Down-Link Interference Coordination Mechanism In Two-Tier Femtocell Networks

Over the past decade, the explosive growth of mobile data services traffic has put forward higher requirement of capacity of mobile wireless networks. A traditional effective method to enhance the capacity of a wireless system is to narrow the distance between the transmitter and receiver. In this way we can provide a better link quality, and increase the spectrum spatial multiplexing. The traditional method of using macro base stations to provide coverage is too expensive, so in recent years scholars have proposed the various ways, such as using microcell, hot spots, distributed antennas or repeaters to provide wireless data access services. In contrast to these methods, one kind of cheap, low emission power Femtocell (or home base station) has been widespread researched in recent years. The Femtocell station is access point installed by the user, usually indoors to provide better indoor voice and data transmission service. The employing of Femtocell base station would make original single macrocell network into two-tier heterogeneous networks.Two-tier heterogeneous networks often consists of traditional macrocell base station, which is used to provide basic coverage of macrocell areas and, and some Femtocell base stations, used as a lower cost method to provide high quality and reliable service within a small range. However, the problem of cross-layer interference attracts many people’s attention in recent years. If the problem of cross-layer interference is not well-solved, the introducing of Femtocell base station will bring great damage to the performance macrocell, which will affect the overall performance of the system. So how to deal with the problem of interference in two-tier heterogeneous becomes a difficult problem in the development of Femtocell base stations.The traditional way to mange cross-layer interference is to use fractional frequency reuse to seperate spectrum resources between the macrocell and the femtoell layer is. The advantage of doing so is that it can eliminate cross-layer interference in a relatively easy method. However, this static interference coordination mechanism will also lead to the problem of low spectral efficiency. To solve this problem, this paper in-depth study the interference scenario consisted of traditional macrocell and Femtocell network. This paper analyzes and summarizes the existing mainstream co-tier and cross-tier interference coordination mechanism. Their specific properties were also analyzed and compared. Then this paper analyzes the influence of the number of coexistent base station to the spectral efficiency of both victim users and the whole system. On the basis of analysis we present a dynamic interference coordination mechanism. The idea of the mechanism is not completely prohibit Femtocell base station to share the same frequency band with macro base stations. On the contrary, it allows Femtocell base station distance away from the macrocell base station to share the same frequency band as long as macrocell user can satisfy its quality of service. In this paper, we define the distance as the minimum reuse radius and calculate it by modeling the space station into a homogeneous Poisson point process. Then this paper derives the closed-form outage probability as the function of that distance.Simulation results show that the expression can accurately measure the outage probability of victim users. Besides, this mechanism can effectively mitigate interference as well as other increase the overall spectrum efficiency and improve the overall performance of the network.