Tag Archives: GPS

How mobile phones reveal your location

Obviously, when your phone’s GPS receiver is on, your location within 30 feet or so is usually available.

Cellular antenna system on monopole
photo Steve Kazella

There’s another way that remotes, your cellular service provider, 9-1-1 call centers [also known as Public Safety Answering Points (PSAPs)], and law enforcement can determine your phone’s location, even when your GPS is off, or even if your plain-Jane flip-phone has no GPS receiver. It’s called Uplink-Time Difference of Arrival U-TDOA). Here’s a brief simplified video description. Each cell tower has an antenna array with three or four 90 or 120 degree (when viewed from above) antenna sectors. Each tower knows, by comparing your phone’s received signal strength in each sector, which sector your phone is in. By measuring the propagation time for a “ping” to travel between the tower, your phone, and back again, it also knows the range to your phone. In a populated area your phone is likely to be talking with more than one tower, so all that’s needed is to know the bearing and range to your phone relative to two or more towers, and your location can be estimated within maybe a 100 foot radius. (You will be at the intersection of the two or more arcs.)

Even with only one tower talking to your phone, it knows that you are located somewhere along that 90 or 120 degree arc within the sector with the strongest signal. U-TDOA is used in Enhanced 9-1-1 Phase II systems so that first responders may be dispatched to wherever your cell phone is located when you place a 911 call for emergency assistance.

The only way to stop this is to remove the battery from your phone. (Oops. Sorry, iPhone users.) Switching it off won’t stop the communication. Switching it to Airplane Mode will prolly stop it, but there are no guarantees.

Update Here’s a clear explanation of mobile phone positioning techniques.

Visit my website: http://russbellew.com
© Russ Bellew · Fort Lauderdale, Florida, USA · phone 954 873-4695

Google Maps for Android bicycle navigation, part 2

Google MapsRecently I wrote an article about using the Google Maps app on my Android phone to guide me on a bicycle ride. On Thursday, I cycled 18 miles to Thanksgiving dinner with friends. I knew the best route to the destination neighborhood, but relied upon my Android phone’s Google Maps app to vector me the last few miles to the exact address.

When I was within a few miles of my destination, I asked the Maps app to speak directions into my earbuds. Although Maps accurately pinpointed the destination, its route included nonsensical detours which would have added miles to my ride. I ignored the nonsense.

I’m impressed with how useful Google Maps for Android is while cycling, but it’s still buggy. Google states clearly that it’s beta. Use it, but, in the words of Richard Nixon, “Trust but verify”.

It receives good reviews.

Visit my website: http://russbellew.com
© Russ Bellew · Fort Lauderdale, Florida, USA · phone 954 873-4695

Cycling with Android GPS navigation

French bicycles allowed sign
My Android phone worked well as a bicycle navigator.

Yesterday I bicycled about ten miles to a new client, using the navigation software and GPS receiver in my Android phone. When I told Google Maps that I planned to ride a bicycle, it found an unusual route along back streets. I stuck in my earbuds, asked Google Maps for Navigation, and shoved off. A good-quality synthesized voice gave spoken instructions at each juncture. On one heavily trafficked road I must have missed an instruction to turn, which resulted in my pedaling an additional three miles or so.

Aside from that miscue, the phone worked well as a navigator. It chewed through the battery’s charge, though. Its distance resolution seems about as good as my TomTom GPS receiver. As usual, I found the user interface, especially the touchscreen keyboard, to be my biggest problem: it wasted many minutes as I tried to copy, paste, and enter destination data.

Visit my website: http://russbellew.com
© Russ Bellew · Fort Lauderdale, Florida, USA · phone 954 873-4695

TomTom’s portable devices have lost their hipness.

photo: TomTom
Smartphones’ GPS apps have eaten into GPS device sales.

TomTom’s North American sales of its portable GPS units have been falling since consumers have decided that they’d rather use the GPS apps in their smartphones. TomTom’s shares dropped from 56 euros in 2007 to less than 3 euros last month. The company has announced major cuts in R&D, marketing, and payroll overheads. They also will outsource some Netherlands-based manufacturing to less expensive countries. (Does this mean China?) They predict future growth in the OEM automotive and traffic information markets.

