## 5 Simulation Analysis
### Zigbee  
Zigbee is IEEE 802.15.4 based wireless communication protocol that creates a personal area network (PAN) with low energy consumption [32]. Zigbee enhances the battery life of the end devices as it consumes low energy during data transmission. Figure 10 presents the ZigBee architecture where it consists of four distinct layers and they are named as physical layer, medium access control (MAC) sub-layer, network (NWK) layer, and application layer (APL) and is shown in the Figure 10[33; 34]. PHY layer is next to the hardware, and it controls and communicates directly over ZigBee radio. The PHY layer converts the data packets into over-the-air bits during transmission, and vice versa for the reception. MAC layer interfaces the PHY and NWK layers and it also generates a personal network identifier (PAN ID). MAC layer is responsible for network discovery through beacon requests. NWK functions as an intermediary layer between MAC and Application Layers. Furthermore, it manages the mesh networking, i.e., network establishment and routing. Additionally, the NWK Layer protects ZigBee networks by encrypting all data in the NWK Frame. The topmost protocol layer in ZigBee's stack is the application layer, where it comprises ZigBee device objects (ZDO), and the application support sub-layer (APS). Moreover, the manufacturer-defined application objects are parts of the application layer. ZDO is a program that manages and gathers information about a system. The APS sub-layer provides a generic set of services that are  
Figure 9: (a) LoRa based Gateway. (b,c) PCB layout and hardware prototype of safety operation controller. utilized by both ZDO and the manufacturer-defined application objects for enabling an interface between the NWK and APL. ZigBee is quickly expanding the field of The IoT allowing for more efficient wireless sensor-to-machine and machine-to-machine communication. ZigBee is used in industrial monitoring and actuators, home automation, medication, remote sensing, acoustic detection, and smart energy management, among other applications [15; 17]. Advancements in space communication and monitoring system using WSN and ZigBee is analyzed [18]. The ZigBee network is made up of three components, namely: ZigBee routers, ZigBee end devices, and a ZigBee coordinator. ZigBee end device: The end devices are primarily responsible for a ZigBee network's power-saving features. Because these nodes are not used for traffic routing, they can sleep for the majority of the time, extending the battery life of these devices. Zigbee coordinator: This node is in charge of setting up the network, choosing the suitable channel, and allowing other devices to connect to it. In a ZigBee network, it can also be in charge of traffic routing. Zigbee Router: A router can send and receive messages in a network, as well as a link to child nodes, which could be another router or an end device. Figure 11 shows the packet structure employed for communication between transmitter and receiver. Figure 12 depicts the ZigBee framework's working model, in which various network nodes transmit data to the ZigBee coordinator via routers. The simulation was supposed to run for a specific amount of time using the network layer and physical layer characteristics listed in Table 2.  
In this solution, network traffic was formed using those parameters based on the device to coordinator settings. The ZigBee network model's OPNET simulation is tested for examining various network performance indicators. Sent and received traffic statistics, the end-to-end delay between layers, packet delivery ratio, retransmission attempts, and throughput over the channels are all performance parameters of the application and MAC layers. Figure 11: Zigbee Packet structure [35]. Figure 10: Zigbee architecture [16]. * Packet delivery ratio One of the most important performance metrics is the Packet Delivery Ratio (PDR). For all end nodes, the average packet delivery ratio is utilized.