
GPS signals are surprisingly easy to disrupt - douglasfshearer
http://www.economist.com/news/international/21582288-satellite-positioning-data-are-vitalbut-signal-surprisingly-easy-disrupt-out
======
michaelwww
As someone who was recently a delivery driver, the recent addition of GPS
tracking is one of the most annoying things about a delivery job. Far worse
than drug testing. Driving can be difficult and sometimes you need to park and
stretch your legs. I was called into the office for this and queried about
each of my stops. GPS is going to become more prevalent as people like me are
highly motivated to defeat the system, especially working in teams with other
drivers. Of course there are work-arounds. Park at a legit spot on an approved
break and leave all your electronic devices in the vehicle and walk to where
you want to be but don't want them to know about, etc...

However, it is highly doubtful this was done by a delivery driver. There is no
point in jamming the signal for 10 minutes. What could it accomplish? If the
purpose is to take an illegal detour (going against a one way street) the
company has logs of all your trips and will soon figure why you have a 10
minute gap everyday.

~~~
jonknee
> Driving can be difficult and sometimes you need to park and stretch your
> legs.

If your employer doesn't allow legally required breaks you can use the GPS log
in your suit against the company. Otherwise it sounds like you weren't doing
your job.

~~~
tinco
Someone isn't doing their job when they are taking breaks more often than the
legally requirement minimum?

Sounds a bit harsh to me.

~~~
jonknee
Pulling over his delivery truck to go on a walk does indeed sound like not
doing his job as a delivery driver. I don't see many UPS drivers going for
jogs during the day...

~~~
oh_sigh
> I don't see many UPS drivers going for jogs during the day...

What a horrible example. They actually get up and walk around probably dozens
of times per day. That is completely different from long-haul trucking, where
you may only get 2 stretch breaks in a 10 hour period.

------
cschmidt
That reminds me of another Economist article about GPS jamming from 2011:

[http://www.economist.com/node/18304246](http://www.economist.com/node/18304246)

That article was inspired by a trucker who drove by Newark Airport every day,
disrupting GPS service there.

~~~
bjcubsfan
I worked on that, but have not seen that particular article. There are
actually a whole lot of them going by the Newark Airport even today.

------
csense
> surprisingly

GPS signals come from satellites. AFAIK there are about 20-40 GPS satellites.
Let's say each covers at least 1/50 of the Earth's surface area, about 500
million km^2. That's 10 million km^2 per satellite.

What's the max power generation you can fit on reasonable-sized satellite
that's going to be in orbit for decades? I'm guessing not more than 10 kW. So
10 kW / 10 million km^2 means you have .001 watt per km^2.

GPS signals being easy to jam isn't surprising. What's surprising is that you
can detect them with equipment that's small and cheap enough to fit in a
cellphone!

~~~
mikeash
Where it really gets amazing is when you discover that the GPS signal is
around 20-30dB _below_ the noise floor. That is to say, ambient noise drowns
out the signal by a factor of 100-1000. Long-term correlation manages to pull
out usable information from this extremely noisy signal.

An interesting consequence of this is that you don't need a very fancy
receiver, hardware-wise, because your software already has to be extremely
sophisticated. For example, you can use a 1-bit ADC rather than trying to be
more sophisticated about exactly how strong the signal is at any given moment.

~~~
jordanthoms
That's crazy... I think I'll contain my frustration more now when my GPS takes
a few minutes for a cold lock. It's even more crazy because with the latest
GPS systems in phones, I'm able to get a fix with only a very small portion or
even no sky visible.

~~~
mikeash
Interestingly, the cold lock acquisition time is usually gated by the time
required to download the almanac from the satellites, rather than acquiring
the actual GPS signal. The almanac (which is the stuff that basically tells
you where the satellites are, so you can figure out where you are based on
that) gets sent on a side channel at a very slow rate, something like 50bps,
such that it takes about 30 seconds before you have all the data, and any
interruption can mean it takes multiples of that. The main advantage cell
phones have is the fact that they can download that data from the cell network
rather than waiting for it to dribble in from the satellites directly.

