JPH04292022A - Digital radio equipment with non-linear distortion compensator - Google Patents

Abstract

PURPOSE:To realize a non-liner distortion compensator which has a wide distortion compensation range and needs no adjusting work. CONSTITUTION:An analog type transversal equalizers is provided, and the operating point of one or more analog multipliers 6, at least, is set at a position where a non-linear distortion occurs. Further, a control circuit 10 which changes the coefficient of each multiplier by using correlation data between the polarity signal and the error signal of data discriminated from an input signal, and equalizes optionally the distortion component of the input signal.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a digital radio device equipped with a nonlinear distortion compensator for compensating for nonlinear distortion generated in a high-output amplifier on the transmitting side. In digital wireless equipment, the higher the multilevel QAM modulation, the higher the output power of the amplifier HP.
Since it is vulnerable to nonlinear distortion of A, it is necessary to use a small central region with good linearity in the amplitude characteristics of the amplifier, and to provide a large amount of backoff between it and the saturation level. Therefore, it is necessary to use a high-output amplifier with a relatively large saturation output, which increases the device price and power consumption. The present invention aims to improve nonlinear distortion without the need to use a high-power amplifier with a large saturation output.

0002

2. Description of the Related Art Conventionally, nonlinear distortion compensators, negative feedback techniques, and the like have been used to improve the nonlinear distortion of high-output amplifiers. These means are collectively called a nonlinear distortion compensator (linearizer). FIG. 6 shows an example of a typical predistorter method among nonlinear distortion compensators.

In FIG. 6(a), 20 is a distortion generator called a predistorter, and 21 is a high output amplifier (HP).
A). FIG. 6(b) shows the nonlinear characteristics of the distortion generator 20 and the high-output amplifier 21, respectively. As shown in the figure, the nonlinear characteristics of the distortion generator 20 are set to be opposite to those of the high-output amplifier 21, so that the transmitted signal is distorted in advance and input to the high-output amplifier 21. By applying an opposite distortion to the signal, both distortions are canceled out, and a distortion-free, high-power transmission signal can be obtained.

0004

[Problems to be Solved by the Invention] The distortion improvement amount of conventional nonlinear distortion compensators cannot be expected to be very large, and in the case of the predistorter method, distortion compensation cannot be achieved in the region where the opposite characteristics of a high-output amplifier are obtained. Therefore, it is necessary to set the inverse characteristics of the distortion generator to match the individual nonlinear characteristics of the high-output amplifier, and it is time-consuming to make adjustments that take into account the temperature dependence and voltage dependence of the nonlinear characteristics. There was a problem in that it was difficult to obtain sufficient characteristics. An object of the present invention is to realize a nonlinear distortion compensator that has a wide range of distortion compensation and does not require adjustment work.

[0005]

[Means for Solving the Problems] The present invention focuses on an analog multiplier in an analog transversal equalizer, which is one of the optimal filters widely used for equalizing transmission path characteristics in communication systems. However, by imparting nonlinearity to the amplitude characteristics of each multiplier, a nonlinear distortion compensator is realized to compensate for input signal distortion caused by the nonlinear characteristics of a high-output amplifier. FIG. 1 shows the basic configuration of the present invention in an exemplary manner, and a nonlinear distortion compensator according to the present invention is provided in a demodulation system on the receiving side.

In FIG. 1, 1 is an antenna. 2 is a receiving section, which amplifies the received signal and RF-
Performs IF conversion etc. 3 is a demodulator, which modulates the received signal, e.g.
Demodulation is performed according to a method such as phase phase keying (BPSK) or quadrature phase keying (QPSK), and a baseband signal is output.

4 is a nonlinear distortion compensator using an analog type transversal equalizer according to the present invention. 5 is a delay line having an interval equal to the modem clock period T. 6 is a multiplier with nonlinear characteristics. The operating point of at least one multiplier is set such that the operating region spans a nonlinear region. 7 is an adder. 9 is an A/D converter. Reference numeral 10 denotes a control circuit that correlates the polarity signal of the data identified from the input signal with the error signal, integrates the resulting signal, and provides feedback to change the coefficient of at least one multiplier.

[0008]

[Operation] In the nonlinear distortion compensator using an analog transversal equalizer according to the present invention, a multiplier in the equalizer is used as a distortion generating element. The nonlinear characteristics are realized by combining the outputs of multiple multipliers whose inputs are signals delayed by different delay times, so the nonlinear characteristics are more complex than when using a single distortion generating element. can be realized. Furthermore, since the equalization state can be dynamically changed by the automatic equalization function, it is possible to quickly follow variations in the characteristics of high-power amplifiers (HPA) and fluctuations in nonlinear characteristics due to changes in temperature, voltage, etc.

[0009]

Embodiment FIG. 2 shows an embodiment of a nonlinear distortion compensator using a T-space type analog transversal equalizer having an orthogonal two-dimensional configuration. In FIG. 2, I and Q are orthogonal baseband signals of the demodulated I channel and Q channel, respectively. 5 is a T-space (interval) delay line, 6 and 6' are multipliers that perform coefficient calculations, and 7, 7', 8, 8
' are adders, 9, 9' are A/D converters, 10,
10' is a control circuit.

[0010] Each baseband signal of I and Q channels is
The signals are respectively input to delay lines 5 and 5' and delayed by T. A plurality of multipliers 6, 6' respectively multiply signals branched from taps spaced apart by delay lines T by coefficients set from control circuits 10, 10', and output the multipliers to adders 7, 7'. Adders 7 and 7' add the signals output from multipliers 6 and 6', respectively, to obtain an overall representative sum, and adders 8 and 8'
Output to. Adders 8 and 8' further add the output signals of the orthogonal systems, and A/D converters 9 and 9' convert the respective addition results into digital signals to control circuits 10 and 10'. Output to.

