| As one of the key technologies of LTE-Advanced, CoMP has received a lot of attention.Because it is a way to improve the performance of system in an interference limited cellular system,especially joint transmission technology in CoMP provides higher theoretic gains in spectral efficiency. However,this requires user equipments to feed back the channel state information(CSI)of all the base stations,and user data need to be exchanged between all cooperating base stations through the backhaul network.To reduce the feedback and backhaul load,user with strong interference links are feeding back their full CSI.Although efficient,there are two key issues need to solve:(1) The design of limited feedback scheme.The user needs to choice and feed back the CSI related to base stations.(2)The design of joint transmission scheme.To achieve backhaul load reduction,the scheduling and precoding approaches should be carefully designed and achieve good system performance at the same time.This thesis mainly study on the two key issues in joint transmission and put forward the solutions.Firstly,the expression of signal to interference plus noise ratio of the user which fully considering the channel quantization error is derived,and this thesis propose a limited feedback scheme based on collaboration gain.This scheme choices the subset of base stations which can bring greater gain to the user.The simulations show that the scheme can provide a good trade-off between performance and overhead.The secondly,in this thesis,the orthogonal joint beamforming technique of single cell is extended to multi-cell, and proposes a multi-cell combinatorial orthogonal joint beamforming scheme to solve the problem of scheduling and precoding in joint transmission.This scheme has no limitation of the aggregation channel matrix,and the base station can choose the best user to service.The simulations show that the scheme can effectively reduce the backhaul load and has the better performance of the system. |
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