Does cell phones have CC?

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Ryfly

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So, from what i know, cell phones operate like the police radios do.

But i was on my cell phone one day and my call was dropped even though i had full signal. It got me wandering..

So for the cell techs out there, do cell phones montior a control channel just like police radios do? Plus whats causes a call to drop? Does the Tower forget to send out the new data to the phone to what frequency it needs to use? I'm with AT&T and i seem to get alot of dropped calls and when i'm on my cell phone, i'm always wondering how that small little devices work at 60mph down a highway with out a big antenna the police use.


side note, i hope i'm not asking something to illegal here, i'm just amazed how at radio technology.
 

W4KRR

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Yes, cell phones use a control channel similar to what is used on trunked systems. The idea in a cell system is if your signal drops below a certain level, the call is handed off to another cell site that has a better (stronger) signal. For various reasons, this doesn't always happen. Due to interference, obstructions, etc., the signal may drop to a level that is too weak to be picked up, or maybe adjacent cells are over capacity and there are no channels available, etc. Dropped calls can come from many causes.
 

fineshot1

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Yes - Cell Sites do have a data channel and that is what the cellphones lock onto while not already on a call. Many factors can cause a call to drop despite strong signal strength so I do not think I can answer your question to your liking. The cell carriers do not all use the same technology and they dont all work exactly the same but the cellular basics are common to most of the technologies. I beleive AT&T now uses the GSM digital technology and Verizon Wireless uses CDMA digital. Most of the analog has either been shut down or will be soon unless they have a need to keep it active.
 
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chrismol1

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I live less than 1 mile from a cell tower in FULL view of the thing with surronding areas. And sometimes when outisde the call gets dropped. So i think its porbably overload in the tower since theres only 3 of them in the surronding area within a 10 mile radius.

This got me thinking, with a 5 watt VHF handheld that gets about a 2-3 mile radius with stock duck in my surronding area, how do small plastic antenna 1 watt cell signals on UHF get a good signal from down low and be able to penetrate the foilage. I know that the towers have 10 watt transmitters on them and are up high but ya still need the other end to send and recieve. Is it just antenna height or what ?



upstate NY, capital region
 

fineshot1

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chrismoll said:
I live less than 1 mile from a cell tower in FULL view of the thing with surronding areas. And sometimes when outisde the call gets dropped. So i think its porbably overload in the tower since theres only 3 of them in the surronding area within a 10 mile radius.

This got me thinking, with a 5 watt VHF handheld that gets about a 2-3 mile radius with stock duck in my surronding area, how do small plastic antenna 1 watt cell signals on UHF get a good signal from down low and be able to penetrate the foilage. I know that the towers have 10 watt transmitters on them and are up high but ya still need the other end to send and recieve. Is it just antenna height or what ?
Chris - Cellular systems have many cells that all have receivers that can tune to any cell channel. During a conversation when your sig gets low into the serving cell it sends a message to the local switch stating the sig is dropping to an un-acceptable level. The switch instructs all the surrounding cells to tune a receiver to that channel and sample the signal strength. They all report back to the switch and the switch decides on which site to handoff the call to. At least thats how it used to work with all of the older analog cell systems. With the newer digital systems its a bit different and more complex than that but you get the idea now I'm sure. During this process of the handoff many things can happen to cause problems. The problems can happen at both the mobile or the site end and are too nuemerous to list but if you do google search's on the subject there is much info on the web regarding this subject.
 

Gilligan

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chrismoll said:
This got me thinking, with a 5 watt VHF handheld that gets about a 2-3 mile radius with stock duck in my surronding area, how do small plastic antenna 1 watt cell signals on UHF get a good signal from down low and be able to penetrate the foilage. I know that the towers have 10 watt transmitters on them and are up high but ya still need the other end to send and recieve. Is it just antenna height or what ?
From the little bit that I've read about cellular, it's all about their antennas and their super-sensitive receivers. I believe most cell phones are only putting out about a half-watt. The old bag phones years ago were 2-3 watts I think.
 

citylink_uk

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chrismoll said:
This got me thinking, with a 5 watt VHF handheld that gets about a 2-3 mile radius with stock duck in my surronding area, how do small plastic antenna 1 watt cell signals on UHF get a good signal from down low and be able to penetrate the foilage.
Antenna base antennas with very high gain and plenty of sites. You would be very lucky to get a good signal from a tower over a mile away in normal conditions.
 

AZScanner

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Yes they do but not like PD radios do.

Cell phones do have data channels but it's mixed into the wide swath of frequencies they use. It's basically ALL data.

For example, the Police radios have one data channel and many voice channels, like so:

C1: data-data-data-data
C2: voice-voice-voice-voice
C3: voice-voice-voice-voice

and so on.

Today's modern CDMA phones however use one wide chunk of spectrum to hold the "data channel" data plus all the voice data, so that would look more like this:

data-voice-data-voice-data-voice-data
data-voice-data-voice-data-voice-data
data-voice-data-voice-data-voice-data
C1. data-voice-data-voice-data-voice-data
data-voice-data-voice-data-voice-data
data-voice-data-voice-data-voice-data
data-voice-data-voice-data-voice-data

Each "chunk" of data is preceded by a code so your phone knows which "chunks" are for you and which ones are not. Here's a more detailed explanation of how CDMA works: http://en.wikipedia.org/wiki/Code_Division_Multiple_Access

Compare that with our wiki entry about trunking:
http://wiki.radioreference.com/index.php/Trunking_Basics

and you'll see theres some really huge differences.

Hope that helps,
-AZ
 

WayneH

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fineshot1 said:
The switch instructs all the surrounding cells to tune a receiver to that channel and sample the signal strength.
Generally each sector of a cell site has a neighbor list. When a call is established that call is typically on multiple sectors at a site and often on more than one at the same time. This permits seemless roaming and in the event one site drops a call it isn't lost.


In this situation it sounds like the site your call was on couldn't hand off for some reason. Possibly because of capacity issues as others have mentioned.

There are close to an infinite number of scenarios otherwise we would never have dropped calls. There are times where a site can extend its coverage farther than the engineer designed it to so it's possible the cell sites in the area are not aware of it due to it not existing in the neighbor list. RF Engineers monitor dropped call numbers so usually when this starts happening they'll add the over-extending site to neighbor lists it commonly comes on to. It's all depends on the Engineer though.
 

w0fg

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So-called "seamless" roaming may not work when the hand-off is between sites belonging diferent providers; e.g. Verizon to Alltel or vice-versa. That is a very common reason for dropped calls in this area.
 
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