Research Of Sensing And Access Strategy In Cognitive Radio Network With Hybrid Overlay-underlay

With the fast development of wireless communications,the greatly increasing of wireless communication devices increases the users'requirement to QoS of network,leading to more serious problem of spectrum scarcity.Cognitive radio technology solve the spectrum scarcity problem by allowing secondary user to sense and utilize the idle spectrum,and propose a new method for raising the spectrum efficiency.Cognitive radio can be divided into two model:overlay and underlay.With the development of 5G,the combination of cognitive radio and energy harvesting technology not only solve the problem of spectrum scarcity,but also reduce the energy consumption.This paper focus on spectrum sensing and allocation in hybrid cognitive radio networks,and the utilization and effect of energy harvesting in hybrid cognitive radio.The main work is as follows:1.A dynamic spectrum sensing and access model in cognitive radio networks is proposed.This model allows secondary user(SU)to sequentially sense two times if necessary due to the false alarm,and choose different accessing manner according to the sensing result.In practice,sensing results often affect the data transmission in cognitive radio systems.Therefore,a spectrum sensing and access strategy based on hybrid cognitive radio is presented by jointly considering spectrum sensing and data transmission.Compared to the existing works,analytical results indicate that our approach can achieve significant improvements in terms of SU's throughput.2.Access strategy for hybrid cognitive radios with energy harvesting is proposed.In the considered system,secondary user can harvest energy from the primary user's signal and the other ambient sources.The secondary user either operates in one of the two transmission modes:overlay and underlay in order to maximize the throughput,remains in the sleep mode in order to save energy,or harvests energy from the primary channel in order to maximize the remaining energy.We propose an access strategy in which the POMDP framework is used to determine action of the secondary user,and energy threshold is used to determine the transmission mode of secondary user.Simulations show that for certain values of the system parameters,the considered system performs better than overlay-only cognitive radio and a hybrid cognitive radio system harvesting energy only from the ambient sources.