| A key feature of the LTE system is the universal frequency reuse, which means all the cells employ the same frequency band, but results in the inter-cell interference. The LTE system may suffer interferences from the external systems, such as the cordless telephones, bluetooth devices and microwave ovens. In order to acquire higher system capacity and communication quality, LTE system needs efficient solutions to deal with the interference within the system.However, the LTE uplink interference suppression is mainly facing the follow questions:(1) The interference rejection combination method can be used to suppress interference when the base station is equipped with multiple received antennas. In order to realize interference rejection combination, the channel informations need to be known exactly. However, the performance of existing channel estimation algorithms will be seriously deteriorated by the interference;(2) The existence of interference will seriously affects the performance of the system and reduces the throughput. In order to facilitate subsequent signal demodulation process, it is necessary for the receiver to detect interference, including the detection of existence and type;(3) The existing LTE uplink detection method is combination of frequency domain MMSE and Turbo soft interference cancellation, which is not able to suppress interference. It is needed to find detection methods with ability to suppress interference.This thesis mainly focuses on the research of LTE uplink interference suppression, and does several exploratory researchs on the problems mentioned above. The concrete researching contents include the following three aspects:First, three channel estimation algorithms within interference are proposed: the pragmatic linear minimum mean square error channel estimation, the EVD-Based channel estimation based on eigenvalue decomposition and the double domain channel estimation aimed at narrowband interference. In LTE uplink under the condition of EPA channel with narrowband interference, the simulation results show that: when ISR is 0d B, BER is 10-3, compared to the traditional DFT-Based channel estimation, the three suggested channel estimation algorithms can acquire 0.4d B, 1.1d B and 1.5d B improvement respectively.Secondly, an interference detection algorithm is proposed, including the detection of existence and type. The innovation of this algorithm is that a method to eliminate the influence of the desired signal which has high correlation with interference is suggested. And this thesis uses the spatial correlation and time domain correlation of interference to determine the existence of interference and the type of interference, respectively. Simulation results show that: when ISR is 10 d B, the detection probability of this algorithm proposed in this paper is greater than 99%.Finally, an equalization and detection algorithm with ability to suppress interference is proposed. The innovation of this algorithm is that an interference pretreatment module is added on the basis of the existing LTE uplink receiver. And then the received signal is imported to the iterative equalization detecter after pretreatment. Simulation results show that: in LTE uplink under the conditions of EPA channel, ISR is 0d B, two transmitted antennas and four received antennas, the traditional detection algorithm can not work, and the proposed algorithm with one iteration and three iterations can acquire 1.4d B and 2d B improvement compared to first detection.The research in this thesis explores the problem of interference suppression techniques for LTE uplink system, which extends the existing researchs and has theoretical and practical values. And the research results can be applied to LTE, LTE-A system and other systems using SC-FDMA technology. |
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