# Routing in Mobile Wireless Sensor Networks: A Leader-Based Approach+
## 4 Evaluation
### Evaluation Results  
#### 4.3.1 Delivery Rate  
In order to compute the evaluation figures, data messages have been generated at the defined rate of 0.2 per second and its reception checked at the sink node. We have simulated a set of 120 configurations, each one being a combination of the parameters reported in the previous subsection. We have performed at least ten repetitions for every configuration. Variances obtained for each configuration are low, between 0.001 and 0.09, thus the figures presented here refer only to the averages of the results obtained.  
Figure 2 illustrates the values of message delivery rates obtained for LBR1, LBR2, AODV and RASEeR. LBR1 (Figure 1(a)) shows the best performance, followed by LBR2, which is negatively affected by high mobility. AODV (Figure 1(c)) presents low delivery rates in general, and poor scalability. On the other hand, RASEeR provides a decent message delivery rate up to 32 nodes, obtaining nearly 60%. In this protocol, we have observed a problem related to message duplication, resulting in network congestion. Intuitively, global TDMA imposes an upper bound on the number of messages sent per cycle. Consequently, if the number of messages received is continuously higher than that upper bound, eventually it will cause a buffer overflow. This situation can be appreciated in Figure 3, which represents the overall number of messages that each protocol has used in order to route multi-hop communications towards the sink (i.e., excluding the first hop), a parameter with hight impact on energy consumption. Note that, despite LBR1, LBR2 and RASEeR sharing the routing criteria based on the number of hops, RASEeR is very inefficient regarding the number of generated messages.  
As a summary, Figure 4 illustrates some comparative results for the four protocols. Figure 3(a) compares delivery rate for a fixed maximum velocity of 20 m/s, and Figure 3(b) compares delivery rate for a network size of 64 nodes.  
It should be noted that the delivery rate figures for LBR1 and LBR2 benefit in part from the fact of disabling communications, since messages not transmitted do not account in total (We are assuming that a not sent message is managed, and possibly re-sent as new, by the application layer.). Since LBR1 is more reactive than LBR2, this mechanism is activated more frequently in the former. Figure 4(a) shows that effectively LBR1 has sent much less number of messages than LBR2. This is beneficial from an energy efficiency point of view with a positive impact on energy consumption. However, LBR2 is more effective since it delivers a higher absolute number of messages to the sink (Figure 4(b)).  
Recall that, for all the above experiments, we have used a message generation rate of four messages per second and node. During the simulations, we have observed that, in the case of LBR2, the message payload was not completely used. Thus, we have carried out a new series of experiments increasing the message generation rate to 10 messages per second and node. The results can be seen in Figure 6. As shown in Figure 3(a), LBR2 performs better than LBR1 as the rate of message generation increases. While LBR1 has to route each message individually, increasing network congestion, LBR2 is able to take advantage of its ability to send multiple messages in a single packet, increasing the message delivery rate.  
Figure 3: Number of messages routed towards the sink. Results for a maximum velocity of 20 m/s. Note the logarithmic scale on the \(y\)-axis.  
Figure 2: Message delivery rates for the simulated protocols. Results for a generation rate of four messages per node and second. (**a**) LBR1 message delivery rate; (**b**) LBR2 message delivery rate; (**c**) AODV message delivery rate; (**d**) RASER message delivery rate.