The ability for GPS to (sometimes) work indoors these days is indeed pretty
crazy. The signals are already incredibly weak, and you'd think having a roof
and walls and pipes and wiring in the way would make it impossible to read
them.

~~~
jordanthoms
I guess when the signal is already that weak, some roofs etc doesn't make that
much difference.

I'm excited for the new GPS satellites, GPS works well already but with modern
technology in the satellites it should be much better.

------
jjwiseman
The article mentions North Korea's frequent GPS jamming, but doesn't mention
that it's suspected as a cause of the fatal drone accident last May:
[http://lemondronor.com/blog/index.php/2013/3/gps-loss-
kicked...](http://lemondronor.com/blog/index.php/2013/3/gps-loss-kicked-off-
fatal-drone-crash)

I haven't been able to find any more recent info about the incident.

~~~
jandrewrogers
Systems that rely on GPS are defective in their design. US military systems
have never trusted GPS, since inception, because the Soviets had the ability
to destroy the satellites and tinker with the RF.

US military systems are inertially guided only accepting GPS corrections
within the error bounds of their extraordinarily tight inertial measurements.
If the GPS is outside the error bounds, it is presumed to be compromised.
There is no such thing as an intrinsically GPS-guided weapon; they are always
inertially guided with GPS corrections. Modern US inertial systems are similar
to GPS in terms of precision so GPS is increasingly superfluous.

As a consequence, the US military has never been significantly vulnerable to
loss of GPS. Their systems were designed, from Soviet days, to assume that GPS
could be compromised or lost since the Soviets had that ability. Knock out GPS
and you still have to deal with ultra-precise solid-state optical gyros.

Many commercial systems take a cheap shortcut and rely on GPS but, contrary to
popular mythology, US military systems never have.

------
themstheones
I love how it's just some dude running a delivery truck inadvertently doing
this. It's like something out of a movie.

~~~
speeder
There is a legendary tale of a how a random delivery truck took down a whole
popular MMO.

The MMO company had a issue with their own physical logistics, and had to put
their login server across the street in another building.

They put special antennas between the two buildings, to keep the thing
running, and it worked great, until one day, it didn't.

After a while trying to figure what was going on, they noticed that a huge
delivery truck parked illegally (the place where it parked was illegal to
anyone park), and the place he choose made the bulk of the truck metal stay
right between the two antennas...

EDIT: Also when internet was still dial-up, one delivery truck ignoring height
limits managed to cut all phone cables near my town biggest ISP, leaving the
entire city without internet. I did not appreciated it...

~~~
DrStalker
I've heard of a similar issue with a wireless data link across a river that
would cut out once or twice a day, but not everyday, and no one could figure
out why. The answer only came after a few weeks of monitoring and an ametuer
fisherman saying "hey, those are all high tide times!" at which point they
realise that high tide was causing the mast of a docked boat to rise up enough
to interfere, and that the boat was not always in its dock which is why some
days were fine.

~~~
jlgaddis
This is typically off-topic but you found that case interesting you might also
enjoy reading "The case of the 500-mile e-mail":

[http://www.ibiblio.org/harris/500milemail.html](http://www.ibiblio.org/harris/500milemail.html)

------
eCa
Should it not be possible to track the vehicle (if it is only one) by
installing GPS receivers in the area and noticing when the disruption begins
and ends for each receiver?

That, coupled with license plate scanners at those locations, ought to find
the culprit.

(And then they can launch an armed drone to take him/her out...)

~~~
emiliobumachar
The culprit is basically shining a very bright light (at invisible frequency)
in all directions. Catching them should be even easier than your proposal.

(I suppose one could program a missile to follow the light...)

~~~
sbierwagen

      basically shining a very bright light
    

GPS satellites broadcast 500 watts from a 13dbi antenna.

But they're far away. Really really far away, to the tune of 21,000km. (The
Earth is about 12,000km wide.)

By the time the signal makes it to the surface of the planet, the inverse
square law has punched it down to -130 dBi, which is well below the thermal
noise floor of room temp electronics. GPS receivers pull a useful signal out
of a storm of random noise using deep information theory magic, which is
vulnerable to several clever low power attacks.

Even a dumb jammer doesn't need much power, though.

    
    
      one could program a missile to follow the light...
    

[http://en.wikipedia.org/wiki/AGM-88_HARM](http://en.wikipedia.org/wiki/AGM-88_HARM)

"The AGM-88 High-speed Anti-Radiation Missile (HARM) is a tactical, air-to-
surface missile designed to home in on electronic transmissions coming from
surface-to-air radar systems."

