## 5 Conclusions  
Signalling communications have been established through public telecommunications networks via MNOs for railway signalling critical data using 4G and 5G networks. The results demonstrate that the hypothesis is fulfilled since communications between signalling devices based on the prototype can provide the quality of service required in terms of the physical and network layers. The study shows a characterisation of 4G and 5G radio networks, obtaining a non-linear correlation between the signal level parameters and the latency offered by the MNO mobile network. At the KPI level, this study shows how the prototype provides a maximum of 150 ms 99% of the time for low radio values of \(-109\) dBm in 4G and \(-120\) dBm in 5G networks, considering the 500 ms latency threshold allowed for this service. At the system level, it is observed that this system can be extended to the whole signalling system (field elements-IXL, CCC-IXL, among others).  
Figure 9: Field measurements along the Guardo–Mataporquera section from Guardo–Balmaseda Railway Line.  
**Author Contributions:** Conceptualization, A.G.-P. and R.G.C.; Data curation, R.B.A.B.; Funding acquisition, R.G.C.; Investigation, A.G.-P. and R.B.A.B.; Project administration, A.G.-P. and R.G.C.; Software, R.B.A.B.; Supervision, C.B.R.; Validation, C.B.R.; Writing--review & editing, A.G.-P. All authors have read and agreed to the published version of the manuscript.  
**Funding:** This research was funded by Ineco thanks to its Innovation Department under the scope of the 5 siG innovation project carried out during the years 2020-2021.  
**Institutional Review Board Statement:** Not applicable.  
**Informed Consent Statement:** Informed consent was obtained from all subjects involved in the study.  
**Data Availability Statement:** Data presented is original and not inappropriately selected, manipulated, enhanced, or fabricated.  
**Acknowledgments:** The authors would like to thank Thales for the collaboration in the project grating the railway signalling equipment from the Thales laboratory and Adif for allowing these measurements along Guardo-Balmaseda Railway Line. This study is aligned with the plan of deletion of Telephonic Block along approximately 3000 km along the Spanish railway lines.  
**Conflicts of Interest:** The authors declare that there are no conflict of interest regarding the publication of this paper.  
**Abbreviations**  
The following abbreviations are used in this manuscript:  
4G Fourth-generation mobile communications  
5G Fifth-generation mobile communications  
CCTV Closed Circuit Television  
CDF Cumulative Distribution Function  
dB Decibel  
dBm Decibel-milliwatts  
DL Downlink  
FRMCS Future Railway Mobile Communication System  
GNSS Global Navigation Satellite System  
GSM-R Global System for Mobile communications - Railway  
IoT Internet of Things  
IP Internet Protocol  
ITS Intelligent Transport Systems  
IXL Interlocking  
kbps Kilobits per second  
KPI Key Performance Indicator  
LTE Long Term Evolution  
MAC Medium Access Network  
MCPIT Mission Critical Push-To-Talk  
MNO Mobile Network Operator  
MTC Machine Type Communications  
ms Milliseconds  
NSA Non-Standalone  
ObjC Object Controller  
OCC Operation Control Center  
OFDM Orthogonal Frequency Division Multiplexing  
PDCP Packet Data Convergence Control  
RLC Radio Link Control  
RSRP Reference Signal Received Power  
SRRQ  
SINR Signal to Interference plus Noise Ratio  
SLA Service Level Agreement  
TAP Terminal Access Point  
UDP User Datagram Protocol  
UL Uplink