Research On Optimizing To Throughput And Energy Consumption Of Cognitive Multiple Access Systems

The situations about shortage of wireless spectrum resources become worse and worse with the continuous development of wireless communication technique and the diversity of business requirement. As a kind of dynamic spectrum access technology, cognitive radio can effectively relieve the contradiction between the shortage of spectrum resources and the low utilization of spectrum resources, and it has become the current research hot spot. In recent years, the performance of cognitive radio system is discussed by many scholars using different spectrum access technology from different point of view. However, the throughput(effective capacity and effective throughput) and energy consumption in cognitive multiple access system are not enough comprehensively studied and analyzed.The effective capacity is considered by using spectrum sharing in cognitive multiple access system. Secondary users have to be subject to an interference power constraint for avoiding harmful interference inflicted on the primary user. Moreover, the primary user and secondary users operate under statistical quality of service constraints. In this setting, the closed-form effective capacity expressions for both the primary user and secondary users are derived and the impacts of difference parameters on the performance of the primary user and secondary users are investigated. The simulations show the tradeoff between the effective capacity of single secondary user and the number of secondary users for transmitting simultaneously as well as the total effective capacity of secondary users.The effective throughput is studied in cognitive multiple access system by using opportunistic spectrum access. The access strategy is difficultly designed for increasing throughput due to the impacts of collision constraints and imperfect channel sensing, which is rarely investigated. Effective throughput is defined and used as the performance metric for secondary users under collision constraints and imperfect channel state information. In the meantime, the limited number of channel samples are used to estimate the parameter of unknown channel quality distribution. On the basis of above work, the access strategy is designed. Further, the optimization problem is solved and the performance of secondary users under imperfect sensing is analyzed. Moreover, the relationships between the channel quality and the collision probability as well as the performance of secondary users are discussed and the performance of secondary users under perfect sensing and imperfect sensing is compared by simulations. Meanwhile,the proposed access strategy is compared with another one and its validity is verified.In the cognitive multiple access system with mixed access, the sensing time, channels and power are needed to be properly allocated for reducing energy consumption. Therefore, a multi-users multi-channels sensing-based spectrum sharing scheme is considered. The ratio between average energy consumption and the average transmitting data is acted as the performance metric and the interference power is acted as the constraint condition for ensuring the quality of service of primary user. Then the initial optimization problem of energy consumption is constructed. Further, it is transformed into the parametric linear problem after the concave relaxation was used to process it, and an algorithm of minimizing energy consumption is proposed. The impacts of the number of secondary users and channels and the interference power on the energy consumption and optimal sensing time are discussed by simulations. Meanwhile the analysis is verified.