KR100684423B1 - Map decoder for decision function cancellation device - Google Patents

Abstract

1. TECHNICAL FIELD OF THE INVENTION

The present invention relates to a map decoder for the determination function in the interference cancellation device.

2. The technical problem to be solved by the invention

The present invention implements a signal determination process as a MAP (Maximum a Posteriori Probability) decoder in the process of despreading / determining / spreading / removing in an interference canceller, thereby increasing interference and symbol decoding performance of the interference canceller. To provide a map decoder for the decision function in the removal device.

3. Summary of Solution to Invention

The present invention provides probability estimating means for estimating a probability from a result of performing a despreading function when performing a determination function in an interference canceling apparatus that performs despreading, determining, respreading, and interference canceling functions; Metric generating means for generating a metric according to a decoding symbol value for each user from the probability estimated by the probability estimating means; The probability value APP of the symbol is calculated from the metric generated by the metric generating means, and the user-specific decoding symbol value having the maximum probability from the calculated APP is determined and provided as an input value when the respreading function is performed. Decoding symbol value determining means is included.

4. Important uses of the invention

The present invention is used in the determination function of the interference cancellation device.

Map Decoder, Probability Update, Interference Canceller, and Metric Generation

Description

MAP DECODER FOR DECISION FUNCTION CANCELLATION DEVICE}             

1 is an exemplary configuration diagram of an interference cancellation apparatus to which the present invention is applied.

2 is a block diagram of an embodiment of a map decoder for a determination function in an interference cancellation device according to the present invention;

* Explanation of symbols for the main parts of the drawings

21: Probability Calculator 22: Metric Generator

23: user decoder 1 to user decoder K

The present invention provides a Code Division Multiple Access (CDMA) cellular mobile communication system, a Personal Communication System (PCS), a Trunk Radio System (TRS), and other mobile devices used in foreign countries. System capacity in base station receivers of wireless communication systems such as telecommunication systems, next generation mobile communication systems such as IMT-2000 (International Mobile Telecommunication-2000) and UMTS (Universal Mobile Telecommunication System) The present invention relates to an interference cancellation device that can increase the signal-to-noise ratio by reducing interference by estimating and removing another user's signal in order to increase the signal density.

In general, CDMA systems are distinguished by radio channel or user code. Conventional receivers extract and use only the target user's signal using the orthogonality between the codes from the received signals, but interference by other users in the base station receiver of the broadband CDMA to be applied to the wireless service of the next generation mobile communication (IMT-2000) system. An interference canceller is needed to eliminate this problem. That is, the interference canceller estimates and removes signals of other users from the received signal, thereby increasing the signal-to-noise ratio of the desired user, thereby increasing call quality and system capacity. The interference canceller performs a process of despreading / deciding / respreading / interfering a signal received from the antenna and then outputs a first interference cancellation result through a process of despreading / re-determining. In this case, the decision unit between despreading and respreading generally used the simplest binary hard decision method.

However, if the binary hard decision method is used in the temporary decision unit between despreading and respreading, the integration result of the matched filter is only divided by 0-1. This is high. Therefore, there is a problem that the wrong result has a fatal effect on the interference cancellation result by removing the signal that should not be removed. In addition, although the misjudgment may be corrected through repetition of the interference elimination process, it is not necessarily corrected, and even if corrected, the number of repetitions is inconvenient compared to the case where the accuracy of the initial temporary decision is high.

The present invention has been made to solve the above problems, and by implementing a signal determination process in the process of despreading / determining / spreading / removing in the interference canceller with a MAP (Maximum a Posteriori Probability) decoder, It is an object of the present invention to provide a map decoder for a determination function in an interference cancellation device for increasing the performance of the removal device and the symbol decoding performance.

According to the present invention for achieving the above object, a probability estimation for estimating a probability from the result of performing the despreading function at the time of performing the determination function in the interference eliminating device for performing the despreading, determining, respreading, and interference canceling functions. Way; Metric generating means for generating a metric according to a decoding symbol value for each user from the probability estimated by the probability estimating means; The probability value APP of the symbol is calculated from the metric generated by the metric generating means, and the user-specific decoding symbol value having the maximum probability from the calculated APP is determined and provided as an input value when the respreading function is performed. And decoding symbol value determining means.

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.

1 is an exemplary configuration diagram of an interference cancellation apparatus to which the present invention is applied.

As shown in FIG. 1, the interference canceller includes an interference canceller 11, a despreader 12, a respreader 13, and a determiner 14.

The interference canceling unit 11 receives the K respread signals output from the respreading unit 13, adds signals of K-1 other users except itself, and adds the signals of other users summed from their original signals. Subtract the signal.

