The Application Of Turbo Codes In Mobile Communication System

Nowadays, the fast expansion of economy gives both a good chance and a strong motive force for communication systems, and related techniques to develop. This paper will discuss the novel channel error correcting code technique in communication- Turbo codes technique.In 1993, Turbo Codes was first proposed by C.berrou in France, because the performance of Turbo codes achieved the Shannon capacity, recently it has been improved and used in many fields.Firstly, the backgrounds and the recent development are introduced. And the fundamental knowledge of Turbo code is indicated after giving the theory of the channel coding and the rule of the Maximum a posteriori. We mainly present the typical structure, the common interleavers and the decoding algorithms.Secondly, with the help of computer simulation, the error rate performance capabilities of Turbo codes for different conditions in additive white Gaussian noise channel are carefully studied and discussed. Then, draw some useful conclusions from it.Thirdly, talk about the Rayleigh fading channel and Rice fading channel. For providing some references to applying in the communication system, we make several emulations with different mobile velocities and different fading factors.Finally, aim to the faults of conventional soft-output Viterbi algorithm, such as bad performance, high sequence delay and storage requirement, a new algorithm called slide-window modified soft-output Viterbi algorithm (SW-MSOVA)is presented. The performance is improved by reducing the inherent strong correlation between the intrinsic information(input to the SOVA)and extrinsic information(output of the SOVA). Moreover, the sequence delay and storage requirement are reduced by a slide-window scheme. On the other hand, a simplified log maximum a posteriori (Log-MAP) algorithm is presented based on approximation theory. In the simplified algorithm, the optimal square approximation polynomial, whose coefficients are derived from the characteristic equations, is adopted to calculate the correction function. Compared with the original algorithm, the proposed algorithm has advantages of low complexity and lower decoding delay.