Research On Limited Feedback And User Scheduling In Multiuser Multi-antenna Systems

In the multi-user multi-antenna downlink systems, transmitter pre-proceeding has drawn much attention due to its effective suppression or cancel of interference among users and proper distribution of resource management. This thesis mainly address transmition strategies employede in multi-user multi-antenna downlink systems, with foci on limited feedback scheme and user scheduling algorithms. The main contributions of the thesis are summarized as follows.First of all, a limited feedback scheme based on differential normalized matched channel matrix is proposed to avoid the shortages existing in present scheme based on Frobenius norm-based normalized matched channel matrix. The proposed scheme overcomes the shortcoming existing in prior work that the range and probability distribution of the entries in the normalized matrix vary as the number of transmitter antennas increases. Thus the proposed scheme is prospected to decrease the quantization error of Uniform Quantization (UQ) without raising the feedback overhead and convenient to realize the codebook design of the Non-Uniform Quantization (NUQ).Then, when the number of users is small, the performance of conventional per user unitary and rate control (PU2RC) would be degraded with the increase of codebook size, an efficient user scheduling scheme based on relaxing restriction of user group is propose. Using adjacent codewords set, the proposed scheme extends the range of user scheduling and thus promotes the performance of the system. In addition, advantages of conventional algorithms are maintained in the proposed scheme to ensure that the algorithms could be realized conveniently without the sacrifice of the performance.Next, in time division duplex (TDD) multi-user multi-antenna systems, we propose two improved schemes based on orthogonal linear beamforming (OLBF) algorithm to reduce the complexity of operation:OLBF based on SINR restriction (SOLBF) and receiver-assissted OLBF (RaOLBF). SOLBF incorporate user scheduling with compression of user scheduling range, due to which extra operation would be avoided and thus decrease the complexity of algorithm. RaOLBF makes full use of advantage that channel state information at transmitter (CSIT) is easily gathered in TDD systems and realizes its distribution of user group with receivers feedback assisted information to reduce the complexity of operation at transmitter.Finally, the OLBF algorithm is introduced into the system of receiver with multiple antennas. We propose two schemes based on coordinated transmit and receive optimization. Vector norm and eigenvalue are considered respectively as two principles of selecting the first user. A discussion on the performance of the two schemes is provided at the end of this chapter.