Optimal user association based on topological potential in heterogeneous networks

In traditional cellular networks, User Equipments (UEs) always connect to the strongest Base Station (BS), which offers either the maximum Signal to Interference Plus Noise Ratio (SINR) or the best Reference Signal Received Power (RSRP). However, in heterogeneous networks, due to a large difference of transmit power between macrocells and low power nodes, the user association methods mentioned above may lead to unbalance of user distribution between the two kinds of BSs. The goal of our research is to balance the user association between macrocells and picocells while maintain the network performance. We solve the user association problem by introducing the topological potential between UEs and BSs, from which both the channel condition and the number of severing UEs in each cell are considered. Since maximizing the topological potential in network-wide is NP-hard, a heuristic method is proposed to reach a suboptimal. Finally, the tradeoff between association fairness and network throughput is discussed via system level simulation, and a better fairness user association is given compared to the range expansion method in the same condition of network throughput.