Research On Interference Coordination Technology Based On Collaborative Multi-Base Stations

With the rapid development of mobile communication from 1G of analog communication to 4G of digital communication, Long Term Evolution (LTE) was proposed in the conference by 3GPP in 2004 and the requirements of speed and mobility have been enhanced. Base stations locate in the center of the hexagonal cell and radiate the power in a circle to the outside part, so the quality for the cell edge users is quite poor and it can easily be disturbed by the Co-Channel Interference. Therefore, the technology of frequency reuse in multi-cell is analyzed and researched to increase the capacity of the cell edge users and the system by appropriately allocating the frequency and power.The main interference in the communication system is Co-Channel Interference (CCI), adjacent channel interference and inter-modulation interference. In LTE SC-FDMA is used in the uplink and OFDMA is used in the downlink. The benefit of OFDM is to ensure the orthogonality so that the intra-cell interference can be ignored, so the main interference is ICI. There are three ways to mitigate the interference: interference randomization, interference cancellation and interference coordination. Interference randomization just randomize the white noise, the interference is not completely eliminated. Interference cancellation used compensatory way to mitigate the interference and it is used to eliminate strong interference source. Interference coordination is more flexible, it can also be called soft frequency reuse and partial frequency reuse. Different frequency reuse factor is assigned for the center and the edge depending on the situation such as traffic and parameters to get the best communication quality with a good spectral efficiency.The research is based on the widely used technology of LTE. Firstly, new core technology, such as MIMO and OFDM, is studied. And then the multiple access technology of OFDMA and SC-FDMA used in the uplink and downlink is discussed. The emphasis is to analyze and study several ways to avoid interference. The tool of Matlab is used to test the result. The methods can be divided into three parts. The first one, pre-coding technology (LP-DP, JT-MMSE, JT-ZF) is used to calculate the capacity and compared with traditional single-user detection; the second one, using soft frequency reuse programs developed by Huawei and Simens. It has to control the ratio of the transmission power of center user and edge user and allocate different frequency reuse factor in center and edge cell; the third one, using a three-sector or two-sector collaborate virtual cell. We should take the spectral efficiency and throughput into account in order to maximize the channel capacity. It is required to plan in advance for static interference coordination while a network scheduler is required for dynamic coordination. Also, whether to set up collaboration and how to plan the frequency pattern is determined by the traffic and etc.