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UBC Theses and Dissertations

Design and test of a real-time voice communication system for power line communication channels Dorbolo, Rick G.


Intrabuilding electric power distribution lines provide easy access and universal coverage for digital speech communications. However, power line communication channels exhibit unpredictable and variable levels of signal attenuation and noise. To enable effective communication requires appropriate forward error correction of the encoded speech. This thesis describes the design, implementation and testing of synchronization, voice compression and forward error correction algorithms required to achieve a robust real-time communication link across power line channels. Communication was connection oriented and synchronous with a selectable baud rate of 9600 bps or 19200 bps. Synchronization (delineation) was accomplished using a seven bit synchronization marker placed between frames of encoded speech. The encoded speech data was generated using the U.S. digital cellular standard VSELP 7950 bps voice encoder. Error detection and correction bits were added to the speech data to produce aggregate data rates of approximately 9600 and 19200 bps. Error detection of the perceptually significant bits was provided through the use of a seven bit CRC in the 9600 bps encoded speech. The 19200 bps scheme employed an error detection/correction scheme where the amount of protection was based on the perceptual significance of each parameter. The synchronization algorithm was implemented in hardware and tested. Synchronization was maintained at bit-error rates (BERs) greater than 0.1. Subjective testing of the synchronization algorithms under random noise indicated that the 9600 and 19200 bps coding schemes were usable with channel BERs up to approximately 7x10⁻³ and 2x10⁻², respectively. Tests performed on actual power line communication channels indicated approximately equal performance using either the 9600 or 19200 bps coding scheme, due to the comparatively higher BER of the 19200 bps channel.

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