JPH05268108A - Waveform equalizer - Google Patents

Abstract

PURPOSE:To improve the tracking characteristic with respect to waveform distortion due to fading caused in a radio communication propagation path and changed timewise without sacrificing immunity against noise or the like. CONSTITUTION:A transversal filter 13 receives a 1st base band signal signal 102 resulting from a reception signal 101 of a digital radio communication system demodulated and identified by a demodulator 10 and applies filtering to the signal 102 and outputs a 2nd base band digital signal 103. A correlation device 15 makes correlation operation between the 1st base band digital signal 102 and an error signal 105 of a 2nd base band digital signal 103. A stage number variable counter 16 counts the result of correlation and outputs a tap weighting control signal 107 for the transversal filter 13. On the other hand, a distortion speed detector 12 detects a changing speed of a waveform distortion of the reception signal 101 and outputs a stage number switching control signal 108 based on the result of detection. The stage number variable counter 16 changes a change in the count in response to the stage number switching control signal 108.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a waveform equalizer for correcting distortion of a received signal waveform in a digital wireless communication system.

[0002]

2. Description of the Related Art In digital radio communication systems,
When the received signal is distorted due to fading or the like, intersymbol interference occurs and the code error rate deteriorates. Therefore, it is general to automatically equalize the distortion by a waveform equalizer.

FIG. 4 shows an example of the configuration of a conventional waveform equalizer, and the configuration and operation will be described below.

The received signal 101 is a signal which is digitally modulated on the transmitting side and propagated through the space and then received, and is input to the demodulator 10.

The demodulator 10 demodulates / identifies the received signal 101 and outputs the first baseband digital signal 102 to the waveform equalizer 11.

The waveform equalizer 11 includes a transversal filter 13, an error signal generator 14, a correlator 15 and a counter 17.
It is composed of and, and the processing is performed as follows.

The transversal filter 13 filters the first baseband digital signal 102 to shape the waveform, and outputs it to the error signal generator 14 as the second baseband digital signal 103.

The error signal generator 14 identifies the second baseband digital signal 103, outputs the main signal 104 to the subsequent signal processing section (not shown), and corresponds to the residual error component after waveform shaping. The error signal 105 is sent to the correlator 15
Output to.

The correlator 15 outputs the first baseband signal 10
2 and the error signal 105 are input, the correlation calculation between them is performed according to each tap control timing, and the correlator output signal 106 is output to the counter 17. For example, in order to simplify the correlation calculation, the signals used for the calculation are MSB of the first baseband digital signal 102 and M of the error signal 105.
When limited to SB, the correlation result is “1” when the polarities of the two signals match, and “0” is output as the correlator output signal 106 when the polarities of the two signals do not match.

The counter 17 is an N-stage (N is a natural number) counter, which counts +1 when the correlator output signal 106 is "1" and counts -1 when the correlator output signal 106 is "0".

Then, the counter 17 outputs the upper M bits (M is a positive integer not more than N) of the N-bit count output as the tap weighting control signal 107 of the transversal filter 13.

Since the tap weighting control signal 107 output from the counter 17 changes so that the residual error component after the waveform shaping by the transversal filter 13 is minimized, the change is received signal 101. In the range that can be followed, the appropriate waveform equalization can be performed, and the main signal 104 becomes accurate.

[0013]

By the way, under a good condition that the propagation path does not have fading, the tap weighting coefficient of the transversal filter 13 is prevented from easily fluctuating due to instantaneous noise or the like. It is required that the control signal 107 be kept stable. For that purpose, it is desired that the number N of stages of the counter 17 is sufficiently large.

On the other hand, when fading occurs in the propagation path and waveform distortion occurs in the received signal 101, and when the amount of distortion changes rapidly with the passage of time, the tap weighting coefficient of the transversal filter 13 is It is required to change at high speed.

However, in the conventional waveform equalizer 11 described above, the counter 17 that generates the tap weighting control signal 107 is generated.
Since the number N of stages is fixed, if the number N of stages is increased with an emphasis on stability against noise or the like, the change of the tap weighting coefficient becomes slow and the ability to follow the waveform distortion that changes at a high speed with time deteriorates. However, if the number of stages N is reduced by placing importance on the followability with respect to fading, there is a drawback that the stability against noise and the like deteriorates.

The present invention has been proposed in view of the above points, and its object is to temporally change in a propagation path of wireless communication without sacrificing stability against noise or the like. An object of the present invention is to provide a waveform equalizer having excellent tracking characteristics with respect to waveform distortion caused by fading.

[0017]

In order to achieve the above object, the present invention performs filtering by inputting a first baseband digital signal obtained by demodulating and identifying a received signal of a digital radio communication system by a demodulator. A transversal filter that outputs a second baseband digital signal, a correlator that performs a correlation operation between the first or second baseband digital signal and a residual error component included in the second baseband digital signal, and Detects the rate of change of the waveform distortion of the signal, and outputs the tap speed control signal of the transversal filter that counts the correlation result of the correlator and the distortion speed detector that outputs the stage number switching control signal based on the detection result. , A variable stage number counter that changes the amount of change in counting according to the stage number switching control signal. There.

