State metric bit wide control method and device for Turbo code decoder

Abstract

The method makes all measured state values positive generated from forward directed and inverted recursion procedures of MAP decoding algorithm for Turbo codes. Thus, simple normalizing operation can be adopted to reduce bit width of measured state value. Moreover, implementation of hardware is simpler according the measured state values calculated by the disclosed method. When calculating measured path values through forward directed and inverted recursion procedures, the method adds specific offset to the calculation so that all measured path values obtained are positive. Using minimal value in all measured path values in current moment carries out normalization for all measured path values. Advantages are: reducing bit width of measured state values without influence on performance of decoder of Turbo code; reducing area of chip. The invention also lowers complexity of hardware for realizing recursion procedures.

Description

technical field [0001] The invention relates to a method and device for controlling the bit width of a state metric in a Turbo code decoder. Background technique [0002] The principle of the Turbo code is based on the modification of the algorithm and structure of the traditional concatenated code. The introduction of the inner interleaver makes the positive feedback of iterative decoding well eliminated. The turbo code encoder is composed of two recursive systematic convolutional codes (recursive systematic convolutional codes, referred to as RSC codes), an inner interleaver and a deleter. Figure 1 The structure of Turbo code encoder in cdma2000 system is given. According to the different puncture forms of the deleter, the coding rate of the Turbo code can vary from 1 / 6 to 1 / 2. Considering the complexity of decoder implementation and decoding performance, Turbo codes are generally decoded using an iterative maximum a posteriori (MAP) decoding algorithm. Due to the high ...

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Problems solved by technology

However, in order to ensure the performance of the Turbo code decoder, there must be certain requirements for the number of quantized bits in the operation, that is, the number of bits in the operation should not be too small, otherwise the forward and backward path metrics will overflow, and the Turbo code will be greatly deteriorated. decoding performance, which is in contradiction with the implementation scale and operation speed

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