# Building Wireless Control Applications with XBee and LabVIEW
## 2 Related Work  
Several standards are used in process-automation applications, ZigBee being one of the most popular for monitoring applications [9; 14]. This technology provides good support when compared with the Wi-Fi, Bluetooth, and Ultra Wide Band (UWB) standards of the transmission range [15]. In particular, ZigBee networks present some advantages in terms of energy consumption and flexibility, especially in large networks [14]. In ZigBee networks, there should just be one Coordinator node per network that is the controller of the whole network, which is irresponsible for choosing the network channel and organizing it. Since there might be several routes in a ZigBee network, other nodes, Routers, are responsible for maintaining the infrastructure of the ZigBee network. These nodes do not gather data or start the message transmission but only transmit data from router to router, or from the end devices to the coordinator. Finally, end-devices do not route. They are responsible for gathering data and delivering it to the nearby router or coordinator. All ZigBee nodes are designed to be of small size, light weight, and low power consumption. The technology allows the connection of up to 65,535 nodes. ZigBee is suitable for use in monitoring and control applications, such as remote healthcare, industrial control, fire detection, environmental monitoring, and so on [16]. In this work, XBee modules were used. These modules support both the original ZigBee network as well as a vendor proprietary network, known as DigiMesh. In [14], several experiments under different environments have been designed to evaluate the performance of both networks.  
Sometimes different technologies must coexist while using the same bandwidth spectrum, creating severe interference problems. This is the case for ZigBee and Wi-Fi networks, since they typically work at the 2.4 GHz ISM band. Some approaches have been analyzed, in order to alleviate this issue, aimed at achieving a more robust communication [17; 18]. The incipient IEEE 802.15.4e standard proposes a Medium Access Control (MAC) layer that supports collision-free wireless channel access mechanisms for industrial, commercial, and healthcare applications [19].  
ZigBee technology is mostly used for monitoring applications. Nowadays, some monitoring applications have been built over ZigBee, as a result of the introduction of smart grids. In [20], the feasibility of sending messages from intelligent electronic meters to concessionaires, through a ZigBee network, was analyzed. In [21], the networked control of a photovoltaic based AC Microgrid was presented. In this work, both CAN and ZigBee were considered. In [22], ZigBee modules were used for the energy management, efficiency optimization, and metering services, within a smart grid.  
Other applications involved the control of robots or machinery. For example, in [23] the remote monitoring and controlling of robotic arms by means of ZigBee technology was discussed. In [24], a model to control a robotic vehicle by means of using hand gestures with an accelerometer was introduced. In [25], a model predicting a control flocking algorithm aimed at controlling a multi-drone system was presented. In [26], a network-based discrete proportional integral (PI) control aimed at controlling a continuous time linear system was designed. There have also been some works in the field of Industrial IoT. For example, in [27] a monitoring architecture for process automation technologies with low impact on the sensor nodes aimed at industrial set ups was proposed.