Research And Implement Of H-ARQ Scheme Using Serially Concatenated Codes

In communication systems, there are mainly two methods for controlling transmission errors, one of which is forward-error-correction (FEC) and the other is automatic-repeat-request (ARQ). Hybrid techniques that combine FEC and ARQ are generally considered to be the best error-control techniques, and may provide much reliability than FEC and high throughout than ARQ. There are two types of hybrid ARQ schemes(H-ARQ), type-I and type-II. In a type-II scheme, the first transmission usually includes information bits and a limited amount of redundant bits for error detecting. These are only intended for determining the reliability of the transmission, as if it was a pure ARQ scheme. If a retransmission is needed, additional redundant bits for error correcting are sent.Concatenation of an inner code and an outer code may provide a high coding gain and the capacity of a long code to correct errors . An interleaver was introduced between the two encoders to scatter bursts of error produced by the inner decoder.In this thesis, a new H-ARQ scheme that uses progressively decodable serially concatenated codes for retransmission is proposed. In the proposed scheme, the outer code comprising several block codes for error detection in parallel, and the inner code employing a recursive systematic convolutional (RSC) code for error correction , are linked by an interleaver. Retransmitted sequences of the inner code and packets are combined with previously transmitted packets to be progressively decoded by the same Viterbi decoder. The extrinsic information will be exchanged between outer and inner codes. Improved error and throughout performances of the proposed scheme can be achieved at low signal-to-noise ratios.In the thesis, the following aspects are implemented.Propose the research progress of H-ARQ and express the packet combing techniques in H-ARQ schemes .Evaluate the bit-error bound of serially concatenated codes(SCC), and present the design guidelines and iterative decoding algorithms of SCC .A new H-ARQ scheme that uses progressively decodable serially concatenated codes for retransmission is proposed with its design guidelines. Theoretical bounds on total number of transmitted bits and throughput performance are derived. Finally, the simulation results are given.