Power Control and Beamforming for Femtocells in the Presence of Channel Uncertainty

Femtocells that are installed in existing macrocellular networks form a two-tiered heterogeneous network, yielding an interference problem between the two layers. How we can mitigate the interference is of great concern for the deployment of femtocells. When the femto base station has perfect channel information, it can mitigate the interference through transmit power control and beamforming. However, it may not be feasible to get perfect channel information due to unavoidable impairments such as channel estimation, quantization, and feedback delay. In the presence of such channel uncertainty, we consider the combined use of transmit power control and beamforming for femtocells in heterogeneous wireless communication environments. By analyzing the effect of channel uncertainty parameters on the performance, we determine the transmit power level to provide the desired signal-to-interference-plus-noise ratio (SINR) of the indoor cell edge femtouser and the beam weight to maximize the output SINR of the macrousers and femtousers by mitigating interference in a collaborate manner. Finally, simulation results show that the proposed scheme is quite effective in the presence of channel uncertainty.