2. OBJECTIVES
What is FDMA?
Features of FDMA.
Advantage of FDMA.
Disadvantage of FDMA.
What is TDMA?
Features of TDMA.
Advantage of TDMA.
Disadvantage of TDMA.
4. Total system bandwidth is divided
into narrow frequency slots. Each
user is allocated a unique
frequency band or channel.
1
7
6
5
2
3
4
(FDMA)
Frequency Division
Multiple Access
6. Systems used for low/medium traffic intensity.
Narrow band interference resistance of the
channel, but sensitive to interference.
Simplicity of work equipment.
Difficulty of insertion of the signaling associated
with the call.
Limitations for quality improvement.
Features of FDMA
7. Numbers of Channels in FDMA
Let,
Btotal = Total system bandwidth,
Bguard = Guard band at edge,
Bch = Single radio channel bandwidth.
Then the number of channels in a FDMA System:
N =
Btotal − 2Bguard
Bch
8. Numbers of Channels in FDMA
Example:
AMPS (Advanced Mobile Phone Service) uses FDMA with,
Btotal = 12.5 MHz,
Bguard = 10 kHz and
Bch = 30 kHz
N =
12.5 × 106 − 2(10 × 103)
30 × 103
N =416
9. Advantages of FDMA
If channel is not in use, it sits idle.
Channel bandwidth is relatively narrow
(30kHz).
Simple algorithmically, and from a hardware
standpoint.
Fairly efficient when the number of stations is
small and the traffic is uniformly constant.
Capacity increase can be obtained by reducing
the information bit rate and using efficient
digital code.
No need for network timing.
10. Disadvantages to using FDMA
The presence of guard bands.
Maximum bit rate per channel is fixed .
Small inhibiting flexibility in bit rate capability.
Does not differ significantly from analog system.
12. Several users share
one frequency
channel.
Users have to wait
for their turns to
transmit or receive.
0 1 2 3 4 5 6 7 0
0 1 2 3 4 5 6 7 0
(TDMA )
Time Division Multiple Access
TDMA Frame
TDMA frame length = 4.615 ms / 8 Time slot
14. Access Complexity: Strict time synchronization.
For high capacity systems Traffic.
Simplification of multi-channel stations.
Delay in communication.
Need for digitization of information.
It achieves high quality.
Possibility of using a single carrier frequency for both
directions of communication.
Features of TDMA
16. Advantages of TDMA
Flexible bit rate.
No frequency guard band required.
No need for precise narrowband filters.
Extended battery life.
The most cost-effective technology for upgrading a current analog
system to digital
17. Disadvantages to using TDMA
Requires network-wide timing synchronization.
Requires signal processing for matched filtering and
correlation detection.
Demands high peak power on uplink in transient mode.
Multipath distortion.