Nonbinary Hybrid ARQ In Wireless Communications

In wireless communications, especially in satellite communications and the third-generation (3G) mobile telecommunications, data transmission has played and will play more important role due to the rapid traffic increase in multimedia data and other data exchange. While the adverse channel causes so many challenges when transmitting data with high-reliability. Automatic-repeat-request (ARQ), which helps transmit data at very low error rate, has been proposed to combat the bad channel. A lot of ARQ schemes have come into being, and they have different characteristics in terms of com-plexity and throughput. The tradeoff between the two aspects is always a dilemma, which is especially outstanding in high-speed data communications, where complexity of ARQ becomes the main factor and determines whether a practical system can work. In the dissertation, we try to find some new ARQs, which can achieve comparative throughput with low complexity.Firstly, a syndrome-based type-I nonbinary hybrid ARQ (HARQ) is proposed, which makes full use of the powerful error-detection and -correction capacity of Reed-Solomon (RS) codes, and can be combined with the existing RS decoder easily. In this scheme, the negative acknowledgment (NACK) is generated by of the syndrome of the received word. According to the location where error-detection is performed, two structures are proposed. One is syndrome-ahead HARQ, and the other is syndrome-behind HARQ. We analyze how bit error rate (BER), average delay, and throughput of the two structures vary with the maximal number of transmission attempts, and find that syndrome-ahead structure is suited for short codes with poor error-correction capacity, while syndrome-behind structure is suited for long codes with powerful error-correction capacity. These two kinds of HARQs complement each other at different signal to noise ratios (SNRs). With the maximal retransmission number of eight, BER of the HARQs can be very close to their lowest value, obtained by infinite retransmissions. In com-parison with FEC system, the HARQs can greatly improve the reliability of the system even if only one retransmission is provided, and simultaneously, the average delay and throughput can be guaranteed. In addition, its advantage is further demonstrated by anapplication in transmission of compressed image over Rayleigh fading channel.Secondly, a nonbinary type-II HARQ based on invertible RS codes is proposed. Information part and parity check part are transmitted separately. Parity check part will not be transmitted if information part is received error-free when channel state is good. Otherwise, parity check part will be sent. If no errors occur in it, the parity check part itself can retrieve the information by invertible process. If errors occur, the parity check part will be combined with the previously received information part to build an error-correction code, and try to recover the information. This kind of HARQ can match channel states very well. Throughput, reliability, and average delay have been analyzed, and compared with those of a binary type-II HARQ and a turbo-TCM type-II HARQ. Nonbinary HARQ outperforms its binary counterpart in terms of throughput, reliability and average delay. Although turbo-TCM can provide more throughput than nonbinary HARQ at low SNRs, the complexity is too high. Moreover, it encounters very serious throughput floor in a wide range of SNR, while nonbinary can obtain satisfactory throughput and surpass the turbo-TCM HARQ scheme in this range.Finally, adaptive scheme using nonbinary type-II HARQ is proposed to improve the throughput in a cell. HARQs with different coding lengths and modulation schemes are allocated according to the SNR of received signal. Throughputs of adaptive modu-lation, adaptive coding, and joint adaptation schemes are analyzed, and optimal switch-ing threshold of SNR is obtained. In comparison with non-adaptive HARQ, adaptive schemes can get much higher throughput in the given cell. Among the three adaptive schemes, adaptive modulation is t...