~~~
JonnieCache
_> pull a useful signal out of a storm of random noise using deep information
theory magic_

Any keywords I can look up as to how this is done?

~~~
Robin_Message
[http://en.wikipedia.org/wiki/GPS_signals#Demodulation_and_de...](http://en.wikipedia.org/wiki/GPS_signals#Demodulation_and_decoding),
currently paragraph 4 describes pulling out the data.

Basically, even though the signal is below the noise floor, part of the signal
is the output of a pseudo-random number generator with known properties, so by
setting up your own PRN, and then trying different (time) alignments, the
correct alignment will stick out, despite the noise (which all averages out).
Once you have the time alignment, you can read the rest of the signal, and
then you can tell how far you are from that satellite ((it's clock - your
clock) / c). Repeat for other satellites and you're done.

Can't find any good references, but that's what our information theory
lecturer said! Also, it explains why a hot start is quicker than a cold start
(if you know where you are, and the accurate time, you know what alignments to
try to start looking for the satellite signals.)

------
rayiner
GPS signals are _unsurprisingly_ easy to disrupt. It's a location mechanism
that depends on one-way communications and triangulating an extremely
precisely-timed signal between at least three far away satellites. Position
fixes don't rain down like mana from heaven.

------
ihsw
Interestingly, Google's successor to BigTable -- Spanner -- utilizes GPS
clocks and atomic clocks to maintain consistency of their data across
globally-distributed data stores.

[http://en.wikipedia.org/wiki/Spanner_(database)](http://en.wikipedia.org/wiki/Spanner_\(database\))

~~~
sargun
Also, Google uses accurate atomic clocks in each of their datacenters, so when
their GPS connectivity gets cutoff, they can still keep time. Almost everyone
does.

------
ballard
A paper on GPS jamming countermeasures

[http://servv89pn0aj.sn.sourcedns.com/~gbpprorg/mil/gps4/GPS-...](http://servv89pn0aj.sn.sourcedns.com/~gbpprorg/mil/gps4/GPS-
Vulnerability-LosAlamos.pdf)

Ultimiately, the lack of MAC and encryption makes civilian GPS MITMable.

(Discliaimer: I worked at Trimble.)

------
bobdvb
Many many years ago I was a specialist in satellites for a major European
broadcasting company. We had a problem with couriers who used radar speed trap
jamming devices. They had really noisy oscillators which leaked huge
quantities of out of band noise into the dished which were located near the
courier drop off point.

We initially used an expensive spectrum analyser attached to a spare LNB
(pointed at the parking area) but that needed you to notice the noise. So I
used a USB enabled RF power meter interfaced to Excel (so sue me, it was a
rush job and we weren't equipped for development). A script ran which fetched
values, when there was a spike in received power it played an alarm and
flashed the screen.

The next step was to ask security to hold anyone in the carpark while a large
angry engineer went to give the courier a piece of his mind. It worked,
courier companies were informed, people were shouted at and I believe it
stopped.

There are probably better ways of doing this, but it was effective and built
from spare parts.

------
leif
I didn't know GPS hammers were a thing but now I want one. Thanks, LSE.

~~~
leif
Jammers. Thanks, iPhone.

~~~
skeoh
Make sure it is legal to own/operate one in your jurisdiction before buying
any sort of jammer.

------
drivingmenuts
They seem to be taking it awfully casually, as if it's all some minor
misunderstanding between gentlemen.

~~~
afterburner
Well it is Britain.

------
eli
Isn't GPS clock sometimes used to set up high-speed network connections? Maybe
someone is jamming GPS to mess with a particular HFT application.

------
ChuckMcM
As this becomes more annoying people will start watching for terrestrial GPS
transmitters and start busting them.

------
scotty79
I guess we should migrate towards non GPS position tracking faster:
[http://www.darpa.mil/NewsEvents/Releases/2013/04/10.aspx](http://www.darpa.mil/NewsEvents/Releases/2013/04/10.aspx)

------
teyc
There's an Australian company who's got a land based positioning technology.
It does not rely on satellites and I think it holds a lot of promises
especially for airports.

