Number of channel in FDMA system

In an FDMA/FDD system, a single user occupies a single channel while the call is in process. The single-channel is two simplex channel that is frequency duplexed with a separation.

 The number of channels that can be simultaneously supported in an FDMA system is given by : 
N =  Bt - 2 Bguard  /  Bc   
Where,

 Bt  = Total spectrum allocation 
Bguard  =  Guard band allocated at the edge of the allocated spectrum
Bc = Channel bandwidth         
                    
For example:

Bt  = 10 MHz
Bguard = 10 KHz
Bc = 30 KHz

Find the number of channels available in the FDMA system?

             N =  Bt - 2 Bguard  /  Bc 
  
              = 10 * 106 – 2 * 10 * 103 / 30 * 103

          N  = 333

Each cellular carrier is allocated 333 channels.