Design of a digital mobile radio network for a rail-bound mission-critical wireless network

Abstract

The migration from analogue to digital communication systems has become a strategic imperative for industries that depend on mission-critical communication (MCC), such as the railway sector. This study investigates the feasibility and implementation of a Digital Mobile Radio (DMR) network as a replacement for the legacy Private Mobile Radio (PMR) analogue infrastructure used in railway MCC. The research evaluates various digital technologies—Terrestrial Trunked Radio (TETRA), Long Term Evolution (LTE) and Digital Mobile Radio (DMR)—through comparative analysis, technical specifications and practical deployment considerations. DMR is identified as the most suitable technology due to its spectrum efficiency, superior voice quality, low power consumption and cost-effectiveness. A pilot DMR site was designed and configured using Wireless Radio Planning (WRAP) simulation software, incorporating link budget calculations, antenna configurations and terrain-based propagation modelling. The pilot site was implemented to validate the simulation outcomes, using a Tait TB9300 repeater, Webb CR400 antenna and Hytera PD785 handheld radio. Measurements focused on key performance indicators, including Received Signal Strength Indicator (RSSI) values ranging from −72 dBm to −119 dBm; harmonic distortion, with second and third harmonic suppression of 56.87 dB and 59.30 dB respectively; and system power efficiency, achieving a 57% reduction in current consumption compared to analogue mode. The results demonstrated close correlation between predicted and actual performance, with a mean absolute percentage error (MAPE) of 2.53%. The DMR system met regulatory requirements, including harmonic suppression thresholds set by the Independent Communications Authority of South Africa (ICASA) and the International Telecommunication Union Radiocommunication Sector (ITU-R), thereby affirming its technical compliance and operational robustness. This research presents a validated implementation model for adopting DMR in railway communication systems, supporting reliable, scalable and secure voice communication infrastructure for Transnet and other mission-critical applications.