JPH0865206A - Cdma system receiver - Google Patents

Abstract

PURPOSE: To improve the reception quality of the CDMA system receiver. CONSTITUTION: A digital signal in several bits obtained by A/D conversion and oversampling is given to a correlation device such as a matched filter 4, in which inverse spread processing is applied to the signal. Sum of squares of an output of the matched filter 4 is obtained, a clock recovery section 8 detects a peak position of a received signal and delayed waves being several samples around the peak are selected. An interval of the delayed waves is detected from a signal received by a tap controller 9 and subject to timewise averaging therein over several symbols to estimate the state of dispersion in the delayed signals thereby deciding a tap interval of an adaptive filter 7. Plural delayed waves from the matched filter 4 are given to the adaptive filter 7, only required taps are operated by a control signal from the tap controller 9, a transmission line is estimated by using a training signal, a desired wave component and an interference wave component are separated. The signals are synthesized and recovered data 6 are provided as an output.

Description

Detailed Description of the Invention

[0001]

The present invention relates to a CDMA (code division)
The present invention relates to a receiver using the on multiple access method.

[0002]

2. Description of the Related Art A receiving apparatus using a CDMA system can separate a plurality of delayed waves when despreading if the delay dispersion is larger than the spreading chip width. Then, a path diversity effect can be obtained by combining these plural delayed waves. However, received waves that are greatly affected by interference,
When there is a received wave of only interference, the quality of the received signal after combining is deteriorated. To that end, the paper by Akiyo Higashi et al. (199
Received by inserting a training signal into the transmission signal, estimating the desired wave component or the interference wave component using an adaptive algorithm, and separating them, as described in 2nd IEICE Spring Conference B-301). It has been proposed to improve the quality of the signal.

FIG. 5 is a block diagram showing the configuration of a conventional CDMA system receiver. In FIG. 5, the signal received by the receiving antenna 1 is amplified by the receiving unit 2 and is A / D converted by the A / D converting unit 3 (sampling interval = n / T, 1 / T
= Chip speed, n: integer), and the despreading is performed by the matched filter 4 forming the correlator. The output of the matched filter 4 is input to an adaptive filter 18 composed of a transversal filter that synthesizes a plurality of delayed waves, the transmission path is estimated by an adaptive algorithm, and a desired wave component and an interference wave component are separated. The reproduction data 6 is output after the combination.

Further, the clock reproducing section 8 detects the peak position of the received signal and reproduces the clock. Adaptive filter 18
The tap position of is determined around this reproduced clock.

FIG. 6 is a block diagram of the adaptive filter shown in FIG. 5. The adaptive filter 18 is composed of a transversal filter, and the adaptive filter input 5 is input to a tap 10 having a chip interval. Then, in the line estimator 11, the error 12
The training signal 15 is used to estimate the transmission path by an adaptive algorithm so that the sum of squares of the difference between the output of the adder 13 and the output of the discriminator 14 is minimized, and interference with the desired wave component of each delayed wave Separate the wave component, determine the weighting of the multiplier 16,
Optimal weighting is performed by the multiplier 16. And adder
The weights from the multiplier 16 are added in 13 and the added output is discriminated by the discriminator 14 as positive or negative, and the reproduction data 6 with few errors is obtained.

[0006]

However, in the above-mentioned conventional CDMA receiver, when the taps of the transversal filter forming the adaptive filter are chip intervals and the delay spread is smaller than the spreading chip width, despreading is performed. However, the delayed wave cannot be separated, and the path diversity effect is small. Further, regardless of the delay dispersion state, if the tap interval is made smaller than the chip width from the beginning, the amount of calculation increases, and there are unnecessary taps depending on the delay dispersion.

Further, considering the overlay of the macro cell and the micro cell in order to accommodate the receiver having a fast moving speed and the receiver having a slow moving speed, the delay dispersion states are different in each service area.

In view of such a point, the present invention makes the tap interval variable according to the state of delay dispersion, separates the delay wave even when the delay dispersion is smaller than the spreading chip width, and improves the reception quality by the path diversity effect. The purpose is to improve.

[0009]

In order to achieve the above object, the present invention is provided with a tap controller for controlling the tap interval of a transversal filter which constitutes an adaptive filter, and a tap selection switch to spread a delayed wave. According to the above, the tap interval is made variable, and the amount of calculation is reduced and the quality of received data is improved as compared with the case where the tap interval is made smaller than the chip width from the beginning.

[0010]

According to the present invention, with the above configuration, the tap resolution is improved by controlling the tap interval by the tap controller and the tap selection switch, and the delayed wave is separated even when the delay dispersion is smaller than the chip width. It is possible to improve the reception quality. Further, the amount of calculation can be reduced as compared with the case where the tap interval is smaller than the chip width from the beginning.

[0011]

1 is a block diagram showing the configuration of a CDMA system receiver in an embodiment of the present invention. 1, parts 1 to 6 are the same as the parts 1 to 6 of the conventional example of FIG. 5 described above. 9 is a tap controller,
The tap interval is controlled by the received data selected from the clock recovery unit 8. Reference numeral 7 is an adaptive filter composed of a transversal filter, which comprises a tap 10, a channel estimator 11, an adder 13, a discriminator 14, and a multiplier 16 as shown in the block diagram of FIG. The tap interval can be switched by the tap selection switch 17 by a control signal from. 6 except the tap selection switch 17.
The operation of the conventional adaptive filter is the same. The number of taps 10 of the adaptive filter 7 is N.

