Research On Blind Channel Hopping Rendezvous In Multi-Radio Cognitive Wireless Networks

In the situation where spectrum resources are becoming increasingly scarce,cognitive networks aim at improving the utilization of spectrum resources,and utilize the idle resources as non-authorized users.The cognitive user(CU)in the cognitive network firstly sense the spectrum resource,and when it detects the spectrum holes unoccupied by the primary user(PU)in the current environment,it can access the spectrum resource.The media access control(MAC)function of a cognitive wireless network mainly includes spectrum detection,channel access,and spectrum switching,and its implementation depends on the efficient and reliable various control information exchange between cognitive users.For this reason,neighbor cognitive users can dynamically find communication frequency bands unoccupied by authorized users to exchange control information by hopping on multiple channels and hopping to the same channel in the same time slot.In particular,when each cognitive user independently generates its channel hopping sequences,the control information exchange mechanism is based on a blind channel hopping rendezvous.The advantage is that it does not depend on any fixed control channel and does not require cognitive users to interact with each other's control information such as clocks,channel hopping sequences,and node numbers in advance.It can effectively counteract the dynamic occupancy of authorized wireless users and avoid control channel saturation problem caused by single frequency band based control information exchange.In order to effectively improve the performance of the control information exchange,this thesis conducts an in-depth study on the channel hopping rendezvous mechanism of cognitive radio networks(CRNs)with multiple radios.First of all,this thesis proves through stringent mathematical derivation that any two cognitive users with synchronous and asynchronous clock can achieve the theoretical lower bound of the number of antennas needed for blind channel hopping rendezvous in each time slot,which is used to guide the design of multi-radio blind channel hopping rendezvous mechanism.Secondly,based on the theory of relaxed cyclic difference set(DS)mathematics theory,this dissertation proposes two channel hopping rendezvous mechanisms called DS-SCH and DS-ACH for multi-radio cognitive networks with synchronous and asynchronous time clocks to support any two cognitive users rendezvous in each time slot.Based on these two types of blind channel hopping rendezvous mechanisms,a multi-radio cognitive wireless network can complete control information exchange on any number of communication channels with minimal delay regardless of their clock offset,and effectively reduce the number of transmission collisions caused by control information exchange on the same channel at the same time,which is particularly suitable for delaysensitive application scenarios such as real-time voice communication and emergency communication.Again,we show that if the DS-SCH or DS-ACH is constructed based on a special kind of difference set(ie,minimum difference set),then they can effectively approximate the theoretically lower bound of antennas required for blind rendezvous in each time slot and an arbitary number of channels of synchronous or asynchronous channel hopping mechanisms,which can minimize the hardware complexity required for the cognitive wireless network to achieve the shortest control information exchange delay.Network simulation based OPNET modelor shows that under the dynamic occupation of the primary user(PU)on the channel,our proposed two blind channel hopping rendezvous mechanisms outperform the existing ones in the various network performance metrixs like average throughput,average delay,data packet drop ratio and control information retransmission times.