Research On Coordinated Beamforming And Energy Efficiency Optimization In Downlink Multi-cell MIMO Systems

With the growing demands of convenient communication, the rapid development of new wireless communication technology is promoted.As a key technology of3GPP LTE, BSC among multicells can have spatial diversity gain by virtual MIMO, effectively suppress ICI and improve spectral of the systems. However, as the promotion of MIMO technology in cellular system, multi-cell cellular systems usually have geographically separated antennas and several obstacles for its realization. First is the selection of base stations or mobile stations participate in cooperation in order to optimize system performance with lower complexity. Furthermore, in order to multi-cell cooperative process, large amount of data and CSI are exchanged between BSs, which bring serious burden to backhaul. In addition, how to collaborate to suppress the inter-cell interference is a new topic. Therefore, study on technologies in downlink of the cellular network, especially about beamforming, user scheduling, and limited feedback and other means are important research topics in order to achieve the maximum degree of interference suppression so as to increase the capacity. Based on the traditional MIMO technology, the dissertation analyzes the advantages of a multi-cell cooperative process, proposes some novel methods and new ideas and gets some research results about the selection of collaborative users and feedback, a multi-cell downlink beamforming algorithm as well as the application of channel state information. To sum up, the main work is as follows:Firstly, in terms of the reduction of complexity, the idea of multiuser diversity to MU-MIMO system is applied and takes SINR as a measure of the channel quality, and selects a maximum multi-user diversity MIMO channel scheduling method presented, An selective maximum multiuser diversity (SMUD) scheduling scheme which can reduce feedback load while preserving most of the capacity performance in MIMO Channels is proposed, each user compares its maximum SINR with the set-threshold and only those who fall above along with the index transmit antenna are sent back to the base station. The base station allocates independent channels to the users with the highest SINR. Average capacity and feedback load for the proposed method are obtained and shown to match the simulation very well. Note that the channel capacity of MIMO system is a function of the eigenvalues of the channel matrix, an antenna selection algorithm is presented based on the eigenvalue decomposition of channel matrix, which can solve how to choose user in MU-MIMO system when each user has only one receiving antenna. The scheme of select feedback and user options in multi-cell MIMO system are introduced.Secondly, the virtual SINR, a new measurement of inter-cell interference in multi-cell MIMO system is proposed, according to this measurement a distributed collaborative beamforming algorithms based on the local CSI is presented, considering not only to minimum the noise and interference, but also the channel quality of the direct link, the biggest advantage of the algorithm does not need iteration. The problem how to adjust beamforming vector is researched when the CSI is uncertain., several algorithms are simulated in the context of a network with uncoordinated co-channel interferers finally, and simulation results reveal that the proposed algorithm outperforms than the distributive bargaining solution (DBS).Thirdly, in order to obtain better sum-rate performances, beamforming design problem to reduce the same frequency interference is studied in the frequency multiplexing multi-user multi-cell wireless network, Multi-cell multi-user wireless network beamforming system model is established, downlink beamforming is design as Bayesian static game, theoretical analysis results with the game theory show that, the collaborative beamforming vector of the optimal performance is a linear combination of selfishness and altruism strategy, the beamforming vector iteration algorithm to maximize sum-rate is presented, and estimation method about composite coefficient based on the statistic of channel state information is proposed. Finally,the results of simulation assess the performance of the algorithm and show convergence of the proposed algorithm.Fourthly, data transmission scheme that combines distributed antenna and collaborative beamforming in the cellular network is introduced, which can improve the power efficiency of the base station. Sum-rate and energy efficiency function, which is impacted by the backhaul.A unified performance definition can compare energy efficiency of the different level of collaboration. To this end, energy-efficient power allocation strategies corresponding to three different level of collaborations are presented. The simulation results further prove the necessity of the new definition.