Study And Implementation Of Turbo-Code Encoding And Decoding

Turbo code were first introduced in 1993 by C.Berrou etc, they are shortened from parallel concatenation recursive systematic convolutional codes whose encoder consists of a parallel concatenation of two or more convolutional codes, and its decoder uses a soft-input/soft-output feedback decoding rule. This kind of code has given rise to a large interest in the coding theory because of they can still achieve small bit error rate at low SNR close to the Shannon capacity limits. In the development of the third generation mobile communication systems, it is well known that Turbo codes are the way of correct coding of high-speeding data channel. The research of Turbo codes includes the design of the encoder, the interleaver and soft-out/soft-in iterative decoding algorithm. The goal of this paper is to study the key issues both in encoding and decoding block and to realize the encoding block by hardware. Firstly, the background of its birth and development trend are introduced. Secondly, some fundamental theory and basic structure of Turbo codes are described. According to this, analyses of different parameters for the performance of Turbo codes are presented and got some conclusions. During the process of simulation, some methods are proposed to improve the performance of BER: used the combined design of interleaver and puncture in encoding part, so, each information bit has corresponding parity bit which have equal protection; put forward linear approximate and fixed approximate to reduce the decoding complexity without notable effect on the performance of Log-MAP algorithm; make use of additional bits at the end of each frame of SOVA. In order to accelerate decoding, block decoding are used to shorten waiting time and a new stop criterion based on external information are proposed to improve decoding time. Last, realized the whole Turbo encoder use VHDL language based on programmable device.