A passive star-configured optical local area network using carrier sense multiple access with a novel collision detector

This work describes design and theoretical performance of a passive star-configured multimode optical fiber local area network that employs carrier sense multiple access with collision detection (CSMA/CD). We introduce a novel collision detection method that uses collision sequences constructed from cyclic error-correcting codes and a sequence weight violation rule. Each transmitter has its own unique sequence and all sequences have identical Hamming weight. The collision detection sequence is inserted in each packet header. Our method enables detection of collisions subject to a wider dynamic range variation than competing methods proposed up to now and is extremely simple. The collision detector consists of a counter which estimates the Hamming weight of the received collision detection sequence. It works both for non-return-to-zero and Manchester coding. The collision detector is analyzed for an avalanche photodiode receiver. The general performance analysis is done both with Gaussian approximations and with method of moments. A dynamic range of 17 dB seems possible for a transmitter with an extinction ratio of 100 and a simple receiver with a fixed threshold. An explicit table of 56 collision detection sequences based on the Golay code is presented.