~~~
dragonwriter
Land-based, non-satellite radionavigation (particular for aircraft) is older
than GPS (or satellites, or even jet engines.) (e.g., VOR, DME, TACAN, etc.)

~~~
adestefan
Don't forget about LORAN.

------
rhodey
"The signals are weak. Mr Curry likens them to a 20-watt light bulb viewed
from 12,000 miles (19,300 km)."

no, just no.

------
samspenc
Bane?

------
jessriedel
In principle, GPS jammers are illegal, right? FCC regulations or some such?

~~~
wmf
In principle, you'd read the article before commenting.

~~~
michaelwww
What, you didn't read it for him?

------
VLM
"receivers cost £2,000 per vessel"

Hmm, yes kind of like how a new GPS costs $5K, because the first .mil model
did cost that much. Or all computers currently cost millions of dollars
because the first ones did.

~~~
ThatGeoGuy
As somebody who's primary field of study is GPS / Navigation / Positioning,
I'd like to remark that survey grade receivers such as in the eLoran stations
can cost much, much more than £2,000.

Their price isn't so much the hardware itself, in fact, most of the receivers
seen in cell phones today cost less than $1USD. However, when dealing with
more accurate receivers, the receivers typically need extensive calibration
and testing. I mean, it's possible to get measurements from GPS accurate to
1mm, but you need to have both a careful setup and very good knowledge about
the errors associated with your receiver. So yeah, these receivers are
actually quite expensive, and most of it is because the calibration on
repeatability and stability of these sensors is of the utmost importance.

On a secondary note, survey-grade receivers are typically not as prone to
jamming as consumer-grade receivers, mostly because they can use multiple GPS
frequencies / can collect over a wider bandwidth. There's a lot more to it
than that, but effectively the point I'm making is that the receivers spoken
of in the article are not the same as everyday GPS receivers.

If you want to see how crazy the prices on these receivers can get, look no
further than
[http://www.surveyorsmart.com/product.sc?productId=548](http://www.surveyorsmart.com/product.sc?productId=548).
I doubt many surveyors would go for that particular model by Leica, as it is
definitely expensive, even for survey equipment standards, but it's not unreal
in terms of pricing.

~~~
joosters
1mm?

~~~
andrewcooke
you can google the spec sheet for the receiver described. it can measure
carrier phase to 0.2mm rms. that translates to an accuracy after post-
processing of 3mm horizontal (with a fancy antenna).

the trick is to use the carrier itself, which is higher frequency than the
signal modulated on it. also, relative offsets are easier that absolutes
(removes many systematic errors).

i wrote (the software for part of) one of these (not for leica, for some
geophysical survey company) back in the day (although it was not mm
resolution!)

~~~
jrockway
Current GPS receivers have a couple sources of error, including processing
slowness and ionospheric delays. If you don't know what the ionosphere looks
like, you can't be accurate to 0.2mm. There are ground stations that measure
this (based on the fact that they aren't moving so any change in the GPS-
calculated position means ionospheric changes) and transmit the correction
data to other GPSes, but this doesn't get you to 0.2mm, at least not for a
moving object.

~~~
bigiain
TO be fair, Andrew wasn't claiming 0.2mm accuracy in position measurement - he
was quoting the devices ability to resolve phase difference in the carrier
wave (and noted that is an order of magnitude or so better than the resulting
position accuracy).

Having said that, I wonder what the magnitude of ionospheric changes have on
the phase difference of the carrier signals from satellites in different
directions?

(Even though I know how it works, the idea of getting millimeter precision in
measuring distances to something that's at least 20,000km away and traveling
at almost 4km/sec seems like very black magic to me… Surely that can't
actually _work_ in practice…)

~~~
andrewcooke
i don't know what current state of the art is and even 3mm sounds crazy good
when i think about it (i was just repeating the spec sheet). i wonder if it
that also requires separate / multiple receivers to fully model the
ionosphere?

~~~
bigiain
As I understand it - once you can get the time-based position fix accurate
enough, you add in the phase information from the 1.2GHz carrier wave - with a
wavelength of ~200mm, resolving that to 0.2mm seems reasonable.

The problem of working out which of the peak/troughs in the carrier wave
you're in almost certainly requires terrestrial DGPS assistance
([http://en.wikipedia.org/wiki/Differential_GPS](http://en.wikipedia.org/wiki/Differential_GPS)).
If you can use that to get ~100mm precision - that allows you to use the phase
difference in the 200mm wave length to get sub mm measurements.

Like I said, I understand how it works – I just find it hard to believe it's
actually practically possible… Deep magic…

