Research On Key Techniques In Lte-Advanced Heterogeneous Networks

With the improvement of the internet and wireless communication technologies, smart terminal devices are widely popular, and thus give birth to a large number of new businesses, most of which are data services and based on multimedia. This trend makes the explosive growth of people’s demand for mobile data services. The future of wireless mobile communication will face the challenge of rapid growth of mobile traffic. An effective way to meet this challenge is to deploy low power Small Cells under the coverage of conventional macro base stations (MBSs), so that the tier of MBS can coexist with the tier of Small Cell to constitute a heterogeneous networks, from which the rapid growth of data traffic demand can be coped with via the cell splitting gain and the closer distance between the user and the base station.The research of this thesis is sponsored by the Fundamental Research Funds for the Central Universities:"Interference management technology of Small Cell based on LTE-Advanced"(Grant No.2013RC0111);the foundation from China Information Technology Consulting Institute:"Coverage enhancement technology research of LTE". The research work is carried out from the introduction of LTE-Advanced and the survey of heterogeneous networks with its key techniques, mainly focused on the techniques that can improve the cell splitting gain of heterogeneous networks, which are interference management, load balancing and coverage optimization techniques. The main contents and achivements of the research are summarized as follows:(1) The import background of LTE-Advanced heterogeneous netwoks is described, and then the morphology of the products and the deployment of application of the Small Cell in heterogeneous networks are classified and compared, with the brief introduction of network mode of heterogeneous networks at the same time. Atter that, the challenges and the research issues of LTE-Advanced heterogeneous netwoks are analyzed. Finally, the research status of LTE-Advanced heterogeneous netoworks are analyzed and summarized, and the issues need to be further addressed are also pointed out.(2) In order to reduce the cross-tier interference from the MBS to the Small Cell users when co-channel deployment scenario is considered, a power optimization algorithm based on non-cooperative game is proposed in this thesis. Firstly, a utility function is established based on the non-cooperative game between the users with poor channel conditions which from the two tiers respectively. After that, the existence and uniqueness of the optimal solution for the proposed power optimization problem are proved. Secondly, the proposed power optimization problem is solved by the modified gradient descent algorithm. On this basis, appropriate transmit power of MBSs are set to each protection subframe, so that the cross-tier interference from the MBS to the Small Cell users can be alleviated without reducing the network throughput of the MBS tier significantly.(3) To address the problem of load imbalance in heterogeneous networks which is caused by huge difference of transmit power between MBS and Small Cell, a load balancing scheme is proposed in which the fairness of user association is taken into consideration between and within the tier of MBS and Small Cell. First of all, by introducing the topology potential in data field, the selection criterion of serving cell is changed from estimating the strength of received signal power to evaluating the attractiveness of the stations, so that both the load and the signal strength of the base station can be taken into consideration. Then the throughput of users which experience poor channel condition are improved via the adaptive frequency partition, in which resources with less interference are allocated to the users with poor channel condition. The fairness index of inter-tier and intra-tier are used to have a comprehensive and effective evaluation of the proposed scheme. Simulation results show that the proposed algorithm can take into account the fairness of user association between and within the two tiers in the network at the same time, so that the fairness of the load of heterogeneous networks can be promoted.(4) For resolving the coverage problem in heterogeneous networks under the scenario of dense deployment of Small Cell, a coverage optimization scheme for the network is proposed, which is based on ant colony algorithm. At first, by detecting the events of the coverage overlap and hole in the heterogeneous networks, the coverage problem is modeled as a cost function which includes inappropriate coverage ratio of the network. After that, the ant colony algorithm is applied to find the optimal pilot power of each small cell through the minimization of the cost function, so that the impact on the quality of user communication caused by the coverage problem can be reduced. Simulation results show that the proposed algorithm can significantly reduce the ratio of coverage overlap and hole in the heterogeneous networks, and improve the coverage quality of the network. For different deployment density of Small Cells, the proposed can give the good performance of convergence in these the conditions.