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Radionavigation – The Future Direction Professor David Last President, Royal Institute of Navigation1 Kensington Gore, London SW7 2AT, United Kingdom E-mail: president@rin.org.ukAbstract This keynote paper takes an overview of radionavigation. It contrasts the focus on transportation in thewest with the focus on consumer applications in Japan. Currently, radionavigation worldwide appears to bedominated by global satellite systems, chiefly GPS. The paper... [收起]
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Radionavigation – The Future Direction

Professor David Last

President, Royal Institute of Navigation
1 Kensington Gore, London SW7 2AT, United Kingdom

E-mail: president@rin.org.uk

Abstract
This keynote paper takes an overview of radionavigation. It contrasts the focus on transportation in the

west with the focus on consumer applications in Japan. Currently, radionavigation worldwide appears to be
dominated by global satellite systems, chiefly GPS. The paper poses the key question of why any alternative to
GPS might be required. It assesses the arguments in respect of: independence of the US; a share of the market;
the need for more satellites and also more accuracy and integrity; the vulnerability of GPS to interference and
jamming; and GPS’s limited performance indoors. We see that alternatives are required not merely to GPS but
to satellite systems in general. Indeed, in the extreme case of aviation, GPS is unlikely to play any major role in
the near future. For other applications and modes of transport, the case for a terrestrial backup to satellite
systems, and specifically Enhanced Loran (eLoran), is examined. The paper concludes with the author’s
predictions as to the likely future mix of radionavigation systems.

1. INTRODUCTION aviation and maritime GPS systems. But they
recognise that transport is now only a tiny,
Let us take an overview of radionavigation, specialised, part of a radionavigation market that is
where we are now in 2007 and where we are heading. dominated by car navigators and cell-phones - and
even games.
We live in a world where for most people
“radionavigation” means satellite systems, and To the general public, and to many navigators,
satellite systems mean GPS. To understand some of location technology and GPS are now one and the
the fundamental things about GPS, curiously, it pays same thing. Even among navigation professionals,
to look at Japan. GPS is the reference point. They ask: Why on earth
use anything else?
Japan was one of the first countries to see the
potential of GPS. It pushed ahead rapidly with a 2. GPS – WHY USE ANYTHING ELSE?
range of consumer products, eventually establishing
the largest GPS user base in the world, plus a Why set up another satellite system, or retain a
substantial manufacturing industry for satellite terrestrial one? That is the key question in
navigation equipment. GPS sales in Japan have been radionavigation policy. It lies at the heart of the
out of proportion to the size of the country or its European Radionavigation Plan, the US Federal
economy. Well over 10 million car navigators are Radionavigation Plan, and national plans across the
now in use, and the overwhelming majority of the globe.
population have cell-phones, many of which are now
GPS-equipped. There are, of course, some good reasons we
should examine for considering alternatives and
In contrast, when we review radionavigation in additions to GPS: some are political, some
conferences like this in Europe or the US, we think commercial, and some technical.
immediately of the various modes of transport –
especially maritime and aviation - and we tend to 2.1. Ownership and independence
concentrate on a few safety-critical applications.
Only then do we perhaps consider the use of The most powerful argument, the one that has
radionavigation on land and for timing or other driven the development of Galileo in Europe, is that
purposes. The viewpoint is almost always that of a of ownership - the independent control of your own
state provider, or a professional user, of navigation satellite system. Many people have now come to see
services for transportation. GPS as a public utility. Even without considering
transport, the loss of GPS would seriously damage
In Japan, however, they speak first of users and our industry, commerce and telecommunications.
equipment manufacturers and of markets; they focus Yet, control of this increasingly vital part of our
on consumers. Of course, they too have important national infrastructures is in the hands of the US.
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US policy, however, is: to “limit availability of” System (QZSS). But those satellites will serve
its “radionavigation systems in the event of a real or Southeast Asia only, not the whole world like
potential threat of war, or impairment to” US Galileo. And China is talking about its own system.
“national security”. Recent events have shown that So there could well be a lot of satellites up there
the US view of national security is not always the soon, something that will improve the service for
same as Europe’s. everyone.

