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Old 03-20-2017, 7:43 AM
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Default What Is The Maximum Range For AT&T And Verizon?

I have read that AT&T will disconnect calls at 22.4 miles from the tower. I haven't been able to find out what the maximum range for Verizon is, though. Does anybody here ever use the phone apps to find out what tower you are connected to and determine how far you are from it?

I know that there are LOTS of variables, but think of a real world best scenario case. Say the tower is in a great location on shore and you are on the ocean. Would Verizon work out to 20 ish miles, like AT&T, or is the system designed to disconnect the call way before that?
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Old 03-20-2017, 9:36 AM
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For a standard GSM system the maximum cell radius is about 35 km or 22 miles.
In GSM each RF channel is 200 kHz wide and has eight 577 microsecond TDMA time slots.
It takes RF about 6 microseconds to travel 1 mile in the earth's atmosphere and that delay along with other tolerances is how they determine the maximum possible cell radius.

Back when I was in the industry about 20 years ago I was told that the GSM carriers were moving to frequency hopping in order to increase capacity. The handsets could tx and rx their time slot on a different channel each time.
I don't know if the 22 mile limit is the same if they use frequency hopping or if AT&T or Verizon use frequency hopping or even how much of their networks are still GSM.

The other cellular systems that use wideband CDMA don't have the slot timing limitation. I don't know if they have other factors that limit cell radius.
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Old 03-20-2017, 1:55 PM
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I'd been told that it was 16 miles "for the industry" regardless of carrier or protocol. They figured that was far enough for most users, and the range was actually based on signal latency times, the time it took for the tower to "ping" the phone and get a response back from it, or vice versa. If there was too long of a delay in the signal return, the system was (and presumably still is) designed to drop or not connect to that caller, presumably another tower is closer to them.

But this is the kind of "proprietary trade secret" that no one in the cellular business is going to talk abut on the record.

Note also that line-of-sight is only about six miles to the horizon, for radios that are 6' above ground. Anything further also must rely on the additional height above ground of the cell tower, or the user. Without running the exact numbers...if you're "on the ground" and the tower is 100' high, sixteen miles might simply be all that line-of-sight range is going to get.
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Old 03-20-2017, 6:38 PM
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Default What Is The Maximum Range For AT&T And Verizon?

With Extended Range on GSM, you could stretch a call out to 70km's.

Not sure why any carrier would arbitrarily assign a maximum distance when you consider some rural areas have little to no coverage.

Sounds like a myth to me and I'm actually in the business.

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Old 03-20-2017, 7:07 PM
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Maximum distance: For the same reason they don't want you using the cell phones from aircraft. The system is "one size fits all". So if using your phone in a "typical" area results in ten towers receiving your signal, ten towers are debating who should handle your call, tying up network computer resources while they arbitrate that. Now extend the range of the phone, and maybe 50-100 towers have that same discussion. Repeatedly.

That's a lot of resources being consumed.

But if you screen every call, apply a simple latency measure to it and ignore anything outside of a small don't need to waste resources while the cell sites are debating who should handle the call.

There's a lot of policy that goes unpublicized because "Don't confuse the rubes". Or perhaps, don't upset them. For instance, AT&T would never give you a busy signal if you called someone's cell phone and the call could not be completed because the cell phone was logged into a tower that was already at capacity. They'd just shunt you to voice mail, and the person you were calling would never know you had tried to call them. Until the saw a "missed call" or voicemail indicator sometime later.

Fair? No, but it hides the fact that the carrier doesn't have enough capacity to complete calls. And when customers paid per minute to retrieve their also increased profits, since a busy signal was free. Gee....

The cell phone business is about business. The technology isn't a consideration, except as to how it can be made into profit. Encryption? Eavesdropping? Sure, there are techno fixes. But would they help increase profits? Arguably, not as much as selling special encrypted phones to those users who demand them. Or, simply ignoring the issue.

It isn't just cell phones. The landline system has rules and options that are generally not publicized as well. When there's a disaster and the system is overloaded, outgoing calls are given priority over incoming calls. That's in the assumption that folks who are in the disaster area have the greater need, to call OUT to others. Does the average customer need to know this? Not really, so you won't see it mentioned in the front of the phone book. But the info is out there, if someone digs for it.
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