Study Of A Distributed TDMA Protocol In Ad Hoc Networks Based On A New Technique In PHY Layer

A mobile ad hoc network features non-centralization and self-organization.It is being applied more and more widely because of its rapid deployment and strong resistance to damage,and it is a key technology for future wireless communications networks.Directional antenna is a new kind of technology,which has the characteristics of long transmission distance,high communication rate,and strong anti-interference ability.In order to improve the performance of mobile ad hoc networks,broadband ad hoc network communication devices increasingly use directional antennas.Compared with omnidirectional transmission,the conditions for successful directional transmission are more stringent.How to implement distributed link scheduling becomes a key technology for the MAC protocols in directional ad hoc networks.Moreover,how to make full use of the spatial multiplexing gain of directional transmission to improve the throughput of the entire network has become a key issue in the performance optimization of a directional ad hoc network.The ad hoc networking equipment studied in this paper adopts both omni-directional and directional antennas.The omni-directional antenna supports multi-directional simultaneous reception for exchanging control information,and the directional one fulfills data transmission.The new MAC protocol is based on TDMA and optimized on two main parts.The one is the distributed link schedule algorithm based on interference suppression,and the other is the link coexistence test algorithm.The link schedule algorithm adopts a combination of slot pre-allocation and dynamic reservation.In order to find interfered slots,a method using angles to quantify the interference beam coverage is proposed,and the interferences introduced by existing links are effectively decreased.The link coexistence test algorithm tests the newly established links for interference through actual link transmission and releases the interfering links.By the method of "weaving" the coexistence testing into the link scheduling,the time spent in coexistence testing is greatly reduced.For the selection of test-participating links,a method based on omnidirectional receiving detection is proposed.In this method,only those links that have a high probability of interfering or being interfered will be selected,which not only decreases the cost of coexistence testing but also improves the effectiveness of the test.If there appears some interferences,the links with interference will be released as soon as possible to minimize the waste of time slot resources.In this thesis,OPNET is used to model and simulate the new MAC protocol in mobile ad hoc networks.By setting different network topology,node density and service load parameters,the performance of link schedule algorithm and link coexistence test algorithm is verified.The simulation results show that the link schedule algorithm can effectively filter out the time slots with interference and reduce the link interference.After using the link coexistence test algorithm,the number of interfering links in the network is further decreased,and the performance of throughput is effectively improved.