# LoRa Architecture for V2X Communication: An Experimental Evaluation with Vehicles on the Move
## 6 Outdoor Testing and Analysis of the Prototypes
### Testing in Real-World Scenario without and with Kalman Filter
It clearly shows that RSU 1, 2, and 3 do not receive an equal number of data packets for any of the testing speeds- 15, 25, 30, 40, and 50 kmph. This is because of the sudden fluctuation of the RSSI value as the algorithms depend on the RSSI values for switching from one RSU to another. For 25 kmph, OBU switches from RSU1 to RSU2 very early as the fluctuated value reaches the threshold RSSI of -60 dBm and compels the OBU to switch from RSU1 to RSU2. At 25 kmph, the variation of the number of data packets received by RSUs is 53.84% which is the worst case. The number of received data packets by RSUs varies by 10.5%, 23.23%, 7.87% and 30.28%, respectively, for 15, 30, 40, and 50 kmph. This sudden switching between RSUs hampers the reliability of the architecture  
Figure 13: Data points received by each RSU at different speeds of the car without Kalman filter. badly and might cause some unintended maneuvers leading to failing the whole system. This type of erratic transitioning can be avoided with the Kalman filter. The same test is repeated with the Kalman filter in the algorithm as proposed and the number of data packets received by each RSU at a different speed is presented in Figure 14. It shows that the number of data packets received by RSU1, RSU2, and RSU3 at any particular speed is almost the same which depicts the smooth handoff of the RSUs by the data sending vehicle. This is because the Kalman filter stabilized the RSSI values removing any unintended fluctuations of the values. For the speeds, 25, 40, and 50 kmph, each of RSU 1, 2, and 3 received an equal number of data packets -10 data packets at 25 kmph, eight data packets at 40 kmph, and six data packets at 50 kmph. Still, there are some discrepancies, at 15 kmph, both RSU 1 and RSU 3 received 12 data packets each whereas RSU 2 received 13 and at 30 kmph, RSU 1 and 2 received eight data points each, but RSU 2 received eight. With the Kalman filter, the variation of the number of data packets improved by 5.16% and 15.36% for 15 and 30 kmph, respectively. At 25, 40, and 50 kmph, the transition among the RSUs is perfect with 0% variation for each of them where they improved the variation of the number of data packets by 52.84%, 7.87%, and 30.28%, respectively. The small percentage of discrepancies that are still present might be caused by the asymmetrical movement of the traffic and the erratic behavior of the radio signal. At 15 kmph, RSUs received a total of 37 data packets which imply the reception of one data packet every 25.9 m. Similarly, with 25 kmph and 30 kmph, each data packet is received in every 32 m and 38.4 m. This clearly shows a regular pattern of increased distance to receive one packet of data from the vehicle. So, with a higher speed like 40 kmph and 50 kmph, the OBU can transmit a data packet every 40 m and 53.34 m respectively with smooth transitioning between the receiving RSUs which denotes the stability and reliability of the proposed architecture. It is mention-worthy that all the data packets sent by the OBU are successfully received by RSU 1, 2, and 3 with no loss of data packet for both of the tests- without Kalman filter and with Kalman filter. Therefore, the achieved packet delivery ratio of the proposed architecture under a practical scenario is 100%. It denotes the reliability and the robustness of the architecture. The OBU takes an average of 4.57 s for completing one cycle, thus to collect, parse, and send the data to the RSU and other vehicle defined by the algorithm 1 and 2. This time period is very important for the real-time applications of the V2X. This time period can be improved further by implementing the architecture with the processing unit of higher clock speed and higher memory.