| Turbo code is a kind of channel coding which has an excellent performance close to Shannon limit. It has the landmark significance in the history of the development of channel coding, arouses extensive attention from the academic community and has been widely applied in the third generation mobile communication, satellite communication, deep space communication,digital audio broadcasting and so on. In the high speed wireless channel, frequency selective fading caused by multipath effect will leads to loss of sub carrier data in the OFDM symbol. The forward error correction coding is an effective way to solve this problem. By error correction coding between subcarrier, the error subcarrier can be corrected by the encoding of the other no fault subcarriers. The ability of the communication system to fight against the burst interference and frequency selective fading can be greatly improved by introducing the Turbo codes,and the introduction of efficient digital modulation technology can further improve spectral efficiency of the system. Therefore this paper studies how to effectively combine the Turbo codes with the efficient digital modulation and the OFDM modulation technology.Firstly, this paper analyzes the basic principle of Turbo codes and some typical Turbo decoding algorithms. On the basis of that theoretical analysis, the performance of the Turbo codes is simulated by computer. A study is made to research the impact of interval length, the number of iterative decoding and code rate on the BER performance. It is found that the longer interval length, the increased iterative decoding and the decreased code rate will improve the BER performance. At the same time, that will complex the encoding and decoding process. Secondly,a transmission system of Turbo codes combined with efficient modulation is designed. And as the same, the performance of the system also is simulated by computer. Thirdly, an integrated transmission system using the Turbo codes and efficient modulation technique and OFDM technique is designed. And undertake contrasting simulating to the performance of the system before and after the Turbo coding by computer, the results show that the Turbo codes can greatly improve the error performance of the system.Finally, a research is made on the application of Turbo code in the LTE satellite communication system.Three code rates, 1/3, 1/2 and 3/4, as well as five modulation ways, QPSK, 16 QAM, 64 QAM, 16 APSK and 32 APSK, are designed to choose from. The computer is used to simulate the BER performance before and after the Turbo encoding. The findings are, under the same conditions, the BER performance of LTE physical satellite transmission system is greatly improved by bringing in the Turbo codes.In this study, the transmission project designed is the combination of Turbo codes, effective modulation technology and OFDM technology. The study only focuses on the software to simulate, but the implementation of the system on hardware platform is still needed to dig deeper. |
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