Research On Cooperative Communications Mechanism For High Energy-Efficient Spectrum Sharing

With the explosive development of wireless services, spectrum is becom-ing congested and scarce, and energy consumption is growing exponentially. Cooperative spectrum sharing can effectively improve the spectrum and ener-gy efficiencies of the communications by the wireless resource sharing, man-agement and adaptively access the band without changing the fixed spectrum structure. The sharing means includes undelay and overlay model. For the underlay model, the secondary system (SS) can transmit its own data under pri-mary system’s (PS’s) interference constraint. The interference constraint is an upper limit that SS’s transmission can not degrade PS’s performance. However, SS can not transmit its data with higher power because imposed low transmit power with interference constraint even if the licensed system is completely i-dle. For the overlay model, SS relays PS’s traffic, in exchange for dedicated transmission time for SS’s own communication need. Although it minimizes interference to PS, it also incurs numerous overheads such as feedbacks and signallings. In this paper, we focus on the overlay cooperative spectrum shar-ing means, and the main contributions of this dissertation are as follows:1. We analyze the resource allocation in cooperative spectrum sharing based on a single transmission time interval (TTI) scheduling. For single T-TI scheduling,the unlicensed SS relays the licensed PS’s traffics and asks for immediately accessing the licensed band as a return over a single TTI where the channels’state of links are unchangable. We obtain the join-t optimal power and time allocation strategies in closed form by mini-mizing the system energy consumption while guaranteeing both PS’s and SS’s quality of service (QoS). Furthermore, we analyze and compare the energy-efficient performance for different relay means.2. In this paper, we propose the cooperative spectrum sharing based on mul-tiple TTIs scheduling. For multiple TTIs scheduling, the SS adaptively choose to relay or access according to the channels’state in different T-TIs where the channels’state are changable. So, it can effectively utilize the time diversity of the channel fading to greatly improve the system’s performance. In this situation, we analyze the problem that is maximizing the expected total throughput of the sharing with the power constraints of PS and SS, and PS’s QoS. It is formulated as a constrained markov deci-sion process, and the optimal access strategy is achieved by Lagrangian approach and Q-learning algorithm. However, its complexity is exponen-tially increasing with the number of the links increasing.3. We establish a multiple TTIs scheduling cooperative spectrum sharing mechanism based on labor-consumption model with simpler computation complexity compared with that of the markov decision algorithm. In the labor-consumption model, with the PS’s QoS guaranteed, the SU ("work-er") of SS relays ("work") the PS’s traffic to achieve the power and time resources in order to access the licensed band to transmit ("consume"). The worker adpatively choose to work or consume according the owned resources and the "market situations" that can utilize the time diversity of the channels’fading. Furthermore, we discuss the effect of SU’s trans-mission waiting delay on the system’s performance and the number of secondary users holded in multiple TTIs scheduling.