Locking a Sierra Modem to a Specific Cell Channel

In certain circumstances you may wish to lock your modem to a specific cell channel.

This can happen if you have two competing cell towers in your area, which will be operating on different channels, and you wish to only use one tower. The tower you don't want to use may have a stronger signal but is congested and delivers lower speeds than the other, less congested tower.

Under normal usage, your modem will use the tower with the higher signal strength even though it may be congested. Since the towers will be using a different cell channel it is possible to lock your modem to the channel of the lower signal, faster tower. It will then always use that tower, even if the other tower has a higher signal level.

Some information on cell channels as they are used in Australia can be found here.

Channels that are in use for 3G in the different bands are as follows.

Frequency
Channel
850Mhz
4412
 
4436
 
4387
 
4363
900Mhz
3038
 
3081
2100Mhz
10638
 
10812
 
10837
   

 

This technique only works on Sierra modems, as the other makes don't have the necessary AT Commands to accomplish this.

Channel locking is done by issuing AT Commands to the modem and to do this we must go to the Modem section and the Custom subsection.

You enter the AT Command in the command line, press Enter or click Submit, and see the response from the modem in the Response box.

Determine the Channels

This part of the procedure is the trickiest since you have to make the modem connect to the competing towers in order to determine the cell channel used by each tower. The use of a directional antenna is handy in this situation.

When the modem is connected to a tower, check the Network Status subsection and note the Cell ID of the tower. This will be different for each tower. When it is connected to a tower, go to the Custom subsection and enter the following AT Command.

AT!GSTATUS?

In the response box you will see, after a delay of up to 15 seconds, something like the following.

In this case the cell channel is 4436, although your channel will vary. Note this channel number and which cell tower it is associated with.

Now make the modem connect to the other tower. This will probably require you to unplug the modem and replug it in again while blocking it from the original tower. Changing the direction of an antenna is a good way to do this.

Repeat the above procedure of issuing the AT Command and noting the tower's cell channel.

Locking to a Channel

When you have determined which channel is used by the desired tower you can lock your modem to use that channel. It will continue to use that channel even after rebooting the router until the signal from that tower is too low to be usable. It will then use any other signal it can find. To force it back to using that channel again the modem must be unplugged and plugged in again to force a new connection.

Go to the Custom subsection again and enter the following AT Command.

AT!UMTSCHAN=1,4436

replacing the 4436 with the channel from your desired tower.

The modem will reboot and the router may stop working for a period of time, 30 to 40 seconds, before the modem restarts itself and reconnects to the correct tower.

Checking for Channel Lock

You can check the modem and see if the channel locking worked as expected.

In the Custom subsection enter the following AT Command.

AT!UMTSCHAN?

Wait for the response and you should see this.

Enable : 01
Channel : 4436
 

If you get Enable : 0 then the locking did not occur.

Disabling Channel Lock

To disable the channel locking enter the following AT Command.

AT!UMTSCHAN=0

The modem will reboot and the router may stop working for a period of time, 30 to 40 seconds, before the modem restarts itself and reconnects to the tower.