Pulse code modulation (PCM) involves sampling an analog signal at regular intervals, quantizing the sample values, and encoding the samples as digital code. The analog voice signal is sampled 8000 times per second, with each sample represented by an 8-bit binary number. This results in a digital data rate of 64,000 bits per second to represent the original voice signal. Quantization assigns the sample values to discrete levels, introducing quantization error between the original and encoded signals.

1. Pulse Code Modulation

2. Pulse Code Modulation (PCM)
Analog voice data must be translated into a series of
binary digits before they can be transmitted.
With Pulse Code Modulation (PCM), the amplitude of
the sound wave is sampled at regular intervals and
translated into a binary number.
The difference between the original analog signal and
the translated digital signal is called quantizing error.

3. PCM
PCM uses a sampling rate of 8000 samples per
second.
Each sample is an 8 bit sample resulting in a
digital rate of 64,000 bps (8 x 8000).

4. Converting Samples to Bits
 Quantizing
 Similar concept to pixelization
 Breaks wave into pieces, assigns a value in a
particular range
 8-bit range allows for 256 possible sample
levels
 More bits means greater detail, fewer bits
means less detail

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

6. Categories of multiplexing

7. 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

8. FDM

9. FDM process

10. FDM demultiplexing example

11. 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

12. TDM

13. TDM frames

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

15. SAMPLING

16. 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

17. 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.

18. 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

19. 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)

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. PCM ENCODING

23. 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)

24. 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.

25. 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.

26. 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