Transmission of channel coded speech and data over mobile radio channels

The transmission of digital signals over mobile radio channels is addressed. The study is concerned with the performance of the CD900 system, the transmission of digital speech over highway microcells, and methods of channel coding and interleaving to combat errors in mobile radio channels. When the work for this thesis commenced the CD900 system with its time division multiple access and spread spectrum procedures was a leading contender for the pan-European digital cellular mobile radio system. Although the principle of the operation of the CD900 system was known, its performance had not been evaluated. Accordingly this thesis provides a novel analysis of its bit error rate (BER), cochannel interference performance, and traffic capacity. In order to accomodate most of the population with a light-weight handheld portable communicator it is necessary to reduce the size of cells to fit the tele-traffic demand. We have investigated the partitioning of highways into contiguous segments, where each segment is called a microcell, and strings of microcells form a cluster. An innovative approach to the problem was supported by new analytical formulae and simulation results. The BER and segmental-SNR were computed for speech that had been sub-band coded, adaptive differential pulse code modulated or pulse code modulated, then transmitted over Rayleigh fading channels using minimum shift keying. An acceptable performance was obtained, provided both the channel SNR and the signal to interference ratio (SIR) exceeded 25dB. To relax the demands on channel SNR and on SIR, we embarked on an indepth study of channel coding and interleaving. We found that inter-block bit interleaving (IBI) was effective in dispersing burst errors when convolutional coding (CC) was used, whereas a block symbol interleaver was preferred for block codes. The most effective coding scheme for speech signals was the CC(2,1,5) with soft-decision Viterbi decoding combined with an IBI over 448bits. For a toll quality speech, the channel SNR was decreased from 25 to 8.5dB. The preferred arrangement for data transmissions operating with an overall half-rate code nested by an outer Reed-Solomon RS(48,36,6) code over GF(256) with block symbol interleaving over 1920bits, and an inner punctured CC(3,15) with IBI over 2880bits. A huge coding gain of 41.5dB was obtained as the channel SNR needed only to exceed 10.5dB to provide a BER < 10-6. The successful rate of detecting an uncorrectable error was 1 - 10-13. Our approach has optimised the channel coding in digital cellular mobile radio for the transmission of both speech and data signals.