User Association for Load Balance in Heterogeneous Networks With Limited CSI Feedback

Conventional user association (UA) scheme based on max-signal-to-interference-plus-noise-ratio (max-SINR) criterion results in a severe load imbalance problem in heterogeneous networks (HetNets), leading to substantial performance loss. The state-of-the-art solutions to load imbalance mostly formulate the UA problem as a complicated global optimization that requires full channel state information (CSI) between every base station-user pair. Therefore, searching for optimal UA scheme imposes extremely high complexity as well as signaling overhead, and thus limits its practical applications. In this letter, the UA problem is reformulated as a local optimization at the macro base station, and is solved with only limited CSI feedback, where each user reports the synchronization signal powers instead of full CSI. After that, a low-complexity successive offloading (SO) scheme is derived. Numerical simulations demonstrate that the SO scheme achieves near optimal performance with much lower complexity.