The control circuits 10 and 10' identify data from the A/D-converted digital signal, determine the error signal and polarity signal from the desired waveform, correlate them, integrate the results, and send the signal to the multiplier 6. , 6' are fed back to the coefficient settings. In this way, the coefficients are controlled in a direction such that the error signal converges to zero, and equalization is performed. According to the present invention, appropriate nonlinear characteristics are given to some or all of the multipliers 6, 6', so that a better equalization level than conventional equalizers can be achieved for input signals with nonlinear distortion. It can be realized.

As a method of introducing nonlinear characteristics into the multipliers 6 and 6', as shown in FIG. 3(a), bias is applied to the operating center point on the operating characteristic curve of the multiplier. is applied to the saturation region, or by lowering the power supply voltage of the multiplier to narrow the width of the linear region, or by inserting a nonlinear element with S-shaped saturation characteristics at the output of the multiplier. You can use methods such as compressing high-level output.

In FIG. 4, instead of the T space type analog transversal equalizer of FIG. 2, the delay space of the delay line 5 is set to T'(T>T'
) is an embodiment using a fractional type transversal equalizer, which can shorten the equalization processing time for input signals with complex distortions.

In each of the embodiments described above, the nonlinear distortion compensator is provided in the demodulation system on the receiving side, but it can also be provided in the modulation system on the transmitting side to directly remove distortion from the transmitted signal. FIG. 5 shows the configuration of this embodiment. In FIG. 5, 11 is a baseband signal, 12 is a nonlinear distortion compensator according to the present invention, 13 is a modulator, 14 is an oscillator that generates a carrier, 15 is a high power amplifier (HPA), 16 is an antenna, and 17 is an RF- Down converter that performs IF conversion, 1
8 is a demodulator (DEM), and 19 is an A/D converter.

The nonlinear distortion compensator 12 belongs to the same system as the predistorter system shown in FIG. The present invention is superior in this respect. The input baseband signal 11 is passed through the nonlinear distortion compensator 12
is given a distortion with a characteristic opposite to that of the high-output amplifier 15,
The signal is phase-modulated by a modulator 13, distortions are canceled by a high-output amplifier 15, and the signal is output and transmitted from an antenna 16.

A part of this output transmission signal is branched to a down converter 17, and a demodulator 18 demodulates the baseband signal. The demodulated baseband signal is converted into a digital signal by the A/D converter 19 and input to the nonlinear distortion compensator 12. The control circuit of the nonlinear distortion compensator 12 is as follows:
Regards the demodulated baseband signal in digital signal format as an equalized output signal, calculates the error signal and polarity signal, updates the coefficients of each multiplier in the direction where the error becomes zero, and removes distortion from the output transmission signal. do.

[0017]

Effects of the Invention In conventional multilevel QAM radio equipment, in order to use the high-output amplifier in the linear region, it is necessary to provide a large back-off of the high-output amplifier and increase the saturation output. Conversion was inhibited. Further, even when a predistorter is used, there is a drawback that sufficient distortion cannot be removed and the adjustment burden is large. In contrast, in the present invention, by using a nonlinear distortion compensator using a commonly used analog transversal equalizer, distortion can be removed with high precision with a simple configuration without the need to upgrade the level of a high-output amplifier. This makes it possible to further reduce costs and power consumption.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the basic configuration of the present invention.

FIG. 2 is a configuration diagram of an embodiment of a nonlinear distortion compensator using a T-space type analog transversal equalizer.

FIG. 3 is an explanatory diagram of an example of nonlinear characterization of a multiplier.

FIG. 4 is a configuration diagram of an embodiment of a nonlinear distortion compensator using a fractional analog transversal equalizer.

FIG. 5 is a configuration diagram of an embodiment in which a nonlinear distortion compensator is provided in a modulation system.

FIG. 6 is an explanatory diagram of a conventional example of a predistorter system.

[Explanation of symbols]

1 Antenna 2 Receiving section 3 Demodulator 4 Nonlinear distortion compensator 5 Delay line 6 Multiplier 7 Adder 9 A/D converter 10 Control circuit

Claims (4)

[Claims] 1. In a digital radio device, at least a T-space analog type transversal equalizer operating in a timing relationship corresponding to a clock frequency of a modem is provided, and the operating point of at least one analog multiplier of the T-space analog transversal equalizer is provided. is set at a point where a nonlinear distortion component occurs, and the coefficients of each multiplier are changed using correlation data between the polarity signal of the data identified from the input signal and the error signal to optimize the distortion component of the input signal. A digital radio device that has a nonlinear distortion compensator that compensates for nonlinear distortion of an input signal, and is equipped with a control circuit that equalizes the input signal. 2. In a digital radio device, a fractional type analog transversal equalizer using delay lines arranged at short time intervals is provided for at least a timing corresponding to the clock frequency of the modem, and at least one of the One or more analog multipliers are given nonlinear distortion characteristics, and the coefficients of each multiplier are changed using correlation data between the polarity signal of the data identified from the received signal and the error signal, and the distortion component of the received signal is A digital wireless device with a nonlinear distortion compensator that is equipped with a control circuit that optimally equalizes and compensates for nonlinear distortion. 3. A digital radio device, wherein the nonlinear distortion compensator according to claim 1 or 2 is used in a demodulation system to compensate for nonlinear distortion of a received signal. 4. A digital radio device, wherein the nonlinear distortion compensator according to claim 1 or 2 is used in a modulation system to compensate for nonlinear distortion of a transmission signal.