The shape of the waveform is affected by two mechanisms:
Both of these mechanisms cause the pulse shape to degrade as a function of distance. During the time that the transmitted pulse can still be reliably identified, the pulse is thus regenerated. The circuit that perform this function at regular intervals along a transmission system are called regenerative repeaters.
The source decoder accepts the output sequence from the channel decoder and, from knowledge of the source encoding method used, attempts to reconstruct the original signal from the source.
where, n is bit of quantizer.
To compress the signal at transmitter and expand the signal at receiver is combinely called as companding. Compression and expansion is done by passing the signal through the amplifier having non-linear transfer characteristics.
There are two types of companding techniques μ-law companding and A-law companding.
where, μmax = 225
where, Amax = 87.6
The two main differential coding schemes are:
where, Δopt = Optimum size of Δ
Hunting is the second problem, this occur when message is almost constant.
The adaptive delta modulation is scheme in which, step choose step size in accordance with message signal’s sampled value to overcome slope overload error and hunting. If the message varies at a high rate, then step size is high and if message is varying slowely, then step size is small.
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1. What is Pulse Code Modulation (PCM)? |
2. What is the role of quantization in PCM? |
3. What is the difference between uniform and non-uniform quantization? |
4. What is companding in PCM? |
5. What is the difference between μ-law and A-law companding? |
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