Wireless Ad Hoc and Sensor Networks

Optimized Energy and Delay-Based Routing 389CH A4856AB1485 BS26C37(a)9FIGURE 8.20 (a)Steps to select a relay node: (a) A, B, C are the CHs and 1, 2, 3, …, and 9 are the node IDs.In the first step, CH A sends out HELLO packets to all the nodes that are in range andreceives RESPONSE packets. CH A first checks if its distance from the BS is greater thannode 4, 8, 5, and 6. If it is, then a list is created with the information of all nodes that are inrange with CH A.In the OEDSR protocol, routes are selected, based on the bestlink_cost_ factor of all nodes in range to the CH or a relay node. Initially,a CH broadcasts HELLO packets to all the nodes that are in range andreceives RESPONSE packets from all the relay candidates that are in thecommunication range as shown in Figure 8.20a. The RESPONSE packetscontain information such as the node ID, energy available, average E2Edelay, and distance to the BS. After receiving RESPONSE packets, CHneglects those nodes whose distances to the BS are greater than the distancefrom the CH to the BS. This ensures that the route does not take alonger or cyclic path to the BS. If the RESPONSE packet is received fromthe BS, then it is selected as a next hop node, thus ending the routediscovery procedure. Otherwise, the CH broadcasts a HELLO packet tothe next CH in the subnetwork with the list of candidate RNs.Once the next in-sequence CH receives the HELLO packet, it checkswhether it is in communication range with any of the listed nodes or not.Then it creates a new list of candidate RNs. The same procedure is carriedout for all the CH. Finally, if more than two nodes are selected as candidateRNs, the node with the highest link_cost_ factor is selected as the RN.Selection of RNs is illustrated in Figure 8.20b and Figure 8.20c. If a CHdoes not have a common RN, then it sets up a separate route using thelink_cost_ factor to the BS such that it is optimal from the CH. Figure 8.20dshows the route for the remaining CHs, determined in the same way asexplained previously.The advantage of using this routing method is that it reduces the numberof RNs that have to forward data in the network, and hence the schemereduces overhead, number of hops, and communication among nodes to