Turbo Code's Application On WCDMA Channel Decoding

Turbo Code is the one of most advanced channel coding and decoding technologies at present. Since its appearance, Turbo Code has attracted much interest because of its excellent performance approaching to Shannon Limit. It was honored the greatest discovery of channel coding since Ungerboeck put forward Trellis Coding Modul-ation(TCM).Channel coding and decoding is a very critical part of mobile communication system and it has great effect on the error-correcting performance and signal-to-noise ratio limit of mobile communication system. And thereby it has great effect on Mobile Communication System.Generally WCDMA adopts convolution code or Turbo Code as its channel coding and decoding scheme. As a result of computer simulation, under spe-cial parameters and Add White Gauss Noise (AWGN) channel, the BER performance of Turbo Code is very close to Shannon Limit.This paper mainly discussed the principle, iterative decoding idea and algorithm of Turbo Code. The software simulation, hardware implementation was also given. Based on the speciality of wireless channel of WCDMA, we constructed the corresponding simulation model of Turbo Code,and made some simulation on the impact of code rate,frame size, iteration times and interleaver to Turbo Code. Because of unnecessary time delay and power consuming of fixed times decoding,we put forward a ne-w kind of iterative decoding algorithm,that was variable iteration times decoding. The simulation result showed that the times of variable iteration times decoding decreased 1 times compared with fixed 5 times decoding when SNR is within 0.1 dB and 1.3dB. Based on the simulation result of parameters of Turbo Code, we implemented the hardware of variable iteration times decoding Turbo Code based on LOG-MAP algorith-m with VHDL on FPGA XC2S200 of Xilinx company. We achieved the performance of SNR=1.15dB when BER=10^-6. Compared to fixed 5 times iterative decoding, the variable iteration times decoding saved the decoding delay of 4.1ms and 20% power consuming. Based on the simulation result, we implemented the Turbo decoding of WCDMA's 144kbps data service with less iteration times.Then the conclusion such as complexity and time delay Analysis was given. Finally the simulation waveform was presented and the future research direction was supposed.