The Research And Implementation Of Key Technologies Of Multi-user Access Based On CRAHN

In recent years,multimedia digital trunking system has been widely used in all walks of life.For emergency communications, to combine cognitive radio technology, Ad Hoc network technology and wireless broadband communication technology, Cognitive Radio Ad Hoc Networks(CRAHN)was proposed.This network can be temporarily formed without base stations or other communication facilities.This network have advantages,such as raising the utilization ratio of the frequency and high flexibility of the network.This paper mainly focuses on the research of multi-user access and communication scheduling scheme of a multi-level clustering CRAHN.First,This paper presents a hybrid access mechanism based on the multi-level clustering CRAHN. In this network,we use a common control channel and several data channels,different cluster use different data channel.We describe the frame structure which can be divided into CP time and CFP time and the frame’s working process is described in the paper.At last,we describe the environment of the MAC access mechanism.Secondly,for the hybrid MAC access mechanism,we proposed Frame Bursting EDCA(F-EDCA)in CP time and time slot management strategy used in CFP time.To solved the QoS of audio business becoming deteriorate when the network’s bored is huge.,we proposed F-EDCA to transmit audio business in CP time.F-EDCA occupy channel by sending N short frame,so it can continuously sends N short audio frame.It reduces the aduio business’ delay,delay variation and ensure the QoS of audio business.We proposed time slot management strategy used in CFP time.It use Slot_Table and Available_Slot_Table to management time slot.We just study time slot management when it is a jump.Thirdly,we use MATLAB to simulate the hybrid MAC access mechanism based on CRAHN.The simulation include initializing of CRAHN,network throughput,Frame Bursting EDCA.The simulation results show that the hybrid MAC access mechanism is feasible and can improve the performance of the system.Finally,we design node’s communication scheduling scheme after startup including initializing of CRAHN,network maintenance,how to choose and update master node or cluster node and so on.The MAC protocol uses a transmitter and two receivers,the transmitter responsible for sending data and command,a receiver responsible for receiving data,the other one can receiving data and cognitive available spectrum when it is free.On this basis,we design state machines by communication software design method :MSC.To perfect the node working process,at last,we proposed the node communication between clusters and within a cluster.