Distributed cooperative device-to-device transmissions underlaying cellular networks

Device-to-device (D2D) communications underlaying LTE-advanced have proven to be efficient in improving network performance and offloading the traffic of the base station. Through sharing radio resources with cellular users (CUs), D2D communications can significantly enhance the overall spectral efficiency. In this paper, we propose a distributed cooperative D2D transmission scheme to improve the overall system throughput without deteriorating the quality of service of CUs. With cognitive capability, D2D users sense the cellular transmission and switch between the concurrent and cooperation modes in a decentralized way. In particular, D2D users transmit concurrently with the CUs during the initial cellular transmission timeslot, while D2D transmitters serve as relays to compensate for the degradation to the cellular transmissions in the cellular retransmission timeslot, referred to as cooperation mode. Two types of cooperation are exploited to improve the network performance: cooperation between CU and D2D pairs, and cooperation among D2D pairs. We derive exact closed-form expressions of both cellular throughput and D2D throughput over Rayleigh fading channels, and give the analysis of the network energy efficiency. Simulation results validate the theoretical analysis and show the superiority of the proposed scheme.