stored in the RAM 320 in polar coordinate representation. . Input signals 311-I, 311-Q are input to coordinate converter 520
A signal 521-r expressed in polar coordinates.

521-θ. In addition, AD converter output 351
-I and 351-Q are also converted to signals 541-r and 541-θ expressed in polar coordinates at the output 540 of the Shobara transformer. The subtraction circuit 530 converts 521-r to 541-
subtract r, and the subtraction circuit 535 calculates 541 from 521-θ.
- Subtract 〇. The result of this subtraction becomes the error to be detected. The configuration of the correction signal generation circuit 370 in this case is shown in FIG. 5(C). The output of the subtraction circuit 530.535 is input to the input terminal 503. 504 and is multiplied by p (p is a constant less than 1) in the correction signal generation circuit 560. R.A.
Correction signal generation circuit 5 from M320 output 321.322
60 output is subtracted by a subtraction circuit 570. Adaptive control becomes possible by writing this subtraction result into the RAM 320.

By doing this, it is possible to automatically make the output of the nonlinear amplifier have the correct transmission signal waveform in accordance with the characteristics of the nonlinear amplifier.

(Problem to be Solved by the Invention) This conventional method can follow changes in the input characteristics of a nonlinear amplifier, but when the signal power changes due to the imbalance of conversion loss during frequency conversion in the modulator/demodulator, the transmission spectrum changes. It may not be possible to prevent the deterioration of

A commonly used orthogonal modulator/demodulator modulates and demodulates a complex signal by multiplying the real component and the imaginary component by carrier waves that are 90 degrees out of phase with each other. The modulator converts the baseband signal into RF
When converting low signals, conversion losses occur due to the mixer. If this conversion loss differs between the real component and the imaginary component, the amount of distortion of the modulator output signal at the amplifier will increase for a modulator input of the same amplitude.

To explain using FIG. 2, consider a circle centered at the origin 0. When the quadrature modulator input signal is represented by points on the circumference, the amplitudes of all signal points on the circumference are r. However, during modulation, the conversion losses of the real component and the imaginary component are different. For example, if the real component becomes smaller than the original signal waveform, the modulator output signal becomes elliptical as shown by the broken line.

This is because although at the modulator input the signal amplitudes at points A and B are equal r, at the modulator output the two signal amplitudes are different. If the two signal amplitudes are different, the amount of nonlinear distortion in the amplifier will also be different, and multiple levels of distortion will exist for input signals of the same amplitude, so accurate nonlinear compensation cannot be achieved by controlling the amplitude.

The same thing can be said for the demodulator, and if the conversion loss differs between the real component and the imaginary component, the signal amplitude after demodulation will differ for a demodulator input of the same amplitude. Even if this signal is subtracted from the input sample value signal series, the amount of additional distortion for the same amplitude is not determined, and stable control cannot be performed.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a transmitter that overcomes such drawbacks during modulation and demodulation and controls the transmission spectrum so that it does not deteriorate due to nonlinearity of the amplifier or imbalance in frequency conversion loss of the modulator and demodulator. It is in.

(Means for Solving the Problems) In order to solve the above-mentioned problems, the transmitter provided by the present invention uses a sample value signal sequence representing a complex signal in polar coordinates as a first sample value signal sequence. a predistortion adding circuit that inputs the input signal, predistorts the input signal sequence so as to compensate for nonlinearity of the amplifier, and outputs the distorted signal as a second sample value signal sequence expressed in polar coordinates; ;
a first coordinate converter that converts the output of the predistortion adding circuit from a set of signals expressed in polar coordinates to a signal expressed in 1ffl rectangular coordinates; a first output signal of the output of the coordinate converter is input; a first amplifier that modulates the first amplifier output signal; a second output signal of the coordinate converter output with a carrier wave orthogonal to the carrier wave of the first modulator; a second modulator for modulating: the first amplifier for calculating an effective value of the first and second modulator output signals to equalize the average power of the first and second modulator output signals; a first effective value calculation circuit that outputs a control signal for adjusting the gain of the first amplifier to the first amplifier; an adder that adds the first and second modulator output signals; and inputs the adder output signal. a third amplifier that receives a part of the second amplifier output signal as an input signal; a first demodulator that demodulates the third amplifier output signal; and a second amplifier that demodulates the third amplifier output signal. a second M modulator for demodulating the output signal with a carrier wave orthogonal to the carrier wave of the first modulator;
the third demodulator output signal so as to equalize the average power of the first and second demodulator output signals;
a second effective value calculation circuit that outputs a control signal for adjusting the gain of the amplifier to the third amplifier;
a second coordinate converter for converting the demodulator output signal from a set of orthogonal M coordinate represented signals to a set of polar coordinate represented signals; a subtraction circuit that subtracts the output of the coordinate converter; and a correction amount generation circuit that receives the output of the subtraction circuit, calculates a correction l used for correcting the contents of the predistortion addition circuit, and outputs it to the predistortion addition circuit. It is characterized by consisting of.

