Performance bound of ad hoc Device-to-Device communications using cognitive radio

The aim of this paper is to study the achievable throughput of an ad hoc Device-to-Device (D2D) communications with cognitive radio capabilities coexisting with cellular user equipment (UE) in the same macrocell. Specifically, we consider ad hoc D2D systems with non-orthogonal resources sharing instead of D2D with infrastructure support. The main objective is to find out how much throughput a device in a D2D pair can achieve in the presence of another D2D pair and a cellular user over fading channels. A closed-form expression for statistics, the Moment Generating Function (MGF) and Complementary Cumulative Distribution Function (CCDF) of multiple interferers in Nakagami-m fading channels in cellular system are presented. By using these expressions, we derive the device throughput for multiple D2D systems in a cellular system. Furthermore, the upper bound for the probability of false alarm, which is required to achieve a certain throughput is deduced. The results of this paper illustrate how the transmission probability and sensing performance affect the achievable throughput in cognitive D2D systems. In addition, these results serve as guidance for the deployment of cognitive D2D systems without infrastructure support.