Multiplexing, Frequency Division Multiplexing (FDM), Time Division Multiplexing (TDM), Wavelength Division Multiplexing (WDM), Code Division Multiplexing (CDM)

concept of Multiplexing
Frequency Division Multiplexing (FDM)
FDM signal generation
Time Division Multiplexing (TDM)
Synchronous vs statistical
Wavelength Division Multiplexing (WDM)
Code Division Multiplexing (CDM)

1. Topics
•concept of Multiplexing
•Frequency Division Multiplexing (FDM)
–FDM signal generation
•Time Division Multiplexing (TDM)
•Synchronous vs statistical
•Wavelength Division Multiplexing (WDM)
•Code Division Multiplexing (CDM)

2. .
Multiplexing vs. No Multiplexing

3. Multiplexing
Multiplexor (MUX)
Demultiplexor (DEMUX)
Sometimes just called a MUX

4. Multiplexing : Applications
Four communication applications that would be
prohibitively expensive or impossible without
multiplexing are:
1.Telephone systems
2.Telemetry
3.Satellites
4.Broadcasting (radio and TV)

6. Frequency-division multiplexing (FDM)

7. FDM process

8. FDM demultiplexing example

9. FDM signal generation
FDM process
each telephone generates a signal of a similar
frequency range
these signals are modulated onto different carrier
frequencies(f1, f2, f3)

10. FDM signal generation
modulated onto different carrier
frequencies
Requires its own carrier frequency
Composite
signal
FDMmultiplexingprocess,time-domain

11. FDM signal generation
FDMmultiplexingprocess,frequency-domain

12. FDM signal generation
Demultiplexing
separates the individual signals from their carries
and passes them to the waiting receivers.

13. FDM signal generation
FDM demultiplexing process, time-domain

14. FDM signal generation
FDMdemultiplexing,frequency-domain

15. FDM: Composite signal spectrum
WHY???? BW
signal<< BW
medium

16. FDM: Composite signal spectrum
For telephony, the physical line is divided (notionally) into 4kHz bands or channels, i.e.
the channel spacing is 4kHz. Thus we now have:f
Bandlimited
Speech
Guard Bands
4kHz
guard bands -to reduce adjacent channel crosstalk.

17. Analog hierarchy

18. Frequency Division Multiplex
Advantages:
no dynamic coordination
needed
Disadvantages:
waste of bandwidth
if traffic distributed
unevenly
guard spaces
k
3 k
4 k
5 k
6
f
t
c
Channels
k
i

19. Frequency Division Multiplexing

20. Time Division Multiplexing

21. TDM

25. TDM

26. Asynchronous TDM

27. Asynchronous TDM

29. TDM(cont’d)
Examples of asynchronous TDM frames
a. Case 1: Only three lines sending data

30. TDM(cont’d)
b. Case 2: Only four lines sending data

31. TDM(cont’d)
c. Case 3: All five lines sending data

32. TDM(cont’d)
Inverse Multiplexing
takes the data stream from one high-speed line and
breaks it into portion that can be sent across
several lower speed lines simultaneously, with no
loss in the collective data rate

33. TDM(cont’d)
Multiplexin
g and
inverse
multiplexin
g
high-speed breaks it into
portion

34. Statistical TDM Frame Formats

35. Interleaving
The process of taking a group of bits from each
input line for multiplexing is called interleaving.
We interleave bits (1 -n) from each input onto
one output.

36. Interleaving

37. Synchronization
To ensure that the receiver correctly reads the
incoming bits, i.e., knows the incoming bit
boundaries to interpret a “1” and a “0”, a
known bit pattern is used between the frames.
The receiver looks for the anticipated bit and
starts counting bits till the end of the frame.
Then it starts over again with the reception of
another known bit.
These bits (or bit patterns) are called
synchronization bit(s).
They are part of the overhead of transmission.

38. Framing bits

39. Digital hierarchy

40. DS and T line rates

41. T-1 line for multiplexing telephone lines

42. T-1 frame structure

43. E line rates

44. TDM slot comparison

45. Wavelength-division multiplexing (WDM)
WDM is an analog multiplexing technique
to combine optical signals

46. Prisms in wavelength-division multiplexing and demultiplexing

47. Dense Wavelength Division
Multiplexing (DWDM)
Dense wavelength division multiplexing is often called just wavelength
division multiplexing
Dense wavelength division multiplexing multiplexes multiple data streams
onto a single fiber optic line.
Different wavelength lasers (called lambdas) transmit the multiple signals.
Each signal carried on the fiber can be transmitted at a different rate from
the other signals.
Dense wavelength division multiplexing combines many (30, 40, 50, 60,
more?) onto one fiber.

49. Code Division Multiplexing (CDM)
Old but now new method
Also known as code division multiple access (CDMA)
An advanced technique that allows multiple devices to transmit on the
samefrequencies at the sametime using different codes
Used for mobile communications