Research
Brief
Data analysis for a cost effective Global Navigation Satellite
System based locator with simple augmentations
T892 - October 2013
Background
This research was carried out on behalf of the Future
Communications and Positioning Systems Advisory Group
(FC&PS) a sub group of the Vehicle/Train Control and
Communications System Interface Committee (V/TC&C SIC) and
has shown that requirements for many railway applications can
be met by low cost Global Navigation Satellite Systems (GNSS)
based solutions that are suitably designed and configured.
A 'low grade' solution comprising a high sensitivity consumer
grade GNSS and single axis (heading) gyroscope can be used to
improve position availability if it is augmented with inputs from
other systems such as an odometer and change of direction
indicator and uses appropriate hybridisation algorithms.
There are many current and future rail applications in which
location is the key element. GNSS in rail offers potential, but there
are availability and integrity issues to consider. This research has
trialled a series of equipment types and hybrid design solutions in
a railway environment, to assess their ability to address these
'problem' areas.
Aims
The aims of this research were:
 To develop a locator interface specification. This is intended
to help the system developer to understand the GNSS
receiver formats and data inputs that are needed.
 To identify railway applications requiring location
information and how GNSS might be able to support these.
 To provide guidance on the use of GNSS in general and to
provide support for an up-date to RSSB Guidance Note GE/
GN8578 - Guidance on the Use of Satellite Navigation.
 To evaluate options for increasing the availability of
positioning information through GNSS and the use of simple
augmentation solutions to provide this.
RSSB R&D Programme
Block 2 Angel Square
1 Torrens Street
London EC1V 1NY
enquirydesk@rssb.co.uk
www.rssb.co.uk/research/pages/
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Data analysis for a cost effective Global Navigation Satellite System based locator with simple
augmentations
T892 - October 2013
Findings
The findings of this research have re-enforced those found in
previous research (RSSB Projects T510, T671, T042, T031 refer)
that GNSS on its own, can typically provide a horizontal accuracy
of between three to five metres with an availability of 95% in an
'open sky' environment. As noted previously, this level of
performance is highly dependent on this particular environment.
The augmentations and enhancements deployed during this
research have led to a number of significant improvements in
performance over those observed previously. Examples have
included performance during GNSS outages where the
equipment has been dependent on detecting a GNSS signal as a
train traverses a short 40 metre open area beyond a road over the
track, before entering a tunnel some 160 metres in length and
then stopping at a station on exiting the tunnel.
In this example, a high grade solution (see description outlined
below) showed a position error before entering the tunnel of some
1 to 1.5 metres and an error of 1.5 to 2 metres on exiting. In
contrast, a medium grade solution (see description outlined
below) recorded an error of some 300 metres, as the three axes
accelerometers were not correctly detecting the stop after exiting
the tunnel, (so the first solutions flagged as 'with GNSS' after the
outage, were probably giving little weight to the overall solution).
A low grade solution however (see description outlined below),
when augmented by inputs from the odometer and direction of
travel indicator, was able to give an error before entering the
tunnel of 1 to 3 metres and an error of only 2 to 6 metres on
exiting.
This was found to be consistent for the low grade solution during
more demanding outages as the trains travelled through
Birmingham New Street station. In this area there are periods of
15-20 minutes in which satellite signals are available only
intermittently. Even in the worst cases the errors from the low
grade solution only increase by 20 to 30m. Analysing
performance using all GNSS outages up to 30s shows that in 95%
of cases the error increase is less than 8m.The performance of
the low grade receiver remained comparable to or better than the
high grade professional receiver throughout this period which
demonstrates the usefulness of this approach. It should be noted
that few areas on the GB rail network routinely demand a GNSS
outage of more than 30 seconds during normal operations.
The research has demonstrated that GNSS works well in open
environments. However, the low grade solution comprising a high
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sensitivity consumer grade GNSS and single axis (heading)
gyroscope can be used to improve position availability if it is
augmented with an input from other systems such as the
odometer, change of direction indicator and uses appropriate
hybridisation algorithms. More complex and expensive solutions
have not so far been able to demonstrate better results than those
obtained using this method.
This research concludes that the requirements for many
applications on the railway can be met by low cost GNSS-based
solutions that have been suitably designed and configured.
Deliverables
This research has provided:
 A Locator Interface Specification - this defines the standard
GNSS receiver formats and the essential data inputs that
are needed.
 A Locator Architecture report - This document outlines a
standard architecture design for the locator.
 An Applications Catalogue - this has identified more than 50
potential applications covering:
 Signalling and control
 Operations applications
 Engineering applications
 Client applications
 Infrastructure operations
 RSSB Project T990 - Development of a strategy on train
positioning, developed as a result of this work.
