Digital Communication Differential PCM - Digital Communication

What is Digital Communication - Differential PCM?

Differential PCM (DPCM) technique is the process of preventing the redundant information that is formed when the highly correlated samples are encoded by PCM technique. A sampled value which is calculated from its previous output is used to summarize them with the quantized values.

DPCM Transmitter

It contains Quantizer and Predictor as well with two summer circuits. Below is the pictorial representation of DPCM transmitter.

DPCM Transmitter

The signals at each point are named as −

  • x(nTs) is the sampled input
  • x ^ ( n T s ) is the predicted sample
  • e(nTs) is the difference between the sampled input and predicted output, generally known as prediction error
  • v(nTs) is the quantized output
  • u(nTs) is the predictor input that is the summer output of the predictor output and the quantizer output

The predictor outputs the assumed samples from its previous outputs. The quantized versions of the input signal x(nTs)x(nTs) is given as input to this predictor.

Quantizer Output is represented as −

Differential

Where q (nTs) is the quantization error

Predictor input is the sum of quantizer output and predictor output,

Differential

To regenerate the original input, the same predictor circuit is used to decode.

DPCM Receiver

DPCM receiver contains a decoder, a predictor, and summit circuit. Below is the DPCM receiver.

DPCM Receiver

The encoded receiver input is same as the encoded transmitter output in the absence of noise.

The input to the decoder is processed and that output is summed up with the output of the predictor for output.

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