# Experiencing LoRa Network Establishment on a Smart Energy Campus Testbed
## 2 LPWAN and LoRa
### Related Works
The study applied 3 channels and a 1% duty cycle as the fixed parameters and simulated the packet reception ratio for a given packet length and number of nodes. As a result, although the packet length is small at 10 bytes, the packet reception rate decreases exponentially because of the increasing number of collisions as the number of nodes increases. Notably, it converges to almost zero when more than 1500 nodes are deployed. On the contrary, a small number of nodes decreases the probability of collision, but the throughput is limited by the duty cycle. [PERSON] et al. [21] analyzed the scalability of large-scale LoRaWAN using the NS-3 simulator. LoRa MAC has been modeled as a pure ALOHA network that does not consider the capture effect or interference characteristics. Instead, the authors generated a LoRa error model from a preliminary simulation that measured the bit error rate on the baseband and used it as an interference model in the simulator. The simulation result shows that the packet reception ratio varies depending on how SF values are assigned when nodes are deployed. Performance is very poor when all nodes have the same SF. Assigning SF values randomly results in better performance than the fixed SF assignment, but it is still low: only a 20% ratio with 5000 nodes. They improved the performance by about two times compared with the random assignment method by using a PER (packet error rate) strategy that assigns the minimum SF value at which the PER falls below a certain threshold. The authors ran another experiment that set the size of an application payload to 8 bytes and used a single channel. In this experiment, they increased the data period from 600 s to 60,000 s, varied the number of gateways from 1 to 4, and then evaluated MAC performance. Their results confirm that the PDR increases exponentially as the data period increases. With respect to the gateways, the PDR achieves 70%, 89%, and 96% when 1, 2, and 4 gateways are deployed in an area with 10,000 nodes that send data every 600 s. This illustrates the possibility of using multiple gateways to improve LoRa performance in a dense environment. Our experiments used the LBT scheme on multiple channels, so it is impossible to compare our results to theirs directly. However, both results indicate that there is a trade-off between the number of nodes and the data period to achieve a given level of LoRa MAC performance. [PERSON] and [PERSON] [22] applied a Carrier-Sense Multiple Access (CSMA) technique to LoRa to improve LoRa scalability. When a node has a packet to send, it performs a Clear Channel Assessment (CCA) to test whether there is an ongoing transmission on a channel. The node transmits the packet only if the channel is clear; otherwise, it backs off for a random interval of time, with \(k\) slots of 1's, where \(k\in[0,2^{n}-1]\). The authors further proposed CSMA-10, a variant of CSMA, where the node listens to the channel, named the Clear Channel Gap (CCG), for an interval of 10 ms before attempting transmission. Their experimental results show that the proposed method can mitigate the probability of packet collision. This allows the deployment of 5500 nodes with a 90% PDR, whereas a general LoRaWAN deployment only allows less than 500 nodes to achieve the same packet delivery ratio.