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GNSS Underground Tunnels

Tunnel GNSS: Challenges and Solutions for Underground Navigation

Global Navigation Satellite Systems (GNSS) such as GPS are now just an accepted part of how we navigate the world. I remember a trip I made in the ‘90s, where I travelled from Far North Queensland to Sydney using paper maps. Now I don’t even visit my mother without using ‘satnav’!

This is not because I don’t know where she lives, but I want to take advantage of real time traffic data. This includes possible changes in optimum route as I travel.

To use these signals you need a clear view of the sky. Your mapping software will deal with momentary loss of this view and make assumptions that you are driving safely in a tunnel.

Tunnel Navigation and GPS/GNSS

The need for Tunnel Navigation and Tunnel GPS/GNSS is easy to see, but how can it be delivered? Without a sky view you have no signals, and if you just receive a signal outside and then repeat it underground you will simply have the location of the antenna that is mounted outside – wherever you are in the tunnel.

There are a couple of interesting solutions are currently being trialled. Waze is deploying Bluetooth beacons in tunnels to augment navigation and traffic data for their map users. At Chronos, we partner with Syntony to deliver a simulated GPS satellite signal that transmits the position as if you could see the sky. This allows standard GPS receivers such as a smartphone to position you where you are rather than the equivalent location at street level.

These GPS signals themselves can be transmitted from existing communications infrastructure commonly installed in tunnels to support emergency services communications and mobile networks – a ‘leaky feeder’ coaxial cable network throughout the tunnels.

Road Tunnels

A road tunnel with underground junctions does pose a problem for road users not familiar with the road layout. This is likely to be an increasing issue as cities try to reclaim land for leisure use, cycling and walking rather than the car.

The Autopista de Circunvalación (Orbital Motorway) M-30 in Madrid is a perfect example of this. It is the inner ring road for Madrid, serving the central areas, with many junctions underground – particularly in the southern section.

Initially all at surface level, in the last 20 years or so the Calle 30 (Street 30) project of Madrid City Council has progressively relocated the road into tunnels – the longest motorway tunnels in Europe – and reclaimed land for urban redevelopment.

Metro Rail

As a user, the navigation element is not so important. You will get on and off trains at stations whether there is tunnel GPS or not. However, it would still have use in stations on multiple lines, enabling you to change trains in an efficient way.

In an emergency, the use of tunnel GPS or GNSS could be vital in delivering your location through services such as the European E112. If you were on a station platform, it may well locate you nominally in the middle of the platform but in the tunnel themselves could locate you to within a meter or two.

Metro Personnel Safety and Emergency Services

Tunnel GPS does offer an easy-to-use means of locating all staff working in tunnels. It can also serve as a means of guiding them to ports of safety within the tunnel network. Tunnel GPS is supported by standard GNSS receivers in smartphones and standard issue communications equipment such as handheld radios and so has a relatively low impact on network infrastructure.

Likewise, should a major incident occur, knowing the location of emergency services personnel, who may be operating in zero or near zero visibility, may literally be lifesaving.

Mining Safety and Asset Tracking

The same requirements for personnel safety and guidance to safe places apply in mine systems. The Tunnel GPS system can usually be easily integrated into the mine management suite should leaky feeder infrastructure installed.

This personnel location data can also be useful in managing ventilation and other mine support systems. If a tunnel has no people in it, your management system could reduce ventilation to that area.

As well as people, plant and machinery can also be located using Tunnel GNSS, allowing an optimum use of resources. This also ensures plant is in the mine in which it is most needed.

Autonomous Vehicles

We are still in the early days in the story of Autonomous Vehicles. However, as systems move to Full Automation at Level 5, GNSS position will play a role in maintaining autonomy. Adoption of Full Autonomy would be difficult if the vehicle dropped out of Level 5 when entering a road tunnel.

For mass market passenger vehicles, the cost of an Inertial GNSS system is likely to be prohibitive. An Inertial system adds to the simple satellite systems with information on your trajectory. These systems can tolerate a loss of satellite signals of up to two minutes and maintain your position and bearing.

LIDAR (Light Detection and Ranging) systems will be key in Autonomous vehicles. They detect where you are and where you are heading but can also detect the position/movement of other objects. This enables you to build a 3D picture of your situation in real time.

Level 5 Full Automation is not permitted with a single input. This is why Tunnel GPS is so important in maintaining continuity when the view to the sky is momentarily lost.


Tunnel Navigation and people/asset tracking are now attainable with existing tried and tested GPS simulation technologies. Using communications infrastructure already in place in many instances, and supported by standard GNSS receivers common in smartphones. It offers a step change in navigation and safety critical systems with minimal disruption.


Please visit the Chronos Times area of our website to read the latest Insights and Bitesize articles, learn about our attendance at recent Events and much more.

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