But, can we truly be independent of GPS? The 2.4. Better accuracy and integrity
US has said that if Europe operates Galileo in a
theatre of conflict from which it has withdrawn GPS, The accuracy of GPS is dominated by
it will jam Galileo! That leaves little room for uncertainties in the time delays as the signals pass
European independence. And at the same time, through the atmosphere, enroute from satellites to
Europe is also recognising that there is very little receiver. We achieve the highest accuracy by using
market for a totally independent Galileo, with augmentations in addition to GPS.
separate Galileo receivers and paid-for services.
These systems: WAAS (Wide-Area
So, Europe and the US have now agreed to use Augmentation System), EGNOS (European
the same codes and frequencies. This will let low- Geostationary Navigation Overlay System), MSAS
cost receivers pick up both GPS and Galileo. Users (MTSAT Satellite Based Augmentation System),
will neither know nor care that there are two separate maritime coastal radio beacons, Eurofix, and others,
systems. Galileo, and Japan’s proposed new QZSS are all designed to give higher accuracy by the use of
too, will cooperate with GPS, not compete with it. differential navigation techniques. Each of their
So, probably, will future satellite systems from China reference stations monitors the GPS satellites
and India. I suggest: independence is a myth, received at a precisely known location. It determines
although one powerfully attractive to European the errors in the timing of the incoming signals.
politicians! Corrections for these errors are then distributed to
users’ receivers, which apply them and so achieve
2.2. A share in the rewards metre-level accuracy, or better.

Another driver for Galileo is Europe’s wish to These augmentation systems also deliver higher
share in the economic rewards of satellite navigation. integrity: that is, they ensure that receivers truly are
The US has stated that Galileo has “generated a huge where they say they are. And if a satellite goes faulty,
… commercial … industry” for it. European nations the reference stations detect the fault and tell the
naturally want their share of this industry and see users immediately. But these augmentations are not –
launching their own satellite system as the key to as many people think - radionavigation systems;
getting it. without GPS itself, they are of no use.

But, remember this: Japan has shown that you 2.5. Interference and jamming
do not need to own and operate a satellite system to
make money from satellite navigation. For every Because of the very weak signals received from
navigation satellite, there may be a million receivers, the satellites, GPS is vulnerability to interference and
each with a display system and many with jamming. The US Government’s Volpe Report spells
communications capabilities. So, the money is made out the risks we take if GPS is our only means of
on earth, not in space! It seems that “sharing the navigation, or the only source of precise timing for
rewards” by running your own satellites may be our telecommunication networks, as it often is.
another politicians’ myth.
The Report says that: interference to GPS,
2.3. We do need more satellites whether unintentional or intentional, can be reduced
but never eliminated; that losing GPS would cause
Certainly, having more satellites is a good thing. severe safety and economic damage to the US; that
The shortage of satellites is especially felt on land, GPS is a tempting target to individuals, groups, or
especially in city centres with their urban canyons. countries hostile to the US; and that GPS can be
Galileo, if it comes to fruition, will add some 30 jammed, or receivers spoofed into giving hazardously
satellites to the 30 of GPS. That will mean 60 misleading information. It recommends the use of
satellites in total - and not only for Europe, but for backup systems and procedures in critical
the whole world. applications. The US Department of Transportation
(DoT) has worked hard to develop these.
Japan is planning to add even more GPS-
compatible satellites with its Quasi-Zenith Satellite A jammer that radiates a signal of just one
milliwatt (one thousandth of a watt) can kill GPS
第2页
throughout a building, a more powerful one across a do need more satellites than GPS offers so a Galileo
wide region. Such a jammer can prevent GPS from system compatible with GPS could bring better
working on vessels entering harbours or operating in accuracy and integrity. Then, we will continue to
coastal waters. It could block GPS receivers in need to augment GPS in order to achieve the highest
phones, cars, and aircraft and disrupt the use of GPS accuracy and integrity. We will still need
for synchronising cell-phone sites and the electric augmentations even with Galileo. GPS is vulnerable
power grid. I doubt that in most European countries to interference, jamming and spoofing. So, too, will
there is anyone equipped, trained and legally Galileo be and any other satellite system that shares
authorised to track down a powerful jammer installed the GPS frequency bands. And, no satellite system
in a car and operated intermittently. works satisfactorily indoors

