Study On Routing Algorithm In Wireless Transmit System Based On Ad Hoc Network

Ad Hoc network is a kind of wireless mobile network without supporting of wire communications infrastructures. It does not need existing network infrastructures. Every node can join and leave the network at any time. Every node in the network is either a transmitting device or a receiving device, and also a router. All these nodes collaborate and construct multi-hop wireless network with capability self-organization. Multi mobile nodes in the network within limited space range can implement temporary connection. The wireless mobile network provides a flexible connection mode for mobile nodes in limited space range. The difference between Ad Hoc network and general network is without centralized administration and mobile network topology. Therefore developing dynamic routing protocol accommodate to Ad Hoc network is the first when implement Ad Hoc network function. IETF established the Ad Hoc group to study special routing protocol for Ad Hoc network in 1997. Nowadays a plentiful and substantial research production has been obtained. The application of Ad Hoc network has been broadly extended.When engineering machinery group constructing in open country, in general these machines stay in separate place and always transform from one place to another. Therefore the basic communications infrastructures hardly cover with these machines. With the continue rising of automation level, the traffic exchanged among these machines in engineering machinery group is becoming more and more large. The old communication system adopted by machines in same group no longer accommodate to these features of engineering machinery group.It is the developing direction for the future that the engineering machinery group makes the Ad Hoc network as communication system for data exchange.The Ad Hoc network architecture is flat or hierarchical. Nowadays the Ad Hoc network is use at various fields from office automation to digital military command system. The Ad Hoc network covers a large scope from hundreds miters to hundreds kilometers. The size of the Ad Hoc network is change. The number of nodes in the Ad Hoc network is variable.The most important aspect is selecting or developing an efficient and reasonable routing protocol when designing the Ad Hoc network. The goal of Ad Hoc network routing protocol research is developing routing protocol of speediness, exactness, efficient and scalable.There are two kinds of ad hoc routing protocols: table-driven routing protocol and on-demand-driven routing protocol. Table-driven routing protocol includes destination-sequenced distance-vector (DSDV) routing protocol, wireless routing protocol (WRP) and so on. On-demand-driven routing protocol includes dynamic source routing (DSR), Ad-hoc on-demand distance-vector (AODV) routing protocol and so on.In order to improve speed of packet deliver for data transform, all kinds of typical routing protocols are analyzed and compared with each other combining with the features of engineering machinery group in this paper. Due to the simple and efficient, DSR routing protocol was selected as the routing protocol in this paper when the Ad Hoc network was designed.The full name of DSR is dynamic source routing protocol. According to the content, DSR routing protocol mainly contains route finding and route maintenance mechanisms. Source indicates source routing, or routing from one node to the other. Dynamic indicates position change of node. This position change always leads change of route from one node to another. The DSR essential is a process of finding and storing routes, and at the same time updating routes continually according to the network topology changes and storing the changed routes.The main shortcoming in dire need of solving for DSR is the existing of outdated routes (no longer available routes) in node. These outdated routes will affect the data transmit. Protocol prescribes whether a route in source node is outdated will be judged after the top node of a link inquires the next node time after time. This will lead to increase the latency time and occupy the precious wireless channel resources and increase the risk of network congestion.On one hand, outdated routes can come into being at any time. On the other hand, there is no method to identify whether a route is outdated. Therefore the question about outdated routes is becoming serious. It restricts the performance of DSR and efficient of network. To identify a route is updated and eliminate the bad effect of outdated route as early as possible will decrease the latency time and depress the risk of network congestion.In practice, every part of the engineering machinery group is vehicular. The data expressing speed, direction and time of the vehicle can easily be collected. Consequently the positions of communication nodes can be identified. Combine with the covering range of the wireless signal, an idea to identify outdated routes in time using information about the nodes relatively positions is proposed in this paper. This proposed idea improved the traditional DSR routing protocol.In order to identify outdated routes, list of next hop nodes and list deleted next hop nodes addresses are created in the memory of every network nodes. The next hop nodes list will be used for nodes mainly examined and with high risk of communication link likely break. The deleted next hop nodes addresses list will be used for judging whether a route is no longer available in time. Theory analysis already proved that the improved DSR has the ability of identifying whether a source route is outdated in time. The improved DSR also decreases the enquiry time and waiting time for accessing the unreachable next hop node, and the time of occupying wireless channel. So the risk of network congestion is decreased.In order to approve the proposed method can improve the network efficient, OPNET a network simulation tool is used for simulation in this paper. Ad Hoc network model and simulation platform were constructed. The improved DSR was implemented at the simulation platform. The simulation result shows that the improved DSR improves network performance and is more adaptive to engineering machinery group constructing environment.In the process of protocol improving and simulation, there are some shortages and something to be farther researched. For example, the link in the network is supposed to be symmetry in this paper, and the case of unsymmetrical link is not deeply analyzed. At in addition, the time to identify the outdated routes is a special time and needs further study. The identification of outdated routes can be implement combine with movement rules of nodes, and through analyzing the probability model of node movement rules and using the model.