## 3 Communication Technologies for Improved Energy Efficiency and Safety in Railways
### Narrow-Band Internet of Things for Distributed Supervision and Control  
As mentioned earlier, 5G New Radio (NR) networks have already superseded the bandwidth and data throughput of GSM-R networks, thus becoming instrumental for the introduction of novel technologies in future railway Information and Communication Technologies (ICT). These may include Industrial IoT and other \"cross-industry\" solutions for traffic system integration with other industrial or public systems [108]. These can be broadly classified as wide-bandwidth (i.e., high data rate) services such as real-time video data feeds, and narrow-bandwidth (low data rate) IoT services such as those related to metering (low refresh rate sensors) [134]. About two-thirds of total IoT applications are characterised by low data transmission rates [134], thus making NB-IoT a pervasive technology and emphasising the need for highly reliable NB communications in the future Industrial IoT framework. Some of the key characteristics of NB-IoT systems include [134] (i) a low power consumption, which makes them highly autonomous as they use battery power alone (with battery lives extending well over 10 years); (ii) enhanced coverage and low latency sensitivity; and (iii) compatibility with LTE cellular networks. These features make the NB-IoT devices that are already present within existing mobile networks good choices for a multitude of services in areas with poor signal coverage [135]. Moreover, there is a possibility to use these systems for a wide variety of purposes, such as security and safety, logistics and transport, agriculture, manufacturing, health care, as well as smart city, smart home, retail, utilities, and energy applications [136], as shown in Figure 5. In railways, user data can be weather-related (precipitations, wind speed and direction, relative humidity, temperature, and similar), as well as security information-related (e.g., occupancy and motion detection). To make the NB-IoT technology even more pervasive, new access methods for multiple devices are currently being investigated [137], along with data transmission error correction solutions [138] and intelligent queuing and data traffic prioritisation algorithms [139]. Since a railway system's safety integrity level (SIL) primarily depends on the closed and limited safety functions of a product or a system that is used within it, the utilisation of extended-reliability components would favourably affect the final SIL level. Since NB-IoT devices are frequently designed with a long service life, autonomous operation, and high reliability already in mind, their utilisation may contribute to the SIL level improvement. This may be achieved by using a transmission code and safety code [140] along with different cryptographic techniques [141] to ensure the correctness of data transfer, which can be easily programmed within the NB-IoT node embedded microcontroller system. It is also critical that the latter possesses a fault-tolerant architecture [142], wherein using tried and tested hardware would also increase the microcontroller system reliability [143]. By  
Figure 5: Key features of narrow-band IoT technology based on cellular LTE networks [131]. using all of these measures, it would be possible to achieve a high SIL 4 level of the NB-IoT remote sensor node, which would be characterised by less than \(10^{-9}\) faults per hour (see discussions in [142; 144]), which would be required to reliably monitor the integrity and safety required by the monitored systems [145]. Naturally, a safety analysis should be performed at all operational stages of the equipment lifecycle [146]. A principal schematic depicting the structure of an NB-IoT sensor node and its communication with the host (server) is shown in Figure 6 for the case of collecting the atmospheric data along the track (i.e., temperature, relative humidity, and wind speed and direction) presented in [36]. There, the remote sensor node provides unstructured data for processing to obtain useful information about the track conditions.