JPH07162361A - Adaptive equalizer - Google Patents

Abstract

PURPOSE:To prevent an equalizing characteristic from being deteriorated and to obtain an effective characteristic by changing the follow-up characteristic of an adaptive filter in accordance with fading variation estimated from an output of a known signal detecting correlator. CONSTITUTION:A signal obtained by periodically inserting a known signal into a transmitting signal is inputted to a correlator 1 and the adaptive filter 4 and the correlator 1 executes correlation operation between the same reference signal as the known signal and the received input signal, an error detecting part 5 obtains an error between a correlation result and an output from the filter 4 which is obtained by processing the received input signal and a coefficient updating part 3 updates the coefficient of the filter 4 in accordance with the error. A fading variation estimater 8 estimates fading variation generated due to variation in the moving speed of a mobile object by the output of the correlator 1 without requiring external information and the updating part 3 changes follow-up algorithm to a value matched with the variation based upon the estimated variation and executes coefficient updating operation.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an adaptive equalizer in a digital mobile radio receiver.

[0002]

2. Description of the Related Art FIG. 4 is a block diagram showing an example of a conventional equalizer of this type. In the figure, 1 is a correlator, 2 is a reference signal generator, 3 is a coefficient updating unit, and 4 is an adaptive unit. filter,
Reference numeral 5 is an error detector, 6 is a determiner, and 7 is a switch. Further, FIG. 2 is a diagram for explaining a signal form used in this type of wireless communication.

Next, the operation will be described. In mobile radio such as a portable radio device, the characteristics of the transmission line change very rapidly due to the movement of a moving body, and therefore, as shown in FIG. In addition, a sharp known signal is inserted into the original transmission signal to be transmitted, so that it can follow changes in the characteristics of the transmission path. That is, on the reception side, in the correlator 1 shown in FIG. 4, the same reference signal as the above-mentioned known signal generated from the reference signal generator 2 is used to perform a correlation calculation with the reception input signal to obtain the reception input. The position (width) of the known signal inserted in the signal is detected, the switch 7 is switched to the reference signal generator 2 side, and the error between the received input signal and the output from the adaptive filter 4 is detected by the error detection unit. 5, an error signal is obtained, which is input to the coefficient updating unit 3 to update the coefficient of the adaptive filter 4 according to the error. The updating of the adaptive filter 4 is performed by feedback control so that the absolute value of the error signal becomes sufficiently small, that is, the waveform distortion of the equalized signal becomes small.

When the internal state of the equalizer using the known signal is set by the above operation, the switch 7 is switched to the decision unit 6 side. That is, the output of the decision unit 6 does not cause a decision error unless the equalizer is sufficiently converged and the change in the state of the transmission path is abrupt, so that the output between the decision unit 6 and the output of the adaptive filter 4 is detected. Then, the error detection unit 5 obtains an error signal.
The operation of following the change of the transmission path is performed while updating the coefficient of. Further, when the equalizer cannot follow in the transmission signal portion, the operation of resetting the state of the equalizer again using the next known signal is performed.

[0005]

As described above, the conventional equalizer compensates the distortion while tracking the change of the transmission line by using the known signal inserted in the transmission signal, and obtains a good reception characteristic. However, there is a problem in that the fluctuation of the moving speed of the moving body is not taken into consideration and therefore the reception characteristic is deteriorated.

That is, although the fading changes due to the fluctuation of the moving speed of the moving body, the conventional adaptive equalizer has no means for estimating the fading fluctuation amount. That is, the tracking characteristic of the coefficient updating unit is set so that it can follow the maximum moving speed, but since the actual moving speed constantly changes, it is possible to compare with the case of optimizing for the actual moving speed. There is a problem that the characteristics deteriorate.

The present invention has been made to solve the above problems, and provides an adaptive equalizer capable of adaptively changing the tracking characteristic according to the amount of fading fluctuation accompanying the fluctuation of the moving speed. Is intended.

[0008]

An adaptive equalizer according to the present invention uses an output of a known signal detecting correlator used in a conventional method, estimates a fading variation amount by this, and obtains the obtained fading variation amount. It is characterized in that the tracking characteristic of the adaptive filter is changed according to the estimated value.

[0009]

In the adaptive equalizer of the present invention, by adding a simple circuit, it is possible to obtain an equalizer having optimum characteristics even with respect to the amount of fading fluctuation due to fluctuations in the moving speed of the moving body.

[0010]

Embodiments of the present invention will now be described with reference to the drawings. FIG. 1 is a block diagram showing an embodiment of the present invention, in which 1 is a correlator, 2 is a reference signal generator, and 3 is a reference signal generator.
Is a coefficient updating unit, 4 is an adaptive filter, 5 is an error detecting unit, 6
Is a determiner, 7 is a switch, and 8 is a fading fluctuation amount estimator. In the configuration shown in FIG. 1, the configuration other than the fading fluctuation amount estimator 8 is the same as that of the conventional equalizer, and the description overlapping with the description of the conventional equalizer shown in FIG. 4 will be omitted. FIG. 3 is a block diagram showing the configuration of the fading fluctuation amount estimator 8. In the figure, 11 is a correlator, 12 is a memory, 13 is an LPF, and 14 is a fluctuation amount estimator.

