The Research Of Beamforming Techniques For Single-User And Multi-User Limited Feedback Systems

The fast developments of wireless communication technologies have put forward higher and higher demands on advanced transmission technique. How to improve the data rate and the spectral efficiency of the system has become a dramatically challenge that next wireless communication system designing are faced with.Adopting Multiple Input Multiple Output (MIMO) technology is one of the most notable characters of wireless communication system. It can improve the capacity and frequency spectrum effectiveness of the system doubled without increasing bandwidth and power. Beamforming is a kind of key technique of MIMO. Even under the finite feedback condition it can still get the near capacity that MIMO system can reach when it has accurate channel state information (CSI). So it makes the effectiveness and reliability of the system enhance remarkably and could satisfy the high demands for frequency spectrum effectiveness and system capacity of the fourth generation wireless communication.This paper mainly studies beamforming technologies in limited feedback system of single-user and multi-user. First it reviews the basic knowledge of wireless communication: Multi-path fading and typical wireless channel model, MIMO system introduction, multi-user diversity (MUD), beamforming technique in MIMO system and user scheduling algorithm in limited feedback system of single-user and multi-user. The following two chapters mainly researches beamforming technologies in single-user and multi-user limited feedback systems and proposes several effective algorithms and proposals of beamforming schemes. The chief originalities are listed as follows:(1) A new dynamic antenna mode scheduler in MIMO systems is designed to deal with the throughput degradation due to the small number of users in the random beamforming (RBF) and the feedback increase due to the large number of users in the eigen-beamforming (EBF). Inspired by Game Theory, a system cost function is proposed in the new scheme and enables the system dynamically to switch between the EBF and RBF antenna mode to overcome the disadvantages of the two methods. System performance can be improved when the number of users is small, and be guaranteed the performance with less feedback quantity for large number of users, thus optimizing wireless communication system performance.(2)Due to the spatial correlation of the real MIMO channels, an improved finite-rate feedback beamforming algorithm based on the correlation channel statistic was proposed by the use of random vector codebook to quantize the CSI. The novel beamforming scheme only needs limited feedback CSI and can exploit multi-user diversity gain and array gain simultaneously. Superior to the conventional beamforming and coherent opportunistic beamforming (COBF), the novel beamforming is neither in need of lots of feedback information nor sensitive to instantaneous change of channel. The simulation results show that the performance of the proposed scheme is better than that of the conventional beamforming and approximates to that of COBF with only0.2bps/Hz performance loss. So the proposed proposal in this paper can not only reduce system feedback greatly, but also has stronger robustness for CSI feedback and make use of spatial correlation of the real MIMO channels better.(3)To reduce system feedback and improve system performance we propose a new beamforming scheme based on channel quality interference ratio (QIR) which is quantification standard. This quantification standard can guarantee the quality of quantification of channel and minimize the interferences between its sub-channels. It has much better performance than traditional quantification principle and uses DFT (Discrete Fourier Transform) base as codebook quantification CSI. At last we simulation in limited feedback condition our proposal’s overall performances are better than RBF and in low signal to noise ratio condition are better than EBF. It improves system performance a lot. Therefore this proposal guarantees the whole performance of the system under limited feedback condition.(4) We proposes a novel beamforming proposal based on equivalent channel Eigen-values product (EVP) which is quantizing criterion concerning on research of improving system whole performance proposal that the now existing beamforming technique barely involve and give attention to system capacity and bit error rate (BER) performance. At the same time we give the formula of EVP quantizing criterion which jointly consider the channel capacity and the BER performance of the overall system. Compared with the traditional quantification standard which only considers channel capacity or system BER, it has more advantages. Through computer simulating this proposal can obviously improve system BER and channel capacity. Therefore it is a kind of good beamforming proposal.At last we study the influence of MUD and accurate CSI on multi-user limited feedback system in detail. And we detailedly stimulate and test it from the experimental perspective, verifying the effect of each parameter on system performance. In addition, we introduce and analyze two typical beamforming techniques of multi-user finite feedback system:Per Unitary basis stream User and Rate Control(PU2RC) and Zero-Forcing Beamforming (ZFBF), making detailed analysis from both the theoretic and experimental aspects with the present researching achievements.In a word, these beamforming algorithms and proposals effectively solve the existing problems of beamforming techniques in the present single-user and multi-user limited feedback systems and verify its effectiveness by simulation. Our researching and proposed beamforming schemes have some theoretic and actual meanings. It also has broad application perspectives and values for reference.