(Function) In the present invention, the modulator calculates the effective value from a set of modulation signals after performing orthogonal Shobara transformation on a set of predistortion circuit output signals expressed in polar coordinates using a coordinate converter, and By controlling the power of one modulating signal so that the average power of the modulating signals is equal, the frequency conversion loss of the modulator output is kept balanced. Similarly, on the demodulation side, the frequency conversion loss of the demodulated signal is kept balanced.

By doing this, stable control can be performed and changes in the amplifier and modem can be accommodated, and the instability of the circuit can be extremely reduced.

(Example) Next, the present invention will be explained in more detail by giving examples of the invention of the present application.

One embodiment of the present invention will be described with reference to FIG.

Signals 100-r and 100-θ inputted from input terminals 51 and 52 represent amplitude and phase components of a signal sequence obtained by expressing a complex signal in polar coordinates and quantizing samples. Predistortion adding circuit 11 receiving signals 100-r and 100-θ
0 outputs signals 111-r and 111-θ which are polar coordinate representations of complex signals without adding distortion to compensate for the nonlinearity of the amplifier. In the coordinate converter 120, inputs 111-r and 1
Signals 121-I and 12 representing 11-θ in Cartesian coordinates
1- Output Q.

Signals 121-1 and 121-Q are each converted to analog by a digital-to-analog (DA) converter 130,
131-I and 131-Q are output.

131-I, the amplifier 145 receives the control signal 15.
1, the gain of the amplifier 145 is controlled so that the average powers of the signal 141-1 and the signal 141-Q are equal, and a signal 146 is output. A specific example of the effective value calculator 150 is shown below.
This effective value calculator 150, shown in the block diagram in FIG.
, 1010-Q and two smoothing circuits (e.g. integrators)
The effective value of the modulator output is calculated by 1020-I and 1020-Q, and the subtracter 1030 calculates the difference in the average power of both signals over a long period of time, and a control signal 151 proportional to the difference is obtained. When the gain of the amplifier 145 is controlled in response to the control signal 151, there is a method of controlling the base current of a transistor amplifier. In adder 160, signals 141-1 and 141-
Q is added and converted into a complex signal, which is output to the amplifier 170.

The output of amplifier 170 is output to output terminal 53, and a portion thereof becomes signal 171. Amplifier 2 with signal 171 as input
45 receives the control signal 251, controls the gain of the amplifier 245, and outputs a signal 246. Signals 246 and 171 are demodulated by mixers 240-I, 240-, respectively.
It is demodulated by the output signal of the oscillator 180 at Q and becomes baseband signals 241-I and 241-Q. The effective value calculator 250 receives baseband signals 241-1 and 241-Q.
is input, and two smoothing circuits (for example, integrators) calculate the effective values of both signals, and output a control signal 251 that is proportional to the difference in average power between the two signals. Similar to the modulator, the gain of the amplifier 245 is controlled in response to this control signal 251. Baseband signals 241-I and 241-Q are sample quantized in an analog-to-digital (AD) converter 230 resulting in signals 231-1 and 231-Q. The coordinate converter 220 receives an input signal 231 expressed in rectangular coordinates.
-I and 231-Q are converted into signals 221-r and 221-θ expressed in polar coordinates and output. In the subtraction circuit 200, the signals 100-r and 100- are originally supposed to be transmitted.
The coordinate converter outputs 221-r and 221-θ are each subtracted from θ. The predistortion adding circuit 110 converts the signal (100-r, 10G-〇) to the signal (111-
I, 111-Q) is performed correctly to compensate for the nonlinearity of amplifier 170, the output of subtraction circuit 200 will be O. When this output is not 0, the output of the subtraction circuit 200 is doubled in the correction amount generation circuit 210 (p is a constant of 1 or less), and input to the front 7L distortion addition circuit 110 to rewrite the compensation distortion amount. Further, the gains of the amplifiers 145 and 245 are adjusted so as to keep conversion losses during modulation and demodulation balanced, and if the amplifier input does not exceed the maximum input amplitude of the amplifier, the output of the subtracter 200 becomes O. In addition, in this embodiment, the outputs of the amplifiers 145 and 245 are connected to the mixer 1.
40-1.

However, the object of the present invention can also be achieved by replacing the amplifiers and mixers and using the outputs of the mixers 140-I and 240-1 as inputs for the outputs of the amplifiers 145 and 245.

(Effects of the Invention) As explained in detail above, the transmitter of the present invention automatically adjusts the output of the nonlinear amplifier to the correct transmitted/multiplied signal waveform for any modulation method according to the characteristics of the nonlinear amplifier. It can be done.

