Interference Cancellation And User Scheduling In Cognitive Radio MIMO Networks

With the advent of new high data rate wireless applications, as well as growth of existing wireless services, demand for additional bandwidth is rapidly increasing. According to the recent report of FCC(Federal Communication Commission), the spectrum is not utilized efficiently across time and frequency. To realize opportunistic spectrum access and intelligent resource allocation, Cognitive Radio (CR) technology is a promising and innovate radio technology which is capable of sensing spectrum and of adjusting the system parameters according to the radio environment. Multiple-Input/Multiple-Output (MIMO) system is another technique to increase spectrum utilization efficiency. It can enhance the system performance significantly with the increase of the spatial dimension and diversity by using multiple antennas. MIMO and CR are considered as two key technologies for the next generation wireless communication. By using these techniques, wireless systems will have higher data throughput and service quality, better spectrum and power efficiencies as well as wider range of business. Under the framework of MIMO and CR technologies, this thesis mainly investigates efficient joint beamforming and user scheduling algorithms to maximize the sum-rate throughput of the cognitive system and also gives the development of an extendable CR framework which combines the multi-antenna technology with spectrum sharing technology for different scenarios. The specific innovations of the thesis are as follows:(1) According to the problem occurring in the cognitive MIMO downlink network that certain users may suffer unfairness based on certain user scheduling strategies, an improved Proportional Fair Scheduling (PFS) is proposed in this thesis. To reduce the feedback of the MIMO uplink, receiver antenna selection at each cognitive user is considered; Zero-forcing Beamforming (ZFBF) is utilized to cancel inter-user interference in the studied system. Furthermore, due to some cognitive radio users coexisting with a primary user, the system schedules the cognitive users based on the correlation between the users' channel matrices, which makes all selected cognitive users :1) near-orthogonal to the primary user; 2) near-orthogonal to each other. This criterion aims to achieving higher sum-rate of the CR network while reducing the multiuser interference. The simulation results show that the proposed scheme can realize the near fair resource allocation among all cognitive users at the expense of certain sum-rate loss.(2) A three-stage multi-hop cellular downlink transmission scheme is proposed, which is designed for spectrum sharing and involves beamforming, MIMO relaying strategy, multi-user scheduling and system design of the frame structure. The research results show: a)by using MIMO relaying, the main cellular system can obtain high data speed performance; b)the proposed three-stage scheme of joint scheduling and transmission of the main network can take into account the high and low data rate zone user communications; c)when the MIMO relaying also be used as a secondary user network base station, it can effectively support the nearby secondary users'communications.