Operational region of overlay D2D communications

An important enabler towards the successful introduction of any new element/feature to the cellular network, such as the ability to allow for direct, device-to-device (D2D) communications, is the investigation and characterization of the operational conditions, e.g., density of users, where its deployment will enhance performance. This paper attempts to provide a mathematically rigorous characterization of the set (region) of operational conditions, for which overlay D2D communications enhance performance in terms of average user rate. Using tools from stochastic geometry, and for the practically interesting case of a heavy loaded network, the operational region is identified in closed form as a function of a variety of parameters reflecting a wide range of operational conditions. It is shown that, under the appropriate deployment scheme, D2D communications can be beneficial not only in the typically assumed regime of “proximal communications” but to a wide range of operational conditions that include D2D link distances comparable to the distance from the cellular access point(s) as well as significantly large user densities.