Gain control in modulation and demodulation in the transmitter of the present invention is for changes in signal waveforms due to imbalance in frequency conversion losses due to modulation and demodulation, and changes in signal amplitude due to modulation and demodulation and changes in amplifier gain also cause distortion. Nonlinear compensation can be performed without any problems.

[Brief Description of the Drawings] Figure 1 is a block diagram showing one embodiment of the invention of the present application, Figure 2 is a block diagram showing an embodiment of the invention of the present application;
Figure 1 shows the signal trajectory due to frequency conversion loss in the modulator/demodulator in the embodiment, Figure 3 is a block diagram showing a conventional modulator with an adaptive linearization circuit, and Figure 4 shows the signal generation circuit in Figure 3. 5(a) is a block diagram showing a specific example of the error detection circuit shown in FIG. 3; FIG. 5(b) is a block diagram showing a specific example of the correction signal generating circuit shown in FIG. 3; FIG. 6 is a block diagram showing the first conventional adaptive modulation device, and FIGS. 7(a), (b), (c), and (d) are 16-value Q
A diagram showing distortion caused by an AM nonlinear amplifier, FIG. 8(a),
(b) and (C) are diagrams showing the waveforms of various parts of the first conventional modulator with adaptive linearization circuit, FIG. 9 is a diagram showing the input/output characteristics of the nonlinear amplifier, and FIG. 10 is the diagram shown in FIG. FIG. 2 is a block diagram showing a specific example of an effective value calculator 150 of FIG. 51, 52... Input terminal, 53... Output terminal, 11
0... predistortion adding circuit, 120. 220...Coordinate converter, 130...Digital-to-analog converter, 1
40-I, 140-Q... mixer which is a modulator, 145. 170. 245...Amplifier, 150.
250... Effective value calculator, 160... Adder, 1
80... Oscillator, 200... Subtraction circuit, 210...
- Correction amount generation circuit, 230...Analog-digital converter, 240-I, 240-Q...Mixer which is a demodulator, 301, 302. 303... Input terminal, 304... Output terminal, 310... Amplitude calculation circuit, 320... Rewritable memory (RAM), 3
25... Signal generation circuit, 330... Digital-to-analog converter, 340... Quadrature modulator, 341...
Oscillator, 345... Orthogonal demodulator, 350... Analog-digital converter, 360... Error detection circuit, 3
70... correction signal generation circuit, 401. 402.
403°404...input terminal, 420. 425...
・Coordinate converter, 430°435... Adder, 503.
504...Input terminal, 505°506...Output terminal, 520. 540...Coordinate converter, 530°53
5, 570... Subtraction circuit, 560... Correction signal generation circuit, 600, 602... Input terminal, 601...
・Output terminal, 610...RAM, 620...ROM
, 630... digital-to-analog converter, 635...
... Bandwidth limiting filter, 640 ... Quadrature modulator, 6
51... Oscillator, 660... Demodulator, 670...
Analog-digital converter, 680...Subtractor, 6
90... Correction amount generation circuit, 691... Adder, 10
10-I. 1010-Q... square law detector, 1020-1, 1
020-Q...Smoothing circuit, 1030...Subtractor.

Claims (1)

[Claims] A sample value signal sequence representing a complex signal in polar coordinates is input as a first sample value signal sequence, and this input signal sequence is previously distorted to compensate for the nonlinearity of the amplifier.
a predistortion adding circuit that outputs the distorted signal as a second sample value signal series expressed in polar coordinates; a first coordinate converter that converts the signal into a signal expressed in orthogonal coordinates; a first amplifier that receives a first output signal of the output of the coordinate converter; a first amplifier that modulates the first amplifier output signal; a second modulator that modulates a second output signal of the coordinate converter output with a carrier wave orthogonal to a carrier wave of the first modulator; outputs of the first and second modulators; a first control signal that calculates an effective value of the signal and outputs to the first amplifier a control signal that adjusts the gain of the first amplifier so as to equalize the average power of the first and second modulator output signals; an effective value calculation circuit; an adder for adding the first and second modulator output signals; a second amplifier for inputting the adder output signal; and a part for inputting the second amplifier output signal. a third amplifier for demodulating the third amplifier output signal; a first demodulator for demodulating the second amplifier output signal with a carrier wave orthogonal to the carrier wave of the first modulator; a second demodulator; calculating the effective values of the first and second demodulator output signals and adjusting the gain of the third amplifier so as to equalize the average power of the first and second demodulator output signals; a second effective value calculation circuit that outputs a control signal to be adjusted to the third amplifier; a second coordinate converter for converting the signal into a signal; a subtraction circuit for subtracting the output of the second coordinate converter from the first sample value signal sequence; 1. A transmitter comprising: a correction amount generating circuit that calculates a correction amount used for correcting the contents of the additional circuit and outputs it to a predistortion adding circuit.