Wireless Ad Hoc and Sensor Networks

388 Wireless Ad Hoc and Sensor Networks8.8.1 Optimal Relay Node SelectionThe link_cost_ factor, which is defined as the ratio of the energy availableover the product of the average E2E delay and the distance from the nodeto the BS, is given byErnLink _cos t _ factor =Delay × Dist(8.4)where Er n is the energy available in the given node obtained from thebattery monitor, Delay is the average E2E delay between any two CHs,and Dist is the distance from the given node to the BS. In Equation 8.2,the energy available at a node has to be higher whereas the average E2Edelay and the distance to the BS have to be at a minimum to select anoptimal route that renders a long network lifetime. Therefore, a relay nodeon the optimal route should maximize the link_cost_ factor. Ensuring thatthe delay and the distance to the BS are minimal will help reduce thenumber of hops and the overall delay in routing the information from aCH to the BS. When multiple RNs are available for routing, an optimalRN is selected such that the link_cost_ factor is maximized. The nodes thatare common between the CH are taken into consideration to becomecandidate RNs. Figure 8.19 shows the relay-node selection for the proposedOEDSR in contrast with OEDR wherein RNs have to satisfy certainstringent requirements such as maximizing the number of two-hop neighbors.The details of the relay-node selection in OEDSR are discussed next.CHNodeRelay nodeBSNodes awayfrom BSIdentifying thebest relay nodeIdentifying thebest relay nodeFIGURE 8.19Relay node selection.