Research And Simulation Of TDMA Slots Assignment Mechanism In Ad Hoc Networks

Ad hoc network is a kind of wireless multi-hop temporary autonomous system, which consists of mobile nodes equipped with wireless transceivers.Because it doesn't have infrastructure and can network fast,it is widely used in military and civilian fields.MAC protocol is in the middle of the network layer and physical layer, it decides the communication node how to share the wireless channel,and plays an important role in the performance of the network.MAC protocol based on TDMA has the advantages of packets transmission with no packet conflict and bounded max packet delay.,the approach has been widely applied in many large capacity point-to-multipoint voice communication systems.In the research of slot assignment based on TDMA,there are two problems which are slot assignment and slot synchronization to be solved.In the communication base on TDMA,every node use the channel resource exclusively in its own slot,and slot synchronization is a prerequisite for realization of conflict-free transmission.However,ad hoc network does not have the center node to send the information of synchronization,nodes in the network can only perceive the information one-hop neighbor node away,so how to realize slot synchronization in ad hoc network is one of the difficulties currently.A study is made on the slot synchronization algorithms of Ad hoc networks,and then simulation is performed to verify the convergence of the slot synchronization algorithm.A slot assignment strategy based on TDMA is proposed in the paper after a research on slot assignment approaches with consideration of the hidden terminal and the exposed terminal problems in wireless Ad hoc network.The time frame is divided into control slot and trafficslot.Each node in Ad hoc network owns a control slot, which reserves trafficslots for the node to send data.Slots reservation will be implemented through the transfer of node's handshake information and the update of node's state.Then a method of trafficslot assignment is provided,when node in the ad hoc network wants to send message,the source node selects a trafficslot randomly, analysis the relate node's states to decide whether it is successful or unsuccessful to appoint the traffic slot.The trafficslot assigned to the node doesn't release until the node have send all the data.The nodes make full use of the trafficslot by means of the continuous reservation of trafficslot in each frame.Finally,a performance simulation(?)and analysis are performed on the proposed slot assignment strategy.Simulate the network performance with the saturated and unsaturated business by setting different simulation scenarios:grid networks and random networks.Analyze and compare the network throughput,delay and fairness indicators,the results showed that:the slot assignment method is effective and feasible.