Joint Mode Selection and Resource Allocation in Device-to-Device Communications

Background & Objective: In this paper, we convert the problem of joint mode selection and resource allocation in in-band underlay device-to-device (D2D) communications into two subproblems. First, by using the closed-form expressions for the outage probability of both single-cell direct and relay-aided D2D communications in Rayleigh fading channel, a distance-based procedure is derived which introduces proper mode. For the relay-aided mode, considering the throughput and respected geometry, we find the suitable relay area which supports a D2D pair. Secondly, we optimally allocate the radio resources based on three schemes, minimizing the total outage probability, maximizing the total throughput, and maximizing the total diversity gain. According to the numerical analyses, it is indicated that the Hungarian and Bipartite-matching (BP) algorithms offer the same results higher than the random algorithm. In addition, it is demonstrated that the optimization problem based on the diversity gain have the higher diversity gain compared to the others because it considers the outage probability and throughput in a joint manner. Results & Conclusion: As a final remark, in the view of the diversity gain, the performance of the diversity gain-based scheme as well as the throughput-based scheme for amplify-and-forward (AF) and Decode-and-Forward (DF) scenarios are approximately the same.