## 7 Performance Evaluation and Analysis
Figure 10: Transmission loss (dB) in 4-chain, 2-chain, single chain-based routing and PEGASIS. Figure 13 shows the comparison of average energy consumption between 4-chain, 2-chain and single-chain based routing schemes. In the single-chain based scheme, energy consumption is increased suddenly due to death of intermediate nodes in the chain. Death of any intermediate node affects many child nodes and increases their energy consumption. In PEGASIS, average energy consumption is very high at the beginning due to random selection of chain head. The chain head at a larger distance from the sink consumes a large amount of energy. Reverse transmission in the chain also occurs as the nodes nearer to the sink also forward data towards chain head. The absence of a secondary chain head in PEGASIS causes quick energy depletion of the primary chain head. In C-PEGASIS, the average energy consumption decreases with the passage of time. This  
Figure 11: Path loss (dB) in 4-chain, 2-chain, single-chain based routing and PEGASIS. Figure 12: Network throughput in 4-chains, 2-chains, single-chain based routing and PEGASIS. decrease is due to the death of nodes because energy consumption is directly related with the number of alive nodes. Figures 14-16 show the impact of node density on path loss, network lifetime, and end-to-end delay. These results are obtained for \(E_{0}=2J\). By varying the number of nodes from \(50\) to \(250\), all the compared protocols show moderate decay in path loss as shown in Figure 14. This is due to the fact that the communication distance decreases as the number of nodes are increased-leading to moderate decay in path loss. Similarly, a general trend in Figure 15 is first increased and then decreased in the network lifetime as the node density is increased from \(50\) to \(250\). The initial increase in network lifetime is due to the fact that increased number of nodes communicate at relatively small distances, which leads to decreased energy consumption and ultimately prolonged network lifetime. However, further increase in node density leads to decreased network lifetime because high node density means increased congestion/interference which leads to high packet drop rate. In such situations, the dropped packets are re-transmitted that require surplus energy, which thus leads to decreased network lifetime. Finally, Figure 16 shows a steady increase in end-to-end delay as the node density is increased. The reason is associated with re-transmissions, _i.e._, high re-transmission rate means high end-to-end delay. Figure 14: Impact of node density on path loss. Figure 13: Average energy consumption (J) in 4-chains, 2-chains, single-chain based routing and PEGASIS. **Remarks:** In UWSNs, data flows from high depth nodes to low depth nodes and finally towards the sink (at the surface of water). As per our cylindrical network area assumption, addition of another sink at the surface of water would not lead to any significant change in results because the surface area is not too much large. Thus, we suggest a single sink to be placed at the surface of the water. It is also worth mentioning that the routing overhead of our proposed schemes is relatively high as compared to the existing schemes; however, the proposed schemes show significant improvement in terms of networks lifetime as well. Thus, the negative aspect (high routing overhead) is negligible as compared to the positive aspect (prolonged network lifetime).