Research On Limited Feedback In Comp Systems

Limited feedback and coordinated multi-point (CoMP) technology are nowqualified as the key technology of the fourth generation wireless communication dueto the advantages on the cellular edge user’s throughput and saving the feedbackpayload. In CoMP system, the adjacent cellular base station (BS) can take part in thecooperation transmission to improve the system throughput. On the other hand,channel state information (CSI) plays a key role in wireless resource management andcellular throughput. All BSs in CoMP system take cooperative transmission accordingto the CSI, but the accuracy of CSI impacts the CoMP system with great probability.Hence, limited feedback is always employed in CoMP system, and which use the waybased on codebook quantization aiming to saving the feedback payload. But affectedby quantization error, BS cannot reconstruct the perfect CSI. For promising thesuperiority of CoMP system, efficient limited feedback strategy becomes one of thehot research focuses.We first consider the phase information (PI) feedback in joint transmission (JT)system. In multi-cell system, feedback payload with conventional feedback strategywill increase linearly with the number of BS, and when JT is employed, phaseambiguity occurs in conventional channel direction information (CDI) feedback,which leads to the receiver signal can’t be coherently superposed and unnecessarysystem throughput loss. In order to solve the problem, we propose an adaptivefeedback scheme with CDI and PI, and users decide the allocation of the feedbackbits according to the transmission channel gain, the interference channel strength,and relative phase information of the received signals from different base stations,which enables pre-adjustment of the phase at the base stations in order to achievecoherent combining of received signals at the user node. Simulation results showthat the proposed scheme remarkably improves the system throughput performancewithout increasing the feedback overhead.Limited feedback in coordinated scheduling/beamforming (CS/CB) system is alsoconsidered, where the transmission terminal designs the precoding matrix to cancel the inter-cell interference according the CSI and users must feedback the CSI to allcooperative BSs. For improving the feedback bits efficiency in limited feedbackpayload, we give the close form solution on the adaptive feedback bits allocationaccording to the relationship between feedback delays of different channels andsystem throughput. Then users decide the allocation of the feedback bits accordingto the different feedback delays in channels aiming to improve the efficiency offeedback resource. Simulation results show that the proposed scheme canremarkably improve the CoMP system throughput performance when the feedbackdelays become larger.We investigate the channel feedback optimization in network multiple-inputmultiple-output (MIMO) systems with limited feedback resource. We propose aselective feedback optimization scheme to exploit channel asymmetry and derivefeedback bit allocation which allows an adaptive feedback bits according to user’sselected channel path-loss and backhaul delay. Simulation results show that byallocating more feedback bits to the user with small feedback delay and path-loss ordecreasing the bit number of users with large feedback delay and path-loss willfurther improve the efficiency of feedback overhead.In this dissertation, following the standardization of3GPP in the fourthgeneration wireless network, we have achieved some achievements on the limitedfeedback in CoMP system. Also, we propose some further investigation TDD limitedfeedback scheme for the heterogeneous net (HetNet) system, which includesdesigning of feedback parameter, feedback protocol, and feedback resourceallocation.