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UBC Theses and Dissertations

Design, implementation and testing of a flexible, intelligent modem architecture for power line communications Buternowsky, Barry


Intrabuilding electric power distribution lines provide easy access and universal coverage for data communications. However, power line communication channels exhibit unpredictable levels of impedance, attenuation and noise. To enable effective communications requires appropriate modulation schemes and communication protocols. This thesis describes the design, implementation and testing of a modular, flexible, intelligent modem architecture, based on binary phase-shift keying (BPSK). The modem operates at user selectable baud rates of 2.4, 4.8, 9.6 and 19.2 kbps. Most of the design is digital, to facilitate eventual implementation using VLSI. A microcontroller resident on the modem enables judicious allocation of data link layer functions between modem and host microcomputer. Data link functions performed by the microcontroller include byte and packet synchronization, and control of host-modem communications. The overall data link protocol design results in a flexible, user specified packet format and length, which accommodates to different data rates. The modem architecture is designed for use with various medium access protocols including CSMA, polling or token passing. Addition of forward error correction capability in the form of on-board hardware is also feasible. Evaluation of the modem architecture was performed in a four-storey industrial building which contains good, fair and poor quality communication links. Results for same phase and cross phase transmissions were collected and analyzed for two different test environments: (1) short length links of approximately 30 meters within the same room location; and, (2) moderate to very long links (greater than 60 meters) among different floors. Results from tests (1) indicate that same phase transmission is in general advantageous over cross phase transmission. This advantage for BERs less than 10-3 for transmission at 19.2 kbps can be large as 27 dBmV. Evaluation of results from tests (2) indicate that power line channel communication characteristics are directly related to the channel's length. The BER was found to be in a range from 10-1 to 10-3 for transmission at 19.2 kbps . Comparison of channel throughput for continuous one-way transmission without forward error correction indicates 2.4 kbps would be appropriate for long distance,4.8 and 9.6 kbps for medium distances, and 19.2 kbps for relatively short distances.

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