# MCST Scheme for UAV Systems over LoRa Networks
## 2 LoRaWAN Network Architecture  
LoRa is a physical layer or modulation technique for long-range low-power wireless communication. LoRa generally follows the standard of IEEE 802.15.4 for the low-rate wireless personal area network. LoRa is mainly used to feature low-power operation, low data rate, low cost and complexity, long communication range and long battery lifetime [14; 15]. As shown in Figure 1, LoRa wide area network (LoRaWAN) is organized as a star network topology, in which the end devices connect to the network server through the gateway. The end device is the low-power end device, which supports the services or IoT applications. The gateway is the communication device that connects the end devices in the LoRa network to and from the server. The network server monitors the devices, i.e., the end devices and gateways, services, and applications in the network. On top of the LoRa modulation, as illustrated in Figure 2, there are three classes of LoRaWAN medium access control (MAC) protocol that define how the end device proceeds with the communication. Class A is the baseline in which the end device performs the bi-directional communication which is a set of uplink transmissions from the end device to the gateway, and two short receive windows for downlink trans  
Figure 1: An example of LoRaWAN network architecture. to the end device. The end device may initiate the transmission based on their need according to the random time basic ALOHA-type protocol. The gateway initiates the transmission through class B by sending the PNG packet as a ping message to the end device. Besides, the gateway sends a beacon every 128 s for synchronization purposes. With the synchronized beacon, different from random receive windows of class A, the end device opens the scheduled receive windows for downlink transmission. The end device in class C continuously opens the receive window until there is an uplink transmission. Therefore, the end device uses much more power than class A and class B. Plenty of research works have been proposed on LoRaWAN in different approaches [16; 17; 18; 19; 20; 21]. LoRaWAN generally operates as the standard of pure-ALOHA protocol and has the drawback of a high packet loss rate due to collisions [16]. Therefore, [PERSON] et al. applied the concept of slotted ALOHA and acknowledgment for successful transmission on the design of the LoRaWAN protocol in [17]. This work claims that the throughput gain can be achieved around six times compared to the standard LoRaWAN because of the highly successful transmission ratio. Generally, LoRaWAN cannot be implemented with the handshaking mechanism because the end device in the network does not always listen to the incoming transmission. They only wake up to transmit if they have DATA for uplink transmission. To overcome the high packet loss of the transmission, [PERSON] et al. proposed the modified listen-before-talk mechanism in [18] and shows the improvement of channel utilization with energy consumption even in dense wireless networks. Similarly, the carrier-sense multiple access (CSMA) mechanism is considered in the design of LoRaWAN MAC for reducing the collision and optimizing the channel capacity in [19; 20]. Among the different approaches of the LoRaWAN protocol, the authors in [21] showed that CSMA is scalable in terms of throughput and energy consumption. Similar research work to optimize the consumed energy of the LoRaWAN can be found in [22]. Moreover, the ever-increasing number of devices in the network and the growth of traffic still lead to capacity demand and energy consumption for better transmission performance. The existing research considered the approaches of proposing MAC to realize the transmission, minimize energy consumption and optimize the throughput in the network. The aforementioned research works show a lack of investigation into the approach of the transmission scheme over LoRa networks.