Mobile Association for Wireless Heterogeneous Networks with Cooperative Relays: Optimal Framework and Implementation Schemes
Heterogeneous networks improve the spectrum efficiency and coverage of wireless communication networks by deploying low-power nodes on top of the conventional network nodes. In this paper, we consider a heterogeneous cellular network with multiple low-power relay nodes (RN) deployed in each cell using in-band wireless backhaul link between the RN and the base stations (BS). The RNs work cooperatively with the BSs on the downlink communication towards the user equipments (UE). Due to the disparity between the transmit powers of the BSs and the RNs, mobile association schemes developed for the conventional homogeneous networks may lead to a highly unbalanced traffic pattern with most of the traffic load being concentrated on the BSs. In this paper, we propose a new mobile association framework for the heterogeneous wireless networks with node cooperation. The proposed framework aims to maximize the network capacity and balance the traffic load among the network nodes. A pseudooptimal solution is obtained for the proposed mobile association framework using a centralized algorithm that applies gradient-descent method. To enable online implementation, we then introduce a distributed algorithm using a pricing mechanism. Numerical results show that a prominent improvement in network capacity can be achieved by the proposed mobile association scheme compared with the conventional counterpart. Moreover, compared with the proposed pseudo-optimal solution, the proposed pricing-based distributed algorithm only suffers a small loss in network capacity and thus can be used as an efficient online implementation.