# Internet of Bikes: A DTN Protocol with Data Aggregation for Urban Data Collection
## 6 Performance Evaluation of IoB-DTN
### Impact of IoB-DTN by Varying the Transmission Power  
Now, we evaluate IoB-DTN protocol by varying the transmission power of sensors. It is a significant parameter for IoB-DTN since it can influence on the communication range of sensors, as shown in Figure 13, thus influencing several metrics. In our previous simulated scenarios, the transmission power value was set to 10 mW which gives \(\sim\)350 m as communication range. Here, we appraise fours values of this parameter: 1 mW, 5 mW, 10 mW and 20 mW. We present the average results obtained for ten scenarios simulated with different paths of bikes in each scenario. In Figure 13, the highest value of the transmission range achieves the longest communication range.  
Figure 14 shows the average delivery rate by varying the transmission power value. We notice that the delivery rate increases by raising the transmission power value. This behavior was expected, as, by increasing the communication range, each node will encounter more nodes and more base stations, hence allowing to obtain a higher delivery rate. It is also interesting to remark that the use of lower duty cycle improves the delivery rate.  
The average delivery delay of received packets is depicted in Figure 15. It is important to point out that the transmission power does not impact the delivery delay comparing it to the buffer size and the duty cycle parameters. This indicates that the dynamics of the network impacts more the connectivity than the sending range. The increase of the buffer size as well as the duty cycle provide a higher delivery delay. In that case, more data packets are stored in the buffer for a longer time.  
Figure 12: Delivery delay for NP buffer management policy.  
Figure 14: Average delivery rate.  
Figure 13: Average communication range.  
Figure 15: Average delivery delay.  
Figure 16 shows the average throughput. Here, we note that the throughput is impacted by the transmission range. It increases slightly by raising the transmission power values. It is important to mention that the impact of the buffer size and the duty cycle is still significant since all packets stored in the buffer are forwarded at each duty cycle.  
Figure 17 shows the average protocol cost of IoB-DTN protocol by varying the transmission power values. It represents the average number of transmitted and received packets in all simulated scenarios. We consider all communications either bike-to-bike or bike-to-bike station. We can see two columns for each case: the first column depicts all transmitted packets and the second represents all received packets. On the one hand, the first column has three fields: _NPSN_ (number of packets sent to nodes), _NASN_ (number of acknowledgments sent to nodes) and _NPSG_ (number of packets sent to gateways). On the other hand, the second column has two fields: _NPRN_ (number of packets and acknowledgments received by nodes) and _NPRG_ (number of packets received by gateways). Figure 17 clearly illustrates the impact of the increase of the transmission power value on the average number of forwarded and received data packets in the network. This is an evident consequence since the transmission range increases by raising the transmission power of sensors which will encounter more nodes and more base stations. Hence, this allows more communications with other nodes and gateways. It is also interesting to notice that the use of a high duty cycle offers a small duty cycle. Indeed, in that case, the data packets spend more time to be stored in the buffers, thus allowing to have fewer communications.  
According to the results obtained in this section, we can argue that IoB-DTN protocol with a high transmission power and a small duty cycle can provide a better delivery rate, delivery delay and throughput. It has a high energy performance. The value of the transmission power of sensors is chosen depending on the needs of the designers of the network. In next sections, we consider 10 mW as transmission power since it offers the compromise among all evaluated metrics.