The despreader 12 is composed of a filter bank and receives a signal in which several user signals are mixed, and outputs K signals obtained by despreading each user.

The respreading unit 13 receives the determined signal, multiplies the spreading code given for each user and the fading value of the channel, and reproduces the original signal.

The determination unit 14 receives the despread K signals and performs binary determination. The determined K signals are input through the respreading unit 13. Here, the detailed description of the determination unit is as described later.

That is, the interference canceller repeatedly performs the inversion, determination, respread, and interference cancellation function until the desired signal quality is reached, and then outputs K user signals.

2 is a block diagram of a map decoder for determining a function in an interference cancellation apparatus according to an embodiment of the present invention, and includes a probability calculator 21 for estimating a probability from a result of performing the despreading function, and the probability calculator. A metric generator 22 for generating a metric according to a user-decoded symbol value from the probability estimated at 21, and a probability value APP of the symbol from the metric generated by the metric generator 22, and calculated A decoder 23 for each user is provided to determine a decoding symbol value for each user having a maximum probability from an APP and provide the input value when performing the respreading function.

Here, the map decoder implemented for multi-users has parameters that consider interference between users by extending the parameters of the map decoder for a single user.

That is, the map decoder consists of a function of calculating a probability, a function of calculating a metric, and a decoding function for each user. The flow of processing K user signals input to the decoder is based on a probability calculator 21 / metric generator 22 /. In the order of the user decoder 23, the K signals decoded as shown in Fig. 2 are re-input to the metric generator 22.

를 입력받아 APP

를 계산한다. 그러나, 다중 사용자 환경에서는 확률

가 다중 사용자 간섭때문에 전체 벡터 y에 상관하게 된다. 따라서, 입력 메트릭은

, 출력 확률은

이 된다. In general, the map decoder decodes an A Posteriori Probabaility (APP) of the received channel symbol. That is, the metric

Take input APP

Calculate However, in a multiuser environment, the probability

Is correlated to the overall vector y due to multi-user interference. Therefore, the input metric is

, The output probability is

Becomes

을 받아들여 다중 사용자 환경에서의 k 번째 사용자 심볼의 확률을 다음의 [수학식 1]과 같이 계산한다. Probability calculator 21 stores K user symbols from matched filter banks.

Calculate the probability of the k th user symbol in the multi-user environment as shown in Equation 1 below.

를 받아들여 메트릭

를 다음의 [수학식 2]와 같이 계산한다.Here, the metric generator 22 is the probability calculated by the probability calculator 21.

Accept metrics

Is calculated as shown in Equation 2 below.

는 복호된 K개의 심볼 확률의 곱이다.here,

Is the product of the decoded K symbol probabilities.

The user decoder 23 of the map decoder receives a metric from the metric generator 22 and estimates a posteriori probabaility (APP) of a symbol to determine a data bit having a maximum probability.

The APP is estimated by tracking the trellis diagram in the forward and reverse directions, and is expressed as Equation 3 below.

과 역방향 메트릭

은 재귀적으로 구해지며, 양방향 매트릭스를 구하여 APP를 추산하는 과정은 다음과 같다.Where forward metrics

And reverse metrics

Is obtained recursively, and the process of estimating APP by obtaining a bidirectional matrix is as follows.

First, the initial value is set as shown in Equation 4 below.

Second, the y _t is input as shown in Equation 5 below.

Calculate and store as above.

Third, β is calculated after receiving all y sequences, and is represented by Equation 6 below.

Finally, the APP is calculated as defined in Equation 4 above, and the symbol having the maximum probability is determined.

와 맵 복호기의 판정모듈의 결과인

를 이용하여 갱신된 확률

를 계산한다.When the interference canceller repeatedly performs the inversion, determination, respread, and interference cancellation functions until the desired signal quality is reached, the metric generator 22 of the map decoder outputs the probability calculator 21.

And the result of the decision module of the map decoder

Probability updated using

Calculate

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

As described above, the present invention implements a map decoder in consideration of a multi-user environment and combines it with an interference canceller, thereby improving symbol accuracy in a MAP decoder and improving interference cancellation effects of an interference canceller as the symbol accuracy increases. There is an effect that can be raised.

Claims (1)

When performing the judgment function in the interference canceling device that performs the despreading, determining, respreading, and interference canceling functions, Probability estimating means for estimating a probability from the result of performing said despreading function; Metric generating means for generating a metric according to a decoding symbol value for each user from the probability estimated by the probability estimating means; The probability value APP of the symbol is calculated from the metric generated by the metric generating means, and the user-specific decoding symbol value having the maximum probability from the calculated APP is determined and provided as an input value when the respreading function is performed. Decoding symbol value determining means Map decoder for the determination function in the interference cancellation device comprising a.

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