Research On The Technology Of Inter-cell Interference Mitigation In LTE

In LTE systems, the SC-FDMA and OFDMA technique are used for uplink and downlink transmission, respectively. Because the orthogonality of different subcarrier, users can differ from each other based on these techniques. At the same time, the data stream is distributed over these subcarriers and so the interferences don’t exist among users in the same cell. But when the frequency resource is universally reused in each cell of the system, the users suffer from the serious inter-cell interference. Therefore, in order to improve overall system performance, Long Term Evolution(LTE)targets to reduce inter cell interference.According to the differences of adopted techniques, Interference mitigation technique can be divided into interference randomization, interference cancellation, interference coordination and power control. In this dissertation, the critical technologies about inter cell interference coordination are reached. Also, some inter cell interference coordination schemes and its basic theory is reached.In 3GPP LTE networks, the frequency reuse schemes such as fractional frequency reuse(FFR)and static soft frequency reuse(SFR)are used to improve system capacity. The allocation of transmit power and subcarriers to each cell in these schemes are fixed prior to network deployment. This limits the potential performance of these frequency reuse schemes. In this paper, an adaptive soft frequency reuse(ASFR)algorithm is proposed, aiming at optimizing the system throughput while guaranteeing the minimum data rate requirements for both cell center and cell edge regions. The ASFR algorithm can adaptively adjust the major and minor subcarriers, and their respective transmit power in each cell according to the system traffic loads. In the ASFR, the optimal resource allocation in each single cell is first determined by using exhaustive search and greedy descending methods. Then the single cell resource allocation is repeated iteratively among all cells until the system throughput does not change any more. Simulation results show that the ASFR algorithm yields an SFR resource allocation after a number of internal iterations. It is also shown that the ASFR algorithm improve the cell edge user throughput and achieves higher system throughput compared with several traditional frequency allocation scheme. These advantages reveal that the proposed algorithm is more preferred for the LTE system.