DSP-based Realization Of Convolutional Turbo Code

In1993, the convolution Turbo code which is proposed by C.Berrou has beenidentified as the third generation of mobile communication technology code scheme.Convolution Turbo codes convolutional coding and random interleaver technologytogether solve the random coding problem.By using SISO iterative decodingalgorithms that is based on maximum likelihood estimation,the decoding performancecan be very close to the Shannon limit. This paper introduces the convolution code ofTurbo coding and decoding of DSP implementation which are based on IEEE802.16edevelopment.The SISO decoder affects the performance of the whole decoder, differentalgorithms have their advantages and disadvantages. For example, the MAP decodingalgorithm has a higher accuracy but is more complicated.Max_Log_MAP decodingalgorithm accuracy decreases but the realization is simple which is suitable forreal-time communication system where the precision requirement is not so particularlyhigh.This paper will take the Max_Log_MAP as the decoding algorithm.The coding and decoding are discussed separately, and they will be simulatedtogether. Convolution coding part introduces Turbo coding principle, and discusses itsrealization in DSP. Similarly, the decoding part firstly introduces the general decodingprinciple and the derivation of MAP and Max_Log_MAP decoding algorithm.Andthey will be contrasted to several common decoding methods for the realizingcomplexity, system performance and general aspects.Then the appropriate decodingmethod will be selected to achieve CTC decoding.After Discussing of various algorithm principle,realization process, the difference ofdecoding algorithm and the influence factors of decoding accuracy and speed of allaspects, especially the code block lengths, iterative decoding number, modulation, andrate of decoding accuracy and throughput rate effect in the simulation,The result isgiven finally under the influence of various factors.This paper uses OMAP-L138chip as hardware platform whose structure andproperties of DSP characteristic are very suitable for real-time communicationsystem.The DSP core has internal hardware multiplier and8function units which canbe executed in parallel have comparison, shift operations such as multiplication.And ithas a very high degree of parallelism. In addition,the water technology, C64x+’sspecial instruction set and structure and technical features make this chip owns a highefficiency.