Study On A TDMA Protocol Based On Pure Directional Antennas In Ad Hoc Networks

Because of the advantages of longer communication distance,higher frequency spatial multiplexing and less link interference,directional transmission becomes one of the key technologies for improving MANET performance.Besides the condition satisfying omnidirectional transmission,a successful directional transmission requires the aim between the beams of both transmitter and receiver.Under the condition of pure directional transmission,which means no omnidirectional tx/rx capabilities at all,this brings new challenges to the design of the TDMA protocol in a mobile Ad Hoc network.Firstly,based on the study of the neighbor discovery algorithm in a mobile Ad Hoc network using pure directional antennas,the neighbor discovery by fast scan(NDFS)is proposed in this paper.Without external timing devices like GPS,neighbors can be discovered rapidly by the "locating scan" and "sending scan".Besides,the neighbors achieve synchronization with master-slaver mode in the discovery process.However,in a mobile Ad Hoc network using pure directional antennas,multiple links are allowed in one hop at the same time,which may bring about the slot collision.Therefore,to solve the problems,link scheduling by suppression check(LSSC)is proposed in this paper.When allocating the slots,the access control of interfering links is realized by the link coexisting condition.Thus,the slot collision can be effectively avoided during the link scheduling,which eventually reduces the link interference and improves the network throughput.Furthermore,nodes' mobility may lead to the following situations:(1)a node moves to its neighbor beam from its original communication beam,resulting in the beam switching;(2)a node moves out of the communication range of its neighbor nodes,giving rise to the neighbor missing;(3)links having no or minor interference previously have greater interference caused by random movement,resulting in the link failures.Meanwhile,the external interference sources may also lead to the link failures.To solve the above problems,the link maintenance algorithm is proposed in this paper,including the link interference prediction based on the "link distance",the link failures detection and adjustment based on the statistical information and the beam switching assisted with business slots.Quantifying the link interference based on the link distance,the interfering links can be predicted and adjusted in advance.By collecting the link information,the reason for link failures can be determined and dealt with in time.When the beam switching occurs,business slots are used to interact beam switching information with its neighbors and help realize the beam switching,and thus shortening the switching time.During the process of the beam switching,the sending of business packets are restrained,avoiding interference with other nodes.To be noted that in the dense network,the superiority of the link maintenance algorithm becomes more visible.At last,the simulation for the TDMA using pure directional antennas in a mobile Ad Hoc network is carried out with OPNET network simulation software.The simulation results show that the neighbor discovery algorithm can shorten the discovery time,improve the discovery probability and accelerate the process of building and accessing networks observably.In addition,the link scheduling and the link maintenance algorithms can make the most of the advantages of the pure directional antennas,to reduce the network interference and increase the network spatial multiplexing and throughput,which eventually improves the performance of the network.