3.3 Energy-Efficient Geographic Opportunistic Routing

The EGOR that applies the local forwarding candidates selection algorithms GetM-A or GetM-B to get is described in Table 3.5, where node i (i ≠ destination D) is routing a packet and the forwarding candidates' ijs are trying to relay the packet collaboratively. Here we do not consider any mechanism to route around voids (when ). If the packet becomes stuck due to no node being available for forwarding, it is dropped (line 14 in Procedure A). Mechanisms such as FACE routing (Bose et al. 1999) or perimeter forwarding in GPSR (Karp and Kung 2000) can be applied here to deal with the communication void problem but it is beyond the scope of this chapter. Retransmission limitation is applied. If the retransmission number (RN) reaches the limitation (RL) (line 11 in Procedure A), the packet will also be dropped (line 12 in Procedure A). It is worth mentioning that there is a last-hop behavior (line 7 and 8 in Procedure A) in EGOR. When the sink D is in the available next-hop node set , we calculate the forwarding set by eliminating D from . Because sink D is not energy constrained, its receiving energy cost should not be counted when maximizing the energy efficiency. After calculating the , D should be added into the forwarding candidate set, since the packet always has a chance to reach D whatever the link quality from i to D is when D is the neighbor of i.

Table 3.5 The procedure of EGOR when node i is forwarding the packet