Iterative Decoding of Concatenated Codes.

This thesis is concerned with the area of decoding techniques of concatenated, error correcting codes using various soft-in/soft-out decoding algorithms, as well as with the construction of these codes. Initially, we consider in some detail the theory behind a communications systems, whereby the transmitter, channel and receiver are quantified and analytically defined. We use these definitions to define soft-decision decoding algorithms of error correcting trellis codes, after having considered the theory behind the construction of such codes, where both of the common classes of convolutional and block codes are treated. We then move onto concatenated coding schemes, considering both traditional, serially concatenated coding schemes whereby the outer code is decoded by means of hard-decision decoding methods, as well as new soft-decision decoding schemes. We treat in some detail the construction of parallel concatenated codes, decoded by means of iterative decoding algorithms, also denoted Turbo Codes. We then extend the principles introduced in this part to also apply to serially concatenated codes of Reed-Solomon and convolutional codes. Finally, we consider spectrally efficient coded modulation techniques using iterative decoding techniques. The main research achievements resulting from this work include: The reduction in complexity and decoding delay latency of iterative decoding schemes involving traditional, parallel concatenated Systematic Recursive Convolutional (RSC) codes, as well as several novel code and decoder configurations using these codes. The development and application of soft-in/soft-out decoding algorithms of serially concatenated convolutional and Reed-Solomon codes. Non-iterative and iterative decoding algorithms are investigated and presented in this thesis, for both the AWGN and Rayleigh fading channels. A major finding of this research is that serially concatenated coding schemes appear more suitable for systems in which very low Bit Error Rates are required than do parallel concatenated schemes. These results apply for both AWGN and Rayleigh fading channels. The proposal and investigation of spectrally efficient coded modulation schemes involving binary BCH and non-binary Reed-Solomon codes for which very high spectral efficiency may be obtained, even when used with modulation schemes with a small alphabet. This work has also resulted in a novel, low complexity demodulation algorithm for giving soft outputs at the bit level for non-binary modulation schemes.