On SINR biasing for optimal cell range expansion in two-tier wireless hetnets

Cell range expansion (CRE) for traffic offloading and load balancing in wireless heterogeneous networks (HetNets) is commonly realized by introducing a positive bias to the user received signal-to-interference-plus-noise ratio (SINR) of the small cell pilot signals when determining cell association. The small cell coverage is then expanded without needing to increase the transmission power. Higher energy and spectral efficiency is achieved accordingly. Most existing work on CRE focused on examining effectiveness of this technical approach but somehow ignored the impact of choosing different CRE bias values. This work presents preliminary results of an investigation of optimal biasing strategies for CRE in wireless HetNets. Specifically, the bias optimization problem for general design objective is formulated. The framework is first simulated in a two-tier HetNet with one single macro base station (BS) and a few small cell BSs scattered uniformly on a ring surrounding the macro BS. A unified CRE bias is adopted to all the small cell BSs. The impact of adjusting the bias value is examined for different design objectives. Simulation results reveal that changing the CRE bias value can significantly improve performance. However, it is also observed that for different performance measures, the results exhibit different trends and behaviors with respect to the bias value. The work is also extended to the scenario where different small cell BSs may adopt different CRE bias values.