Research On The User Selection Of Multi-antenna Multiuser Systems

MIMO is a key technology of wireless communication, which can greatly improve the spectrum efficiency and quality of wireless communication system. Multiuser MIMO is a hot research topic in recent years. User selection is very important for MIMO system utilizing multiuser diversity to improve system performance. This thesis analyzes the user selection problem in different MIMO multiuser systems, and proposes user selection algorithms for them.The requirement and development of wireless communication as well as the research status are summarized in the beginning. Then the different channel models for multiplex antenna systems are given. And the system capacities for single user and multiuser multi-antenna systems are analyzed.A new improved quasi-orthogonal inserted Walsh codes method is proposed, which makes the code number for spreading spectrum system greatly increased. Then a new uplink access system using the proposed improved quasi-orthogonal inserted Walsh codes is proposed. The new system can greatly increase the number of users accessing at same time. The analysis of validity and capacity of the new scheme is given. Then two user selection and code alignment algorithms for improving the capacity of the new system are proposed. Those two algorithms are both based on the correlations of multi-antenna channels and codes among different users.For the multiuser MIMO block diagnolization system, the analysis of the system capacity is given. A new improved norm-based user selection algorithm is proposed base on heuristic orthogonalization and channel correlation estimation among users. Then the analysis of capacity and computational complexity of the proposal is given. The simulation result shows the proposal can greatly reduce the computational complexity, at the cost of little capacity loss. The proposal gives an effective tradeoff between the capacity and the computational complexity.For the differential unitary modulation technology, the analysis of performance and unitary matrix generation method is summed up. A new system that combines differential unitary space time modulation and block diagnolization is proposed. The new system can overcome the problem that each user's receiver must know the receive matrix related with the others' channel state information in the traditional block diagnolization system. Then a new capacity estimation method for the new system is proposed, and a new user selection and adaptive modulation algorithm based on capacity estimation is proposed.At last, this thesis sums up the problem of using cognitive radio (CR) in the wireless cellular system. A new cognitive wireless cellular system based on signaling by existing own spectrum is proposed. The main characterics of the cognitive radio cellular system are summarized, and the multi-path channel model is extended which is suitable for the cognitive radio cellular system. Clustered OFDM is adopted to reduce the feedback rate. A user selection strategy based on capacity threshold for feedback is proposed, and the performance of the proposal is given by simulations.The proposed multiuser selection algorithms of this thesis utilize the main characteristics of different multiuser multi-antenna systems, they can get salient multiuser diversity, improve the system performance, and reduce the computational complexity. All the researches in the thesis will cast some bright light on the design of the practical multi-antenna multiuser diversity system.