Joint subchannel and power allocation in two-tier OFDMA HetNets with clustered femtocells

Efficient power and subchannel allocation methods are required for orthogonal frequency division multiple access (OFDMA)-based femtocells to mitigate both co-tier and cross-tier interferences. In this paper, we study the problem of joint power and subchannel allocation in a densely deployed femtocell network with constraints on co-tier and cross-tier interference and minimum datarate requirements. A convex optimization problem is formulated and the solution of the problem is obtained numerically. For this joint resource allocation problem, the effect of clustering (or cooperation) is studied as well, where femtocells are placed in disjoint groups. The performances of distributed resource allocation (i.e., without clustering) and centralized resource allocation (i.e., with only one cluster) are compared against clustering-based (i.e., semi-distributed) resource allocation. Numerical results show that, in a dense environment, with femtocells closely located to each other, the effect of co-tier interference becomes significantly dominant and clustering is a very effective technique in such a densely deployed environment to improve the sumrate capacity of the femtocells.