On the Design of Error Control Coding for Wireless Communication Systems

Sammanfattning: New wireless services such as mobile Internet, multimedia streaming and high speed packet data access are making their way to the market. Availability of low-cost equipment providing high transmission quality and efficient spectrum utilization is crucial to the success of these services. This thesis is a collection of papers that address an important step in this direction: efficient error control coding, with high flexibility and low complexity. In particular, we discuss the design of codes, decoders and incremental redundancy transmission that can provide increased throughput in systems based on convolutional and parallel concatenated Turbo codes. Papers I to IV deal with low-rate Turbo codes for code-division multiple-access systems. It is demonstrated that super-orthogonal Turbo codes can achieve better error performance than maximum free distance convolutional codes at low signal-to-noise ratios on the additive white Gaussian noise (AWGN) channel. Design criteria for low-rate Turbo codes that result in performance improvements compared to the super-orthogonal Turbo codes are presented. Termination techniques are studied and it is concluded that no termination of either component encoder causes severe performance degradation, while the differences are small between the other investigated termination strategies. Papers V and VI evaluate the performance of incremental redundancy transmission over the block-fading Gaussian collision channel. For low channel loads, binary convolutional codes give throughput performance close to the achievable limits with binary signaling, while, at high channel loads, significant throughput gains are to be obtained by improved coding strategies such as Turbo coding and adaptation of modulation order and code rate to the channel conditions. Papers VII to X address list sequence decoding in concatenated systems with an outer error detecting code and an inner error correcting code. An efficient low-complexity algorithm that provides both soft symbol output and a list of decoded sequences, ranked in order of a posteriori probability, is presented and applied to joint source-channel and Turbo decoding. Analytical error performance expressions for list sequence decoding with genie-assisted error detection on the AWGN and flat Rayleigh fading channels are provided. Significant performance gains are at hand with list sequence decoding relative to single sequence decoding in future systems, or, with backward compatibility, in existing systems.