Distribution line communications using CSMA access control withpriority acknowledgements

The authors describe the use and performance of CSMA (carrier-sense multiple access) with priority acknowledgements for medium access control on distribution power line communication networks. Such networks suffer from highly variable, ever-changing, and unpredictable signal-to-noise ratio. The architecture of the CSMA implementation is described, along with its advantages relative to other access control schemes. The best packet length, in terms of throughput maximization, was found to approximate 1000 bits. Delay-throughput performance is measured, and the particular effects on performance of the power-line channel behavior are ascertained. Extensive tests were conducted on intrabuilding lines using channel bit rates from 1200 to 19200 bits/s, with FSK (frequency-shift keying) and spread-spectrum PSK (phase-shift keying) modems transmitting at 3 V RMS at frequencies ranging from 40 to 120 kHz. The reported results include potentially difficult cases involving transmission across power phases     

Personal computer communications on intrabuilding power line LAN'susing CSMA with priority acknowledgements

Intrabuilding power lines provide a readily available and easily accessed network for personal computer (PC) communications within buildings. The use and performance of carrier-sense multiple access with priority acknowledgements (CSMA/PA) on such networks is described. The communication characteristics of intrabuilding power-line channels are summarized and found to suffer from highly variable and unpredictable signal-to-noise ratios and bit-error rates. The advantages of CSMA/PA relative to polling and token-passing access protocols are discussed. The architecture of a CSMA/PA implementation is described. The choice of the best data-link packet length is determined from throughput measurements to be approximately 1000 bits. Delay-throughput performance is measured at 1.2, 2.4, 4.8, and 9.6 kb/s using a phase-shift-keyed (PSK) spread-spectrum modem. Results are included for the potentially difficult problem of transmission across power phases. A discussion of results obtained and their implications for PC intrabuilding communications is also included     

A simple packet retransmission strategy for throughput and delayenhancement on power line communication channels

A new communication protocol is developed and evaluated for use on power line distribution networks. The protocol involves retransmission of unacknowledged packets, which are sent in either single or multiple ( N) copies in accordance with estimates of communication link quality. Multiple packet copies can be code-combined at the receiver using majority voting on each bit position in order to reduce packet error rates. Adaptive link quality estimates are based on the receipt or absence of positive acknowledgements. Information throughput efficiency is calculated and N optimized in terms of system variables. The performance benefits of code combining are demonstrated. The algorithm is implemented and tested using a five-station intrabuilding power line communications network operating at 1.2, 2.4, 4.8 and 9.6 kbit/s data rates. Substantial throughput and delay improvement occur on poor quality links without degrading performance on good links     

Performance analysis of CSMA with priority acknowledgments(CSMA/PA) on noisy data networks with finite user population

An analytical procedure is developed to calculate delay and throughput performance of CSMA/PA (carrier sense multiple access with priority acknowledgments). Time-axis slotting and Markov chain analysis are used to determine the channel backlog per cycle. A cycle includes information packet access and transmission time followed by acknowledgment transmission or time-out. Throughput and delay performance are then calculated in terms of the number of network terminals, the network packet error probability, the packet generation rate, and the mean information packet retransmission delay. Fixed-length information and acknowledgment packets are assumed. Calculated results show excellent agreement with measured delay and throughput performance for two distinct five-node intrabuilding power line networks operating at data rates from 1.2 to 9.6 kb/s