Mode switching for device-to-device communications in cellular networks

Mode switching is one of the most important features of device-to-device (D2D) communications since it can bring more freedoms for potential D2D pairs. In this paper, we investigate optimal D2D mode switching to maximize the network spectrum-efficiency (SE). We formulate the optimal SE problems in three D2D transmission modes, dedicated mode, reusing mode and cellular mode, while guaranteeing the quality-of-service (QoS) requirements for both the D2D pairs and the regular cellular users (RCUs). Bisection algorithm is adopted to solve the quasiconvex optimization problems in the dedicated and cellular modes through transforming the original problem into a sequence of convex feasibility problems. For the reusing mode, concave-convex procedure (CCCP) is used to solve the difference of convex (D. C.) optimization problem. Simulation results show that system SE can be improved significantly with the proposed mode switching algorithm compared with the single mode transmission without mode switching.