 A Requirements Analysis document - this defines metrics,
assigns values and allocates these to the potential system
components.
 A Data Analysis report - this provides an analysis of position
results from the research.
 A Database and Viewing tool - the research data and use of
a proprietary (Google Earth) viewing tool.
 A GNSS Buyers' Guide - this is intended to provide a quick
reference guide and is structured around a series of
questions and answers. It provides guidance on choosing a
GNSS receiver and understanding product sheet
specifications.
 A report comparing Hand-held vs On-train GNSS Receivers
- this compares the performance of inside vs roof antenna,
where availability is similar, but accuracy is poorer. The
report notes a significant variation in performance between
devices that is determined by the processing algorithms as
RSSB
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Data analysis for a cost effective Global Navigation Satellite System based locator with simple
augmentations
T892 - October 2013
well as the basic conditions and components. The report
concludes that hand-held devices may be suitable for less
critical railway applications.
 Recommendations on how to update Guidance Note GE/
GN8578 - Guidance on the Use of Satellite Navigation
These documents have been published on the RSSB SPARK
system. They demonstrate the results of a series of practical trials
of GNSS systems in a railway environment and are intended to be
of interest to system developers, train operating company
engineering and operations staff and anyone who has a general
interest in the use of GNSS systems within a railway environment.
Method
GNSS equipment sets using a variety of receiver types and
complementary sensors were trialled. These included:
 A low grade solution, comprising a high sensitivity GNSS,
single axis gyroscope, odometer and direction of travel
input.
 A medium grade solution comprising a high sensitivity
GNSS, three axes gyroscopes and three axes
accelerometers.
 A high grade (reference) solution comprising a professional
GNSS, three axes gyroscopes and three axes
accelerometers.
These equipment sets were trialled on a Class 323 electric unit
London Midland train on the Redditch to Litchfield route. This was
a repeatable route, operated over demanding conditions, through
multiple track layouts, and included low speed operation through
Birmingham New Street Station.
Additionally, equipment used previously on RSSB Project T510 Obtaining data to assess the dependability of GNSS information
and accuracy of odometry - comprising two survey grade GNSS
receivers with an integrated inertial system, was enabled for
EGNOS (European Geo-stationary Navigation Overlay Service)
high sensitivity GNSS via a software up-grade. This equipment
was operated on a Class 170 diesel unit operated by Greater
Anglia on the Norwich to Cambridge route, at both low and high
speeds in an 'open skies' environment through remote areas.
The trials involved dividing the track into 100 metre sections and
assessing the performance per section from multiple journeys for
satellite availability, position availability and position accuracy.
Plots were drawn for the average number of satellites in each
section, average signal to noise values, and accuracy per track
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section. A statistical analysis was then prepared for like
environments, including obstructed (urban), intermediate (interurban) and open environments.
Next Steps
This research was intended to be of use to the railway industry
primarily in the area of systems development by providing
practical trials based experience of the performance of a number
of GNSS systems and simple augmentations in a railway
environment. It provides an overview of the GNSS locator
interface requirements and architecture, and is intended to be of
use to train operating company engineering and operations staff
who will be required to work with these systems.
The findings of this research now provide guidance and support
to those who may be new to the area of GNSS and who may need
to consider a purchase of GNSS, by providing an understanding
of the basic concepts, performance and design options for the
systems that are presently available.
In this respect, it will help a number of decision makers in the
railway industry to better understand the capabilities and
limitations of GNSS and the list of applications that this
technology might be able to support. It will help these staff to
choose appropriate technology solutions and design options and
help them to avoid over specifying these systems to meet their
application needs.
The output of this research is already being used in support of
RSSB Project T990 - Development of a strategy on train
positioning, being developed in support of the longer term vision
for the railway as published within the 2013 edition of the Rail
Technical Strategy.
It will also be used to up-date Guidance Note GK/GN 8578 Guidance on the use of satellite navigation and RSSB is intending
to combine this up-date with further up-dates to related Guidance
Notes GK/GN 0602 - Guidance on train rooftop antenna
positioning and GK/GN 8579 - Guidance on digital wireless
technology for train operation. One option that is being
considered is to combine the guidance provided by these three
guidance notes into one new guidance note. This would draw
upon the work of related projects T739 - Train roof antenna
positioning and performance study and T964 - Operational
communications.
RSSB
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Data analysis for a cost effective Global Navigation Satellite System based locator with simple
augmentations
T892 - October 2013
Contact
For more information please contact:
Head of Engineering Research
R&D Programme
RSSB
enquirydesk@rssb.co.uk
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RSSB