# Design and Performance of a XBee 900 MHz Acquisition System Aimed at Industrial Applications
## 2 Related Work  
There are several standards available to be applied in monitoring applications [21]. Some industrial applications developed with wireless technologies are described in [22; 23]. Sometimes, the IEEE 802.11 standard is used at industrial communications, but in general, it does not ensure the QoS requirements. Some studies propose using WiFi coordinated channels to achieve a real-time deterministic behavior at industrial applications [24]. Other studies propose algorithms specifically aimed at control applications [2]. However, these approaches are still experimental, and this technology does not seem adequate for stringent, deterministic applications. The most popular standards used at industrial applications are based on the IEEE 802.15.4 standard, such as ZigBee, WirelessHART, ISA100.11a and WIA-PA [18]. The applicability of this standard to sensor networks for industrial applications is analyzed in [25]. The performance of this standard is compared against Bluetooth and WiFi under various conditions for embedded control systems [26]. Currently, there is a lot of research for introducing new MAC mechanisms to the IEEE 802.15.4 standard that make wireless sensor-actuator networks more deterministic. For example, 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 [27; 28]. Other amendments are also under research, such as the introduction of time-slotted channel hopping (TSCH) techniques aimed at providing more predictable latency, higher energy efficiency and communication reliability [29]. Other experimental approaches aimed at providing deterministic and reliable communication have been proposed in [30]. However, these approaches are still under development and, currently, do not seem adequate for being implanted in production applications. Some of the available IEEE 802.15.4 standards, such as WirelessHART, are starting to be accepted at industrial applications [31]. This standard, specifically aimed at industrial wireless sensor-actuator networks, adopts TDMA mechanisms at the MAC layer to ensure the schedulability of the applications [32]. However, it is not considered safe yet, and new mechanisms are being proposed [33]. In addition, WirelessHART-powered devices tend to be costly. Undoubtedly, the most popular IEEE 802.15.4 technology is ZigBee. One of the advantages of this popularity is the availability of products at a very low cost, such as the XBee series. This technology has been thoroughly used in monitoring applications in different domains, such as remote healthcare, industrial control, fire detection and environmental monitoring. Some works describe the application in smart grids devices [34; 35; 36]. This technology is frequently used in home/building automation applications [37; 38; 39]. It is also an interesting alternative for outdoor applications, such as those found in agriculture [40; 41]. This technology is used very commonly in industrial applications. For example, [42] presents a control and monitoring system for a robotic hand. In [43], it is used for controlling a vehicle. In [44], it is used for the diagnosis and detection of faults, based on power consumption modeling, in an industrial robot. In [46], its application for industrial trace heating is described. In [47], a data acquisition application deployed inside ships is described. The design of a sensor node for structural health monitoring is presented in [48]. One of the advantages of ZigBee/IEEE 802.15.4 technology is that it is the only mainstream technology able to operate outside the 2.4 GHz band [18]. Actually, some applications operate at the 868 and 900 MHz bands [41; 49; 50; 51], proving that XBee modules are already mature modules to be introduced at industrial applications.