Interference management for D2D communications underlay macro-small cell networks with imperfect channel estimation

Direct Device-to-Device (D2D) communication permits to offload the network, increase the capacity, and extend the cellular coverage. In D2D systems, user equipments (UEs) do not necessarily communicate via evolved Node Base station (eNB); instead, they are allowed to communicate directly with each other. This underlying communication generates interference due to reusing the same resources of the conventional cellular network. Therefore, efficient interference management techniques are required to keep the interference under control. Most of the existing results assume perfect channel state information (CSI), which is considered to be an unrealistic assumption. In this paper, the problem of interference management for underlay D2D users in a two-tier heterogeneous macro-small cell network is studied assuming imperfect CSI. The effect of channel estimation error on the coverage probabilities of D2D and cellular users is investigated. We also derive an expression for the D2D optimal power that aims to maximize the coverage probability and the signal-to-interference-plus-noise ratio (SINR) of both links while satisfying minimum quality of service (QoS) requirements (SINR target).