Houdt, “Multiple access algorithms without feedback using combinatorial designs

A new class of multiple access algorithms for systems without feedback is introduced and analyzed. A finite population of users is assumed, where each user transmits a packet R times within the next N time slots (and all packets have an equal length of one slot). To improve the performance achieved by randomly selecting these R slots, user codes are invoked such that any two users will only transmit simultaneously in at most one slot, i.e., 2-(N, R, 1) designs. We argue that in most cases, the set of user codes can be generated easily using cyclic designs and provide a method to select T user codes from the set of user codes SN,R in case the user population consists of T < |SN,R| users. We further demonstrate how larger populations, with T> |SN,R|, can still benefit from these user codes in two different manners. Closed formulas that express the success probability of a packet are provided for all population setups. Finally, a comparison with the random selection strategy demonstrates the performance gain realized by the new multiple access algorithms and some engineering rules to optimize the performance are provided. Multiple access algorithms without feedback were first developed during the early 1980s by Massey [1]. In this setting, a set of M users shares a time-slotted random access channel. The idea was to assig