Joint User Association and Power Control for Load Balancing in Downlink Heterogeneous Cellular Networks

Abstract

Instead of achievable rate in the conventional association, we utilize the long-term rate to design two types of association strategies for load balancing in heterogeneous cellular networks (HCNs). In the first type, we try to balance the network loads by maximizing the weighted sum of long-term rates. Based on this type, we introduce a power control (PC) to mitigate the network interference and reduce the energy consumption in the second type. Since the long-term rate of any user associated with some base stations (BSs) mainly depends on the achievable rate received by this user from the selected BS and the load of this BS, it can be used as a key factor of association design for load balancing in HCNs. To solve the first association problem, we design a one-layer iterative algorithm by converting the original sum-of-ratio form into a parameterized polynomial one. By combining it with a PC algorithm, we give a two-layer iterative solution for the second problem. Specifically, the outer layer performs a user association using the algorithm mentioned in the first type, and the inner layer updates the transmit power of each BS using a power update function. At last, we give some convergence and complexity analyses for these proposed algorithms. As shown in numerical results, the proposed strategies have a superior performance than the conventional association, and the second association strategy achieves a higher load balancing gain and energy efficiency than conventional scheme and other offloading strategies.