JPH088786A - Adaptive equalizer - Google Patents

Abstract

PURPOSE:To obtain an adaptive equalizer which has an automatic frequency control function, the followup ability for a high speed fading and an excellent operation also for a multifading. CONSTITUTION:An ideal signal 15 is inputted in a transversal filter 16 estimating the state of a transmission line and a signal which is close to an input signal 13 is inputted in a delay detector 1T. In the delay detector 17, an estimation phase difference 18 is obtained from this input signal 13. From a delay detector 11 where the input signal 13 is inputted, a reception phase difference 19 is obtained. The square of an error 20 from which the estimation phase difference 18 and the reception phase difference 19 are subtracted is calculated by an arithmetic unit 21. The result is inputted in a MLSE equalizer 22, and the most likely ideal signal 15 becomes a hard decision output signal 14.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is an adaptive equalizer which is used in a receiver for mobile communication, performs automatic frequency control (AFC), and operates well against high speed fading, multipath fading, etc. It is about.

[0002]

2. Description of the Related Art FIG. 4 shows a block diagram of a demodulator having a conventional automatic frequency controller. In FIG. 4, 1 is an automatic frequency control device for detecting and correcting a frequency offset of a received signal, 2 is a demodulator for demodulating the received signal, 3 is an input signal, and 4 is a hard decision output signal of output data.

The operation of the conventional example will be described. The input signal 3 is input to the automatic frequency control device 1, where the frequency offset is detected, the frequency peak of the input signal 3 is converted to the optimum frequency peak position, and the input signal 3 is input to the demodulation device 2. The demodulator 2 demodulates the input signal having no frequency shift into the hard decision output signal 4 by the delay detection means or the adaptive equalizer means.

As described above, in the demodulator using the conventional automatic frequency control device 1, the automatic frequency control device 1 and the demodulation device 2 have different configurations and perform their respective operations.

[0005]

However, the delay detection means used in the conventional demodulation device has poor reception performance against multipath fading, and the adaptive equalization means used in the conventional demodulation device has the disadvantage. However, there is a problem that the reception performance is good for multipath fading, but the reception performance is poor as compared with the differential detection means for fast fading without delay waves.

The present invention solves the above-mentioned problems of the prior art, has an automatic frequency control function, has followability for high-speed fading, operates well even for multipath fading, and It is an object of the present invention to provide an adaptive equalizer capable of improving the clarity of the.

[0007]

In order to achieve this object, the present invention comprises a differential detection means for differentially detecting a received signal, and an adaptive equalization means for demodulating a signal from the differential detection means, It is characterized by performing automatic frequency control.

Further, the delay detection means and the adaptive equalization means are configured to correct the delayed wave of the received signal and the degraded signal characteristic due to the linear distortion.

[0009]

According to the above construction, by providing the adaptive equalization means and the differential detection means, the automatic frequency control function is provided, the followability with respect to the fluctuation due to the high speed fading is high, and the reception is also possible with respect to the multipath fading. The performance is good.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT An embodiment of the adaptive equalizer of the present invention will be described in detail below with reference to the drawings.

FIG. 1 is a block diagram showing the outline of an adaptive equalizer according to an embodiment of the present invention. This embodiment takes as an example a demodulator in a receiving device of a mobile telephone connected to a base station by a wireless line. .

In FIG. 1, reference numeral 11 is a delay detection device for delay-detecting an input signal, 12 is an adaptive equalization device for demodulating the delay-detected signal, and 13 is a baseband band of radio waves sent from a base station through a wireless line. An input signal, which is a received signal modulated into a signal, and 14 is a hard decision output signal.

FIG. 2 is a detailed diagram for explaining the operation of the adaptive equalizer of the present embodiment, in which 15 is an ideal signal, 16 is a transversal filter which estimates the state of the transmission path, and 17 is one symbol before. A differential detection device that performs differential detection based on the current signal and the current signal, 18 is an estimated phase difference, 19 is a received phase difference, 20 is an error between the estimated phase difference 18 and the received phase difference 19, and 21 is an operation for obtaining the square of the error 20. An apparatus, 22 is an MLSE (Maximum Likelihood Sequent Estimate) equalizer that demodulates a data sequence from the square of the error 20, and 23 is a coefficient estimator that updates the coefficient of the transversal filter 16.

Next, the operation of this embodiment will be described.
The input signal 13 is input to the differential detection device 11, decomposed into an in-phase component and a quadrature component, and input to the adaptive equalization device 12. The adaptive equalizer 12 corrects the frequency offset variation and the variation due to fading, and outputs a hard decision output signal 14.

