Coding and equalisation for fixed-access wireless systems

This Thesis considers the design of block coded signalling formats employing spectrally efficient modulation schemes. They are intended for high-integrity, fixed-access, wireless systems on line-of-sight microwave radio channels. Multidimensional multilevel block coded modulations employing quadrature amplitude modulation are considered. An approximation to their error performance is described and compared to simulation results. This approximation is shown to be a very good estimate at moderate to high signal-to-noise ratio. The effect of parallel transitions is considered and the trade-off between distance and the error coefficient is explored. The advantages of soft- or hard-decision decoding of each component code is discussed. A simple approach to combined decoding and equalisation of multilevel block coded modulation is also developed. This approach is shown to have better performance than conventional independent equalisation and decoding. The proposed structure uses a simple iterative scheme to decode and equalise multilevel block coded modulations based on decision feedback. System performance is evaluated via computer simulation. It is shown that the combined decoding and equalisation scheme gives a performance gain of up to 1 dB at a bit error rate of 10-4 over conventional, concatenated equalisation and decoding