J. Lee, K. Tripathi, and H.A. Latchman (USA)
Medium Access Control (MAC), CSMA/CA, OFDM, Power Line Communications (PLC) and Contention Window (CW)
Power Line Communication (PLC) systems, which have been around since 1950’s but were never thought seriously of as communications method due to low speed, high cost for development, are now gradually spreading to local area networks and broadband over power line as a realistic and practical means of communications. This is thanks to the technological advances such as new modulation schemes. Based on orthogonal frequency division multiplexing (OFDM) and carrier sense multiple access with collision avoidance (CSMA/CA), the HomePlug 1.0 was developed, and is now the most commonly used technology of power line communications. It supports up to 14 Mbps transmission rate on the power line physical layer. However, just as in 802.11, the throughput performance of this original scheme becomes critical when the number of users increases. In this paper, we propose a constant contention window based medium access control protocol algorithm of HomePlug 1.0 under the assumption that the number of active stations is known. An analytical and simulation framework is used to find the optimal values of contention window size for best performance. We also describe a more realistic node estimation algorithm that each station can implement independently to find the number of contending stations. The modified scheme shows significant enhancement of medium access sub layer performance under saturation conditions.
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