Differential pulse-code modulation (DPCM)

1. DIFFERENTIAL PULSE-
CODE MODULATION
(DPCM)
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2. Cont’d
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3. Differential pulse-code modulation
(DPCM)
• Exploits the use of lossy data compression to remove the redundancy inherent in a
message signal, such as voice or video, so as to reduce the bit rate of the
transmitted data without serious degradation.
• In effect, increased system complexity is traded off for reduced bit rate,
therefore reducing the bandwidth requirement of PCM.
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4. DPCM…
• DPCM, the scheme to be considered for channel-bandwidth conservation,
exploits the idea of linear prediction theory with a practical difference:
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In the transmitter, the linear prediction is performed on a quantized version of the
message sample instead of the message sample itself, as illustrated

5. DPCM…
• The resulting process is referred to as differential quantization.
• The motivation behind the use of differential quantization follows from two
practical considerations:
• In order to cater to both requirements in such a way that the same structure is
used for predictors in both the transmitter and the receiver.
• The transmitter has to perform prediction error filtering on the quantized version
of the message signal rather than the signal itself,
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1. Waveform encoding in the transmitter requires the use of quantization.
2. Waveform decoding in the receiver, therefore, has to process a quantized signal.

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8. DPCMTransmitter
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9. DPCM Receiver
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From the foregoing analysis, we thus observe that, in a noise-free environment, the linear predictors in the
transmitter and receiver of DPCM operate on the same sequence of samples, mq,n
It is with this point in mind that a feedback path is appended to the quantizer in the transmitter

10. DELTA MODULATION
(NEXT)
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