Three Signaling Systems for Double Access to an Active Satellite

An active satellite is modeled as a repeater with a summer at its input and with a constant power output. The effectiveness of the following digital communication strategies for a constant bandwidth are compared in terms of R
copm
of the resulting channel: 1) "time pulsing," 2) "frequency division," and 3) "CW signaling,'' where both transmitters simultaneously use the entire bandwidth while transmitting not necessarily synchronized or equal power signals, which are chosen from the same
M
-ary alphabet and have identical duration. R
comp
formulas are obtained, and parametric families of their curves are given. Among others, the following conclusions may be drawn: 1) For sufficiently high signal-to-noise ratios, CW signaling is best, the potential improvement increasing with increasing alphabet size. 2) Noncoincidence of time intervals of the two transmitters improves the performance of CW signaling.