Ultra-reliable V2X communication: On the value of user cooperation in the sidelink

The 5G system and its service for ultra-reliable low latency communication are considered key enablers for enhanced use cases of vehicular-to-everything (V2X) communications, paving the way towards automated and autonomous driving. Reliability in a wireless link can be improved substantially if a large degree of channel diversity can be exploited. The V2X sidelink can offer numerous independent communication links between a target car and its neighbours, and the diversity offered by these links can be made available by cooperative retransmission of data packets received from a prior multi-cast transmission. This paper elaborates on the value of user cooperation in the sidelink for attaining ultra-reliability in V2X communications by analysing the reliability gains in dependence of the number of cooperating users and for considering an additional retransmission, if the latency budget allows. Analysis reveals that the attainable gains scale with up to one order of magnitude per cooperative user. If strong differences in the power per link due to path-loss effects are taken into account, gains are obviously degrading, though the degradation can be kept at a moderate level if an additional retransmission with appropriate user grouping is considered.