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Posted Jan 15, 2010
3:31:37 AM
how many simultaneous voice calls can a cell site tower handle?

You know those big tall cellphone towers, how many simultaneous voice calls can each of them handle?

100 simultaneous calls for 2G? 200? simultaneous calls for 3g?

 

And can AT&T tell how many cellphones are in range of a specific tower and can AT&T tell how many cellphones are connected to your network throughout an entire city?

You know those big tall cellphone towers, how many simultaneous voice calls can each of them handle?

100 simultaneous calls for 2G? 200? simultaneous calls for 3g?

 

And can AT&T tell how many cellphones are in range of a specific tower and can AT&T tell how many cellphones are connected to your network throughout an entire city?

how many simultaneous voice calls can a cell site tower handle?

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Jan 15, 2010 6:33:14 AM
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I am not sure of the maximum, but it depends on the connection.  The old TDMA network would not handle as many as the GSM network, and the GSM network can not handle as many as the 3G network.  In addition, a call from a 3G phone can be GSM or 3G voice (3G can be data only or data and voice).  Also, the number of data connections would effect the maximum.

 

I am sure that at&t could give you counts of connections by tower, but due to the mobile nature of the cell network, the numbers would be constantly changing.  By city, I am not sure, since tower ranges can go across city limits.  Although at&t can locate a phone, I doubt that it is done for every phone in the network.

I am not sure of the maximum, but it depends on the connection.  The old TDMA network would not handle as many as the GSM network, and the GSM network can not handle as many as the 3G network.  In addition, a call from a 3G phone can be GSM or 3G voice (3G can be data only or data and voice).  Also, the number of data connections would effect the maximum.

 

I am sure that at&t could give you counts of connections by tower, but due to the mobile nature of the cell network, the numbers would be constantly changing.  By city, I am not sure, since tower ranges can go across city limits.  Although at&t can locate a phone, I doubt that it is done for every phone in the network.

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Jan 15, 2010 6:39:59 AM
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Just looking at the many configurations of cell towers out there would tell me that capacity can vary significantly from tower to tower.... Depending on design.

 

I would also be shocked if AT&T did not have some mechanism to monitor tower (network) utilization, real time.  

 

As for how many are in range....  I don't think any phone in standby mode, transmits it's presence continuously, does it?   It would be difficult to pin down the number of phones in range, if they are just "pinging" the network intermittently.....

Just looking at the many configurations of cell towers out there would tell me that capacity can vary significantly from tower to tower.... Depending on design.

 

I would also be shocked if AT&T did not have some mechanism to monitor tower (network) utilization, real time.  

 

As for how many are in range....  I don't think any phone in standby mode, transmits it's presence continuously, does it?   It would be difficult to pin down the number of phones in range, if they are just "pinging" the network intermittently.....

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Jan 15, 2010 9:52:17 AM
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yallknowme wrote:

You know those big tall cellphone towers, how many simultaneous voice calls can each of them handle?

100 simultaneous calls for 2G? 200? simultaneous calls for 3g?

 

And can AT&T tell how many cellphones are in range of a specific tower and can AT&T tell how many cellphones are connected to your network throughout an entire city?


It's complicated.

 

For 2G, the number of calls depends on how many channels are allocated to a cell. Each channel is 100kHz in each direction and traditionally was dividided in 8 timeslots, serving 8 calls, but with newer voice encoders this could potentially double. How many channels are allocated depends on how much spectrum the carrier has available, how much traffic they expect in that area etc. The channels that are used in one cell can't be used in the immediately neighboring ones, so it's a balancing act. Also note that typically a base station is typically configured with three sectors, each covering about 120 degrees, each of the being essentially a different cell. Among other things, this makes it easier to reuse channels (you can safely use the same channel in neighboring base stations on sectors that are facing away from each other), which is key to increasing capacity.

