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wireless train communications systems


INTRODUCTION
For wireless train communications systems the Global System for Mobile Communications-Rail (GSM-R) or the Universal Mobile Telecommunications System (UMTS) are standards for passenger communications. Both provide only very limited data rates. The high-speed train communications channel has been published in [3] emphasizing the aspect of unidirectional versus directional antennas. This paper highlights the effect of polarization in this specific environment. Current communications antennas are mounted on the train’s roof, based on the principle of !/4-antennas, which requires an adequate metallic ground plane (with ! being the wavelength). In contrast to handheld mobile devices the alignment of the train antenna will not change with the train motion in polarization, in elevation and merely little in azimuth.



PRINCIPLE
Each mobile uses a separate, temporary radio channel to talk to the cell site. The cell site talks to many mobiles at once, using one channel per mobile. Channels use a pair of frequencies for communication. One for transmitting from the cell site, the forward link, and one frequency for the cell site to receive calls from the users, the reverse link.
Communication between mobile units can be either half-duplex or full-duplex. In case of half-duplex, transmit and receive communications between the mobile units are not at the same time, i.e. talking and listening can not be done at the same time. In case of full-duplex communication, transmit and receive communication is at the same time, i.e. one can talk and listen at the same time.


APPLICATION
Automatic Train operation's critical alarms.
Train status and alarm information
Passenger information system control
Train passenger emergency system
Closed circuit TV system

wireless train communications systems


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INTRODUCTION

For wireless train communications systems the Global System for Mobile Communications-Rail (GSM-R) or the Universal Mobile Telecommunications System (UMTS) are standards for passenger communications. Both provide only very limited data rates. The high-speed train communications channel has been published in [3] emphasizing the aspect of unidirectional versus directional antennas. This paper highlights the effect of polarization in this specific environment. Current communications antennas are mounted on the train’s roof, based on the principle of !/4-antennas, which requires an adequate metallic ground plane (with ! being the wavelength). In contrast to handheld mobile devices the alignment of the train antenna will not change with the train motion in polarization, in elevation and merely little in azimuth. Characteristic for high-speed train tracks is the widely stretched environment along the track with predictable.

Abstract

This paper characterizes the polarization dependence of the high- speed train communications channel. With a three-dimensional ray tracing simulation tool the narrow-band channel characteristics are determined for various polarizations and two typical environments. The results show that the channel characteristics can be optimized by selecting the proper polarization. For this purpose two options result: either the long-term fading amplitude can be maximized or the short-term fading can be minimized.

PRINCIPLE

Each mobile uses a separate, temporary radio channel to talk to the cell site. The cell site talks to many mobiles at once, using one channel per mobile. Channels use a pair of frequencies for communication. One for transmitting from the cell site, the forward link, and one frequency for the cell site to receive calls from the users, the reverse link.
Communication between mobile units can be either half-duplex or full-duplex. In case of half-duplex, transmit and receive communications between the mobile units are not at the same time, i.e. talking and listening can not be done at the same time. In case of full-duplex communication, transmit and receive communication is at the same time, i.e. one can talk and listen at the same time.