Cooperative D2D communications in the uplink of cellular networks with time and power division

Cooperative device-to-device (D2D) communication is proposed as a promising technology to improve the spectral efficiency in crowded communication networks. In this paper, we consider a transmitter-receiver pair, operating in the D2D transmission mode, overlaying the cellular network. The D2D transmitter (DT) acts as a relay for the undelivered packets of cellular user equipment (CUE). We consider the case in which the DT transmits its own data along with the relayed data using superposition coding in the uplink. We investigate how the time slot is split between the cellular network transmission and the D2D transmission. Moreover, the optimal approach to split the DT power between the transmission of the DT data and the relayed CUE data is explored. Our main objective is to achieve the maximum D2D throughput. Towards this objective, we describe the system using a queuing theoretic model and formulate an optimization problem to maximize the throughput of the D2D link by allocating time and power for DT while satisfying the stability conditions for the queues of the system. Finally, numerical results show the merits of our system, with optimal time and power allocation, as compared to the constant time or power allocation scenarios, in terms of the maximum achievable D2D throughput.