## 4 Active Systems
### From Short- to Long-Range Communications  
Based on RFID characteristics, Near Field Communication (NFC) is a wireless communication interface that works over small distances, typically shorter than 10 cm. Devices using NFC can create their own RF field or retrieve the power generated by another device. The former happens when  
Figure 19: Data rate vs. Range—active radio communication technologies. Figure 18: WUR—active architecture. the device is sending data, while the latter happens when it is receiving. The communication is performed at 13.56 MHz with ASK modulation, with an approximate power consumption of 60 mA. This technology is widely implemented all over the world in smartphones and other tracking devices. The set of applications ranges from simple identification to micropayments [18; 121]. BLE is an evolution of the traditional Bluetooth technology more adapted to IoT solutions. In its latest version, BLE can perform communications at a maximum distance of 1000 m in an open field, and near 400 m indoors. It works at the 2.4 GHz Industrial Scientific and Medical (ISM) band, and it can be used to send data up to 2 Mbit s\({}^{-1}\). Its power consumption depends on the chip used; however, it usually is between 6 mA and 10 mA. In terms of applications, BLE is widely used in devices that need to communicate with smartphones [122; 123]. WirelessHART is a communication protocol built upon IEEE 802.15.4 developed by the Hart Communications Foundation. It uses the 2.4 GHz band to create a mesh network where each participant station serves simultaneously as a signal source and a repeater. This process automatically adapts in the presence of interference from other networks, self-interference, or radio shadows, and it creates a reliable mechanism that occurs until the message reaches the final receiver. The communication is coordinated with Time Division Multiple Access (TDMA), synchronizing the network participants in 10 ms time-frames. WirelessHART modules can have a transmit current of 57 mA when transmitting at 14 dBm, and a current of 28 mA when receiving in high-gain mode. The overall link budget can achieve 122 dB and the data rate 250 kbit s\({}^{-1}\) (IEEE 802.15.4). Regarding its distance of communication, it is pointed to be 300 m indoors and up to 2000 m in line of sight. As mentioned, this technology is particularly interesting due to its resilience and delivery capabilities, which are crucial aspects in Industrial Internet Of Things (IIoT) [124; 125; 126]. Another protocol widely used in IIoT is ISA100.11a, which is by far the most complex and customizable standard. The network works based on contracts between devices that need to be signed before a transmission can occur. These contracts can be periodic or non-periodic [10]. As they are based on very similar hardware, ISA100.11a RF modules have identical metrics in power consumption, range, and link budget [127]. The big difference between protocols resides in its goal, while WirelessHART is designed to establish and assure interoperability between manufactures, ISA100.11a has many options for users to ensure compatibility between devices in the network [10]. Nevertheless, there are also dual-standard solutions that increase flexibility, management capacity, and reduced power consumption due to a decrease in network complexity [125]. The following short-range interface under analysis is IEEE 802.15.4 (standard which defines the physical and medium access control layers of the well-known ZigBee), which is a communication protocol created to communicate small amounts of information. It uses an open standard protocol that can perform communications at a maximum distance of 100 m with a maximum throughput of 250 kbit s\({}^{-1}\). Its power consumption can vary between 10 mA and 12 mA, and it also operates in the 2.4 GHz ISM frequency band. Zigbee is mainly used in home automation as well as in monitoring and control in industrial processes [85; 128].