Study On MU-MIMO In IEEE 802.16m

Multiple-input multiple-output (MIMO) techniques are an important area in IEEE 802.16m because of their potential for high user throughput and spectrum efficiency. The research in MU-MIMO includes uplink and downlink. The paper first analyses the single base station MU-MIMO in downlink. Multiuser interference is an important factor influencing the system performance, and precoding is an efficient technique to eliminate the multiuser interference. There are two kinds of precoding techniques in IEEE 802.16m:codebook based precoding and sounding based precoding. In MU-MIMO with codebook based precoding, the paper proposes an improved scheme to suppress the multiuser interference by adjusting the precoding matrices. In MU-MIMO with sounding based precoding, the paper uses block diagonalization algorithm to eliminate the multiuser interference. But it has some disadvantages. The first one is that the algorithm is no longer available when the antenna number of receiver is larger than that of transmitter. So the paper gives an enhanced block diagonalization algorithm to weaken this limitation. The second disadvantage is that the algorithm does not consider the inter cell interference. So the paper presents a new algorithm which coordinates the transmitter and the receiver to suppress the interferences from other base stations. What is more, the paper gives a scheme to use the block diagonalization algorithm and other improved algorithms in FDD mode.Then, the paper discusses the system model of multi-base-station coordinated MU-MIMO in downlink. The preprocessing algorithm at transmitter and the detection algorithm at receiver are presented. The paper also gives two kinds of coordination methods:fixed coordination and dynamic coordination. The simulation results prove that coordinated MU-MIMO can greatly improve the system performance.Finally, MU-MIMO in uplink is discussed. The paper proposes the coordinated detection algorithm and a novel scheduling algorithm which combines the proportional fair algorithm and the orthogonal criteria to improve the system performance.