Spread ALOHA for VSATs

Abstract

Spread ALOHA is a multiple access protocol using conventional ALOHA packets spread in time, so that the packet contention interval at the output of the packet receiver is not increased. Packets transmitted using a Spread ALOHA protocol can overlap in the physical channel with high probability, but still be separated at the output of a matched filter, so that the probability of overlap at the receiver output is low. Spread ALOHA operation of a data channel combines several characteristics of ALOHA channels and Spread Spectrum channels. The use of Spread ALOHA can achieve certain efficiencies and simplicities of operation which are not possible in conventional ALOHA channels or conventional Spread Spectrum channels. In particular, for the case of a large number of small earth stations accessing a single satellite transponder in a data network, no signaling technique is possible which can achieve a higher average data throughput for a given average power and a given bandwidth than Spread ALOHA. This report is preliminary only. It contains an explanation of the basic elements of a Spread ALOHA channel together with some notational material which serves to emphasize the connection between Spread ALOHA, conventional Spread Spectrum and algebraic coding theory. A more detailed report will be provided at a later date.