KR20010056806A - Apparatus and method of demodulation in soft-decision channel decoder - Google Patents

Abstract

PURPOSE: A method and a device for demoduling soft decision channel decoder are provided to unify and quantize a receiving symbol by using a signal-to-noise ratio of the receiving symbol as a weight value, thereby weighting the receiving symbol and to demodulate the receiving symbol by allocating a linear metric to each quantization level. CONSTITUTION: A matching filter(21) removes a noise by filtering a signal received from an exterior. An estimator(22) estimates a signal-to-noise ratio transmitted from the matching filter(21). A weighting device(23) weights a signal transmitted from the matching filter(21) and the signal-to-noise ratio transmitted from the estimator(22). A sampling unit(24) samples the signal outputted through the weighting device(23) to a symbol period. A quantization device(25) quantizes the sample in the sampling unit(24) to Q-level. The weighting device(23) compares the signal-to-noise ratio with a predetermined value, and if the signal-to-noise ratio is less than a predetermined value, a weighting is performed. The quantization device(25) allocates a uniform linear metric to each quantization level.

Description

Demodulator in soft decision channel decoder and its method {APPARATUS AND METHOD OF DEMODULATION IN SOFT-DECISION CHANNEL DECODER}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a demodulator in a soft decision channel decoding apparatus and a method and a computer readable recording medium recording a program for implementing the method. And a computer-readable recording medium having recorded thereon a program for realizing the method.

1 is a block diagram of a conventional communication system, which includes a signal generator 11, a channel encoder 12, a modulator 13, a transmission processor 14, a demodulator 15, and a decoder 16. Equipped.

As shown in FIG. 1, the channel encoder 12 is a block code such as Reed-Solomon code, convolutional code, Trellis-Coded Modulation (TCM) in order to reduce error of information bits due to noise or distortion of a signal by a channel. The channel coding method is used to cope with errors caused by channels.

The modulator 13 receives the output of the channel encoder 12 and converts the digital signal into an analog signal suitable for the channel. Therefore, the signal converted into an analog signal by the modulator 13 is transmitted to the transmission processor 14. The signal received by the demodulator 15 is filtered by a matched filter 151 to remove noise, and then sampled at symbol period in the sampler 152.

Then, the sample normalized from the sampler 152 to the symbol period T is quantized to the Q level through the quantizer 153.

For example, assuming quantization at eight levels, the quantizer output is three bits. Assume that an Es, 8-level quantizer is used for energy of a transmission symbol in a binary phase shift keying (BPSK) modulation scheme. The metric optimized for Es / No = 0dB in this quantizer is shown in Equation 1 below.

Where j is the quantization level and m _j is the metric. However, in actual implementations, a linear metric is assigned to each quantization level.

In general, channel decoders include hard decision decoding and soft decision decoding. The hard decision decoder quantizes the channel reliability information to two levels to perform decoding. In an actual soft decision channel decoder, the decoder receives finite level channel reliability information from the demodulator to perform decoding. That is, decoding is performed by quantizing the demodulator output to the Q level. Commercial decoders are implemented with low complexity without sacrificing performance at optimal decoding performance. In addition, a signal that is usually quantized to eight levels (ie, three bits) is provided from a demodulator. In addition, decoding is performed by assigning a linear metric to each quantization level.

Therefore, the metric assigned to each conventional quantization level has a limitation in assigning an appropriate value according to the statistical characteristics of the received signal, that is, the signal-to-noise ratio (SNR). Accordingly, there is a need for a method of improving performance of a soft decision decoder by assigning a metric to a quantization level.

The present invention has been made to solve the above-described problems, by weighting the received signal using the signal-to-noise ratio (SNR) of the received symbol as a weight and uniformly quantizing the received signal. An object of the present invention is to provide a demodulator in a soft decision channel decoder for assigning and demodulating a linear metric to each quantization level, and a computer readable recording medium recording the method and a program for implementing the method.

1 is a block diagram of a conventional communication system.

2 is a block diagram of an embodiment of a demodulator in a soft decision channel decoding apparatus according to the present invention.

* Explanation of symbols for the main parts of the drawings

21: matching filter 22: estimator

23: weighting machine 24: sampler

25: quantizer

According to another aspect of the present invention, there is provided a demodulator in a soft decision channel decoding apparatus, comprising: filtering means for filtering out a received signal transmitted from the outside to remove noise; Estimating means for estimating a signal-to-noise ratio (SNR) of the signal filtered by the filtering means; Weighting means for weighting a signal transmitted from said filtering means and a signal-to-noise ratio transmitted from said estimating means; Sampling means for sampling the weighted signal by the weighting means in a symbol period (T); And quantization means for quantizing the values sampled by the sampling means and assigning a uniform linear metric to each quantization level.

The present invention also provides a demodulation method applied to a demodulator of a soft decision channel decoding apparatus, comprising: a first step of filtering a received signal transmitted from the outside and estimating a signal-to-noise ratio (SNR) of the filtered signal; Weighting a received signal according to the estimated signal to noise ratio; And a third step of sampling and quantizing the weighted signal with a symbol period T to assign a uniform linear metric to each quantization level.

