Multicast Protocol Simulation And Study In Ad Hoc Networks

Since it is known, Ad Hoc network has received great concern, and become a communication research object of academia and industry. It is a dynamically reconfigurable wireless network with no fixed infrastructure or central administration. Due to the limited radio propagation range of wireless devices, its routes are often "multihop", so it is also called "multihop" network. Because it is configured quickly and its devices are portable and flexible, Ad Hoc network has broad application prospects whether in military or civilian areas.In a typical ad hoc environment, network hosts work in groups to carry out a given task, and multicast can provide support for these applications. However, multicast protocols used in static networks do not perform well in ad hoc networks, because the dynamic of ad hoc networks may undermine the multicast structure, and the protocols don't have quick fixes ability. Furthermore, multicast trees usually require global information of link state or distance vector of the network, however collect these information may cause network congestion especially in large and limited bandwidth network. So, the research of multicast protocol in Ad hoc networks has a great value.Recently, scholars found that use the "hop count" as the routing path selection-criteria doesn't well adapt to Ad Hoc Networks. Because using "hop count" ignores the quality of the wireless link, such as the signal to noise ratio and stability of the link. So in this paper, a multicast protocol is proposed based on link stability. The stability link has higher packet delivery ratio, thereby reducing the number of packet retransmission, and has a long maintenance time, thereby reducing the happenes of link breakdown and the maintenance overhead of the protocol. According to wireless signal transmission characteristic, an estimate link stability method based on signal received power is proposed in this paper. Through real-time monitor the received power, the mothod estimates the changes of the distance between two nodes, using probabilistic statistical method. Although this method is less accurate than using GPS, it is better than just by neighbor changes to predict node mobility. As multicast tree is more vulnerable to the impact of instability link, this paper also proposed a multicast protocol based on this method. It has designed the join and leave mechanism of group member, also inluding the multicast tree creation and maintance mothod. The protocol has simple mechanism, can choose stable path as route and reduce the occurance of routing loops, and to be with the stability evaluation mechanism, it can predit the link which will be broken in a moment. Finally, we test the protocol through simulation, and analyze its performance from more than one side.The opportunistic routing is a newly proposed routing method, and the difference with the traditional routing is delivering a packet in an uncertaint path. In traditional routing, the packet's forward path is built before the transmission. However, the opportunistic routing takes the broadcast of wireless environment as an advantage, do not certain a specific next hop neighbor, but as long as a neighbor received the packet, the routing can continue. This approach reduces the number of packet retransmission, and improves the network packet delivery ratio. While the study of opportunistic routing on multicast is less, this paper will explore the menthod of opportunistic routing on multicast, and design an opportunistic multicast routing protocol. This protocol is based on tree structure, but the packet is not forwarded along this tree which is just as a support structure. The protocol restricts the packet forwording through the multicast tree, to ensure that each group member can receive the packet and avoid endless packets routing. We also design packets opportunistic forwording mechanism on multicast in this paper. The mechanism coordinates the operation of neighbor node to avoid packet collisions, ensure that the packet can be routed to the destination node, and also has the advatage of mulitcast. Simulation results show that the opportunistic multicast routing has a significant advantage in packet delivery ratio than traditional multicast routing, also has a higher efficiency.This paper uses OPNET as a simulation tool, described the structure, simulation mechanisms and wireless channels of OPNET in detail. Wireless channel is a radio channel simulation, but it is the basis for wireless simulation. In the end of this paper, there are some summarizes of my research, next steps of my work, and prospects of reasearch on ad Hoc network multicast.