Research On Broadcast In Mobile Ad Hoc Network

In order to communicate in the environment without fixed infrastructure, there comes the Mobile Ad Hoc Network (MANET). A MANET is composed by a set of nodes communicating with each other via multihop wireless links. Each node can only directly communicate with those nodes that are in its communication range. Intermediate nodes forward messages to the nodes that are more than one hop distance from the source node. The technology of Ad Hoc helps people to communicate with each other whenever and wherever they want, and it provides effective solutions for the scenes such as disaster relief, military and temporary communication applications.A significant issue in the design of Ad Hoc network is routing protocols. Since the nodes are mobile, the topology of the network is constantly changing, which causes traditional Internet-Based Routing protocol unable to adapt to this characteristic. So it needs some specialized routing protocols. Broadcast is widely used in the Ad Hoc network routing protocols, more frequently used in the routing found operation of passive routing protocols such as AODV and DSR. In addition, it is useful to broadcast the entire network in some applications, such as the alert of invasion in military, the abnormal alarm in environmental monitoring. Blind flooding is widely used in Ad Hoc network to broadcast. Though it is simple and can provide high coverage, it causes large number of redundant packet and leads to the broadcast storm problem, which makes lower efficiency. Now there comes some schemes to deal with this, such as Probabilistic Based Schemes, Area Based Schemes and Neighbor Knowledge Schemes, they can reduce the broadcast storm somewhat, but not very well or very complicated. As result, it is of great significance to design new broadcast protocols for Ad Hoc network. Discuss the problems which effect broadcast and provide some algorithm to solve these problems.When broadcasting in sparser maps, because there are large amount of collisions between the nodes which are adjacent to each other, the reachability of the network is not high enough. Present a time-slice-based V broadcasting algorithm. Different from most of the existing broadcasting algorithm, this algorithm believes the reachability and average latency are much more important than saved rebroadcast in the practical application of Ad Hoc network. So the time-slice-based broadcasting algorithm increases the reachability first and then tries to reduce the numbers of the redundant nodes. This thought is completely contrary to the idea of the existing schemes which try to increase the reachability by reduce the redundancy. This algorithm can work with any existing broadcasting algorithm in combination, which can make adjacent nodes scattered at regular intervals of time, thereby reducing the collision between neighbouring nodes and then increase the reachability and lower the average latency at the same time. This algorithm can also be used in denser maps, where the reachability is high enough. Therefore, it is not obvious to use this algorithm to raise the reachability in denser network although it's useful.Most of the application scenes of Ad Hoc network are dense. When broadcasting in denser network, the average latency of the entire network is very high. The reason is when many of the nodes are close with each other, they are affected by the mechanism of 802.11. The oriented-based broadcast algorithm can used to solve this problem. This algorithm can select some nodes that are out of the radius from each other to rebroadcast at the same. It can reduce the collisions and make the packet spread faster to the edge of the network. In military scene, combat units that are equipped with Ad Hoc wireless sensor can also equipped with GPS. In military applications the GPS information can be fetched to use immediately. So the oriented-based broadcast algorithm is more suitable in the military scene.The reason of high latency in denser network is the MAC protocols of the wireless nodes impacted by the backoff mechanism of IEEE 802.11. though 802.11 is the standard protocols for wireless LAN, it is not fit for Ad Hoc network. So when used in Ad Hoc network there will come lots of problems. In order to make some new protocols and algorithm suitable for Ad Hoc network, Game theory is used to model the DCF mechanism of the IEEE 802.11, which can provide convenience to research of the DCF mechanism and improve the flaws of existing algorithm. Present two solutions for the problems in oriented-based broadcast algorithm. Finally, use the NS2 to simulate the time-slice-based algorithm and oriented-based algorithm, compared them with existing algorithm. In the same experimental conditions, new schemes have better efficiency and reduce energy consumption in the same time, which is very useful for the routing and the applications of Ad Hoc network.