Reuters reported last week, Route unclear for struggling TomTom.

Two years ago I wrote an article about how pleased I was with my new entry-level TomTom GPS. I still am. Smartphones are fine for GPS info, but they rely upon continuous data connections with cell towers to display maps: if they lose their (billable time) data connections, their maps no longer update. By contrast, maps are built into portable TomTom GPS devices; all they need are signals from at least 3 GPS satellites.

Since the early 1970’s, the Oakland-based band Tower Of Power has asked, “What Is Hip?”. (Answer: Hipness is what it is. Sometimes hipness is what it ain’t. What’s hip today might become passe’.)

Visit my website: http://russbellew.com
© Russ Bellew · Fort Lauderdale, Florida, USA · phone 954 873-4695

LightSquared’s problems highlight RF spectrum limits.

Navstar 2F GPS satellite
Navstar-2F satellite of the Global Positioning System (GPS)
photo: USAF
Big money wants to deliver wireless broadband everywhere. Doing so may deliver big problems everywhere.

About a year ago, a combined satellite and terrestrial cell-tower broadband network named LightSquared announced its intentions. It looked like LightSquared had its FCC (Federal Communications Commission) ducks in a row so that it could begin building immediately.

Now, US armed forces, who created, maintain, and depend upon the Global Positioning System (GPS) think that LightSquared’s plans may interfere with GPS signals. In June, a report demonstrated that GPS signals will indeed be interfered with everywhere by LightSquared’s cell towers (which could number 40,000).

photo: Darrenm540

The frequencies in question are in the L-band (1 to 2 GHz). I remember when this band was almost empty. Now it’s a crowded superhighway for many satellite signals, GSM cellphones, GPS signals, radar signals, etc. (Link to graphic image of America’s ridiculously crowded radio frequency resource.)

GPS signals are vulnerable
According to L-band authority Richard Abrahams, “GPS signals are generally very weak and need to be well-protected.”

So far, it looks like the Pentagon will oppose LightSquared’s ambitious plans, as will most players in the GPS equipment marketplace. But the battle is heating up and who will win is unclear. Big dollars are at stake, and that will draw politicians.

I’d like to see LightSquared’s plans defeated. Allow Verizon, Sprint, et al to roll out their 4G wireless networks as they’re doing and don’t jeopardize the GPS system.

Visit my website: http://russbellew.com
© Russ Bellew · Fort Lauderdale, Florida, USA · phone 954 873-4695

I love my TomTom GPS. Microsoft doesn’t.

Tom Tom built their GPS devices on the open source GNU/Linux platform, not Microsoft’s proprietary platform.



I’m very happy with my TomTom One 125 car GPS. It’s the best $100 I’ve spent in a long time. (It was on sale at Sears on the Friday after Thanksgiving day. You can find them for that price or less now.) It’s a fantastic product, offering incredible bang for the buck. One reason is that neither TomTom nor its users pay what’s called “the Microsoft tax”; TomTom’s software is built upon the GNU/Linux operating system — not Microsoft’s Windows CE (or whatever they call it this week).

One result of not paying the Microsoft tax is that Tom Tom was able to invest money in a beautiful and functional piece of industrial design and manufacture it to a high standard. So, users benefit.

The empire strikes back

Microsoft is miffed at losing this revenue. It recently filed a lawsuit against TomTom (a Dutch company), claiming that TomTom’s software infringes on eight Microsoft patents, apparently revolving around the FAT (File Allocation Table) and FAT32 file systems. Pundits claim that this lawsuit is aimed at the heart of GNU/Linux: the entire concept of open-source software. Apparently Microsoft chose TomTom — located in Holland — as a target because US legal precedents don’t favor Microsoft’s argument.

Other mainstream consumer devices that sell by the millions (for example, Tivo) have shunned Microsoft in favor of Linux. This lawsuit is equivalent to The Empire striking back at those rogue manufacturers who’ve refused to fall into line and pay “the Microsoft tax”. The outcome of this case will affect how much we’ll pay for cellphones, GPS units . . . and most other devices that are software-driven.

Visit my website: russbellew.com