Enhanced Encoding Techniques In Wireless Communication Systems

This dissertation is devoted to various enhanced error-control encoding techniques in wireless communication systems. The research topics include space-time code modulation and hybrid automatic-repeat-request (HARQ). Both techniques have been used in the 3rd generation mobile communication systems.Error-control schemes in communication systems can be divided into two folds. The first is the forward error control (FEC) and the second is the automatic-repeat-request (ARQ). Both techniques have been widely used in modem communication systems. With the rapid development of the wireless communication techniques, hybrid ARQ emerges as the combination of FEC and ARQ.In Chapter 2, a new differential unitary space-time code modulation scheme based on cyclic unitary group code is proposed for systems with multiple transmit antennas under fast fading channels. By exchanging the sequence of transmitted symbols, this new differential unitary space-time code modulation scheme reduces the influence from time-variance of fast fading channels at the cost of larger processing delay and additional transmission power. For larger processing delay, the additional transmission power is negligible. Theoretical analysis and Monte Carlo simulations are used to investigate the performance of the proposed and conventional differential unitary space-time code modulation schemes. It is demonstrated that compared with the conventional differential unitary space-time code modulation, this new differential unitary space-time code modulation scheme can achieve significant gains under fast fading channels with very little cost.In Chapter 3, a novel multiple trellis coded orthogonal transmit scheme is proposed to exploit transmit diversity under fading channels. In this scheme, a unique vector from a set of orthogonal vectors is assigned to each transmit antenna. Each of the output symbols from the multiple trellis encoder is multiplied with one of these orthogonal vectors and transmitted from corresponding transmit antennas. By correlating with corresponding orthogonal vectors, the receiver separates symbols transmitted from different transmit antennas. This scheme can be adopted in coherent/differential systems with any number of transmit antennas. It is shown that the proposed scheme encompasses the conventional trellis coded unitary space-time code modulation based on the optimal cyclic group codes as a special case. Two better designs over the conventional trellis coded unitary space-time code modulation are demonstrated in this chapter. For both designs, simulations have shown that multiple trellis coded orthogonal transmit schemes can achieve better performance than conventional trellis coded unitary space-time schemes.HARQ is another important enhanced error-control encoding technique. It is one of the key techniques in the high speed downlink packet access (HSDPA) and high speed uplink packet access (HSUPA). Two main problems in the design of HARQ are the design of rate compatible codes and the optimized scheduling of HARQ.A new approach to search the optimal puncturing matrices for the rate compatible punctured Turbo (RCPT) codes is proposed in Chapter 4. This algorithm is based on the density evolution technique and its main goal is to analyze the thresholds of successful decoding for different...