A slotted ALOHA protocol with cooperative diversity

Abstract

Over the last few years, the area of cooperative communications has regained attention within the physical layer community. However, existing works on cooperative random access protocols are relatively scarce and biased towards their physical layer properties, thus leaving unattended important problems of the medium access control (MAC) sublayer such as calculation of the backlog delay, design of appropriate back-off retransmission strategies, and stability evaluation, among many others. This paper partially fills this gap by studying the general performance of a symmetrical Slotted ALOHA protocol in which a cooperative relaying phase is enabled in order to improve the decoding probability of collision-free transmissions. Infinite and finite user schemes are used, and for the latter, Bernoulli and Markov models are further employed to study the steady- and the dynamic-state properties of the protocol, respectively. A stochastic reception model is presented which fairly describes the underlying physical layer events from the perspective of the MAC sublayer, including correct packet decoding probabilities, relay node availability, and error detection capabilities. Important results regarding the boundaries for optimum performance of cooperative relaying schemes and useful guidelines for the design of optimum relaying strategies are here derived and discussed.