Digital Communication: Digital communication refers to the transmission of information using digital signals, where data is represented by discrete symbols or values. It encompasses various techniques for encoding, transmitting, and decoding digital data, including text, images, audio, and video. Digital communication systems offer advantages such as improved signal quality, noise immunity, and the ability to multiplex multiple data streams.
Differential Pulse Code Modulation (DPCM): DPCM is a digital modulation technique used for encoding analog signals into digital form. In DPCM, the difference between the current sample and the predicted value of the sample is quantized and encoded, rather than encoding the absolute sample value directly. This technique can reduce the amount of data required for transmission compared to standard pulse code modulation (PCM), especially for signals with correlation between successive samples.
Delta Modulation (DM): Delta modulation is a simple form of analog-to-digital conversion where the difference (delta) between the current sample and the previous sample is quantized and encoded. In DM, only the sign of the difference (positive or negative) is transmitted, which simplifies the encoding process. However, DM may suffer from quantization noise and limited signal fidelity, especially for rapidly changing or high-frequency signals.
Adaptive Delta Modulation (ADM): Adaptive delta modulation is an extension of delta modulation that dynamically adjusts the step size or quantization level based on the characteristics of the input signal. Unlike fixed-step delta modulation, ADM can adapt to changes in signal amplitude or frequency, resulting in improved signal fidelity and reduced quantization error. ADM is particularly useful for encoding signals with varying dynamics or signal-to-noise ratios
3. Differential Pulse
Code Modulation
• The samples that are highly correlated,
when encoded by PCM technique, leave
redundant information behind. To
process this redundant information and to
have a better output,
• It is a wise decision to take a predicted
sampled value, assumed from its
previous output and summarize them
with the quantized values.
• Such a process is called as Differential
PCM (DPCM)technique.
4. DPCM ( Transmitter)
• The signals at each point are named as −
• x(nTs) is the sampled input
• xˆ(nTs) is the predicted sample
• e(nTs) is the difference of sampled input and
predicted output, often called as prediction error
• v(nTs) is the quantized output
• u(nTs) is the predictor input which is actually
the summer output of the predictor output and the
quantizer output
6. DM (Delta
Modulation)
The sampling rate of a signal should be higher than the
Nyquist rate, to achieve better sampling.
If this sampling interval in Differential PCM is reduced
considerably, the sampleto-sample amplitude
difference is very small, as if the difference is 1-bit
quantization
then the step-size will be very small i.e., Δ delta.
Delta Modulation
The type of modulation, where the sampling rate is
much higher and in which the stepsize after
quantization is of a smaller value Δ,
such a modulation is termed as delta modulation.
9. Adaptive Delta
Modulation
• In digital modulation, we have come across
certain problem of determining the step-
size, which influences the quality of the
output wave.
• A larger step-size is needed in the steep
slope of modulating signal and a smaller
stepsize is needed where the message has a
small slope. The minute details get missed
in the process. So, it would be better if we
can control the adjustment of step-size,
according to our requirement in order to
obtain the sampling in a desired fashion.
This is the concept of Adaptive Delta
Modulation.
