Turbo Code Technology And Its Application In OFDM

Due to their near Shannon-Capacity excellent performance ,Turbo Codes have received a considerable amout of attention from the academia of communications and informatics since their introduction.With the development of Turbo Code, they have been included in the specifications for both the WCDMA ,DMA-2000 and TD-CDMA third-generation cellular standards.OFDM is adopted as a standard for the next moblie communication .The application of Turbo Codes in coded orthogonal frequency division multiplexing(COFDM) is researched in this paper.A novel COFDM scheme is proposed.It employs Turbo Codes,OFDM modulations and different coding technologies and is termed as Turbo Coded OFDM. Firstly,the iterative decoding algorithms in typical parallel serial concatenated system based on Turbo Principle are discussed. Log-Map,Max-Log-Map, Costant-Log-Map, Linear-Log-Map decoding algorithms are proposed after a depiction of MAP algorithm. Comparison to MAP, Linear-Log-Map reduces complexity with only a negligible loss in BER performance,and Linear-Log-Map is adapted to real-time communication systems. Secondly,we build simulation platform and investigate some parameters:RSC structure,interleave sizes,the number of iterations,and rate.simulation results that turbo codes have good performance in low SNR over AWGN channels because iterative decoding and random code of Shannon's channel coding theorem are used very well for turbo codes. The coding channel model over Rayleigh fading channels is addressed, and it's corre-sponding simulation method is given.A modified Log-MAP algorithm is proposed for Turbocodes in Rayleighflat-slow-fading channels with imperfect channel state information, The simulation results are significant to design Turbo codes in wireless channel.On the application of Turbo Code in OFDM,the TURBO-OFDM scheme is presented.Simulation results that adopted turbo as its channel coding ,OFDM can get extra coding gain.