Auto-Tuning of Downlink Power of LTE Femtocells Adaptive to Various Interference Conditions

Femtocell base stations are required to set proper downlink transmit power under various building environment. Conventional power setting techniques use a fixed power offset over received power level of the strongest macrocell base station to expand indoor femtocell coverage along with mitigating the interference leakage to the outdoors. However, the power offset has not been adequately optimized for various interference conditions, leading to degradation of macrocell or femtocell throughput. We propose an auto-tuning scheme of the power offset adaptive to the various interference conditions such as size of buildings where femtocell mobile stations exist, and distance to a street where macrocell mobile stations exist. The proposed scheme automatically tune the power offset so that the femtocell throughput can increase while maintaining the macrocell throughput based on macrocell mobile stations´ interference detection reports and their totalization. According to the Long-Term Evolution system level simulations, the proposed scheme tuned the power offset to a proper level depending on various building conditions and can improve the throughput. If the power offset is commonly tuned among femtocells in macrocell, a newly deployed femtocell can employ a proper setting from the beginning of its operation.