# An Approach to Designing Critical Railway Voice Communication
## 2 Related Work  
The requirements of the FRMCS for better connectivity, data rates, encryption, and availability, as well as low latency, can be met by 5G radio technology known as New Radio, which appears to be a critical enabler for FRMCS. In [4], the authors evaluate the performance of existing technologies that support off-net communications in the FRMCS. In [5], the authors describe a protocol-based prototype and discuss their results, which demonstrate the key performance indicators of 4G and 5G for critical FRMCS communications. The 5G New Radio latency of critical control communications performance for industrial systems is studied in [6]. The results of the trials, which investigated the signal propagation of the ultra-high-frequency spectrum dedicated to FRMCS, are presented in [7]. The FRMCS' capacity for satellite communications is evaluated in [8]. Railway communication applications require extended coverage, especially in tunnels and mountainous areas with highly ridged reliefs, and 5G New Radio provides advanced features such as beamforming and Integrated Access and Backhaul (IAB). The use of the IAB technique for traffic transmission in densified networks is illustrated in [9]. Beamforming allows for the increase in the signal strength for particular users for more efficient data transfer and reduces interference. IAB uses the same frequencies as the device it serves to allow for multi-hop backhauling. Direct device-to-device (D2D) communications are also supported by 5G New Radio. D2D traffic does not go through the network nodes. D2D communications benefit the proximity gain, including increased spectral efficiency, higher data rates, increased capacity, lower latency, and power efficiency. The New Radio sidelink capabilities to support vehicle-to-vehicle communications are discussed in [10]. Critical communication and performance applications are expected to use intensive mission-critical (MC) services specified by 3 GPP that required low setup and transfer latency, high reliability and availability, group communication, accurate positioning, prioritization, pre-emption handling, extended coverage, and strong security [11]. The latency of 5G is projected to be up to 1 millisecond, which is 200 times faster than 4G, the connectivity reliability is projected to be 99.999%, and the maximum data speeds are projected to be 10 Gbps. Due to the low latency and ultra-high reliability of 5G communications, MC services can offer functionality beyond traditional Push-to-Talk services, including group chat, accurate positioning, prioritization, and emergency handling. In [12], the authors evaluate the capabilities of 5G New Radio to support mission-critical services that require efficient group communications, traffic prioritization, and accurate positioning. Group applications are used in one-to-many and many-to-many communications. In 5G, mission-critical services allow for group configuration, the identification of group members, the provision of group status data, and a mechanism for authorizing membership or affiliation. In railways, mission-critical group communications allow for connectivity between train drivers, controllers of the train, and infrastructure managers, allowing for multi-train voice communications between drivers and ground users in various use cases such as train control, banking, or shunting. The accuracy of positioning in representative simulation scenarios in 5G networks is evaluated in [13]. Information about the train's velocity, acceleration, and displacement can be provided by 5G positioning. This allows for the building of digital track maps to improve railway safety and efficiency. The digital track map combined with a variety of sensors, which gather critical train positioning data, can produce continuous and accurate positioning information for controllers and drivers. High-precision positioning allows supervision that ensures the permitted speeds and movements of the trains.