# LTM-LoRaWAN: A Multi-Hop Communication System for LoRaWAN
## 4 Performance Evaluation
### Result and Discussion  
The delivery rate for all simulated networks is shown in Figures 6 and 7. Figures display the overall success rate for a network, including the generated traffic by devices located at the border of the area. Both figures clearly show that a better delivery rate is achieved using the proposed mechanism for all the network sizes. Almost a 10% increase in the delivery ratio is attained. This is a result of the success in delivering messages of out-of-range devices via the employed multi-hop strategy. The proposed system is seen to function better with more relaxing networks, a network with 5400 s send interval, as shown in Figure 7. This is expected as much amount of traffic in the network causes an increase in the chance of collisions and hence affects the overall efficiency of the network. This is also the case when the number of participating end devices is increased in the step of 100 devices, as can be seen in the figures. Moreover, it can be noted that distant devices in the one-hop system, standard LoRaWAN, ended up using a higher spreading factor with low bandwidth as a result of employing ADR. The use of such a setting leads to higher time on air for transmitted packets. This, however, would increase the possibility of collisions and consequently decrease the overall delivery rate. Figure 6: Packet Delivery rate for networks—one hour send interval. Figure 8 shows the amount of traffic that has been received successfully by the gateway via two hops using the proposed system in comparison to the overall traffic generated by out-of-range devices. Without the proposed system, the whole amount of sent traffic, illustrated in the figure with the blue line, would have been lost. The other line shows the delivered packets by the proposed system from faraway devices to the gateway. It shows the number of packets that have been saved by the proposed system. It has been achieved as a result of enforcing out-of-range devices to postpone their transmissions until they sense a transmission from one of their adjacent devices. The adjacent device is then used as a relaying device to forward the out-of-range device's packet. As the figure shows, the ratio of delivered packets successfully to sent ones deteriorates as the network size grows, especially with 1000 participating devices. This has been experienced for both systems, as highlighted in Figures 6 and 7, and it reveals the sensitivity of the LoRaWAN network regarding scalability. It is also due to the fact that devices located far away and still in the range of the gateway may use lower bandwidth with a larger spreading factor set using the ADR mechanism. Thus, the used network settings result in higher time on air, which increases the chance of collisions, especially with a larger number of devices in the network, and consequently affects the performance negatively. Figure 9 illustrates the performance of the proposed system in terms of the number of received packets by the gateway, which is under the receiver sensitivity. The proposed system achieves better results concerning this metric where less traffic is received below gateway radio sensitivity compared to the baseline, as depicted in the figure. This can be justified by the fact that the proposed system managed to deliver more traffic to the gateway successfully, as shown previously in Figures 6 and 7. Therefore, the number of lost packets due to arriving below receiver sensitivity is decreased compared to the standard  
Figure 8: Successfully received traffic from out-of-range devices. Figure 7: Packet Delivery rate for networks—one and half an hour send interval. LoRaWAN. It is also due to the ability of distant devices in the proposed system to detect themselves as out of the gateway coverage and consequently adopt a lower spreading factor and delay their transmissions until they hear a signal from their neighbors.