Doppler Shift in a Radiating Cable System in Tunnel Environments: A Theoretical Analysis
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© 2019, Springer Science+Business Media, LLC, part of Springer Nature.For many years, radiating cables have been used to provide coverage inside tunnels or underground venues. Due to the progress in transport technology and the increasing demand on mobile communications the necessity of having a clear understanding of the behaviour of the wireless channel in these environments is essential to successfully deploy radiating cable systems. In this context, the main objective of this paper is the study of the Doppler shift generated in a radiating cable system due to a mobile receiver changing positions along a defined path inside a tunnel. Doppler shift is an important effect in mobile communications as it degrades system performance. The study shows that a correct selection of the operating frequency used for the radiating cable can help reduce the Doppler shift and in turn the Doppler spread in the channel. At the same time the study reveals how the Doppler shift of a radiating cable generated by a fast-moving user is related to its radiation pattern, especially at the cable terminations. Finally, Doppler spread is accentuated when the cross section of the tunnel is reduced. These results can be used as a reference for improving the design of radiating cable systems applied in mobile communications with fast-moving vehicles, e.g. high-speed trains.