Performance Analysis Of Highly Efficient Error Correcting Codes In Rician Channels With Low Rician Factors

Rician channel is a typical wireless communication channel model. In this channel model, both of the direct component and scattering components are taken into account. Rician channel is a more appropriatel wireless propagation model which can characterize all random channels scenarios from the AWGN channel to Raleigh channel.We find that research for multi-path Rayleigh channel and typical Rician channel have been more common, and there are more results compared to channels falling in between them. The research about the Rician channels the Rician factor of which is very small but still can not be ignored is still lacking. Considering the communication quality requirements of this particular communication scene of some practical communication systems is not diminished and even higher, such as communication scenarios during aircraft taking off and landing, communication between aircraft and ground stations.This dissertation will begin with this particular scenario, a typical low-Rician channel. We mainly study physical layer transmission technologies based on this channel.Reliability and effectiveness of communication has always been the core of wireless transmission technology. To bring more reliability and effectiveness, our study is very meaningful especially with the increasing scarcity of frequency resources. Error correction coding is a reliable and effective method of data transmission. Currently, the Turbo code and LDPC codes have been proven to be highly efficient error correction codes both of which have excellent performance close to Shannon limit. Due to the moderate complexity, simple structure and flexible design, Turbo codes and LDPC codes have been widely used in wireless communication systems, mobile communications, satellite communications, video broadcasting communications and some other fields. In addition, auto feedback retransmission (ARQ) technique is another technology to provide data transmission reliability. In recent years, the combination of error correction coding and ARQ, which is also called hybrid automatic retransmission (HARQ) is proposed. This technology can effectively use the ARQ retransmission mechanism mainly by the coding rate combined methods for each retransmission. The technology has been applied in the third-generation wireless mobile communication system was applied. Base on these considerations, this dissertation focuses on the adaptability of Turbo codes, LDPC codes and the key physical layer HARQ technology with low-Rician channels.The main contribution of this dissertation is:We compared the average bit error performance of regular LDPC codes based on PEG method and irregular LDPC codes of WIMAX standards in low Rician factor channels. Results show that irregular LDPC codes of the WIMAX standard perform better than the classic LDPC codes generated by PEG methods.We compared the performance of LTE-Turbo codes, irregular LDPC codes of WIMAX standard and LDPC codes based on PEG method in Rician channels with different Rician factors. The results show that low Rician factors affect the performance of error correction codes. When the BER becomes 0.00001, the Rician factor is choosen from the range (-10dB, OdB), the error-correcting code performance will bring about 0.5 to 1 dB difference and this difference is enough to make the performance of Turbo or LDPC codes change from BER=0.01 to BER=0.00001. When the Rician factor is less than-10dB, the Rician channel can be equivalent to the Rayleigh fading channel. But when the Rician factor is greater than-10dB, especially when the Rician factor is greater than -5dB, its performance will be significantly different in Rayleigh fading channel. Therefore, the practical application should be noticed.We compared the performance of LTE-Turbo codes and WIMAX-LDPC codes with different code rates and we found that Turbo codes perform better in the same conditions when the code rate is less than 1/2, and LDPC code perform better at higher code rates, such as 2/3 code rate. We also discussed the performance of different interleavers for Turbo codes and concluded that random interleaver and QPP interleaver have similar performance at low bit rates (1/2) and QPP interleaver performs better in high bit rate (2/3).We also study of the performance of efficient error correction codes with different transmission rates. We find that performance change sensitively with different transmission rates in Rician channels with low Rician factors.We study the throughput, packet error rate and average retransmission frequency performance of LTE-Turbo codes combining with Type-Ⅰ/Ⅱ/ⅢHARQ in channels with different Rician. We get the following conclusions:Under the larger maximum number of retransmissions, TypeⅡHARQ brings more throughput than TypeⅢin the AWGN channel. However, when the SNR is low, TypeⅢbrings about 1dB more gain than TypeⅡand when the SNR is high, TypeⅡbrings about 0.5～0.8dB more gain than TypeⅢin Rayleigh channel. In Rician channel TypeⅢshows the best packet error rate performance and TypeⅠshows the worst packet error rate and throughput performance. At high SNR, TypeⅡbrings optimal throughput performance and at low SNR, TypeⅢhas the best throughput performance. Therefore, in channels with good condition, you can use TypeⅡHARQ and TypeⅢis preferred in dramaticly fading channels. In practical application, retransmission and coding strategies should be chosen based on different channel conditions.