The Analysis Of Power Control For Two-Tier Heterogegeous Netwoeks

Power control is one of the most important resource management technologies in wireless networks.Not only can it alleviate the impact of limited spectrum resources and the limited battery capacity of mobile devices in wireless networks,but also can reduce interferences and improve the network capacity.In recent years,with a rapid increase of the number of wireless services,more than 60%of voice services and data services arise in the indoor environment.Therefore,deploying femtocells is a very effective solution,not only reducing operating costs,but also improving the network capacity and the coverage.The low power femtocell base stations and femtocell users with lower mobility are deployed in an indoor environment,which are located in an existing macrocell network,forming a two-tier network.In the uplink,macrocell users will be affected by cross-tier interferences producted by the femtocell users,and can not reach their minimum SINR targets.Similarly,femtocell users are unable to reach their minimum SINR targets by cross-tier interferences producted by macrocell users and interferences producted by other femtocell users.The co-tier interferences are usually ignored.Therefore,we need an effective power control scheme to reduce the cross-tier interferences:In this paper,we focus on the analysis of uplink power control in the two-tier network,and put forward a specific scheme.First of all,this paper reviews the classical power control methods,and points out connections and differences between these methods.Next,this paper briefly analyzes the power control methods of two-tier networks.Secondly,we introduce the criterion for judging whether a user has a nonnegative optimal power vector in a two-tier network,and get the Pareto-optimal powers of all users.Due to the complexity of the calculation process,the method of estimating the spectral radius of the non negative matrix is introduced in order to get a fast determination.The estimation errors of this calculation process is so big in the two-tier network that this paper estimate the spectral radius of the normalized channel gain only in the single-tier network which only consists of femtocells.This paper finally presents a corresponding power control scheme.Due to the time-varying characteristics of the wireless channel,the optimal power changes with time.We propose a hierarchical power control based on Kalman filter.Using Kalman filter,the current uplink transmit power under the influence of time-varying channel gains due to the shadow fading effect is obtained by estimating the power of the last moment.This proposed method follows the slowly varying channel characteristics under the influence of the shadow fading effect in order to obatain a accurate power allocation.