# Multiple Mobile Sinks for Quality of Service Improvement in Large-Scale Wireless Sensor Networks
## 4 Results and Discussion
### Energy Consumption Evaluation  
In the WSN, one can never talk about network performance evaluation without studying the major concern of energy consumption. For that, in this simulation scenario, we compared the energy consumed by all sensor nodes (Network Energy) by varying the number of mobile and static sinks that monitor the network to study the impact of using multiple mobile sinks on energy consumption in large-scale WSNs (LS-WS).  
The simulation results illustrated in Figure 3a show that the use of a single mobile sink, regardless of the model, decreases the average energy consumed compared to a fixed sink by \(-12.5\%\) for RW up to \(-19\%\) for RD, and the best result obtained with the use of the RD mobility model and the P-LEACH routing protocol with a power gain of \(-20\%\).  
Figure 3: Nodes Energy Consumption with different routing protocols by using multiple statics and mobile sinks, (**a**) Single Sink for the entire network, (**b**) 2 Sinks for 2 sub-networks, (**c**) 4 Sinks for four sub-networks, (**d**) 8 Sinks for 8 sub-networks.  
The simulation results illustrated in the other figures show that the use of multiple mobile sinks decreases the average energy consumption compared to a single static sink, as illustrated in Figure 3a:  
* By using two mobile sinks (Figure 3b) from \(-25.6\%\) for RW up to \(-31.3\%\) for RD and the best result obtained with the RD model and the P-LEACH routing protocol \(-36.1\%\).
* By using four mobile sinks (Figure 3c) from \(-44\%\) for RW to \(-48.3\%\) for RD, the best result was obtained with the RD model and the P-LEACH routing protocol \(-57.5\%\).
* Using eight mobile sinks (Figure 3d) from \(-48\%\) for RW to \(-52\%\) for RD, the best result was obtained with the RD model and the P-LEACH routing protocol \(-59.5\%\).  
It can be drawn from the previous results that the best mobility model is RD, which offers better energy conservation, around \(60\%\) less, with eight mobile sinks, compared to a single fixed sink. More precisely, the sink with RD mobility model moves towards the clusters of sensor nodes to reduce the distance between the sink and the CH and consequently reduce the transmission energy consumption.  
On the other hand, by comparing the different energy scenarios, we notice that using four mobile sinks gives results very close to that of eight mobile sinks.  
So, we can conclude that in terms of profitability, the use of four mobile sinks establishes a good compromise between energy conservation and investment cost (budget of mobile sinks), and we can obtain better energy conservation of \(57.5\%\) less with only four mobile sinks using the RD model and the P-LEACH routing protocol. Since consumed power is expected to increase exponentially as the communication range increases, utilizing a shorter transmission distance can significantly optimize the power consumed by mobile sinks. This implies that the power conservation of the network will be higher, and its lifetime will be extended as the subnet area becomes smaller. Nonetheless, it will incur a higher cost of deploying adequate mobile sinks to cover the area.