| Multi-Input Multi-Output(MIMO)technology can make full use of space resources to reduce bit error rate and improve channel capacity without additional spectrum resources.The degree of MIMO technology improving the performance of system is influenced by the knowledge of channel state information(CSI).The time division duplex system mainly uses channel reciprocity to obtain CSI,while the frequency division duplex system uses limited feedback to obtain CSI.Limited feedback base codebook is one of the most common methods in limited feedback,where a codebook is reserved on both receiver and transmitter,the receiver selects the optimal codeword and sends the corresponding index of the optimal codeword to the transmitter based on channel estimation,then the transmitter decodes the codeword for precoding.Due to the difference of the channel,this paper mainly studies the codebook design for different channel.The research contents include the following aspects:?.In the independent identical distribution channel,discrete fourier transform(DFT)codebook cannot control performance loss caused by the linear receiver,a double codebook design algorithm based on perturbation is proposed.In this algorithm,DFT codebook is designed to be a major codebook,then using unitary matrix codewords in subordinate codebook to disturbance the major codebook.The gain of channel capacity and bit error rate is analyzed in detail.The simulation results show that compared with DFT codebook the double codebook can reduce the performance loss caused by the linear receiver and the codewords search complexity.?.When scatters in channel enviorment aren't sufficient or distance of antennas is relatively small,there will exist spatially correlation in channel.Spatially correlation not only increases the complexity of codebook design,but also affects ergodic sum-rate.In multi-user spatial transmit correlated channel,the correlation of fading channels often leads to ill-conditioned matrix whose condition number has a decisive influence on ergodic sum-rate of high signal-to-noise ratio.In order to reduce that affection,a codebook design algorithm based on channel statistics is proposed.Firstly the loss of ergodic sum-rate in high and low signal-to-noise ratio is calculated using the channel statistics class,then the codeword is designed by combining inserting eigen-matrix and the channel statistics class.The simulation results show that compared with the existing algorithm,this algorithm significantly improves the ergodic sum-rate and has a strong robustness.?.When Doppler frequency is small,channel is temporal correlated.In the design of codebook design,the time correlation between adjacent time channels can be not only used to reduce the feedback overhead,but also used to track the changing of channel in real time.A temporal channel is modeled by the first order guass-markov process,and then the codebook structure,implementation steps and basic properties of Polar-cap differential precoding codebook are introduced in detail.On Polar-cap differential precoding codebook,the codewords are distributed on circumference of a circle,which cannot accurately track the changing of channel.This paper improves the codebook that codewords is distributed on the round surface,and the radius of the codebook is newly designed.The simulation results show that,the improved codebook has better performance in channel capacity than the existing algorithms with the decrease of time correlation coefficient.?.The real wireless communication channel is not only spatially correlated but also temporal correlated.System should not only consider the changing of channel between adjacent time channels to update codebook in real time,also channel is no longer independent distribution and channel optimal quantitative results are no longer even.Firstly,the spatially/temporal correlated channel is modeled;then,codebook design of spatially/temporal correlated channel based on Polar-cap differential precoding codebook is introduced,whose radius of the codebook dosen't consider spatial correlation.To improve this disadvantage,the radius of the codebook is newly desigened.The simulation results show that,the improved codebook has better performance in channel capacity than codebook of spatially/temporal correlated channel based on Polar-cap differential precoding codebook in spatially/temporal correlated channel. |
PDF Full Text Request