Presentation
PCM, Delta Modulation, DPCM
present by
SYED ROHAIL IFTIKHAR
BSET-01173051
INTRODUCTION
Objectives
• PCM (Introduction, Block diagram of PCM,
PCM processes, PCM standards, Bit rate and
bandwidth requirements of PCM, Advantages,
Disadvantages, Application)
• Delta Modulation
(defines, working principle, diagram)
• DPCM(define, working,)
Definations
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
BLOCK DIAGRAM OF PCM
DIFFERENT TYPES OF SAMPLING METHODS
SAMPLING
PCM STANDERED
• There are two standards of pcm namely
• 1) The European Standard
• 2 ) The American Standard
• 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
Quantization of Signal
• Quantization is the process of changing a
continuous-amplitude signal into on with
discrete amplitudes. To communicate sampled
values, we send a sequence of bits that
represents the quantized value. For
16 quantization levels, 4 bits are
required. PCM can use a binary representation
of value
BIT RATE AND BANDWIDTH
REQUIREMENTS OF PCM
• The bit rate of a PCM signal can be calculated form the
• number of bits per sample x the sampling rate
• Bit rate = nb x fs
• The bandwidth required to transmit this signal depends on
• the type of line encoding used. Refer to previous section
• for discussion and formulas.
• A digitized signal will always need more bandwidth than
• the original analog signal. Price we pay for robustness and
• other features of digital transmission.
ADVANTAGES OF PCM
DISADVANTAGES OF PCM
APPLICATION
• Uniform Transmission Quality
• Compatibility of different classes of Traffic in
• the Network
• Integrated Digital Network
• Increased utilization of Existing Circuit
• Low Manufacturing Cost
• Good Performance Over Very poor
• Transmission Paths
• Large Bandwidth required for Transmission
• Noise and crosstalk leaves low but rises
• attenuation
• An integrated Digital network can only be
• realized be a gradual extension of Noise
• In compact disk
• Digital telephony
• Digital audio applications
DELTA MODULATION
• A delta modulation is an analog-to-digital and digital-to-analog signal
conversion
technique used Transfer Data.
Why we used?
• (DM or Δ-modulation) is an analog-to-digital conversion.
DM is the simplest form of differential pulse-code
modulation.(PCM)
Delta Modulation used by Satellite Business Systems or SBS.
To achieve high signal-to-noise ratio, delta
modulation.
DM can change instantly but voice signals can’t not change instantly. DM signal
is smaller than the PCM system
DIAGRAMS OF DM
f signal is large, the next bit in the digital data is 1,
otherwise, it is O .(note)
Demodulation
Demodulation is digital-to-analog signal
conversion.
It’s the reverse System of modulation.
Demodulation was first used in radio receivers.
Simple Implementation of
a DM system
COMPARISON & LIMITATION
• Slope overload (2)When the analog signal has a high rate of change,
the DM can “fall behind” and a distorted output occurs
DPCM
WHY WE ARE GOING FOR DPCM?
• TO IMPROVE THE ENCODING EFFICIENCY OF ANALOG TO DIGITAL CONVERSION.
• INSTEAD OF TRANSMITTING THE SAMPLE VALUES, WE TRANSMIT THE DIFFERENCE BETWEEN THE
SUCCESSIVE
• SAMPLE VALUES.
• M(K) IS KTH SAMPLE, INSTEAD OF TRANSMITTING M(K)
• D(K) = DQ(K) -M(K -1)
• AT THE RECEIVER, KNOWING PRECIOUS SAMPLE VALUE M(K-1) , THE M(K) IS RECONSTRUCTED.
• DIFFERENCE BETWEEN THE SUCCESSIVE SAMPLES IS GENERALLY MUCH SMALLER THAN SAMPLE
VALUES. ’ P M ’ IS
• REDUCED CONSIDERABLY.
• ΔV = / P M L
• PREDICTING THE VALUES OF KTH SAMPLE M(K) FROM PREVIOUS SAMPLE M(K) FROM M(K) CAN BE
ESTIMATED, THEN
• D(K) =M(K) -M(K) AT THE RECEIVER M(K) FROM PREVIOUS SAMPLE AND GENERATE M(K) BY ADDING
D(K) TO
• ESTIMATE M(K)
• DIFFERENTIAL PULSE CODE MODULATION IS A
TECHNIQUE OF ANALOG TO DIGITAL SIGNAL CONVERSION.
THIS TECHNIQUE SAMPLES THE ANALOG SIGNAL AND THEN
QUANTIZES THE DIFFERENCE BETWEEN THE SAMPLED
VALUE AND ITS PREDICTED VALUE. IT THEN ENCODES THE
SIGNAL TO FORM A DIGITAL VALUE.
• BASIC CONCEPT OF DPCM - CODING A DIFFERENCE, IS
BASED ON THE FACT THAT MOST SOURCE SIGNALS SHOW
SIGNIFICANT CORRELATION BETWEEN SUCCESSIVE SAMPLES
SO ENCODING USES REDUNDANCY IN SAMPLE VALUES
WHICH IMPLIES LOWER BIT RATE.
ADVANTAGES OF DPCM
• 1)BANDWIDTH REQUIREMENT OF DPCM IS
LESS COMPARED TO PCM.
• 2) QUANTIZATION ERROR IS REDUCED
BECAUSE OF PREDICTION FILTER.
• 3) NUMBERS OF BITS USED TO
REPRESENT .ONE SAMPLE VALUE ARE ALSO
• REDUCED COMPARED TO PCM
AN ILLUSTRATION OF DPCM'S ADVANTAGES
OVER PCM
• A TYPICAL EXAMPLE OF A SIGNAL GOOD FOR DPCM IS A LINE IN A
CONTINUOUSTONE (PHOTOGRAPHIC) IMAGE.
• FOR ILLUSTRATION, WE PRESENT TWO HISTOGRAMS MADE FROM
THE SAME PICTURE WHICH WERE CODED IN TWO WAYS. THE
HISTOGRAMS SHOW THE PCM AND DPCM SAMPLE FREQUENCIES,
RESPECTIVELY.
• ON THE FIRST HISTOGRAM, LARGE NUMBER OF SAMPLES HAS A
SIGNIFICANT FREQUENCY AND WE CANNOT PICK ONLY A FEW OF
THEM WHICH WOULD BE ASSIGNED SHORTER CODE WORDS TO
ACHIEVE COMPRESSION. ON THE SECOND HISTOGRAM PRACTICALLY
ALL THE SAMPLES ARE BETWEEN -20 AND +20, SO WE CAN ASSIGN
SHORT CODE WORDS TO THEM AND ACHIEVE A SOLID COMPRESSION
RATE.
DIAGRAMS
MERITS OF DPCM
• BANDWIDTH REQUIREMENT OF DPCM IS LESS
COMPARED TO PCM.
• QUANTIZATION ERROR IS REDUCED BECAUSE
OF PREDICTION FILTER
• NUMBERS .OF BITS USED TO REPRESENT .ONE
SAMPLE .VALUE ARE ALSO REDUCED
COMPARED TO PCM.
REAL LIFE APPLICATION