[0018]

In the waveform equalizer of the present invention, the transversal filter receives the first baseband digital signal obtained by demodulating and identifying the received signal of the digital radio communication system by the demodulator, and performs filtering. Second
The baseband digital signal of is output. The correlator performs a correlation operation between the first or second baseband digital signal and the residual error component contained in the second baseband digital signal, and the variable stage counter counts the correlation result and taps the transversal filter. The weighting control signal is output. On the other hand, the strain rate detector detects the change rate of the waveform distortion of the received signal and outputs the stage number switching control signal of the stage number variable counter based on the detection result, and the stage number variable counter counts according to the stage number switching control signal. Change the amount of change.

[0019]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram showing an embodiment of the waveform equalizer of the present invention.

In FIG. 1, a demodulator 10 is used in this embodiment.
, Strain rate detector 12, transversal filter 1
3, an error signal generator 14, a correlator 15, and a waveform equalizer 11 including a stage number variable counter 16. The details of the functions of each unit will be described through the following operations in order to avoid duplication.

In FIG. 1, a received signal 101 is a signal received after being digitally modulated on the transmitting side and propagating in space, and is input to a demodulator 10 and a distortion velocity detector 12 of a waveform equalizer 11.

The demodulator 10 demodulates and discriminates the received signal 101, and outputs the first baseband digital signal 102 to the transversal filter 13 of the waveform equalizer 11.

The transversal filter 13 filters the first baseband digital signal 102 to shape the waveform, and outputs it as the second baseband digital signal 103 to the error signal generator 14.

The error signal generator 14 identifies the second baseband digital signal 103, outputs the main signal 104 to the subsequent signal processing unit (not shown), and corresponds to the residual error component after waveform shaping. The error signal 105 is sent to the correlator 15
Output to.

The correlator 15 receives the first baseband digital signal 102 and the error signal 105, performs a correlation operation between the two in accordance with each tap control timing, and outputs a correlator output signal 106 as a stage number variable counter. Output to 16. For example, if the signal used for the calculation is limited to the MSB of the first baseband digital signal 102 and the MSB of the error signal 105 in order to simplify the correlation calculation, the correlation result is obtained when the polarities of both signals match. It becomes “1”, and when they do not match, “0” is output as the correlator output 106.

On the other hand, the distortion velocity detector 12 receives the received signal 101
The speed of change of the waveform distortion is detected, and if the distortion is changing at a predetermined speed or more, "1" is set, and if the change is slower than that, "0" is set as the step number switching control signal 108. Output to the variable counter 16.

FIG. 2 shows an example of the structure of the strain velocity detector 12.

The received signal 101, which is an input, is input to the band pass filters 20, 21 and 22 and the band pass filter 2
Filters 0, 21 and 22 respectively, and output the band pass filter output signals 220, 221, 222 to the detection circuits 23, 24, 25.

Here, the band pass filter 20 has the center of the pass band at a frequency lower than the center of the band of the received signal 101, and the band pass filter 21 has the center of the pass band near the center of the band of the received signal 101. Band pass filter 2
2 has the center of the pass band at a frequency higher than the center of the band of the received signal 101, and each band pass filter 20, 21, 2
The respective pass bands are set so that the half widths of the two pass bands do not overlap.

The detection circuits 23, 24, 25 detect the levels of the bandpass filter output signals 220, 221, 222 and output the detection circuit output signals 223, 224, 225 to the arithmetic circuits 26, 27.

The arithmetic circuit 26 calculates the difference between the detection circuit output signal 223 and the detection circuit output signal 225, and outputs the arithmetic circuit output signal 226 to the differentiating circuit 28. Here, the arithmetic circuit output signal 226 corresponds to the amount of first-order distortion of the received signal 101.

Further, the arithmetic circuit 27 outputs the detection circuit output signal 2
The difference between the average value of 23 and 225 and the detection circuit output signal 224 is calculated and output to the differentiation circuit 29 as the arithmetic circuit output signal 227. Here, the arithmetic circuit output signal 227 corresponds to the amount of secondary distortion of the received signal 101.

Differentiating circuits 28 and 29 time-differentiate the arithmetic circuit output signals 226 and 227, respectively, and output the differentiating circuit output signals 228 and 229 to the discriminating circuit 30. Here, the differentiating circuit output signals 228 and 229 are the received signal 10 respectively.
It corresponds to the rate of change of the first-order distortion and the second-order distortion of 1.

The discrimination circuit 30 outputs the differentiation circuit output signal 228,
When at least one of 229 exceeds a predetermined threshold value, “1” is output to the variable stage counter 16 as a stage number switching control signal 108, and “0” is output.