Next, the operation of the above embodiment will be described.

The signal received by the receiving antenna 1 is amplified by the receiving section 2 and A / D converted by the A / D converting section 3 (sampling interval = n / T, 1 / T = chip speed, n: integer). The oversampled digital signal of several bits is despread by the matched filter 4 forming a correlator. The sum of squares of the output of the matched filter 4 is calculated, the clock reproducing unit 8 detects the peak position of the received signal, and a delayed wave of several samples is selected with this peak as the center. The selected delayed wave is input to the tap controller 9 and averaged over several symbols over time. The tap interval of the adaptive filter 7 is determined by detecting the delay wave interval from the averaged signal and estimating the delay dispersion state.

The plurality of delayed waves output from the matched filter 4 are input to the adaptive filter 7 and the control signal from the tap controller 9 is used to operate only the required taps 10 by the tap selection switch 17. The transmission signal is estimated by the adaptive algorithm using the training signal 15, and the desired wave component (shown by the solid line) and the interference wave component illustrated in FIGS.
(Dashed line) is separated. These signals are combined and reproduced data 6 is output.

FIG. 3 shows an example of distribution of the desired wave and the interference wave of the line model when the estimated delay dispersion is larger than the chip width, and the tap number N = 6. As shown in FIG. 3, when the delay dispersion estimated not to be attenuated to some extent is larger than the preset maximum number of taps N (N = 6) × chip width a and each delayed wave can be separated, tap 10 The tap interval is set to the chip width, and the reproduction data 6 is output.

However, FIG. 4 shows an example of the distribution of the desired wave and the interference wave of the line model when the estimated delay dispersion is smaller than the chip width, and it is estimated that there is no attenuation as shown in FIG. 4 (1). The maximum number of taps N with preset delay dispersion
When the delay wave cannot be separated by less than (N = 6) × chip width a, the tap interval is set to a fractional interval (1/2 chip width in this example) as shown in FIG. 4B, and the reproduced data 6 is output. . That is, the delay time is estimated by detecting the peak position and averaging in time, and the delay dispersion is controlled by controlling the tap interval to either the chip width or the fractional interval (T / n). It is possible to output the reproduction data 6 having good reception quality regardless of the above. Further, even if the state of delay dispersion changes during operation at fractional intervals and the delay dispersion becomes larger than the chip width, the clock reproducing unit 8 detects the peak position for each symbol and performs temporal averaging. By sequentially estimating the delay time of the delayed wave, the tap interval is switched to the chip width to perform data reproduction.

The clock reproducing unit for detecting the peak position in the CDMA system receiver is originally provided in this kind of receiver, and the hardware scale does not increase.

The tap interval and the number of taps differ depending on the system in which the overlay of the macro cell and the micro cell is considered, the assumed system, and the like.

[0019]

As described above, the CDMA of the present invention
The system receiver can improve the quality of received data by determining the tap interval of the adaptive filter from the state of delay dispersion.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of a CDMA system receiver according to an embodiment of the present invention.

FIG. 2 is a configuration diagram of the adaptive filter of FIG.

FIG. 3 is a diagram showing an example of distribution of desired waves and interference waves in a line model (when the estimated delay dispersion is larger than the chip width).

FIG. 4 is a diagram showing a distribution example of a desired wave and an interference wave of a line model (when the estimated delay dispersion is smaller than the chip width).

FIG. 5 is a block diagram showing the configuration of a conventional CDMA receiver.

6 is a configuration diagram of the adaptive filter of FIG.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Receiving antenna, 2 ... Receiving part, 3 ... A / D converter, 4 ... Matched filter, 5 ... Adaptive filter input, 6 ... Reproduction data, 7, 18 ... Adaptive filter, 8 ...
Clock reproduction unit, 9 ... Tap controller, 10 ... Tap,
11 ... Line estimator, 12 ... Error, 13 ... Adder, 14 ... Discriminator, 15 ... Training signal, 16 ... Multiplier, 17 ...
Tap selection switch.

Continuation of front page (51) Int.Cl. ⁶ Identification number Office reference number FI technical display location H04B 7/005

Claims (1)

[Claims] 1. A correlator such as a matched filter for despreading the received signal using a digital signal of several bits oversampled by an A / D converter of a CDMA system receiver as a received signal, and the correlator. The peak position of the despread signal is detected, a delayed wave of several samples is selected around the peak position, and a clock recovery unit that recovers the symbol clock according to the peak position and the delayed wave selected by the clock recovery unit are selected. A tap with a fixed number of taps in an adaptive filter composed of a transversal filter that synthesizes delayed waves by averaging over several symbols in time, detecting the delay wave interval, and estimating the delay dispersion state. A tap controller that variably determines the interval according to the delay dispersion state, and a transformer that combines delayed waves with taps set by the tap controller. A CDMA system receiver having an adaptive filter configured by a transversal filter.