 

For 3G, it's more complicated, because there isn't a hard limit as with 2G. Theoretically, you could keep adding users, but eventually it would be unusable. The location of the users also affects things. If you start overloading a 3G cell, users that are far are going to start getting affected first. The number of channels is important here too, but there's no simple way to say X calls/channel. Each 3G channel (carrier) is 5MHz wide in each direction, but all cells use the same channels. Typically AT&T uses either one or two channels, depending on the area. I'm not sure if they've deployed a 3rd channel anywhere. Since reuse is not a problem here, the main reasons for not deploying more channels are total spectrum available to the carrier (a 5MHz slice has to be taken out of 2G service) and cost.

 

To further complicate things, you have voice and data on the same channel, so you can't even say X calls/channel without making some assumption about data traffic as well.

 

Your second question is easier to answer. The carrier defines groups of cells that are known as location areas. As an idle phone is moving, it will send a message updating its location only when it crosses a location area boundary, or periodically every few hours (configurable by the carrier). As long as you are moving within a location area, AT&T only knows which location area you are in, not the specific cell, so when it has something for you (a call, a message), it tries to find you in every cell in the location area. Of course, as soon as you have some activity (including the periodic location update mentioned above) they know which cell you are in at the time. They could in theory make each location area contain exactly one cell, and they would then always know which cell you are in, but this would create too much location update traffic and wouldn't help battery life. So, in short, they don't really know how many phones are within range, unless they are currently active or have been active very recently.

 

As for knowing how many phones are connected to the network, that's easy. They have a record of each user and their last location update in a database caller VLR (visitor location register). If you switch your phone off when you're in coverage, your phone will de-register with the network and your record will be deleted. If you drop off (travelling out of coverage, battery dying etc), and the network doesn't receive a location update in a period longer than the periodic location update, you will also get de-registered as the assumption will be that you're no longer there.


yallknowme wrote:

You know those big tall cellphone towers, how many simultaneous voice calls can each of them handle?

100 simultaneous calls for 2G? 200? simultaneous calls for 3g?

 

And can AT&T tell how many cellphones are in range of a specific tower and can AT&T tell how many cellphones are connected to your network throughout an entire city?


It's complicated.

 

For 2G, the number of calls depends on how many channels are allocated to a cell. Each channel is 100kHz in each direction and traditionally was dividided in 8 timeslots, serving 8 calls, but with newer voice encoders this could potentially double. How many channels are allocated depends on how much spectrum the carrier has available, how much traffic they expect in that area etc. The channels that are used in one cell can't be used in the immediately neighboring ones, so it's a balancing act. Also note that typically a base station is typically configured with three sectors, each covering about 120 degrees, each of the being essentially a different cell. Among other things, this makes it easier to reuse channels (you can safely use the same channel in neighboring base stations on sectors that are facing away from each other), which is key to increasing capacity.

 

For 3G, it's more complicated, because there isn't a hard limit as with 2G. Theoretically, you could keep adding users, but eventually it would be unusable. The location of the users also affects things. If you start overloading a 3G cell, users that are far are going to start getting affected first. The number of channels is important here too, but there's no simple way to say X calls/channel. Each 3G channel (carrier) is 5MHz wide in each direction, but all cells use the same channels. Typically AT&T uses either one or two channels, depending on the area. I'm not sure if they've deployed a 3rd channel anywhere. Since reuse is not a problem here, the main reasons for not deploying more channels are total spectrum available to the carrier (a 5MHz slice has to be taken out of 2G service) and cost.

 

To further complicate things, you have voice and data on the same channel, so you can't even say X calls/channel without making some assumption about data traffic as well.

 

Your second question is easier to answer. The carrier defines groups of cells that are known as location areas. As an idle phone is moving, it will send a message updating its location only when it crosses a location area boundary, or periodically every few hours (configurable by the carrier). As long as you are moving within a location area, AT&T only knows which location area you are in, not the specific cell, so when it has something for you (a call, a message), it tries to find you in every cell in the location area. Of course, as soon as you have some activity (including the periodic location update mentioned above) they know which cell you are in at the time. They could in theory make each location area contain exactly one cell, and they would then always know which cell you are in, but this would create too much location update traffic and wouldn't help battery life. So, in short, they don't really know how many phones are within range, unless they are currently active or have been active very recently.

