Distributed power control based on interference in femtocell networks

Abstract

Higher data rates are required in wireless networks. Femtocell is one of the noticeable technology to guarantee high data rates in wireless network with efficient spatial reuse of spectrum. It aims to combine fixed line broadband access with cellular networks by deploying low cost, low power base stations covering the small business environments. Each femto AP should manage its transmission power by itself and consider interference to other femto APs because of the random deployments of the femto APs. In this thesis, an efficient power control algorithm based on a game theory is proposed. Because of the unpredictable deployments of the femto APs which are in a macro cell area, interference to macro users and users in other femto APs in down-link (DL) cause the degradation of the service quality. Therefore, interference mitigation is necessary in femtocell networks and interference should be reflected to the power controlling algorithm. We describe the system model using a non-cooperative game model and formulate a payoff function to provide fairness and to reduce interference. By proving that the proposed system model has a supermodularity, we implement a distributed power control algorithm based on the properties of the supermodular game. By applying best response dynamics to the power control algorithm, transmission power of femto APs will reach the nash equilibrium (NE). Through mathematical analysis and numerical results, we have found that our proposed scheme has similar performance compared to the conventional centralized power control algorithms with respect to the fairness index and average data rates. Furthermore, our proposed algorithm will not lead the divergence of the transmission power to the maximum. It will reduce much interference among the femto APs and to the macro users. Fair resource allocation is guaranteed and interference is mitigated when the proposed algorithm applied to the femtocell environments.