衰落信道下Turbo码性能仿真评估

来源 :华中科技大学 | 被引量 : 0次 | 上传用户:heying423
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In digital communication theory the most commonly assumed model for a transmission channel is the AWGN channel. However, for many communication systems the AWGN channel is a poor model. One fundamental type of non-Gaussian channel which often occurs in practice is the fading channel. Fading in wireless communication is the main obstruction for reliable communications. In order to alleviate the effects of channel fading, we need to use channel coding. Channel coding can offer enhanced error performance for digital communication systems by mapping input sequence into code sequence, which inserts redundancy to the transmission. This paper deals with a new class of channel codes called Turbo-codes, whose performance in terms of Bit Error Rate (BER) are close to the SHANNON limit. The main aim of this thesis is to evaluate the performance of Turbo Codes over certain fading channels. We have used BPSK modulation scheme. We have implemented two channel models viz. Rayleigh and Rician channel models. The BER vs. SNR plots are used as performance measures through the simulations. The simulations will be carried out in Matlab environment. In performing these intensive simulation experiments we considered various parameters such as number of decoding iterations, frame size, constraint length and so on. To validate the simulation, we compared the simulation result with theoretical result. To achieve the simulation result, coding theory related to this research will be studied in detail. From the results of the simulation, we conclude that Turbo code enable reliable communication with power efficiencies close to the theoretical limit predicted by Claude Shannon. However, its iterative decoding scheme increases receiver complexity and processing time as the number of decoding iterations and frame size increase. The performance of turbo codes is much worse under Rayleigh fading channel than that of AWGN and Rician fading channels.
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