What is FDMA?

FDMA allows users to transmit signals simultaneously to satellite transponders with the help of assigning a specific frequency to every user among a channel.

FDMA sub-divide frequency into a several frequency band with non-overlapping.

Each transaction of signal has its own unique radio channel. Channels are probably 30 kHz or less used to transmit or receive channels.

 Frequency allocation made by national policies. Uplink (i.e. from mobile station to base station). Downlink (i.e. from base station to mobile station) uses frequency bands like. Uplink and downlink with frequencies mentioned below :

Uplink	890.2 MHz, 915 MHz
Downlink	935.2 MHz to 960 MHz

• Uplink (UL) and downlink (DL) is will be as written below with the help of one relation

f_d  = f_u + 45 MHz

• For Example :

If UL frequency is :

f_u = 890 MHz + n∙ 0. 2 MHz

Then

f_d = 935 MHz + n ∙ 0. 2 MHz

• Fixed assigned frequency makes scheme very inflexible limits to no. of sender turn into disadvantage of FDMA.

Advantages of FDMA

These systems require a low bit rate. Hence, they offer few advantages 

• There is low inter symbol interference (ISI). Therefore, it reduces the cost.
• It is not necessary to have equalization.
• The implementation is easy. A system can be easily made which provides improvements in terms of speech encoders and also the bit rate is reduced.
• The number of bits required for synchronization and framing are less as the transmission is continuous.

Disadvantages

There are few disadvantages of this technique listed below.

• We need to improve the capacity signal to interference reduction or SNR.
• But also the maximum flow rate per channel is fixed and small.
• The cost of implementation is more as hardware requires narrowband filters. Because of which they cannot be realized using VLSI.
• The channel capacity is reduced because of the guard bands. 
• Hardware implies narrowband filters, which cannot be realized in VLSI and therefore increases the cost.

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