1. MULTIPLEXING TYPES
Frequency Division Multiplexing
Time Division Multiplexing
Wavelength Division Multiplexing

2. Categories of multiplexing

3. FDM
Is the process of translating
individual speech circuits (300-
3400Hz) into pre assigned slots
within the bandwith of transmission
medium. and, the preassigned slots
are always available to each user

4. FDM

5. FDM process

6. FDM demultiplexing example

7. Example 1

8. TDM
The process where a transmission
medium is shared by a number of circuits
in time domain by establishing a
sequence of time slots during which
individual channels can be transmitted…
Thus the entire bandwidth is periodically
available to each channel

9. TDM

10. TDM frames

11. PCM PROCESSES
 Filtering
 Sampling
 Quantization
 Encoding
 Line coding

12. SAMPLING

13. SAMPLING THEOREM
 “ If a band limited signal is sampled at regular
intervals of time and at a rate equal to or more
than twice the highest signal frequency in the
band, then the sample contains all the
information of the original signal”
 Fs= >2fH

14. PULSE CODE MODULATION
• Voice Frequency range 0- 4 Khz
• Sampling the Voice Signal @ 8 Khz
(Double the Max. Frequency as per
sampling theorem) i.e. 8000s/sec
• Sampling time period Ts=1sec/8000
• Ts= 125 microsec
• Time available for sampling each channel,
when we have N total channels=125/N
• In PCM, Time frame=125microsec ;time
available per chl=125/32 =3.9microsec.

15. QUANTIZING
 The process of measuring the numerical
values of the samples and giving them a
table value in a suitable scale
 The finite number of amplitude intervals is
called the ‘quantizing interval’ like
quantizing interval no.1 is 10-20mV; 2 is
20-30mV etc. in a case of 1V signal.
 Linear quantizing is where the quantizing
intervals are of the same size

16. QUANTIZING LEVELS

17. QUANTIZING (one side)

18. QUANTIZING
 Quantization intervals are coded in binary
form, and so the quantization intervals will be
in powers of 2.
 In PCM, 8 bit code is used and so we have 256
intervals for quantizing (128 levels in the
positive direction and 128 levels in negative
direction)

19. QUANTIZING (both sides)

20. QUANTIZATION DISTORTION
 The deviation between the amplitude of
samples at the transmitter and receiving ends
 In linear quantization, the distortion is more
and to decrease the distortion, the no. of steps
in the given amplitude range has to be
increased.
 Due to BW limitations, more quantum levels in
small amplitude region are planned results to
Non linear (uniform) quantization

21. COMPANDING
 Is the process where non uniform quantization
is achieved using segmented quantization
 In companding, to specify the location of
sample value, the following are necessary…
sign of the sample, the segment no., the
quantum level within the segment.

22. SEGMENTATION

23. PCM ENCODING

24. FRAME STRUCTURE
 In PCM we have 32 Ts and Ts 0 (FAW)
carries the synchronization signals and FAW
digit value is X 0 0 1 1 0 1 1 . FAW
transmitted in alternate frame. In FAW unused
frames, supervisory and alarm signals are
transmitted
 Ts 16 carries the signalling information (for 2
channels)

25. FAW/ALARM DIGIT CODES

26. FRAME STRUCTURE
 For carrying the signalling for all 30 chls and
for carrying sync. Data for all frames, in PCM
16 frame pattern is used and it is known as
multi frame
 Duration of multi frame is 2msecs.

27. PCM Standards
 THERE ARE TWO STANDARDS OF PCM
NAMELY
 1) THE EUROPEAN 2 ) THE AMERICAN.
 THEY DIFFER SLIGHTLY IN THE DETAIL OF
THEIR WORKING BUT THE PRINCIPLES ARE
THE SAME.
 EUROPEAN PCM = 30 CHANNELS
 NORTH AMERICAN PCM = 24 CHANNELS
 JAPANESE PCM = 24 CHANNELS
 IN INDIA WE FOLLOW THE EUROPEAN PCM
OF 30 CHANNELS SYSTEM WORKING.

28. EUROPEAN PDH HIERARCHY WITH BIT RATES
MUX BIT RATE PARTS PER CHANNELS
MILLION
2 Mbps 2.048 Mbps +/- 50 ppm 30
8 Mbps 8.448 Mbps +/- 30 ppm 120
34 Mbps 34.368 Mbps +/- 20 ppm 480
140 Mbps 139.264 Mbps +/- 15 ppm 1920

29. Dig. Hier based on 24chl PCM

30. MULTIPLEXING OF ASYNCHRONOUS SIGNAL
 in order to move multiple ASYNCHRONOUS 2 mbps data
streams from one place to another, they are combined
together or “multiplexed” in groups of four.
 this is done by taking 1 bit/word from stream #1, followed
by 1 bit/word from #2, then #3, then #4.
 the transmitting multiplexer also adds additional bits in
order to EQUAL or synchronise the bits in the
multiplexer and the process adopted for such
synchronization is called “justification” bits or
“ pulse stuffing ”

31. JUSTIFICATION TYPES
 Positive justification: Common
synchronization bit rate offered at each
tributary is higher than the bit rate of
individual tributary.
 Positive-negative justification
 Negative justification

32. DIGITAL MUX CONCEPTS
• BYTE INTERLEAVING
• WORD / BYTE / BLOCK INTERLEAVING:
• IF THE CHANNEL TIME SLOT IS LONG ENOUGH TO
ACCOMMODATE A GROUP OF BITS THEN THE
MULTIPLEXED SIGNAL IS CALLED A “ BYTE
INTERLEAVED OR WORD INTERLEAVED SIGNAL”.
A1 A2 A3 A4 B1 B2 B3 B4 C1 C2 C3 C4 D1 D2 D3 D4

33. DIGITAL MUX CONCEPTS
 BIT INTERLEAVING:
 ALTERNATELY EACH CHANNEL CODE CAN BE
SCANNED ONE DIGIT AT A TIME. THE
MULTIPLEXED SIGNAL IS CALLED A “BIT
INTERLEAVED SIGNAL”.
 “BIT INTERLEAVING” IS USED IN HIGHER
ORDER MULTIPLEXING.
A1 B1 C1 D1 A2 B2 C2 D2 A3 B3 C3 D3 A4 B4 C4 D4

34. Encoded FDM USA&canada

35. Encoded TDM Japanese

36. Dig Hier based on 30chl PCM-
Encoded TDM European