The Research On The Key Techniques Of Efficient Turbo Codes For Deep Space Communication

Deep Space Communication (DSC) is the communication between earth anduniverse station such as moon prober or other planets prober which get away from theearth’s gravity. These universe stations leave earth orbit and into solar system, thedistance can reach millions of miles. DSC is more difficult to communicate comparingwith other communication modes, the characteristics of DSC are the very long distanceof transmission and the low receiving signal-to-noise(SNR). The main purpose is to doresearch on channel coding suitable for the DSC channel.The performance of Turbo code can approach the Shannon bound, its performanceis very excellent under lower SNR circumstance as well as it has better capability inresisting attenuation and disturbance, so Turbo codes is suitable for applications in DSCwith lower SNR. But there are still some demerits when it is used in DSC, that is largedecoding delay, considerable computational complexity and error-floor effect. So thispaper focuses on the efficient Turbo decoding algorithm, the design and implementationof interleaver and iterative stopping criteria and so on.This paper firstly presents the Turbo codes theory and analysis the various factorsthat influence its performance.Then introduces some common Turbo decodingalgorithms, the design principle of interleaver and several common iterative stoppingcriteria. Through the introduction of "fitting approximation" idea, the modified algorithmnamed optimum square approximation algorithm is proposed to reduce computationalcomplexity with litter losing of performance. And aiming at reducing decoding delay,this paper designs an effective stopping criterion which can reduce iterations and speedup decoding. Moreover, this paper proposes a modified S-random interleaver to improvedecoding performance according to error-floor effect. By means of computer simulation,these modified methods raised above are all compared, analyzed and verified.Finally, according to DSC channel requirements, this paper selects some parameterswhich recommended by the Consultative Committee for Space Data Systems(CCSDS),and adopt the improved interleaver design scheme, the optimum square approximationalgorithm and the new iteration stopping criterion. MATLAB simulation shows that theimproved algorithm and implementation scheme, which applied in DSC, can improve thedecoding efficiency and obtain better coding gain.