Frequency Division Multiple Access (FDMA) is a channel access method where the available bandwidth is divided into multiple non-overlapping frequency bands and each user is assigned a specific frequency band. Each user can transmit or receive independently in its assigned frequency band without interference from other users. FDMA requires expensive bandpass filters for each frequency band and has strict linearity requirements for the transmission medium. The number of channels in an FDMA system is calculated by dividing the total available bandwidth minus the guard bands by the bandwidth of each individual channel.

1. Frequency Division Multiple
Access (FDMA)

2. Frequency Division Multiple Access
• implemented at the media access control
(MAC) layer
• the user is assigned a specific frequency band
in the electromagnetic spectrum, and during a
call that user is the only one who has the right
to access the specific band

3. Frequency Division Multiple Access
• Total system bandwidth is divided into narrow
frequency slots. Each user is allocated a
unique frequency band or channel
• A user is free to transmit or receive all the
time on its allocated radio channel, but the
cost of transceiver is high, as each has to be
designed on a different band

4. Frequency Division Multiple Access

5. Numbers of Channels in FDMA
• Let Btotal be the total system bandwidth,
Bguard be the guard band at edge, and Bch
the single radio channel bandwidth. Then the
number of channels in a FDMA system:
N =
Btotal − 2Bguard
Bch

6. Numbers of Channels in FDMA
• Example:
AMPS uses FDMA/FDD with Btotal = 12.5
MHz, Bguard = 10 kHz and Bch = 30 kHz
N =
12.5 × 106 − 2(10 × 103)
30 × 103
N =416

7. FDMA vs TDMA
• Frequency division is very simple: all transmitters
sharing the medium have output power spectra in non-
overlapping bands.
– Many of the problems experienced in TDMA due to
different propagation delays are eliminated in FDMA.
• The major disadvantage of FDMA is the relatively
expensive and complicated bandpass filters required.
– TDMA is realized primarily with much cheaper logic
functions.
• Another disadvantage of FDMA is the rather strict
linearity requirement of the medium.

8. Reference
• http://lenst.det.unifi.it/~mucchi/DOCS/ING/3
bis.Multiplexing.pdf
• http://www.thenetworkencyclopedia.com/ent
ry/frequency-division-multiple-access-fdma/
• http://users.ecs.soton.ac.uk/sqc/EZ412-
612/RCL-19.pdf