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.