# A Multi-Technology Communication Platform for Urban Mobile Sensing
## 5 Results
### Network Analysis
#### 5.3.1 LoRa MAC evaluation  
To evaluate the performance and behavior of the implemented LoRa MAC protocol, the obtained results for each day of experiments are presented. They express, respectively, an analysis on: the data  
Figure 13: Multi-technology map over day 2 (**a**) Moliceiro-101; (**b**) Moliceiro-102; (**c**) Moliceiro-103.  
packet delivery ratio, the average number of attempts per channel access, and the backoff time used per node.  
The results for the overall data packets delivery ratio through LoRa technology for each day of experiments are shown in Figure 14: they represent the percentage of data packets that each network node delivered successfully to the gateway after having acquired the medium access. As previously stated, the geographical location where the nodes spend most of its time, the docks, have a noticeable lack of LoRa connectivity to the gateways. A proposal to solve this obstacle has already been presented. Besides, during a moliceiro cruise, various obstacles (such as bridges) can impose the lack of communication or an unexpected loss of packets through this technology. Such conditions led to low delivery rates by the LoRa technology (between 60% and 85%). However, due to our platform's multi-technology capabilities, the information that was not delivered by LoRa will be recovered and forwarded through the opportunistic and delay-tolerant network.  
The results for the overall number of attempts to gain the channel access are presented in Figure 15. They represent the mean amount of attempts made by each node until it was granted with the medium access. A further analysis of the results shows that in general, nodes presenting higher number of attempts per channel access are also the ones with poorer data packet delivery ratios. Therefore, it is concluded that these nodes suffered a lack of a stable communication link between them and a LoRa gateway. Once more, we would like to emphasize that the high mean number of channel accesses attempts presented by the network nodes can be solved and reduced by the introduction of a novel LoRa gateway with a geographical location closer to the city area where the evaluations were performed, in order to guarantee better communication links between the moliceiros and the LoRa gateways.  
The results for the overall backoff time used by each node are presented in Figure 16. They represent the backoff time that each network node had to experience during the experimental period.  
Figure 14: LoRa’s data packet delivery (**a**) Day 1; (**b**) Day 2; (**c**) Day 3.  
Figure 15: LoRa’s mean attempts per channel access (**a**) Day 1; (**b**) Day 2; (**c**) Day 3.  
The high backoff time used by each node reflects the large experimental period per day (seven hours), as well as the number of channel accesses and data packet delivering failures. Therefore, scenarios capable of providing better communication links between the network nodes and the LoRa gateways would increase the data packet delivery rate and decrease the mean number of channel access attempts, resulting in a significant decrease in the backoff time used by each node.