Collision Resolution Protocol via Soft Decision Stochastic Retransmission
José Carlos Marinello, Taufik Abrão · 2019
The recently proposed strongest-user collision resolution (SUCRe) protocol resolves the majority of pilot collisions in crowded machine-type massive MIMO scenarios. We show in this paper that the random access (RA) performance of SUCRe can be improved by replacing the hard decision retransmission rule by a soft decision one, so that each user decides to retransmit or not its pilot sequence with a suitable probability. First, we propose to obtain this probability by mapping the ratio between the signal gain of each UE and the sum of the contenders' signal gains with the aid of a sigmoid function. Then, we propose to determine the retransmission probability of each UE according to the probability of this UE being the strongest contender, while proposing also an approximated probability expression for this event. Our results demonstrate an improvement in terms of a lower number of access attempts and a lower fraction of failed access attempts compared to the SUCRe protocol, while maintaining its features of being decentralized and uncoordinated.