Next, the operation will be described. As shown in FIG. 2, the transmitting side periodically inserts a known signal into the transmission signal and transmits it. This known signal has a very sharp autocorrelation,
It is assumed that a signal having a predetermined pattern is used on both the transmitting side and the receiving side, and is inserted at a rate sufficiently smaller than the transmission signal, and the interval between known signals is sufficiently shorter than the interval between transmission signals. On the reception side, this signal is input as a reception input signal and is input to the correlator 1 and the adaptive filter 4. The operations thereafter are the same as those of the conventional technique described above except the operation of the fading fluctuation amount estimator 8. The same is true, and the points different from the fading fluctuation amount estimator 8 and the conventional technique will be mainly described.

Further, the fading fluctuation amount estimator 8 is described in detail in "Fading fluctuation amount estimator" separately filed by the same applicant as the applicant of the present application. , A correlation calculation between the impulse response characteristic of the transmission path estimated by the position (width) of the known signal in the correlator 11 and the impulse response characteristic before this input from the memory 12 is performed, and the temporal variation of the impulse response characteristic is performed. Then, the fading fluctuation amount due to the fluctuation of the moving speed of the moving body is estimated. Next, the fluctuation amount estimated by the fading fluctuation amount estimator 8 is input to the coefficient updating unit 3, and the coefficient updating unit 3 changes the tracking algorithm to one suitable for the fluctuation amount based on this estimated fluctuation amount. , Coefficient update operation is performed.

A coefficient updating algorithm widely used in the adaptive equalizer for land mobile communication is, for example, RLS (Recursive).
Least Square) method. When this is used, specifically, the tracking characteristic changes due to a parameter called a forgetting factor. Therefore, when the estimated fluctuation amount from the fading fluctuation amount estimator 8 is large, the tracking characteristic is When the estimated variation amount is small, the forgetting coefficient is reduced so as to be improved, and the forgetting coefficient is increased to improve the equalization characteristic and the follow-up characteristic is changed. In this case, the output of the fading fluctuation estimator 8 does not have to be the estimated fluctuation amount, and may have a circuit configuration that outputs the forgetting coefficient itself.

[0014]

As described above, the adaptive equalizer of the present invention adaptively adjusts the tracking characteristic of the equalizer according to the amount of fading fluctuation by adding a fading fluctuation estimator having a simple circuit configuration. There is an effect that it can be changed, the deterioration of the equalization characteristic due to the change of the fading fluctuation amount is prevented, and a good reception characteristic is obtained.

[Brief description of drawings]

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

FIG. 2 is a diagram for explaining a signal form used in this type of wireless communication.

FIG. 3 is a block diagram showing an example of a configuration of a fading fluctuation amount estimator in the embodiment of the present invention.

FIG. 4 is a block diagram showing a configuration of a conventional adaptive equalizer.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Correlator 2 Reference signal generator 3 Coefficient updating unit 4 Adaptive filter 5 Error detecting unit 6 Evaluator 7 Switch 8 Fading fluctuation amount estimator 11 Correlator 12 Memory 13 Filter 14 Fluctuation amount estimator

Claims (3)

[Claims] 1. An adaptive equalizer having an adaptive filter and coefficient updating means for updating the coefficient of the adaptive filter, which requires external information about a fading fluctuation amount caused by a fluctuation of a moving speed of a moving body. Fading fluctuation amount estimating means for estimating without any input, means for inputting an output from the fading fluctuation amount estimating means as a parameter to the coefficient updating means, and changing the following characteristic of the adaptive filter according to the fading fluctuation amount. An adaptive equalizer characterized in that 2. The fading fluctuation amount estimating means, which is provided in advance in the adaptive equalizer, means for periodically inserting a known signal of a predetermined pattern into the transmission signal on the transmission side and transmitting the signal. On the receiving side, a correlation operation is performed using a reference signal that is substantially the same as the known signal, and a means for estimating the impulse response characteristic of the transmission path based on the position (width) of the known signal is used to estimate by the above means. Correlation calculation between the impulse response characteristic of the current transmission line and the impulse response characteristic before this is performed to obtain the temporal variation of the impulse response characteristic,
The adaptive equalizer according to claim 1, wherein the adaptive equalizer is means for estimating a fading fluctuation amount. 3. When the RLS (Recurs-ive Least Square) method is adopted in the coefficient updating algorithm of the coefficient updating means, the output of the fading fluctuation amount estimating means is set to the R
3. The adaptive equalizer according to claim 1, wherein the adaptive equalizer is a forgetting coefficient of the LS method.