Research On Precoding Technique In MIMO Wireless Communication Systems

The pursuit for high data-rate, stable link-quality and high system-capacity is the impetus to the continuous development of wireless communication technology. With this end in view, a series of key techniques are introduced. MIMO and OFDM technology is one of the most typical representatives. MIMO technology, especially the introduction of the dimension of space, enhance the capacity for communications systems in a new way, MIMO channel capacity will increase linearly with the number of antennas increases in the ideal case. However, in MIMO communication systems, the MIMO channel correlation, the user interference, inter-symbol interference, inter-cell interference and other factors, makes the MIMO system capacity limit only to become a theoretical possibility. Therefore, research on advanced transmission technology is a trend for MIMO system.When channel state information is known in the transmitter, precoding technology is a very effective means to solve these problems. With this fact in mind, the precoding technique in MIMO system is explored in depth in this dissertation, which includes:(a) precoding technique for single-cell single/multiple user(s) MIMO system; (b) precoding techniques for multi-cell MIMO system; (c) precoding techniques for MIMO relaying systems and precoding-based codebook design and so on. The main research results of this paper are summarized as follows:1. In sigle-cell MIMO scenarios, for reducing complexity in multi-user MIMO system, a cascade precoding scheme is proposed. For overcoming noise enhancement in ill-conditional channel, a precoding scheme based lattice reduced cascade channel inverse method is also proposed. Based on these schemes, the precoding strategy for multiuser MIMO system is presented under an unified framework. Simulation results show that the proposed schemes can achieve lower complexity and bit error rate under the same scenarios. Meanwhile, a precoding-based semi-blind channel estimation method for MIMO systems is also proposed, compared with traditional algorithm, the proposed method on the accuracy and complexity are significantly improved.2. In multi-cell MIMO scenarios, a new layer-based precoding scheme is presented for multi-cell MIMO system. Based on different criteria, a layered precoding method is adopted in the intra and inter-cell separately.The proposed scheme can obtain a interference spread suppression effect in different regions, and make compensation between different precoding algorithms. To achieve the maximization of the user's signal interference noise ratio as well as the minimization of interference leakage for MIMO network system, an equilibrium precoding algorithm based on banlance strategy is proposed. Mathematics model for precoding algorithm is constructed by introducing interference pricing function and the solution to the precoding vector by Lagrange equation. Dynamic optimization for precoding vector is obtained in the scheme. Finally in simulation the proposed algorithm is compared with conventional algorithms and convergence of utility function is also discussed. The simulation results show that the proposed algorithm performs better than those of existing schemes.3. On the research of coordinated multi-point MIMO systems, a new precoding scheme is proposed for maximizing the weighted sum rates.Construction of the objective function is based on convex optimization theory and the solution to the precoding vector is depended on iterative algorithm.Compared with existing algorithms, the application of the algorithm is not limited to the number of transmit and receive antennas, the threshold of iteration and number of cell coordinated clusters can be adjusted to achieve a reasonable tradoff between complexity and system capacity4. Finally, the codebook design is investigated for precoding techniques. For the tradeoff between overhead feedback and complexity, a diversity-based codebook design scheme is proposed, the roated codebook matrix is introduced with the aid of diversity, adjusting codebook space adaptively, and can effectively improve the performance advantages In the end, simulations are run to demonstrate the versatility and superiority of the proposed scheme.This dissertation investigates the precoding techniques in wireless MIMO systems in depth. More specifically, multiple precoding schemes are proposed concerning to single-cell multiuser MIMO system, multi-cell multiuser MIMO system, and coordinated multi-point MIMO system, respectively. In addition, an improved codebook design scheme for precoding technique is also proposed. This design scheme makes a tradeoff between complexity and performance, finding therefore applicability in practical system.