Research On The Turbo Decoding Based On Respond Correlation In OFDM

As an efficient and mature multi-carrier modulation technology, the biggest feature of OFDM is the high spectrum efficiency, and it has been used as a mainstream modulation technology in the future of mobile communication.Turbo codes, as a low-bit-rate code, has the superior performance near the Shannon limit. The next-generation wireless communication systems required to achieve high-speed and high-performance business. At present, the trend is combine OFDM with Turbo code to get more efficient system to meet new challenges.Log-MAP algorithm is commonly used to be decoding algorithm of Turbo codes in the current communication system, avoiding the complexity of the MAP algorithm. But in OFDM wireless channel, BER of the Log-MAP algorithm is significantly higher than MAP, which requires to improve the more practical of the Turbo decoder to meet the needs of the wireless channel. Based on the previous studies about traditional combination system of Turbo code with OFDM, the characteristics of OFDM are taken into account in the paper. Turbo code is applied to the environment which introduces frequency domain correlation of the OFDM, and it launchs in-depth studies to further improve the overall system performance.Firstly, adopting some formulas to analyze theoretically the correlation in the frequency domain of the OFDM, and then from the perspective of probability, the simulation proves the existence of this feature under different parametric conditions; According to the correlation of ideas, re-encoding processing to the decoder output, and putting forward a statistical method to estimate the output status of the decoder, and taking full advantage of these characteristics to determine whether the decoding unit need to change into the MAP algorithm more error-correcting capability to re-decoding the data frame. The program introduces the concept of "crossing". Bases on the statistical strategy under the decoding output data frame corresponds to the average SNR, times are calculated to meet less than the number of allowable error rate, which has been set in the strategy, and then difference is come to between the two sequential bits ratio of decoder input and send bits ratio of re-encoding output, and record the number of across actually in the frame, if the number is less than allowable errors, the result shows that the error rate can be allowed and the decoding results acceptable; On the contrary, the decoding results are not satisfactory, the error rate is too high, At this time, the frame data will be re-decoding by the corresponding more error correction capability of the decoding algorithm, makeing the system BER approach to the best estimate. Meanwhile, Taking into account Computation and can be realized in hardware of the MAP algorithm, the next data frame will be decoding by the predetermined Log-MAP algorithm. So that achieves a streamlined Turbo decoder structure.Secondly, the architecture model of the Turbo-COFDM system is designed under the relevant conditions on the basis of the theoretical analysis and simulated by computer, mapping out the performance curve of the relationship between BER and SNR, then contrasting the result in the same parameter conditions. It can be learned that the pipelined decoding system performance under the relevant program is superior to the traditional system, but the decoding time consumed will have a little increase; It then proved the need for re-decoding probability is not too high under the relevant program; It can be said that this program is desirable to sacrifice some time for improve the decoding performance, and can meet the quality requirements of most of the communication system. Finally, The paper shows practical significance of the study.