Research On Interference Suppression Technology In LTE Networks

Long term evolution (LTE) networks characterized by orthogonal frequency divisionmultiplexing (OFDM) and multiple input multiple output (MIMO) as the core techniquesoperate on the same frequency, which provides a higher data transmission rate, spectrumefficiency and network coverage ability for the mobile communication systems. Due tothe actual radio channel propagation delay, the interference control become not idealwhen the same frequency is operated in the LTE networks, and the co-channelinterference among the cell edge users might be serious when the same frequency isreused among the adjacent cells, all those will decrease the performance including thetransmission reliability, system capacity and energy efficiency. Based on thedisadvantages above mentioned, the thesis researches the interference suppressionproblems in LTE networks emphasizing on the impact of transmission delay and channelmatrix decomposition. The research contents in detail are as follows:Considering the uncertainty of transmission delay in orthogonal frequency divisionmultiple access channel, a closed-form expressions for interference is analyzed andderived according to the impact of transmission delay, and the relative delay varianceinfluencing on co-channel interference (CCI) is also experimented. In view of theasynchronous and non-correlative characteristic of the interference and the limitations ofthe traditional interference rejection combining (IRC) algorithm, exploiting the low delayand high coding gain advantages of the convolutional code, a Coded-IRC algorithm isproposed in order to suppress interference. The simulation results show that the CCIcoming from delay decreases the bit error rate performance and the Coded-IRC algorithmagainst the limitations of the IRC improves the bit error rate performance.Considering the issues of co-channel interferences in the downlink for LTEmulti-cell multi-user networks, an interference suppression algorithm combiningtriangular decomposition with signal leakage noise ratio (SLNR) is proposed. Thealgorithm eliminates half of inter-cell interference by decomposing the joint channelmatrix and obtains the equivalent system model, exploiting the SLNR and interferencesuppression matrix eliminates the remaining interferences based on the equivalent systemmodel and the vary interference situations of the cells. Theoretical analysis shows that thealgorithm joint triangular decomposition and signal leakage noise ratio will not increaseextra matrix and matrix operation for suppressing inter-cell interference in the receiver,and the receiver processing is simplified and the algorithm complexity is reduced correspondingly. Computer simulations show that the proposed algorithm can effectivelyimprove the system capacity and energy efficiency performance.