Research On Performance Of Key Technologies For Cognition And Cooperation In Spectrum Sharing Networks

The continued growth of requirements on wireless communication services leads to the increase of required wireless spectrum resources for wireless communication systems, and the limited wireless spectrum resources become quite scarce. However, on the one hand, results of the research show that the wireless spectrum resource is very scarce; on the other hand, they also show that the waste of wireless spectrum resource is serious. The reason is that the static spectrum allocation does not match the dynamic spectrum utilization, which causes the available spectrum for allocation to be scarce, but the utilization efficiency of spectrum is very low. Hence, the spectrum efficiency needs to be improved from the perspective of system level through breaking through key technologies of spectrum sharing systems and developing spectrum sharing based wireless communication systems, which is an important way to resolve the above mentioned conflict. In the future, the spectrum sharing wireless network is also one of strategic development directions for wireless communication. This dissertation focuses on the cognitive cooperative relay communication technology and the cognitive interference coordination technology which are key techniques of cognition and cooperation in spectrum sharing networks, and it aims to perfect the related theoretical research. Firstly, the outage performance study on cognitive cooperative relay systems in Rayleigh fading channels is presented. Then, based on this, the dissertation further presents the outage performance study on cognitive cooperative relay systems in Nakagami-m fading channels. Finally, considering the cognitive interference coordination based two-tier co-channel cellular network which is a typical spectrum sharing network, the coverage and energy efficiency study on the downlink transmission in this kind of two-tier cellular networks is presented. The major work and contributions of this dissertation consist in:1. Outage and diversity performance study on cognitive cooperative relay systems in Rayleigh fading channelsThe dissertation firstly investigates the outage and diversity performance of cognitive cooperative relay systems in Rayleigh fading channels. We theoretically derive the exact closed-form expressions of outage probability and diversity order for cognitive cooperative relay systems with different relay selection protocols in Rayleigh fading channels. Based on these, we further study the impact of the peak interference power constraint, the peak transmit power constraint, the number of relay and the relay selection scheme on the outage and diversity performance. During the research, we firstly discover that the received SNRs are correlated in the first phase, which is an important character of cognitive cooperative relay systems with peak interference power constraints. According to the character, we propose a unified analytical framework and corresponding calculation scheme for the outage and diversity performance analysis of cognitive cooperative relay systems. The results show that both the peak interference power constraint and the peak transmit power constraint cause the outage saturation phenomenon, and more relays or selecting better relay can provide better outage performance. The results also reveal that both the peak interference power constraint and the peak transmit power constraint do not affect the diversity performance, but more relays or selecting better relay can obtain better diversity performance.2. Outage and diversity performance study on cognitive cooperative relay systems in Nakagami-m fading channelsBased on the research content of first part, we extend the research on outage and diversity performance of cognitive cooperative relay systems from special fading channels (Rayleigh fading channels) to general fading channels (Nakagami-m fading channels). Utilizing the above proposed analytical framework, the exact closed-form expressions of outage probability and diversity order are derived. Then, we further explore the impact of the channel fading severity on outage and diversity performance. The results show that the outage performance improves with the increase of channel fading severity while the peak interference power constraint or the peak transmit power constraint is small, but the outage performance decreases with the increase of channel fading severity while the peak interference power constraint and the peak transmit power constraint are large. The results also show that the diversity performance improve with the decrease of channel fading severity.3. Coverage and energy efficiency performance study on the downlink transmission in two-tier cellular networks based on cognitive interference coordinationFocusing on the cognitive interference coordination based two-tier co-channel cellular network which is a typical spectrum sharing network, the coverage and energy efficiency performance study on the downlink transmission in this kind of two-tier cellular networks is presented. Firstly, we theoretically derive the exact closed-form expressions of coverage performance based on stochastic theory for two-tier cellular networks with different cognitive interference coordination policies (which include opportunistic access based cognitive interference coordination and distance separation based cognitive interference coordination). Then, we further investigate the optimal energy efficiency performance under a desired coverage requirement for this kind of two-tier cellular networks, and evaluate the impact of the desired coverage performance, the density of femtocells, and the other related system parameters on the optimal energy efficiency performance. The results show that the coverage performance is better in two-tier cellular networks with opportunistic access based cognitive interference coordination than that with distance separation based cognitive interference coordination, but the advantage becomes smaller with the increase of the separated distance. The results also show that the optimal energy efficiency improves with the decrease of desired coverage requirement while the desired coverage requirement is under a threshold value, but it keeps unchanged while the desired coverage requirement is over the threshold value.The research outputs related to this dissertation have been accepted as papers in IEEE journals and conferences.