Synchronization For Distributed Beamforming In Cognitive Radio Networks

With the development of information technology,the growing human demands for wireless communication services lead to the increasing scarcity of spectrum resources for wireless communications.Cognitive radio technique can effectively solve the problem of the shortage of spectrum resources through spectrum sharing and improve the spectrum utilization.Besides,as a key technique which has been widely used,distributed beamforming can effectively improve the performance of the communication system.It can increase the capacity of the system and improve the capability of resisting the interference.By using distributed beamforming technology in cognitive radio networks,we can make better use of the spectrum resources and improve the performance of the secondary network while suppressing the interference to the primary users.This actually optimizes the performance of the entire network.Distributed beamforming is a cooperative technique that allows some separate nodes transmit common information by forming a beam in the direction of the intended destination.Since the separate node is usually equipped with an independent local oscillator,nodes must synchronize their carrier such that the receiver can combine the signals effectively.In cognitive radio networks,distributed beamforming carrier synchronization protocol must also consider the interference to the primary users.That is,the aim of the protocol is to maximize the beamforming gain of the secondary network while limiting the interference to the primary user to some expected threshold.In this paper,a time-slotted round-trip carrier synchronization protocol for distributed beamforming is proposed.It is an open-loop synchronization technique that the transmitters need only a small amount of feedback information from the receiver.By exploiting the broadcast nature of the wireless links in wireless communications,the required time slots for carrier synchronization process are reduced significantly.The performance of the carrier synchronization is also improved in our proposed protocol.In cognitive radio networks,we present a time-slotted round-trip carrier synchronization protocol for distributed beamforming in the secondary network considering the interference to the primary user.The distributed transmitters perform the carrier synchronization protocol under the condition of suppressing the interference to the primary user.The required time slots for synchronization process increase due to the consideration of the primary user.The analysis shows that this protocol can achieve good synchronization performance.