Research On Some Enhanced Technology In Downlink Mimo Transmission

The recent decades has witnessed the rapid development in mobile communication system. Due to the large-scale increase in the number of mobile users and the explosive growth in the amount of traffic, especially the significant increase in data traffic during recent years, there is a requirement to improve the data rate and spectrum efficiency, especially for downlink. In order to meet these requirement, some enhanced MIMO technology are involved in the next generation mobile communication system, including precoding for high order MIMO and enhanced relaying schemes.With the application of high order MIMO, e.g.8Tx antennas equipped at eNB in LTE-Advanced, traditional uniform linear array (ULA), which faces a conflict between spatial multiplexing gain and antenna array size, will be no longer suitable for deployment. In contrast, dual polarized array (DPA) with two orthogonal polarized directions can solve this problem in a good manner, and thus is considered a candidate configuration of antenna array in the next generation mobile communication system by3GPP. On the other hand, in practical system, it is very difficult or even impossible to obtain channel state information at transmitter (CSIT). So limited feedback based, especially codebook based precoding scheme for high order MIMO with DPA deployed is one of the most attractive topics.For UEs at the edge of an eNB cell, the desired signal from eNB is always of low power, while the co-channel interference suffered is of high power in contrast, which certainly lead to a low SINR and makes the quality of communication unsatisfied; however, the growth of data traffic asks for an even higher SINR requirement in the next generation mobile communication system. One of the efficient solutions is to deploy relay nodes in the coverage of eNB cell. The relay node with multiple antennas may apply precoding schemes as what an eNB does; moreover, if the transceiver design can be jointly optimized among all nodes in relay system, the quality of communication for remote UEs may be improved further, and the spectrum efficiency of the whole cell may also be rose. Thus, joint transceiver design in MIMO relay system is also one of the most attractive topics.This dissertation studies some enhanced technology in downlink MIMO transmission, and three research points are included as follows.1. Codebook design for dual polarized high order MIMO channel. In this chapter, this dissertation investigates the mathematical expression of dual polarized MIMO channel in SCM/SCME model, analyzes the right singular vectors/matrices with the knowledge of matrix theory, and finds out their structural feature, which provides theoretical support for codebook design. Previous work on dual poloarized MIMO channel focuses on LOS scenario, while this dissertation takes NLOS scenario into account, and will be an enhancement and supplement to previous work. Then, according to the structures of codewords, two criterions used in ULA deployment is modified, aiming to make them suitable to DPA deployment. Finally, a new DFT based codebook with nested property is designed, whose theoretical and BLER performance is analyzed and evaluated.2. Joint transceiver design in SU non-regenerative relay system. In this chapter, the MSE matrix of the whole relay system is analyzed, under the assumption that optimal receiver is applied at destination node. The MSE matrix is divided into two MSE matrices, each of which is independent of the other and is only associated with local CSI. It is noted that such division has not been referred in non-linear relay system in the previous works. Thus, the joint optimization problem is rewritten as two sub-optimization problems, one of which solves the source node design, the other solves the relay node design. Then, under the assumption of high SNR, a sub-optimal receiver at destination node is derived, with only local CSI available. That is to say, the source and destination nodes do not require global CSI, and all nodes can be designed non-iteratively. Finally, the proposed scheme is analyzed in theory and evaluated by simulation.3. Joint transceiver design in MU non-regenerative relay system. In this chapter, the MSE matrix of the whole relay system is analyzed, under the assumption that optimal transceiver is applied at relay node. The MSE matrix is also divided into two parts, one is related to source node, the other is related to multi-user nodes. Similar to the SU scenario, the source THP precoder is optimized independently; however, an iterative scheme to jointly design the relay node and multi-user nodes is proposed, by which the convergence can be achieved. The main feature of the proposed scheme is that the source node can be designed with local CSI non-iteratively, and the relay and MU nodes can be optimized iteratively without participation of the source nodes. Finally, thejproposed scheme is evaluated by simulation.