A Simulation Study Of Multi-user Access And Communication Scheduling Based On CRAHNs

In recent years, multimedia digital trunking system has been widely used in all walks of life. Inorder to make the construction of network more flexible and convenient, Ad Hoc networkcommunication system has become a new research direction. This paper mainly focuses on theresearch of multi-user access and communication scheduling scheme of CRAHNs (cognitive radioAd Hoc network).First of all, this paper analyzes the advantages and disadvantages of TETRA digital trunkingsystem and Ad Hoc network, find out that digital trunking system is not flexible enough and itcannot support the current transmission of multi-service very well. Usually nodes in TRTRA canonly adopt one-to-one communication mechanism, so the study of the MAC protocol in CRAHNs ismeaningful. For the business needs of emergency communication and wireless application, thispaper proposes a multi-level clustering Ad Hoc network structure to enhance the extensibility of AdHoc network. By the mobile development of fixed nodes in the network and use these nodes asbackbone nodes in preference. These fixed nodes can also act as the gateway connecting Ad Hocnetwork and the Ethernet. For the characteristics of clustering and multi-hop of Ad Hoc network,this paper presents a hybrid access mechanism combining of slot allocation access and competitiveaccess mechanism and designs a reasonable multiframe structure.The MAC protocol designed in this paper consists of a control channel and several datachannels with different frequencies, different clusters communication on different data channels.Ordinary nodes use a pair of transceiver to send and receive data another receiver listen on thecontrol channel, the receivers must scan for idle channels when they are free. The receivers oftherelay between clusters must listen on the data channels of two clusters and forward data for othernodes. This paper proposes the scheme of the construction and the maintenance of the network, theprocedure of a node accessing the network and the slots allocation scheme. The scheme of theconstruction of the network and the throughput of the network are simulated after specific design ofthe MAC protocol.After a lot of study of the cooperative retransmission schemes in Ad Hoc natworks, find out thatthe existing schemes cannot take a balance of the hidden nodes problem and the overhead of thesystem. To solve the problem two new cooperative retransmission schemes are presented in thispaper and the simulation results show that the proposed schemes can solve the hidden nodesproblem with less overhead time.