Guard zone based D2D underlaid cellular networks with two-tier dependence

Device-to-device (D2D) communication is under active investigation and may be a key feature in 5G networks for its great potential in improving network spectral and energy efficiency. Underlaying proximity-based D2D communication links in current cellular networks allows D2D users to opportunistically access the cellular spectrum, thus causing interference not only in the D2D tier but also between D2D and macrocell tiers. In this paper, we consider a D2D underlaid cellular network, in which D2D users reuse macrocell downlink spectrum, imposing guard zones around each active D2D transmitter to avoid nearby interference from both macro base stations (MBSs) and other D2D transmitters. Using spatial models and analytical results from stochastic geometry, we provide bounds and approximations for the D2D and cellular coverage probability, as a means to characterize the performance of D2D underlaid cellular networks with intra-tier and cross-tier dependence. The D2D area spectral efficiency (ASE) is also characterized and an approximate optimal guard zone radius that maximizes a lower bound of D2D network throughput is derived in closed-form. Simulation results validate our theoretical analysis and evince the accuracy of the proposed analytical expressions.