Wireless Ad Hoc and Sensor Networks

Optimized Energy and Delay-Based Routing 3678.3.3 MPR and Energy-Delay Information DeclarationEach node in the network that is selected as MPR, by at least one of itsneighbors, transmits a TC message periodically. The TC message containsinformation about the MPR node’s selector set, which is a subset of theone-hop neighbors that have selected the sender node as a MPR. Moreover,the TC message format is modified to include the link costs (energydelay) between the MPR node and its selectors. TC messages are forwardedthroughout the network like usual broadcast messages, exceptthat only the MPR nodes forward the message to the next hop.The proposed OEDR protocol significantly reduces the overhead intransmitting the cost information, in contrast to a normal link-state algorithm,which uses flooding to broadcast control messages with cost information.In the OEDR protocol, only the MPR nodes (which are a smallsubset of the one-hop neighbors) forward the broadcast control messages,instead of all the neighbor nodes. Moreover, only the nodes that areselected as MPRs generate the TC messages that contain cost information,instead of all the nodes in the network. Also, the size of the TC controlmessages is smaller because it contains the costs of only the links betweenthe source node and its MPR selectors.Each node in the network maintains a “topology table,” in which itrecords the information about the topology of the network obtained fromthe TC messages, along with the link costs. An entry in the topology tableconsists of the address of a destination (an MPR selector in the receivedTC message), address of the last-hop node to that destination (originatorof the TC message), and the cost of the link between the destination andits last-hop. It implies that the destination node can be reached in the lasthop through this last-hop node at the given cost.Whenever a node receives a TC message, it records the information asentries into the topology table with the addresses in the MPR selector setas the destinations, the originator as the last-hop, and the correspondinglink costs. Based on this information, the routing table is calculated.8.3.4 Routing Table CalculationEach node maintains a “routing table,” which enables it to route packetsfor other destinations in the network. The routing table entries consist ofthe destination address, next-hop address, estimated distance to destination,and cost of the path from the source to the destination ( Cost sd , ). Eachdestination has an entry in the routing table, for which a route is knownfrom the given node to the destination. The proposed OEDR protocoldetermines the routes to destinations, by using a least-cost spanning treemethod with the energy-delay product of the links as costs of the edges.By contrast, the OLSR protocol computes the routes, based on a shortest