Extending 5G to Narrow Spectrum Allocations

5G New Radio (NR) has been a great success story since its introduction. It offers high reliability, low communication latency, flexibility, and efficiency that further enable 5G networks to be used for mission critical applications. Currently, there are specialized networks serving industry verticals that would benefit from the NR properties. Key use cases include communications for critical infrastructure such as railways, public safety, and smart energy and infrastructure. These networks often use dedicated spectrum allocations that are narrower than the original minimum operating bandwidth of NR. In this paper, we describe how new flexibility is being introduced into the NR design to allow operation with bandwidths between about 3 and 5 MHz. As a use case study, we focus on railway communications, and study the co-existence of the Global System for Mobile Communications–Railway (GSM-R) and Future Railway Mobile Communication System (FRMCS) based on NR during the decade-long migration period. We discuss the changes required for the NR control channels and signaling and study the effect of the changes on the system performance.