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UBC Theses and Dissertations

Data communications using coherent minimum frequency shift keying on intrabuilding polyphase power line networks Chiu, Frank Kwok King


The suitability of Coherent Minimum Frequency Shift Keying (CMFSK) modulation for data communications on polyphase intrabuilding power distribution circuits is examined. An actual modem was designed and implemented. Average bit error rate (BER) versus received Eb/No measurements were taken for an industrial, commercial, and residential power line environments at 1.2kbps, 4.8kbps, and 19.2kbps data rate. The 19.2kbps BER measurements indicate that a majority of errors are caused by impulses occurring in the power lines, while other errors are caused by momentary reductions of received Eb/No. Occurance of errors coincides mostly with impulses on the power line which are highly periodic with the ac mains voltage. In addition, the BER measurements reveal that CMFSK modulation at 1.2kbps and 4.8kbps data rate is less affected by impulse noise than at 19.2kbps. This finding is attributed to the increased resistance to impulse noise effects as the bit duration is increased. A baseband spectrum spreading technique is proposed and successfully tested to implement low data rate transmissions. Spread spectrum signalling overcomes potential narrow band impairments by sending a wide1 band signal over the power lines. In addition, the reduced power spectral density of the spread spectrum transmission reduces narrow band interference to other power line communications users as well as AM radios and allows higher output power to compensate for path attenuations.

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