Interference Suppression Techniques In Downlink MIMO System With Multi-cell And Multi-user

Multiple Input Multiple Output technology used in base station and mobileequipment is widely recognized as one of the key technologies for the future wirelesscommunications. Based on B3G technology,3GPP proposed the version of evolution ofthe third generation mobile communication system named LTE technology. The mainfeatures of LTE technology is to adopt Frequency Division Multiple Access as the airinterface technology and MIMO technology, as well as link adaptation technology, et al.Each of them can be a good way to improve the data rate, increase the system capacityand the cell coverage, and reduce operating costs. In order to respond to WiMAX，3GPPput forward LTE-advanced, which has high-speed, low bit error rate, low latency andhigh quality of service. LTE-Advanced is a smooth evolution of the existing coretechnology of LTE，and is compatible with all of the features of LTE. And thenintroduce some new technologies，such as carrier polymer technology, multi-antennaextension technology, collaboration communication, and relay technology, et al.However, when MIMO technology is applied to multi-cell, especially the nextgeneration mobile communication LTE-Advanced system, in order to improve theefficiency of spectrum utilization, the cell frequency reuse factor is set to one, so thereis a serious inter-cell interference, especially for the edge users. Finally, it leads to asignificant reduction in the data rate of the edge user. As a result, the multi-cell MIMOsystem is changed to an interference limited system. For the purpose of interferencecancellation， the study of inter-cell interference suppression has far-reachingsignificance. As we known，traditional multi-cell combined method can eliminate theinter-cell interference, however，all users of the channel state information must beneeded, and it’s difficult to obtain the full channel state information due to channelestimation error, feedback delay and bandwidth limitation of feedback channel.In this paper, for the sake of solving the above problem, the interferencesuppression in multi-cell MIMO system was studied. The main contents include: a newmulti-cell collaboration interference suppression algorithm was proposed. All users aredivided into two types, center users and edge users, respectively. Then take a differentprecoding method to suppress interference. Compared with the traditional multi-cellcorrelation algorithm, this method decreases the system complexity, while maintainingthe original performance. How to reduce the amount of uplink feedback for interference suppression is also researched. Then a multi-user MIMO systems with limited feedbackprecoding algorithm is proposed. First, quantify the user channel matrix in the receiverby codebook, as known all codebook have its number. Second, each user only needs tofeed a serial number, rather than the entire channel matrix, which greatly reducing theamount of feedback. Simulation results show that the new approach maintains theperformance of the system. Further more, the system throughput is illustrated on thecondition that the estimated error and quantized error of the channel matrix exit. Theanalytic expression with the throughput, variance of error and transmitted power willbenefit to the channel estimation process and have a good prospect. The paper alsointroduces several methods about codebook construction in limited feedback, and thesimulation about capacity verify the validity of the used codebook.