Here, when the ideal signal 15 is input to the transversal filter 16 which estimates the state of the transmission line, a signal close to the input signal 13 is output and input to the differential detection device 17. The differential detection device 17 differentially detects the input signal 13 to obtain an estimated phase difference 18. In addition, the reception phase difference 19 is the input signal 13
Is obtained from the differential detection device 11. Estimated phase difference 18
The result of subtracting the received phase difference 19 is an error 20, and a square of this error 20 is obtained by the arithmetic unit 21. Error 20
The squared value is input to the MLSE equalizer 22, and the most likely ideal signal 15 becomes the hard decision output signal 14.

Next, the coefficient estimator 23 for updating the coefficient of the transversal filter 16 will be described. FIG. 3 is an explanatory diagram of the LMS (least mean square) algorithm of the adaptive equalizer of the present embodiment, in which 24 is an input signal (X _i ), 25 is a differential detection device, and 26 is a transmission signal sent from the base station. Some ideal signal
(R _i ), 27 is a transmission path estimation state vector (W _i ) which is a state vector of the transversal filter 16, 28 is a transmission path state vector (H _i ) representing the state of the transmission path, 29 is a delay detection device, 30 Is the error (α _i ).

When differential detection is performed on the input signal 24 (X _i ) by the differential detection device 25, the signal after differential detection is the input signal at time i.
Using 24 (X _i ) and the input signal 24 (X _i-1 ) one symbol before,
It is expressed as (Equation 1).

[0018]

[Equation 1]

Here, the transmission channel estimated state vector 27 (W _i )
== Transmission path state vector 28 (H _i ), the error 30 (α _i ) becomes 0, and the ideal signal 26 (R _i ) which is the data sequence transmitted from the base station can be estimated. However, since the transmission line state vector 28 (H _i ) is an unknown state vector, the error 30 (α
Based on the signal _i ), the channel estimation state vector 27 (W _i ) of the transversal filter is estimated using the LMS algorithm.

Since the differential detection is expressed by the equation (1), the signal having the error 30 (α _i ) is expressed by the equation (2).

[0021]

[Equation 2]

The direction of changing the fastest alpha _i ² by alpha _i ² the transmission path estimated state vector 27 (W _i) and partial differentiation in the transmission path estimated state vector 27 (W _i) is obtained.

[0023]

(Equation 3)

Therefore, the channel estimation state vector 27 (W _i ) to be updated is

[0025]

[Equation 4]

[0026] Here, the constant C can be determined so that α _i = 0 when W _{i + 1} has been obtained at the time i, and thus is calculated as in (Equation 5).

[0027]

(Equation 5)

Therefore, the updating W _{i + 1} is transformed as shown in (Equation 6).

[0029]

(Equation 6)

[0030]

[Outer 1]

Next, the case where there is a frequency offset will be described. If there is a frequency offset (Equation 2)
Is transformed into (Equation 7),

[0032]

(Equation 7)

[0033] W _{i + 1} to the α _i ² update to partial differential in W _i of (number 7),

[0034]

[Equation 8]

Therefore, the frequency offset does not participate in updating the transmission path estimation state vector 27 of the transversal filter.

Although the LMS algorithm is used as the coefficient updating algorithm of the transversal filter in this embodiment, other coefficient updating algorithms may be used. Further, although the MLSE equalizer is used as the adaptive equalizer, another adaptive equalizer may be used.

[0037]

As described above, the adaptive equalizer of the present invention has the effect of adaptively compensating the frequency offset by using the algorithm using the differential detection means. Further, by using the adaptive equalization means and the differential detection means, it is possible to estimate the amount of phase change per symbol due to Rayleigh fading, easily update the transmission path estimation state vector of the transversal filter, and It is possible to correct degraded signal characteristics and improve the clarity of voice and data communication.

[Brief description of drawings]

FIG. 1 is a block diagram showing an outline of an adaptive equalizer in an embodiment of the present invention.

FIG. 2 is a detailed diagram showing an adaptive equalizer in this embodiment.

FIG. 3 is an explanatory diagram of an LMS algorithm of an adaptive equalizer.

FIG. 4 is a block diagram showing a demodulator having a conventional automatic frequency control device.

[Explanation of symbols]

1 ... Automatic frequency control device, 2 ... Demodulation device, 3, 13,
24 ... Input signal, 4,14 ... Hard decision output signal, 11,17,
25, 29 ... Differential detection device, 12 ... Adaptive equalization device, 15, 26 ...
Ideal signal, 16 ... Transversal filter, 18 ... Estimated phase difference, 19 ... Received phase difference, 20, 30 ... Error, 21 ...
Arithmetic unit, 22 ... MLSE equalizer, 23 ... coefficient estimator,
27 ... Channel estimated state vector, 28 ... Channel state vector.

Claims (2)

[Claims] 1. An adaptive equalizer, comprising: a delay detection unit that delay-detects a received signal; and an adaptive equalization unit that demodulates a signal from the delay detection unit, and performs automatic frequency control. 2. The adaptive equalizer according to claim 1, wherein the delay detection means and the adaptive equalization means correct the deteriorated signal characteristics due to the delay wave and the linear distortion of the received signal.