Research On The Interference Coordination In LTE-Advanced Carrier Aggregation System

With the development of mobile communication technology, the user traffic and data throughput increases rapidly. The third generation mobile communication system cannot completely meet the users’needs. Therefore,3GPP is committed to studying the evolution of the3G system. In order to meet the requirements of the fourth mobile communication system, LTE-Advanced is the further technology evolution on the basis of LTE. In order to provide higher data rate and support more user traffic demands, LTE-Advanced has new features in frequency bandwidth, the peak rate and compatibility, etc. In the process of the evolution from LTE to LTE-Advanced, wider spectrum demand becomes the important factor that affects the evolution. Therefore,3GPP has proposed the carrier aggregation technology, which can enable users to aggregate multiple component carriers and transmit data over a larger frequency band. As one of the key technologies in LTE-Advanced, carrier aggregation technology can not only significantly improve the peak velocity and the edge rate, but also achieve the higher community capacity.In the LTE-Advanced carrier aggregation system, low power node, such as home base station, was introduced so as to provide better network cover, user experience and system throughput. Even though the introduction of home base stations improves the system performance, it brings many new problems. On the one hand, the random and intensive low-power node deployment makes the interference among low-power nodes severe; on the other hand, the cross-layer interference between macro base stations and low-power nodes also seriously affects users’ traffic experience. Therefore, LTE-Advanced requires an efficient interference coordination scheme to suppress interference and improve users’ performance experience. As for the interference in the LTE-Advanced carrier aggregation system, various standardization organizations and research institutions not only pay attention to traditional interference coordination technologies, but also begin to focus on component carrier selection algorithms. The component carrier selection algorithm is specific interference coordination technique and an effective tool to solve the interference coordination problem in LTE-A carrier aggregation system.The main works of the paper include the following aspects:We briefly expound the carrier aggregation technology in the LTE-Advanced system, including the carrier aggregation type, network deployment scenario, the implementation scheme of carrier aggregation technology and component carrier type. Besides, we collate and summarize the typical interference condition in LTE-A and we have learned that the same-layer and the cross-layer interference under the same frequency band deployment are serious and should be solved promptly.The interference coordination algorithms in LTE-A have been collated and summarized. On the one hand, we make the comparative analysis of each traditional interference coordination technique; on the other hand, we classify and summarize the component carrier selection algorithms which are aimed to address the interference coordination problem. Academics have conducted the extensive and in-depth study of traditional interference coordination technologies in LTE. However, how to apply the component carrier selection algorithm in carrier aggregation system to effectively coordinate inter-cell interference has not been fully tapped. By summarizing existing component carrier selection algorithms, we learn that the cross-interference problems in the two-layer network have never been effectively solved. Meanwhile, the component carrier selection algorithms designed to solve the interference problem in the single-layer network are not adequate.In the two-layer network, low power nodes such as home base stations are introduced, the macro users near low-power nodes suffer severe downlink interference and even drop. Besides, low power nodes cause the interference to each other, which greatly influences users’traffic experience. In order to solve the serious interference problem between cells, we put forward a centralized component carrier selection algorithm. First, the component carrier selection algorithm avoids adjacent interference cells using the same frequency carrier according to the interference coupling relations. Then, we apply the iterative maximum neighbor selection algorithm to configure component carriers and their corresponding carrier states. Finally, the cells can choose available carriers based on the flexible carrier configuration. The simulation results show that the algorithm can avoid the interference between home base stations and macro users and the interference between home base stations, on the basis, maximizes the system bandwidth utilization.In the single-layer network, existing component carrier interference selection algorithms just consider the surrounding interference environment and ignore the impact of traffic load. If one base station occupies all the optional component carriers based on traffic needs, the start-up neighboring cells will have no appropriate component carriers to select. This condition will lead to uneven cell traffic throughput issue and greatly affect user’s experience. To solve this problem, this paper presents a component carrier algorithm which takes both the interference coordination and fair frequency band distribution into consideration. The simulation results show that the algorithm can greatly enhance the throughput fairness among small cells within the scope of tolerable system throughput loss.