In FIG. 1, the variable stage counter 16 is an N-stage (N is a positive integer) counter, and the correlator output signal 10
6 and the stage number switching control signal 108 are input, and when the stage number switching control signal 108 is “0”, the correlator output signal 10
When 6 is "1", +1 is counted, and when the correlator output signal 106 is "0", -1 is counted. Also, the stage number switching control signal 108 is "1" and the correlator output signal 106 is "1".
+2 in the case of, and −2 in the case where the correlator output signal 106 is “0”. Then, the stage number variable counter 16 outputs the upper M bits (M is a positive integer equal to or less than N) of the N-bit count output as the tap weighting control signal 107 of the transversal filter 13.

FIG. 3 shows a configuration example of the stage number variable counter 16.

In FIG. 3, the selectors 30 and 31 select one of the inputs according to the value of the stage number switching control signal 108. When the stage number switching control signal 108 is "0", the selector 30 is +1 and the selector 31 is It outputs -1. When the stage number switching control signal 108 is "1", the selector 30 outputs +2 and the selector 31 outputs -2.

The selector 32 selects one of the inputs according to the value of the correlator output signal 106. When the correlator output signal 106 is "1", the output of the selector 30 is passed and the correlator output signal 106 is "1". If it is "0", the output of the selector 31 is passed.

The output of the selector 32 is added to the value in the register 34 by the adder 33, and the addition result is stored in the register 34 again.

Thus, in FIG. 1, the tap weighting control signal 107, which is the output of the variable stage counter 16, changes so that the residual error component after the waveform shaping by the transversal filter 13 is minimized. Received signal 1
When the rate of change of the distortion of 01 is slow, the tap weighting control signal 107 changes slowly, does not easily fluctuate due to instantaneous noise, etc., and is kept in a stable state. Further, when the change speed of the distortion of the received signal 101 is fast, the tap weighting control signal 107 changes quickly, and it is possible to follow the waveform distortion caused by fading at high speed.
Therefore, regardless of the state of distortion, proper waveform equalization can be performed and the main signal 104 becomes accurate.

In the above embodiment, the case where the number of stages of the stage number variable counter 16 is controlled by the stage number switching control signal 108 is shown. However, the stage number switching control signal 108 is given to the correlator, and the correlator output signal 106 may be weighted and the weighted correlator output signal 106 may be counted by a counter.

[0043]

As described above, in the waveform equalizer of the present invention, the change speed of the distortion of the received signal is detected by the distortion speed detector, and the tap of the transversal filter is detected based on the detection result. Since the amount of change of the weighting control signal per unit time is made variable, waveform distortion caused by fading that changes over time in the propagation path of wireless communication can be performed without sacrificing stability against noise and the like. On the other hand, there is an effect that a waveform equalizer having excellent tracking characteristics can be provided.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing an embodiment of a waveform equalizer of the present invention.

FIG. 2 is a diagram showing a configuration example of a strain velocity detector in FIG.

FIG. 3 is a diagram showing a configuration example of a stage number variable counter in FIG.

FIG. 4 is a configuration diagram showing an example of a conventional waveform equalizer.

[Explanation of symbols]

 10 ……………………………… Demodulator 11 ………………………… Waveform equalizer 12 ………………………… Distortion speed detector 13 ……………… ………… Transversal filter 14 ……………………………… Error signal generator 15 ………………………… Correlator 16 ……………………………… Variable stage counter 101 ………………………… Received signals 102, 103 …………… Baseband digital signal 104 ……………………… Main signal 105 ……………………… Error signal 106… …………………… Correlator output signal 107 ………………………… Tap weighting control signal 108 ………………………… Stage switching control signal 20,21,22 ………… Band Pass filter 23,24,25 ………… Detection circuit 26,27 ……………… Calculation circuit 28,29 …………………… Split circuit 30 …………………… Discrimination circuit 220, 221, 222… Band pass filter output signal 223, 224, 225… Detection circuit output signal 226, 227 ……… Calculation circuit output signal 228, 229 ……………… Differentiator circuit output signal 30, 31, 32 ………… Selector 33 ………………………… Adder 34 ………………………… Register

Claims (2)

[Claims] 1. A transversal filter for inputting a first baseband digital signal obtained by demodulating and identifying a received signal of a digital wireless communication system by a demodulator and outputting a second baseband digital signal by filtering. The first or second baseband digital signal and the second
A correlator that performs a correlation operation with the residual error component included in the baseband digital signal, and a distortion speed detector that detects the change speed of the waveform distortion of the received signal and outputs the stage switching control signal based on the detection result. A variable stage number counter that counts the correlation result of the correlator and outputs the tap weighting control signal of the transversal filter and that changes the count variation amount according to the stage number switching control signal. Waveform equalizer. 2. The distortion velocity detector comprises: a plurality of band pass filters each having a pass band within the band of a received signal and having different pass bands; and comparing the output levels of these band pass filters with each other. 2. The waveform equalizer according to claim 1, further comprising: an arithmetic circuit for detecting the amount of distortion, and a differentiating circuit for time-differentiating the output of the arithmetic circuit to detect the speed of change of distortion.