 

As for knowing how many phones are connected to the network, that's easy. They have a record of each user and their last location update in a database caller VLR (visitor location register). If you switch your phone off when you're in coverage, your phone will de-register with the network and your record will be deleted. If you drop off (travelling out of coverage, battery dying etc), and the network doesn't receive a location update in a period longer than the periodic location update, you will also get de-registered as the assumption will be that you're no longer there.

Re: how many simultaneous voice calls can a cell site tower handle?

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Jan 17, 2010 2:25:01 PM
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Professor
Edited by formercanuck on Jan 17, 2010 at 2:34:47 PM

There are MANY factors:

 

1.  Cell spectrum in use (2g/3g).  10MHz --> 40MHz = big difference

2.  Backhaul.  Single T1 'may' be considered decent for calls only, but adding in EDGE/3G data into the mix will load up the line.

3.  Codec.  Full rate voice vs. half rate voice 'can' give a 2:1 capacity increase, assuming that coverage isn't an issue.

4.  DTX - discontinuous transmission - saving capacity when nobody is talking

5.  2G has a few 'tricks' to increase capacity - such as frequency hopping  to bring capacity closer to 3g.

 

Message Edited by formercanuck on 01-17-2010 02:34:47 PM

There are MANY factors:

 

1.  Cell spectrum in use (2g/3g).  10MHz --> 40MHz = big difference

2.  Backhaul.  Single T1 'may' be considered decent for calls only, but adding in EDGE/3G data into the mix will load up the line.

3.  Codec.  Full rate voice vs. half rate voice 'can' give a 2:1 capacity increase, assuming that coverage isn't an issue.

4.  DTX - discontinuous transmission - saving capacity when nobody is talking

5.  2G has a few 'tricks' to increase capacity - such as frequency hopping  to bring capacity closer to 3g.

 

Message Edited by formercanuck on 01-17-2010 02:34:47 PM

Re: how many simultaneous voice calls can a cell site tower handle?

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Jan 21, 2010 3:06:51 PM
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Edited by redwolfe on Jan 21, 2010 at 3:13:01 PM

I can answer one question, Praptis.  Yes, there are third carrier deployments. 

 

One other limitation is Backhaul.  Reuse is still a problem if you have too many sites in a congested area.  (its not the same term, but its the same effect)  Basically as you stated the coverage shrinks as the site reduces radio power to reduce coverage area as it runs out of resources.

 

 

 

Edit:  One more comment -- almost all handsets have a limit of 3 carriers maximum that they can utilize.  Once you get to 3 (and FEMTO is a fourth) you start having issues.  Thats a problem with the GSM/UMTS standard.

Second edit:  One t1 isn't even close to enough backhaul even for voice.  The minimum at launch 5 years ago was 2 t1s and that was barely sufficient.  Currently minimum is 4 t1s, and 12 t1 deployments are not uncommon.  More and more sites will start launching with IP instead of ATM connections and t1s will be replaced by links to the IP backbone.  I know of a 20 t1 deployment.
Message Edited by redwolfe on 01-21-2010 03:13:01 PM

I can answer one question, Praptis.  Yes, there are third carrier deployments. 

 

One other limitation is Backhaul.  Reuse is still a problem if you have too many sites in a congested area.  (its not the same term, but its the same effect)  Basically as you stated the coverage shrinks as the site reduces radio power to reduce coverage area as it runs out of resources.

 

 

 

Edit:  One more comment -- almost all handsets have a limit of 3 carriers maximum that they can utilize.  Once you get to 3 (and FEMTO is a fourth) you start having issues.  Thats a problem with the GSM/UMTS standard.

Second edit:  One t1 isn't even close to enough backhaul even for voice.  The minimum at launch 5 years ago was 2 t1s and that was barely sufficient.  Currently minimum is 4 t1s, and 12 t1 deployments are not uncommon.  More and more sites will start launching with IP instead of ATM connections and t1s will be replaced by links to the IP backbone.  I know of a 20 t1 deployment.
Message Edited by redwolfe on 01-21-2010 03:13:01 PM

Re: how many simultaneous voice calls can a cell site tower handle?

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