Multi-h synchronisation for codes with long constraints-length

Master Thesis


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University of Cape Town

This dissertation investigates the synchronisation of Multi-h signals with a long constraint length. However, Multi-h codes exhibiting a long constraint length invariably also exhibit a large denominator q. Since traditional methods for synchronising Multi-h signals utilises a q-th power law device, where the frequency spectrum of the qth power of the signal renders all the necessary frequencies for synchronisation, we suspect that a large q could be detrimental. When simulated, it turns out that the qth power law device fails to deliver distinct (and useable) frequency components at a q size of about 8. Unfortunately, the most useful codes have denominators starting at a size of q equals 32. This called for a novel approach to synchronisation. One device that shows much potential is the new Massey-Hodgart coherent MSK demodulator. In a significant departure from standard quadrature structures, this MSK demodulator uses matched filter detection with a pair of reference signals at the two MSK signaling frequencies; an optimal maximum-likelihood bit decision is then formed over two bit intervals. The reference signals are recovered by a pair of decision-switched Costas loops, which are tightly integrated with the demodulator structure. The goal was to modify the Massey-Hodgart MSK demodulator into a Multi-h synchroniser that contained matched filter detection for all the frequencies in the Multi-h signal. The reference frequencies would still be decision switched and recovered by Costas loops.

Bibliography: p. 64.