Improved AODV Routing Protocol For Ad Hoc Networks

AODV(Ad hoc On-demand Distance Vector Routing protocol) is a special case of reactive routing protocol in Ad Hoc networks.In this protocol the source node floods routing request packet to the destination node.When receives the request packet,it sends routing response packet immediately.The middle node sends routing request packet to resume route.But the flooding broadcast causes severe network burden.The established path may contain a passage of link which will break soon.To avoid routing circle,the local repair mechanism has low rate to repair the path.According to the drawbacks of AODV protocol,we bring forward the improved protocol G-AODV(GPS-Aided AODV) based GPS(Global Position System).The node can get coordinates, moving angle and velocity from GPS receiver.According to the relative information in the packet it can judge the link stability between two neighbour nodes and compute the path survival time during two nodes.During the routing request phase,the node uses the link stability judgement rule to limit the quantity of routing request packet.During the routing response phase,the destination node uses new path selection policy.When it receives the routing request packet which arrives for the first time,it postpones sending routing response packet and selects the path of longer survival time to update the reverse route.During the routing maintenance phase,we put forward HOLE-REPLACE routing repair mechanism.This mechanism uses EREQ repair request packet and EREP repair response packet to resume path when the link breaks.It uses link stability judgement rule and adaptive TTL to limit the quantity of EREQ packet.The EREQ packet contains path node list to record the addresses which it passed by.When receives the repair request packet,the nodes which are the downflow node of original path send EREP packet.EREP packet need not reverse route and depending on path node list it can be forwarded to the repair initiation node.G-AODV is realized and tested on the network simulator.In the packet delivery ratio and the packet cost,the improved protocol is better than the original protocol.It can improve packet delivery ratio,and at the same time decrease the broadcast packet quantity.