Performance Analysis of Device to Device Communications Overlaying/Underlaying Cellular Network

Minimizing the outage probability and maximizing throughput are two important aspects in device to device (D2D) communications, which are greatly related to each other. In this paper, first, the exact formulas of the outage probability for D2D communications underlaying or overlaying cellular network are derived which jointly experience Additive White Gaussian Noise (AWGN) and Rayleigh multipath fading. Then, simulation results of the exact formulas and previously respected approximate formulas are compared in MATLAB for both underlay and overlay scenarios. It is shown that the approximate formula in underlay scenario is a good estimate for exact one while approximate formula for overlaying scenario is a good approximation when the average distance between the transmit/receive nodes of D2D pair is less than half of the maximum distance between these nodes or variance of multipath fading is greater than 1.5. In addition, the probability density functions of Signal to Interference plus Noise Ratio (SINR) for underlay and overlay scenarios are found. Moreover, a new scenario is proposed which jointly considers overlay and underlay scenarios. Furthermore, exact and approximate formulas for outage probability and throughput of D2D users in the proposed scenario are derived. Finally, these formulas are compared to underlay and overlay scenarios in three special cases, low, moderate and high traffic loads