PCM - Pulse Code Modulation

PCM :- Pulse Code Modulation
It is the digitization process in which analog signal is represented in digital or discrete form .
It use ordinary analog signal which is digitized at the end office with the help of codec (coder decoder) codec produces 7 or 8 bit numbers .

Codec is inverse of modem -True
It code the digital to analog.
CO  DEC -COder (Analog to Digital) DECoder  (Digital to analog)

PCM is based Nyquest theorem:-
               There are various system for digital transmission:-
1.T₁ carrier system (handle 24 voice channel)
2.Encoding system

There are three methods of PCM:
1.Differential pulse code modulation ( DPCM)
2.Delta Modulation
3.Predictive encoding

1.DPCM :-
Definition :It does not transmit actual sample .It transmit difference between current and previous value .Errors can ignored for voice or speech.

2.Delta modulation :
It is special care of DPCM it uses only one bit per sample .Each sample differs from its predecessor by either +1 or -1 .This is called as a sampling interval .
Granular noise :- The schema which is used for slow changing signal which gives distortion called as granular noise.

3.Predictive encoding : this preemptive to DPCM .Some sampling values are used to protect the next value,for this transmitter and receiver must uses same prediction algorithm.


Data  communication
   characteristics :
1. Delivery     :  Correct destination
2. Accuracy  :  Correct data
3. Timeliness  :  Fast enough
4. Jitter          :  Uneven  delay


Data  representation
1Ttext        :  email
2.Numbers :  Direct  conversion
3. Images   :  pixels
4.Audio      : continous
5. Video     :  movie

Data  flow :
1.Simplex
2.Half Duplex
3.Full Duplex