Interference Alignment Aided by Locally Connected Relays

In this paper, we consider a class of relay networks made up of two partially connected subnetworks. Every subnetwork consists of several relays along with the nearby sourcedestination node pairs being connected to the relays and, is assumed to be fully connected. The two subnetworks are coupled through the so called inter-subnetwork direct links. A linear interference alignment approach exploiting the one-way relaying protocol is applied. The feasibility conditions for interference alignment, i.e., the required numbers of relays in the whole network and in every subnetwork, are investigated. To this end, we develop a graph-based method to model the network topology and introduce the external constraints, from which an upper bound and a lower bound of the minimum required number of relays in a single subnetwork are obtained. Furthermore, we characterize the feasible region for achieving interference alignment in the considered networks using these bounds.