Limited Feedback Technology Study In Cooperative Communication Systems

The basic idea of multi-cell cooperative communication technology is that multiple base stationscoordinate transmissions by sharing user information among themselves via backhaul links.With thebackhaul being bandwidth limited,cooperative strategies that involve the exchange of only userchannel state information (CSI) among base stations offer the best tradeoff between complexity,backhaul load and performance gains.In a single-cell system,users estimate and feedback the CSI ofa single channel over a finite-bandwidth feedback link.However,in a multi-cell cooperativescenario,each user needs to transmit the CSI of multiple channels using the same feedback link.Thisimplies that it is necessary to study the finite feedback techniques to maximize performance gain ina cellular network.In this thesis,limited feedback technologies are investigated for cooperative communicationsystems.Firstly,codeword selection schemes are investigated for single-user cooperativecommunication systems.Specifically,there are two codeword selection schemes for per-cellcodebook,one is joint codeword selection and another is independent codeword selection.Thesystem throughput obtained by the joint codeword selection and the independent codewordselection is analyzed firstly, which shows that joint codeword selection has a better trade-offbetween system throughput and feedback overhead.There exists to be phase ambiguity(PA) in theindependent codeword selection,and feeding back a few phase information (PI) bits in each cell forPAis an effective way to improve the system.performance.Secondly,codeword selection schemes are investigated for multi-user cooperativecommunication systems.We first analyze the structure of CDI of CoMP channel which is theessential information for downlink MIMO precoding.Then we provide a way to quantize the CoMPCDI vector based on the selected per-cell codewords.Next,we present three limited feedbackschemes with optimal joint codeword selection,independent codeword selection,and a jointcodeword selection method.Then we introduce the joint codeword selection scheme and optimizedjoint codeword selection scheme.The independent codewords selection criteria is studied.Theindependent codeword selection is of low complexity, and even outperforms the joint codewordselection if a phase ambiguity is allowed to be fed back.Finally,we propose the bit allocationscheme among per-cell codebooks,aiming at minimizing the average quantization error of theaggregated CoMP channel.Considering the per-cell CDI quantization errors are of unequal importance to the global CDI quantization error,we propose a serial codeword selection schemewhose complexity is quite low but the performance approaches that of the joint codewordselection.It is shown from analysis and simulation that the proposed schemes can achieve acompromise between complexity and performance..Finally,downlink overhead reduction technologies are investigated for a multi-cell cooperativeprocessing system,and feedback load could be reduced by preventing users with low-qualitychannels from feeding back their CSI in this system.Specifically,we introduce the overheadreduction scheme for absolute threshold based SNR,BLR algorithm based scheduling and BLRalgorithm based ZF precoding.For a MCP system,the overhead reduction scheme for relativethreshold based SNR is developed.Simulation results demonstrate that the proposed scheme canachieve a compromise between throughput and overload.