# How Do Satellites Track Mobile Phones? [Technology Explained]

08-08-2009

Have you ever wondered how satellites can track mobile phones? It seems like they’re so far away, yet they can be accurate within about 15 meters. Just how is that done?

The key to tracking any signal, whether it be cellular or radiowave signals, is something called trilateration. In order for trilateration to be used effectively, your phone needs to be picking up on at least 3 satellites – 4, or more, is better.

Your GPS-enabled phone receives a constantly streaming signal, from the satellites, containing information such as the time the signal was sent and the orbital information of the satellite.  Based on that, your phone’s GPS receiver calculates your location in latitude and longitude. It can also calculate your current speed, based on the time between readings and distance covered.

So how exactly does this trilateration thing work?

### How Do Satellites Track Mobile Phones?

Imagine a cone extending down from each of the three satellites covering your location. These cones make ellipses, close to circles, when the hit they Earth. Now, you have three intersecting circles. The centers of those circles are then used in a trilateration equation to determine roughly where you are. The point where all three circles intersect is your position. Let’s see how that might look in a simplified view.

The actual equation is more complex than the scope of this article will allow. However, I think this will give you a good high-level understanding of how it all works.

Since the GPS system employs from 24 to 32  global positioning satellites, your position can be determined almost anywhere on Earth. Take a look at the animation below and you’ll see how multiple satellites can transmit to your phone simultaneously. When there are 4 or more satellites transmitting their signal to your phone, the calculation is far more accurate.  Originally, the GPS receivers could only use data from 4 or 5 satellites at once. Now they can use as many as 20.

What can stop it from being tracked is anything that is going to block the line of sight. For instance, if you are in a building, away from a window, the satellites cannot communicate with your cellphone. So it isn’t a foolproof system.

Not all phones have the hardware to be tracked by satellite, but many do. BlackBerry and Treo are popular brands of cellphones that have satellite-trackable models. If your phone has GPS but doesn’t use satellites to trilaterate, then it is relying on the trilateration of cell towers, or even WiFi, to determine your location. Same principle, slightly different technologies.

Once your phone has calculated your position, how does it let anyone else know what that position is? I wasn’t able to find a definitive answer, but I’m led to believe it does it via your cell signal when a call is made,  or SMS. I bet one of our readers has an answer to this question.

Interestingly, the entire Global Positioning System of satellites is run by the United States Air Force’s 50th Space Wing, located in Colorado. The system has been around for quite some time and was made accessible to the public during President Reagan’s administration.

Of course, there are those people that fear that having their location tracked by their phone will lead to some sort of uber-surveillance. Personally, I don’t see it. How many cellphones are there in the world? What kind of massive server farm would you need to keep track of all that?

Very generally speaking, if law enforcement wants, or needs, to track your phone, then a warrant must be obtained and provided to the service carrier. There are situations of emergency where this process is sped up and may not include the full warrant procedure. Surely you’ve seen at least one story of how a stranded or kidnapped person was found alive, thanks to cellphone GPS services. Due to all those safeguards, the system is reasonably free from abuse and a technology that truly does add to our lives.

Image Credits: 50th Space Wing, Wikimedia Commons

Related topics: GPS, Satellite.

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1. Nostromov
December 7, 2016 at 6:47 pm

"Of course, there are those people that fear that having their location tracked by their phone will lead to some sort of uber-surveillance. Personally, I don’t see it. How many cellphones are there in the world? What kind of massive server farm would you need to keep track of all that?"

Um, that was a joke, right? Just the microprocessor in our person computer has unimaginable power. Here, "For instance, a 3.1-GHz processor has a clock that beats 3.1 billion times per second" @smallbusiness.chron.com/ghz-mean-computer-processor-66857.html

2. Gerry Bond
August 11, 2009 at 8:48 am

You virtually say that you are easing them into the subject by telling white lies. That's patronizing.

• Guy McDowell
August 11, 2009 at 10:18 pm

I prefer to think of it as search engine optimization. That's helping people find the info they need.

3. Guy McDowell
August 8, 2009 at 3:40 pm

Listen, the title is the only thing misleading, and that was intentional. This is because this is a high-level overview of how GPS enabled phones that receive information from the GPS constellation of satellites us e the information to figure out your location.

The common public misconception that satellites are used to track cellphones is one that is perpetuated by media. So if you are an average joe that wants to know how satellites are used to track cellphones, what would you type in the search engine? Maybe something like, "How do satellites track cellphones."

I suppose I could have made it plainer by saying in the first paragraph, "They don't. Phones track satellites." However I felt that was a very awkward way to say it and would push readers away. Instead I chose to ease them into the information that cell phones track satellites and cell phones then calculate their own position based on trilateration.

"your phone needs to be picking up on at least 3 satellites â€“ 4, or more, is better"

"phone receives a constantly streaming signal, from the satellites"

Not once do I say that the phone sends any information to the satellite.

If you can give me such a detailed reiteration of what I've written, then this article doesn't apply to you. Why? Because you know the question put forth in the title is invalid to begin with.

If it makes you feel superior to pick apart technical articles intended to educate the curious non-engineer types, I suggest you spend your time writing letters to Popular Science and USA Today, maybe to every studio that made a movie where satellites DO track cellphones.

• Will Robinson
August 8, 2009 at 4:57 pm

Exactly what I was going to say Guy; It seems every person who read your article has done so on the sole principle of picking it apart and nothing else.

There's nothing worse than turning a pleasant place like MUO into a slanging match over an article that wasn't written in DoD White Paper standards.

