A mobile operator has a total bandwidth of 10 MHz available for the GSM system. In GSM, each channel occupies 200 kHz band, compute the number of channels available per cell if a system uses 3 cell clusters.

(10Mhz/200khz)/3 or (10Mhz / 2*200khz)/3 ?????

Given Data -

Total Bandwidth = 10 MHz

Channel Bandwidth = 200 KHz

Number of Clusters = N = 3

System Type = GSM

To Find -

Number of Channels available per Cell = ?

Formula -

Number of Channels available per Cell = Total Available Channel / Number of Clusters (N)

Solution -

• As the system is GSM, that means it follows FDD (Frequency Division Duplexing) and provides separate channels for uplink and downlink.
• The FDD system does enable true simultaneous transmission and reception of signals.
• To do this FDD requires two channels this may not always use the available spectrum efficiently.
• In networking, there are two cables. Full-duplex Ethernet uses two twisted pairs inside the cable for simultaneous send and receives operations.
• This specifies GSM uses 2 simplex channels to provide full-duplex voice and control channels.

Therefore Here,

Channel Bandwidth = 200 KHz * 2 Simplex channel = 400 KHz/Duplex Channel

Now, Calculate the total available channels

$$ = \frac{10 * 10^6}{400 * 10^3} = 25$$

Total Available Channels = 25

Number of Channels available per Cell = 25 / 3 = 8.34 Channels.