There are many examples of unintentional GPS 3. ALTERNATIVES TO SATELLITES
interference. In one Californian harbour, a couple of
cheap TV antenna units went wrong, causing GPS From these arguments, it follows that we also need
receivers to stop working, or give wrong positions, non-satellite systems, that is, terrestrial systems.
on every vessel in the harbour and for a kilometre out What will these systems be? For many modes of
to sea. It took months to track down the interference. transport, at least in the short term, they will simply
be the systems we used before GPS appeared.
There are GPS jammers for sale on the Web. It
has been said that GPS is a bit like the computer 3.1. Aviation
business before the first virus. I believe we will see
more intentional jamming as GPS is increasingly Take aviation as an example. It has its own
employed for road user charging. navigation technologies, which are well-established,
proven, and standardised world-wide. Indeed, after
2.6. Navigation indoors 29 years of GPS satellite operation, aviation is only
now beginning to get satellite-based landing systems
Imagine that your mobile phone worked well with the availability, accuracy, integrity and
when out in the countryside and in suburban areas. continuity of the Category 1 Instrument Landing
But in the city centre it became intermittent, and System (ILS) first demonstrated in 1938! The US
indoors it stopped working. Our GPS location Federal Aviation Administration has backed off from
services are rather like that. GPS goes from working its satellite-only policy and is providing very little
reliably and accurately on open sites, to not working support for the Local Area Augmentation System
at all deep inside buildings. (LAAS). Neither WAAS nor EGNOS has yet made
much impact in aviation. Indeed, last year’s sales of
Indoor navigation is now a key technical traditional ILS installations were the highest ever. In
battleground, with a range of competing aviation, satellite navigation will win out in the long
technologies. Some researchers try to receive GPS term, but we should not hold our breath!
ever further inside buildings, using very sensitive
receivers with massively-parallel correlators and 3.2. eLoran
passing information to the receiver via a mobile
phone data link, to assist in the acquisition of the For marine and land navigation, the US Volpe
GPS signals. Others use cellular signals for locating Report suggested a role for Loran-C. It described
devices indoors. Both techniques are unreliable and Loran as a viable navigation system for coastal
fairly inaccurate. Another method is to install GPS- maritime operations, for tracking on land, for tele-
like beacons throughout buildings in an attempt to communications timing, and as a potential backup for
provide seamless coverage, outdoors and indoors; aviation. The US DoT set Loran tough goals in terms
that works but it can be very expensive. Then there of accuracy, integrity, availability and continuity:
are systems that employ the WiFi installations within maritime harbour entrance, aircraft instrument
buildings to provide location data. The solution to approaches, and Stratum 1 telecommunications
high-quality indoor navigation may even turn out to timing. The investment of considerable sums of US
be tiny inertial sensors, not radionavigation at all! government money resulted in the development of
But all researchers are agreed: indoors, we certainly Enhanced Loran (eLoran), a high-quality up-to-date
need something beyond conventional GPS. version of Loran, now set to supersede Loran-C.
ELoran met all those goals, and demonstrated cost-
2.7. Summary benefits.

Let us summarise the reasons for considering Let us assess eLoran as a complement to
alternatives to GPS. Owning satellites does not give satellite navigation using the criteria discussed above.
you independence, does not guarantee you a new First, it is owned by individual nations or regions,
industry - and is impossible for most nations. But we which directly share in the rewards. Then, its low-
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frequency signals penetrate forests and are received powerful, more user-friendly, and more cost-
in places GPS does not reach: urban canyons, and effective.
even underground car-parks. The accuracy of
differential eLoran approaches that of GPS, and it has Radionavigation does not pollute the
built-in integrity checking. Loran’s powerful signals atmosphere or have a significant carbon footprint! As
are some 10,000 times less vulnerable to jamming we plan the future, we need to continue to monitor
and interference than the very weak signals of GPS. these developing navigational technologies which
And an eLoran function now can be added to, and promise greater safety, lower costs and more efficient
integrated into, a GPS receiver at low cost. That operations for users at sea, in the air and – most
combination of eLoran with GPS in a single receiver, important of all – for professionals and consumers
closely integrated so as to ensure that eLoran takes alike - on land.
over seamlessly if GPS fails, can give very high
levels of availability, continuity, accuracy and
integrity.

4. THE FUTURE RADIONAVIGATION MIX

So, let me suggest that radionavigation in the
future will consist of:

• GPS in its present form, with future
improved versions to follow.

• Other satellite systems, possibly Galileo and
Compass globally, and QZSS systems
locally. All systems will be mutually
compatible, with receivers mixing and
matching the free-to-air signals of the
various systems. As now, military and
specialised users will employ additional
signals radiated by the same satellites.

• GPS augmentations, including WAAS,
EGNOS and MSAS, maritime radiobeacons,
and Eurofix. Such augmentation systems
will be extended to carry corrections of
additional satellite systems, and possibly
other specialised data services too.

• For aviation, traditional navigation systems
will continue in the short and medium term.
In the longer term, ILS and DME (Distance
Measuring Equipment) will continue, but
NDBs (Non-Directional Beacons) and VOR
(VHF-Omni Range) facilities will be closed.

• Enhanced Loran, principally for maritime
and timing use, with some aviation use.
Low-cost eLoran units will be added to
satellite receivers, integrated so as to take
over seamlessly should GPS fail.

• And, indoor navigation? No technology has
yet emerged as the clear winner.

Radionavigation goes on developing fast and its
markets are expanding rapidly. It is a highly
successful technology, especially GPS, and a star
among science-based, high-tech, industries with
vigorous growth, and products that are ever more
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