I'm fully aware of how all this works and I like to read other people's takes on the subject and, as such I thought it was fairly obvious who the article was aimed at. I'm sure the others would have too; should they have read it at a reasonable distance instead of atop their high-horses.

Still, I thought it was fairly intro into the subject. Thanks.

• Guy McDowell
August 9, 2009 at 4:23 pm

Much obliged!

Yes, MUO is not intended for the geekcore, but for people who want to make use of the technology all around them and understand it a bit better.

4. Airmon
August 8, 2009 at 1:44 pm

I agree - Satellites don't track cellphones, cellphones track satellites and from that information they can work out your position ( GPS ). The satellite doesn't know where your cellphone is, the transfer of information is entirely one way, from the satellite to the GPS receiver.
You might also note that most ( if not all ) phones allow you to turn off location services which also saves energy and makes your battery last longer. This won't prevent the phone system from getting a general idea of your position by locating you from the towers ( say, for a 911 call ) but will prevent your phone from knowing your exact, GPS located position.

• Guy McDowell
August 8, 2009 at 3:30 pm

Again, you've restated what I've said in the article, and just added a little bit about turning the GPS services off. There's nothing wrong with the article.

5. Peter
August 8, 2009 at 12:27 pm

When using a GPS-enabled device the Satellites do not even notice this, because they constantly only send timecodes and their position. Using this data the phone can calculate its position as i understand.
So no tracking is happening at any time.

• Guy McDowell
August 9, 2009 at 4:19 pm

Sweet Jeebus! That's exactly what I wrote in the article. Does anyone actually read the article or just slag on titles.

6. quantum_flux
August 8, 2009 at 12:00 pm

Well, if Cellphones store routing coordinate info in a spreadsheet format (time vs GPS position), which they do for the breadcrumb feature, then it's entirely possible to put a chip in the phone that transmits that data periodically on a timed querie or perhaps upon manual querie.

• Guy McDowell
August 8, 2009 at 3:28 pm

Which is how tracking software that cell companies sell you works - roughly.

7. Doug Winter
August 8, 2009 at 11:29 am

I suggest the author pulls it and tries again later!

• Guy McDowell
August 8, 2009 at 3:27 pm

The facts are accurate.

8. Jim Smith
August 8, 2009 at 11:24 am

I agree with Fraser Smith's comment.'Satellites do NOT track mobile phones.'
The phone calculates it's position from the timing of signals received from the satellite and from the satellite's position.

The phone can be tracked if it THEN uploads it's GPS derived position to the cellular network.

As previously mentioned the phone can also calculate its position by triangulation from cell-sites although probably less accurately than via GPS. Again this position would need
to be uploaded to the network to allow the phone to be tracked.

The network however can track the phone without the phone
and triangulation although in rural areas with large cells
this is less accurate as only 1 site may be in range covering a large area. This tracking can be done without
the phone making a call - it need merely be on. This is
how the network 'knows' which site to use when someone
calls the phone.

The original article is misleading and may worry some people.

• Guy McDowell
August 8, 2009 at 3:27 pm

You basically rewrote my article with essentially the same information. The title is misleading, but again, it is intended to draw the mislead.

9. kaz
August 8, 2009 at 9:54 am

Tracking cell phones for everyone in the US:

There are 271,000,000 cell phones in the US. There are on the order of 10^6 cell towers. A datagram containing a unique ID for each phone and a unique ID for the tower nearest that phone could therefore store each of those IDs in 32b, for a total packet size of 64b or so.

Let us assume that at any time, one out of three people are moving fast enough to be changing cells, and that the people who are changing cells do so at a rate of, on average, 1 cell / minute.

(packet size) * (# of phones) / (proportion moving) / (s/min)
64 bytes * 271000000 / 3 / 60 / (1024^2) ~= 100Mbps

This amount of bandwidth would cost a private company about \$10k-\$15k/mo - much less than many web companies use; not exactly infeasible for the government...

I'm not saying the government is tracking our phones en masse or planning to, but technologically it would be no big deal.

• Guy McDowell
August 8, 2009 at 3:26 pm

Interesting. But I'm not going to check the math, so I'll take your word for it.

10. Fraser Smith
August 8, 2009 at 9:47 am

Please... Satellites do NOT track mobile phones. That implies active involvement from the satellites. Actually, mobile phones and GPS receivers track satellites. Yes, the download ephemeris info from the constellation but then they use that info to calculate a position based on the knowledge of where each satellite is at a specific time.

• Guy McDowell
August 8, 2009 at 3:25 pm

Fraser, the title might be a bit misleading, but it is there to address the question put forth by people who think that their phones are tracked by satellite.

If one were to search for, "How does my GPS enabled cell phone track multiple satellites to calculate my approximate position?" well, I'd say they already knew the answer.

The average person would not search for such information. They would simply wonder how cell phones could be tracked by satellite.

• audey
August 9, 2009 at 12:25 am

Guy, that's bull. A better title would be how does GPS work?. Not to mention you reinforced the Satellites tracking Phones angle multiple times through out the article. When 911 operators locate a phone, it is either GPS information the phone has sent over the GSM network, or if lacking GPS, signal strength triangulation.

• audey
August 9, 2009 at 5:54 pm

Ooops, my bad. 9th paragraph. very sorry.

• Jerry Kardashin
October 13, 2017 at 11:36 pm

Okay here is how it works, there are a group of assholes, trying to decide how it works, a little bit, of what each asshole says, is how it works. Get it!