In this chapter, we studied the geographic opportunistic routing strategy with both routing and energy efficiencies as the major concerns. We proposed a new routing metric that evaluates EPA per unit of energy consumption so that the energy efficiency can be taken into consideration in routing. By leveraging the proved findings in Chapter 2, we proposed two localized candidate selection algorithms with O(M3) and O(M2) running time in the worst case, respectively, and Ω(M) in the best case, where M is the number of available next-hop neighbors of the transmitter. The algorithms efficiently determine the forwarding candidate set that maximizes the proposed new metric for energy efficiency, namely the EPA per unit of energy consumption. We further propose an EGOR framework applying the node selection algorithms to achieve the energy efficiency. The performance of EGOR is studied through extensive simulations and compared with those of the existing geographic routing and opportunistic routing protocols. The results show that EGOR achieves the best energy efficiency among the three protocols in all the cases while maintaining very good routing performance. Our simulation results also show that the number of forwarding candidates necessary to achieve the maximum energy efficiency is mainly affected by the reception to transmission energy ratio but not by the node density under a uniform node distribution. Although the EPA can be maximized by involving the most number of nodes in GOR, in terms of energy efficiency, only a very small number of forwarding candidates (around 2) is needed on average. This is true even when the energy consumption of reception is far less than that of transmission.
1 For different MAC protocols, the energy consumption of control packets may be different. However, the energy consumption is likely to be a nondecreasing function of the number of forwarding candidates. So ignoring it will not affect the upper bound analysis of the energy efficiency in this book.
2 In sensor networks, the energy consumption of reception is comparable to that of transmission see the MICA2 datasheet at https://www.eol.ucar.edu/rtf/facilities/isa/internal/CrossBow/DataSheets/mica2.pdf, so is non-negligible.
3 Please refer to Zuniga and Krishnamachari (2004) for a complete description of the model.