Downlink Interference Management In Femtocell And Macrocell Overlaid System

In cellular networks, it is estimated that 2/3 of calls and over 90% of data services occur indoors. However, some surveys show that many households and businesses experience a poor indoor coverage problem. It has been identified that indoor coverage problem is the main reason for churn, which is very costly for operators. How to provide good indoor coverage cost effectively is thus a demanding challenge for operators.The recent development of femtocells provides a fresh opportunity for operators to address the poor indoor coverage problem. Femtocells are low-power cellular base stations that operate in licensed spectrum. They are typically deployed indoors to improve coverage and provide excellent user experience. The deployment of a large number of femtocells will have an impact on the macrocell layer.Thus this may create serious mutual interference between femtocell and macrocell as well as among femtocells.In this paper the background of femtocell is introduced, the concept of the home base station is explained, and several traditional indoor coverage technologies are summarized. Then the composition and the network structure of femtocell is discussed, and the key issues of it’s deployment as well as the influence on the existing network are pointed out. Besides, several existing interference management strategy is summed up. Moreover interference management issues from power control and spectrum allocation schemes are considered.The major work of this paper are two aspects: Firstly, aim at the suburbs environment we proposes a cross-tier interference management algorithm which is based on joint power control and subchannel allocation. We apply the iterative water filling algorithm to mitigate the femtocell to the macrocell interference in a creative way. Before an improved resource block allocation algorithm based on SINR is carried out to allocate the subchannel to femtocell users, the scheme will use an iterative power algorithm to make a predistribution for the power of femtocell base station. Then make a further adjustment for the power of femtocell base station. Simulation results are given to support the advantages of the proposed solution, showing that more than 60% capacity gain at-8d B SNR and 5% gain at 6d B can be achieved compared with equal power algorithm; Secondly, To against the problem of the co-tire interference, this article proposes a clustering based subband allocation strategy: first, constructing a weighted interference graph base on the user measurement report mechanism. then, according to the interference graph, the disjoint IFI-minimizing clusters are formed by a clustering algorithm. last, a kind of proportional fair algorithm assigns subbands to each cluster. The simulation results show that: compared with the traditional fixed resource block allocation algorithm the proposed scheme can maintain the average SINR of femtocell user at a high level even the density of femtocell base station is increases,and the femtocell user’s fairness between clusters tend to be optimal.