Multiplexing Techniques such as TDMA FDMA CDMA WDMA

1. MULTIPLEXING
FDMA
TDMA
WDMA
CDMA
By:
Shadab Siddiqui
M.Tech LEOC
DIAT, Pune

2. MULTIPEXING:
• One path many user.
• The process of combining multiple signal onto
a single transmission link.
• It is used for maximum utilization of channel
capacity.
• To accommodate more data channel user.
• It is used to increase the bandwidth to exploit
the capacity of an optical fiber.

3. Types of multiplexing:
• FDM: Frequency division multiplexing (oldest
multiplexing technique)
• WDM: Wavelength division multiplexing
• TDM: Time division multiplexing
• CDM: Code division multiplexing

4. Time Division Multiple Access (TDMA)
• Each user is allowed to
transmit only within
specified time intervals
(Time Slots). Different users
transmit in different Time
Slots.
• When users transmit, they
occupy the whole frequency
bandwidth(separation
among users is performed in
the time domain).

6.  TDM is used to multiplex digital signals.
 LPF is used to band limit the given message signals.
 Commutator is a rotating switch which rotates in anti-
clockwise direction with uniform speed.
 Commutator is used to sample multiple number of
continuous signal simultaneously
 Time taken by commutator to make one complete rotation
is known as frame time Ts
 TDMA requires a centralized control node i.e Time frame is
required to synchronization of all the users.

7. TDMA:
• Speed synchronization has to be maintained
between comm. and decomm.
• The frame so-defined is divided into time
slots, and each user is assigned a Time Slot in
which to transmit its information.

8. Frequency Division Multiple Access (FDMA)
• FDM is used to multiplex
continuous signal.
• Each user transmits with no
limitations in time, but using
only a portion of the whole
available frequency bandwidth.
• Different users are separated in
the frequency domain.
 The major disadvantage of FDMA is the relatively
expensive and complicated bandpass filters
required.

9. FDMA:

10. WDM
(Wavelength Division Multiplexing)

11. Basic Difference:
• WDM and FDM are interrelated.
• WDM is commonly applied to an optical carrier
while FDM typically applies to a radio carrier.
• In WDM all the signals will arrive at the same time
while in TDM they will arrive serially ie one after
other.
• In WDM single fiber multiple wavelength but in
TDM single fiber one wavelength(uses single RF
carrier).

12. • The problem with FDM is that it can not utilize
the full capacity of the system because we need
to ensure the adjacent band do not overlap each
other (wastage with the guard band).
• Although system has the capacity then also in
some cases the channel can not pass the actual
signal.
• In TDM the time is divided into multiple smaller
units called slots and each user is given a slots to
transmit its signal. Each user have the entire
bandwidth of the channel for the short duration
of time.

13. Fig: WDM system

14. WDM:
• The concept was firs published in 1978 and by
1980 WDM system were being realized in the
laboratory.
• The first WDM system combined only two signals.
• Modern system can hand-up upto 160 signals.
• More popular in telecom because they allow to
expand the capacity of the network without
laying more fiber.

15. In optical fiber:
• As data transmission gets more and more heavy,
the need of high rate transmission technology is
increasing, the target is high speed high capacity
transmission technology.
• These requirements are achieved using
multiplexing in optical fiber, where high speed
and great capacity demands are met.
• Different signal with specific wavelength are
multiplexed into a fiber for transmission.

16. WDM SYSTEM:
• Low loss BW of fiber 1200 to 1600 nm.
30 THz Bandwidth
• Capable of carrying 300,000 channel of
10Mbps.(standard BW of video signal)
• Pulse width required few tens of femto second
in TDM which is impossible to achieve.
• Using high quality LASER light of different
wavelength it is possible to achieve the BW in
WDM.

19. • As the time progress the LASER technology is
far more matured and spectral width is
significantly reduced one can essentially put
multiple channel even within a window of
optical fiber.
• Now the channels are closely packed this
system are now called dense WDM (DWDM)
means within a band/window we have
multiple carrier transmission.

20. WDM Standard:
• ITU specified G.692 standard for WDM the
reference frequency is taken as 193.10 THz.
This corresponds to 1552.524 nm.
• ITU has specified that every 100GHz we can
put another channel so spacing specified for
DWM channel is 100Ghz(=0.8 nm at 1552nm).

21.  WDM systems are divided into two different
wavelength pattern coarse and dense wdm.
CWDM
• Short-range communications
• Wide range frequencies
• Wavelength spread far apart 20nm
• Breaks the spectrum into big chunks
• Light signal is not amplified
• Low cost compared to DWDM
• Simple implementation
DWDM
• Long-haul transmission
• Narrow frequencies
• Tightly packed wavelengths 0.8nm
• Breaks the spectrum into small pieces
• Signal amplification is used
• High cost
• Complex Implementation

22. Code Division Multiple Access (CDMA)
• In CDMA each user is assigned a unique code sequence
(spreading code), which it uses to encode its data signal.
• The receiver, knowing the code sequence of the user,
decodes the received signal and recovers the original
data.

23. CDMA
• Different user use same frequency at the same time , but
with different spreading code.
• Generate a pseudo random code with a higher rate than
the data to be transmitted.
• Each user is assigned a unique PR code.
• Each user transmits it’s information by spreading with
unique code. Direct sequence spread spectrum is used.
• Users are separated by code not by time slots and
frequency slots.
• CDMA is power limited system.
• The bandwidth of the coded data signal is chosen to be
much larger than the bandwidth of the original data
signal, that is, the encoding process enlarges (spreads)
the spectrum of the data signal.

24. Thank You!