COLLISION-TYPE MULTIPLE-USER COMMUNICATIONS

A collision-type multiple access system is investigated in which every user transmits symbols from a common N-ary frequency-shift-keyed sign al alphabet, We present a series of information-theoretic properties o f the associated mathematical channel model. In the absence of noise, we calculate a large system approximation to the sum capacity, which i s used to show that, in the limit, the combining of the multiple-acces sing and coding results in no loss in capacity, compared to a fixed-al location scheme, The presence of thermal noise or undetected users inf luences the capacity. Bounds on the capacity of the channel in the pre sence of thermal noise are calculated, as well as the capacity of the system in the presence of interfering users, Finally, a new iterative multiuser detector, the Consensus decoder, is described and simulation performance results are shown. It is demonstrated that this decoder c an operate to within approximately 70% of the channel capacity.