I was talking with someone a few days ago who seemed technically savvy who claimed that the current popular smart phones that give GPS style position info were actually using a sophisticated version of triangulating the cell signal characteristics between cell towers to accomplish this, and they did not really have dedicated GPS antennas built in.
In looking at reviews of these phones the online reviews seem to assume they do indeed have dedicated GPS antennas.
Who’s right?
They do both. Cellphone tower triangulation (which isn’t very sophisticated) is used first hand, because it gives good accuracy and takes way less of a toll on the battery. When such triangulation isn’t possible because enough towers aren’t in range, the GPS comes into play.
I help design and write device drivers for cell phones. I’ve worked for two major North American companies doing this.
Some very cheap cell phones use triangulation without having a dedicated GPS chip or antenna.
However, most of the ones I’ve seen use real GPS.
The last time a device I worked on shipped without dedicated GPS and antenna was about 2005.
-D/a
Why should one method use more power than another? Wouldn’t they both be based on passive reception?
I believe the confusion stems over what aGPS, or assisted GPS, is. For some reason a lot of people seem to think it’s not “true” GPS and is just some sort of advanced triangulation method.
It is not the same as cell-tower triangulation. iPhones from the second generation onward have all had aGPS. The first generation had cell-tower triangulation, which was reasonably in the ballpark of where you actually are, but not good enough (at least in my experience) for turn-by-turn navigation.
The phone radio needs to be on anyway for phone calls so adding the location calculations to it does not add much. GPS has additional RF circuitry that needs to be turned on.
You can look at the spec sheet of any major phone online, often Wikipedia will have the details. These spec sheets are very good about telling you exactly what sort of radios and other hardware are inside the devices. There are also major websites dedicated to ripping apart new phones from Apple and etc and going into detail about what is inside and often where each part was manufactured in what specific factory by which company in China.
I remember when phones first started to have location-based services or rudimentary navigation software some phones had only cell tower triangulation while some had real GPS receivers and you had to be sure to do your research if you wanted one with a real GPS receiver. These days I think it’s been essentially industry standard for all “smart phones” released in the past few years to have a real GPS receiver.
iPhones have dedicated GPS units, phone radios and WiFi radios and use all three to do location. iPod touches have only a WiFi radio and use only that to do location. iPod non-touches have no radio and do not do location.
Some smartphones also use WiFi hotspot data to find your location quicker. But precision and accuracy-wise, I don’t think that beats GPS either.
Do E911 requirements require a GPS or does cell tower triangulation suffice?
GPS is the most accurate source available in most situations. WiFi and cell towers are faster, as you and some others have stated.
I haven’t checked the E911 requirement recently…last I looked, cell tower was good enough. But that was probably 6 or 7 years ago. I’ll see if I can find a recent statement.
-D/a
Ok…a quick bit of research says yes, triangulation techniques are valid E911 solutions.
Thinking this through a bit, I realize that
Not all devices need to comply to E911, but something like 95% do.
-D/a
My phone is not only not a smartphone; it’s the bottom-of-the-line, free with two year renewal model. And it still has GPS for use with E911. There’s no way for the user to access it directly, but it’s there.
astro: Is your question about GPS receivers & computers, or GPS antennas?
IANA Phone engineer, but it’s at least plausible that a phone with a dedicated GPS receiver/processor chip might nonetheless share a single common antenna with the WiFi & phone radios.
[Before anybody trots out the bit about physical antenna size needing to be tuned to frequency, that’s 100% true for simple low tech 1960s antennas & radios. Wideband antennas & digital receivers are pretty remarkable these days. In a highly space-constrained environment like a smartphone it’s plausible to use one advanced antenna for several purposes at quite different frequencies.]