PULSE CODE MODULATION

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PULSE CODE MODULATION

• Designed by Ian Browne
• Siobhan Darby
• Noel Skehan
• Fiona Hussey

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Pulse Code Modulation (a definition) PCM is a
form of digital transmission that converts analog
data to coded pulse signals. First, the
amplitude of the voice conversation is sampled,
then, it is encoded into binary form.
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A Brief History PCM was invented by A.H.
Reeves in 1937. There was a slow development but
gradually PCM became the most efficient
modulation technique. The development of the
transistor changed the situation dramatically.
The first major commercial usage of PCM was for
the transmission of multiplexed telephone
channels, using multipair audio cable.During
the 1950s PCM was used to a great extent.
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How PCM works (Some of the techniques used)
a) Sampling b) Quantizing c) Encoding d)
Regeneration e) Decoding f) Reconstruction
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Transmission Requirements Transmission of 2nfm
pulses/sec requires a bandwidth of at least nfm.
Therefore, the bandwidth required for PCM is, in
the ideal case n times as great as the bandwidth
required for transmission of the analogue signal.
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Applications and Uses PCM is beneficial in
providing greater traffic capacity. Cost wise
PCM is not too expensive with the main cost in
the terminal equipment. The first main junction
PCM system was introduced by the American
Telephone and Telegraph Co. in 1962. THE B.P.O.
24-CHANNEL JUNCTION PCM SYSTEM is an example of
a JUNCTION PCM system.
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Advantages and Disadvantages of using
PCM Advantages a) Uniform Transmission
Quality. b) Compatability of
Different Classes of Traffic
in the Network c)
Integrated Digital Network.
d) Increased Utilisation of Existing Circuits
e) Low Manufacturing Cost
f) Good Performance Over Very Poor
Transmission
Paths Disadvantages a) large bandwidth required
for transmission b)
Noise and crosstalk levels low but
risesattenuation
c) An integrated digital network can
only be realised
by a gradual extension of
digital links in theexisting (analogue)
network
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Future Developments Future developments will
include 1) Visual Telephone 2)
Sound Programme 3) Broadcast Television