Will 4G mobile broadband spell the end of GPS?

A battle is raging on the other side of the Atlantic.

It’s a battle about use of the airwaves, or more precisely “radio spectrum,” by two rival American technologies.

In one corner is the well established Global Positioning System (GPS), the enabler of location services the world over. Facing up in the opposite corner is a fourth generation (4G) mobile broadband network from a company called LightSquared.

LightSquared is currently seeking a Federal Communication Commission (FCC) licence to operate its network and proposes to ultimately install around 40,000 transmitting beacons across the USA.  The network will also be supported by a satellite that is already in orbit.

Our surveyors rely on GPS technology everyday.

The nub of the problem is that the band of radio spectrum allocated to the LightSquared network is adjacent to the band allocated to GPS.  This causes interference to GPS because the LightSquared signals are much more powerful and therefore swamp out the weak GPS signals.  The interference problem has been confirmed by two independent tests.

This is a major problem.

GPS and other satellite systems such as the Russian GLONASS and upcoming European Galileo are now heavily relied upon, not only for positioning (we use the service day-in day-out to help keep Great Britain’s mastermap up-to-date) but increasingly for providing accurate timing, for the mobile ‘phone networks for example.

They are also starting to be used as part of “Safety of Life” systems such as aircraft navigation and landing.

Both camps are lobbying the FCC and fighting their corners.

GPS supporters have formed the “Coalition to Save Our GPS” whilst LightSquared are arguing that GPS has had an “easy ride” and for too long has been allowed to leak outside it’s allocated spectrum.

Save Our GPS

LightSquared have offered a change to the proposed network which involves using different frequencies and lower power at the base stations which they say limits the interference.  However they are also arguing that GPS receivers should be forced to update so that they filter “out of band” signals such as LightSquared’s and also operate more closely in their allotted spectrum.  It would obviously be a long an expensive process to implement this solution.

At the moment, the issue if confined to the United States, but commentators in Europe are also watching the debate with interest since the developing Galileo service uses some of the same frequencies as GPS.

We can expect this fight to rumble on for some time yet…

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21 Responses

  1. Good article. This argument has been rumbling on for quite some time. It seems that some regulatory authorities may be driven more by the $ rather than common sense. We have to hope that the Military and the aviation authority will be able to throw some weight and sense at the argument.

    You can read more about this on GoGeo: http://www.gogeo.ac.uk/gogeo-java/resources.htm?&cat=2&rid=3234

    And an article on our reliance on GPS: http://gogeo.blogs.edina.ac.uk/2011/03/08/do-we-rely-too-much-on-gps/

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  3. How much relevance does this have to the UK?

    Fierce Wireless have reported on this issue and said that “there was more interference with the the upper portion of the 1525-1559 MHz L-band than the lower portion”

    The proposed 4G auction in the UK is in the 800MHz and 2.6GHz ranges so I’m not sure that we need to be worried about 4G interfering with GPS in the UK.

    This is only a guess though, and I haven’t been able to find anything that tells me for definite what the GPS spectrum use in the UK is.

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  7. GPS uses the same spectrum every where. There are currently 2 main frequencies in use, L1 and L2, with others coming into use as part of GPS modernisation. L1 is centered on 1575.42MHz and L2 is centered on 1227.60MHz.

    The proposed LightSquared band goes up to 1559 MHz and this is adjacent to the band within which L1 sits. A diagram here shows the frequency allocation around the 1559MHz boundary.

    The problem is that L1 does not stay within it’s allocated band and leaks across into the 1559MHz area as indicated in this diagram.

  8. Thanks Mark, that’s really helpful.

    So, the issue with 4G and LightSquared is confined to the US then, as our proposed 4G spectrum isn’t anywhere near these frequencies. If we allocate something else close to the lower end of the L1 band we might encounter similar problems though.

    Does that sound about right?

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  10. Yes Simon that’s correct. Without modification to the way that most GPS receivers work most will suffer some sort of interference from much more powerful services in adjacent bands.

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