In underlay cognitive radio networks, secondary users can share the spectrum withprimary users as long as the interference caused by the secondary users to primaryusers is below a certain predetermined threshold. It is reasonable to assume thatthere is always a large pool of secondary users trying to access the channel, whichcan be occupied by only one secondary user at a given time. As a result, a multi-userscheduling problem arises among the secondary users. In this thesis, by manipulatingbasic schemes based on selective multi-user diversity, normalized thresholding, transmission power control, and opportunistic round robin, we propose and analyze eightscheduling schemes of secondary users in an underlay cognitive radio set-up. The system performance of these schemes is quantified by using various performance metricssuch as the average system capacity, normalized average feedback load, schedulingoutage probability, and system fairness of access.In our proposed schemes, the best user out of all the secondary users in the systemis picked to transmit at each given time slot in order to maximize the average systemcapacity. Two thresholds are used in the two rounds of the selection process todetermine the best user. The first threshold is raised by the power constraint fromthe primary user. The second threshold, which can be adjusted by us, is introducedto reduce the feedback load. The overall system performance is therefore dependenton the choice of these two thresholds and the number of users in the system giventhe channel conditions for all the users. In this thesis, by deriving analytical formulas and presenting numerical examples, we try to provide insights of the relationshipbetween the performance metrics and the involved parameters including two selectionthresholds and the number of active users in the system, in an effort to maximizethe average system capacity as well as satisfy the requirements of scheduling outageprobability and feedback load.
展开▼
