# Opportunistic Multipath Routing in Long-Hop Wireless Sensor Networks
## 4 Performance Evaluation
### Energy Consumption Versus End-to-End Distance and Link Reliability  
In this section, we demonstrate the effect of the link reliability and end-to-end distance on energy consumption. We perform an evaluation while increasing the end-to-end distance when the link reliability is 80% and 90%. To investigate the energy consumption when achieving the same packet delivery ratio, the failed packets during the transmission process are retransmitted.  
Figure 8 shows the energy consumption versus the end-to-end distance when the link reliability is 90%. When the scale of the network size is small, RRDLA consumes the smallest amount of energy because it exploits only one of the best paths found by the learning algorithm. REER consumes the second least energy amount because it uses only two paths. The proposed scheme requires a higher energy than RRDLA and REER. This is because the proposed scheme grants transmission opportunities to all of the neighbor nodes. That is, as the number of receiving packets is greater than those of RRDLA and REER, the proposed scheme consumes more energy. RGMR consumes more energy than the other protocols because it constructs several paths to satisfy the required packet delivery ratio. In summary, with regard to energy consumption when the scale of the network size is small, the proposed scheme and RGMR could satisfy the required packet delivery ratio without packet retransmission. However, although RRDLA and REER perform packet retransmission to satisfy the required packet delivery ratio, the energy consumption of the retransmission is less than the energy consumption for multipath construction and transmission. However, as the scale of the network size increases, the proposed scheme consumes less energy than the other protocols. The reason for this is that there is little difference between the cases where bifurcation is performed or not based on opportunistic routing because the proposed scheme always grants all of the neighbors to the neighbor nodes. The energy consumption of RRDLA and REER increase depending on the increase in the number of retransmissions. RGMR consumes the most energy because it continues to increase the path to achieve the requirements.  
Figure 7: Packet delivery ratio vs. end-to-end distance with 80% of link reliability.  
Figure 9 shows the energy consumption versus the end-to-end distance when the link reliability is 80%. Similar to the case with a link reliability is of 90%, all of the protocols consume more energy as the end-to-end distance increases. However, the energy consumption of the proposed scheme is similar to that of a packet delivery ratio of 90%. This is because the proposed scheme scarcely retransmits the packet, courtesy of the characteristic of opportunistic routing, which improves the link reliability. However, for the other protocols, as the packet delivery ratio of each path is degraded, the ratio of the retransmission increases. In addition, RGMR cannot construct enough paths when the scale of the network size increases over 800 m\({}^{2}\) and needs to perform retransmission. Thus, the energy consumption slowly increases compared with more path construction.