The present invention also provides a demodulator for a soft decision channel decoding apparatus having a processor, the method comprising: filtering a received signal transmitted from the outside and estimating a signal-to-noise ratio (SNR) of the filtered signal; Weighting a received signal according to the estimated signal to noise ratio; And a computer-readable recording medium having recorded thereon a program for realizing a function of sampling and quantizing the weighted signal in a symbol period T to assign a uniform linear metric to each quantization level.

The above objects, features and advantages will become more apparent from the following detailed description taken in conjunction with the accompanying drawings. Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

2 is a block diagram of an embodiment of a demodulator in a soft decision channel decoding apparatus according to the present invention.

In the present invention, a linear metric is assigned to each quantization level, which is represented by Equation 2 below.

In the present invention, the signal-to-noise ratio of the received signal The output of the matched filter 21 is weighted with. Thereafter, this value is sampled in the symbol period T, and then uniformly quantized and a linear metric is assigned to each quantization level and input to the decoder. The signal received by the demodulator passes through a matched filter 21 and is sampled with a symbol period T.

That is, as shown in FIG. 2, the demodulator estimates a signal-to-noise ratio (SNR) of the matched filter 21 for filtering out a signal received from the outside to remove noise, and a signal transmitted from the matched filter 21. An estimator 22, a weighting unit 23 for weighting a signal transmitted from the matching filter 21 and a signal-to-noise ratio transmitted from the estimator 22, and a signal output through the weighting unit 23 A sampler 24 for sampling in the symbol period T and a quantizer 25 for quantizing the samples normalized in the symbol period T from the sampler 24 to the Q-level.

Here, the weighting unit 23 compares the signal-to-noise ratio with a predetermined value and weights only when the signal-to-noise ratio is smaller than the predetermined value. The quantizer 25 then assigns a uniform linear metric to each quantization level.

Looking at the operation of the demodulator of the present invention in more detail as follows.

First, the matched filter 21 has an impulse response matched to a transmission signal transmitted to the channel by the modulator 13 of FIG. In other words, assuming that the signal transmitted from the modulator 13 is s (t) , the impulse response of the matching filter 21 is expressed by Equation 3 below.

Here, T is a symbol period of a transmission signal, and * is a conjugate conjugate. In addition, it is assumed that the symbol timings of the transmitter and the receiver are aligned. Before sampling the output of the matched filter 21 in the symbol period, the estimated signal of the received signal estimated by the estimator 22 is estimated. The value of the matching filter 21 is weighted. This weighting is carried out in the weighting unit 23.

The signal transmitted from the weighting unit 23 is sampled at symbol period T in sampler 24, and quantizer 25 quantizes this value to a Q level and a uniform metric (i.e., uniform for each quantization level). , Assigns Equation 2)

The present invention described above is not limited to the above-described embodiments and the accompanying drawings, and various substitutions, modifications, and changes can be made in the art without departing from the technical spirit of the present invention. It will be apparent to those of ordinary knowledge.

The present invention as described above has an effect of improving the performance of the channel decoder while using the conventional finite level quantizer and the soft decision decoding apparatus. In particular, in a mobile communication channel in which channel characteristics change with time, reception power changes due to fading. In this environment, the allocation of channel metrics according to the present invention can improve the performance of the decoding apparatus.

Claims (4)

In the demodulator in the soft decision channel decoding device, Filtering means for filtering out a received signal transmitted from the outside to remove noise; Estimating means for estimating a signal-to-noise ratio (SNR) of the signal filtered by the filtering means; Weighting means for weighting a signal transmitted from said filtering means and a signal-to-noise ratio transmitted from said estimating means; Sampling means for sampling the weighted signal by the weighting means in a symbol period (T); And Quantization means for quantizing the value sampled by the sampling means and assigning a uniform linear metric to each quantization level Demodulator in soft decision channel decoding apparatus comprising a. In the demodulation method applied to the demodulator of the soft decision channel decoding device, A first step of filtering a received signal transmitted from the outside and estimating a signal-to-noise ratio (SNR) of the filtered signal; Weighting a received signal according to the estimated signal to noise ratio; And A third step of sampling and quantizing the weighted signal with a symbol period T to assign a uniform linear metric to each quantization level Demodulation method in a soft decision channel decoding apparatus comprising a. The method of claim 2, The second step, And demodulating the signal-to-noise ratio (SNR) with a predetermined value and weighting only when the signal-to-noise ratio (SNR) is smaller than the predetermined value. In a demodulator of a soft decision channel decoding device having a processor, Filtering a received signal transmitted from the outside and estimating a signal-to-noise ratio (SNR) of the filtered signal; Weighting a received signal according to the estimated signal to noise ratio; And Sampling and quantizing the weighted signal at a symbol period (T) to assign a uniform linear metric to each quantization level A computer-readable recording medium having recorded thereon a program for realizing this.