On the Coverage Problem in Device-to-Device Relay Networks

The device-to-device (D2D) relay technology is one of the key technologies in 5G networks, and its coverage problem is important as it determines key properties in network management. However, the traditional relay coverage theories (e.g., based on the received signal-to-interference-plus-noise ratio) are not optimal for D2D relay due to the dynamicity in backhaul resources of D2D relays. In this letter, we study the coverage problem in D2D relay networks with theoretical derivation and experimental simulation using stochastic geometry. In particular, we formulate the coverage problem to maximize the overall system downlink rate, and then the domain optimization problem is transformed into a 0-1 integer programming problem. We propose a novel algorithm to obtain the optimal solution by greedily including the best locations into the coverage. Simulation results verify the theoretical solution and show that the optimal coverage is surprisingly in an irregular shape that excludes the D2D relay. The results also obtain the best relay location and show the performance gain than the existing scheme.