User Cooperation for 5G Wireless Access Networks

Device-to-device (D2D) connectivity is one of the main enablers for future fifth generation (5G) radio access networks. In this paper, we introduce a new model for user cooperation in 5G radio access networks termed frequency-selective soft forwarding (SF). SF is based on soft-processing by a target user equipment (TUE) of selectively forwarded soft information data by a set of cooperating user equipments acting as mobile relays towards the TUE. SF exploits the inherent frequency selectivity and broadcast nature of the downlink radio access channel for the sake of enabling efficient user cooperation and seamless integration of D2D connectivity into cellular radio access networks. Several variants of SF are investigated, including centralized and distributed approaches, thus offering various tradeoffs of performance versus signaling overhead cost. We also propose a hybrid cooperation mode selection strategy which leverages the performance benefits of SF and the low-overhead cost of decode-and-forward (DF) relaying to enhance the performance of 5G radio access networks. Exhaustive simulation results using a state-of-the-art long-term evolution-compliant link-level simulator show that the proposed user cooperation strategies well outperform baseline cooperation schemes relying on conventional DF and approach the performance of optimal joint reception with significantly lower cost in terms of D2D resource utilization and signaling overhead.