Research On Resource Allocation Strategy In Non-slotted Energy Harvesting Cognitive Radio Networks

With the development of wireless communication technology and the expansion of user groups,the number of wireless devices and the demand for spectrum are increasing day by day.The unreasonable use of spectrum caused by fixed allocation scheme aggravates the contradiction between spectrum demand growth and spectrum shortage.As a dynamic spectrum access technology,cognitive radio can meet transmission needs of unlicensed users and improve the utilization of licensed spectrum bands by spectrum sharing.At the same time,the increases of wireless devices and the enhancement of mobility expose drawbacks of traditional power supply methods,so the application of energy harvesting technology in wireless communications has been paid attention to.Energy harvesting cognitive radio networks,which combine the two aforementioned technologies,can simultaneously solve the problem of spectrum allocation along with energy supply for wireless devices,and is one of the research hotspots in the field of wireless communication.In energy harvesting cognitive radio networks,the rational allocation of time,energy and spectrum resources can maximize the transmission performance of secondary users under the premise of guaranteeing the communication quality of primary users.Under the assumption of timeslot synchronization,some research progress had been made in resource allocation.While,timeslot synchronization is difficult to achieve in many practical scenarios,especially when primary users transmit data in a non-slotted way.However,up to now,little research had been done on non-slotted energy harvesting cognitive radio networks.In view of the above situation,this paper studied the resouree allocation strategies of non-slotted energy harvesting cognitive radio networks,and had achieved the following research results:(1)For the case where a secondary transmitter receives RF signals from unlicensed bands for energy harvesting,an opportunistic spectrum access scheme with variable transmission duration was proposed for the secondary users.In this paper,aiming at maximizing the throughput of secondary users,the energy harvesting time and transmit power was optimized under the constraints of energy causality and primary users'outage probability.The optimal allocation strategy and two suboptimal strategies with lower time complexity were obtained by exhaustive search algorithm,differential evolution algorithm and objective function relaxation method respectively.Simulation results showed that under the proper parameter settings,the two suboptimal strategies were very close to the optimal strategy.In addition,the superiority of the scheme in the non-slotted scene was proved by comparing the throughput with the fixed timeslot division strategy.(2)For the case where a secondary transmitter receives the primary signals for energy harvesting,a segmented spectrum access scheme based on the ACK acknowledgement mechanism was proposed for the secondary users.In this scheme,the secondary user judged whether to perform spectrum sensing according to the remaining energy level;determined whether to transmit according to the sensing result;in the transmit process,using the ACK mechanism to monitor the transmit status of primary users,and thereby determined whether to continue the transmission.Under the constraints of peak transmission power and collision probability,the optimal timeslot division and transmit power allocation strategy for maximizing secondary users'throughput was obtained.Finally,simulation results were used to analyze the influence of different parameter settings on the optimal strategy's throughput.And through the comparison with the un-segmented spectrum access scheme,it was proved that the segmented spectrum access scheme had higher throughput performance.This thesis consists of 5 chapters,including 22 figures,3 tables and 68 references.