Delta Modulation in communicaion
Delta Modulation
Delta Modulation (DM) is another method to convert analog signal into digital and uses single bit to achieve digital transmission of analog signals. Note that transmission of 10-bit is costlier than transmission of 2-bit.
Standard PCM uses 8 bits to represent each sample. Bits/sample can be further reduced in DPCM
- Note that 8 bit/sample is the telecommunication industry standard.
- Ideal representation of sample value takes ∞ (infinite) number of bits, which is impossible.
- If number of bits/sample increases, quality of transmission & reception increases
DM uses high sampling rate than PCM i.e., fs is very higher than 2fm i.e., fs>>>fm. So, adjacent samples are very near to each other. This increases correlation (similarity) between adjacent samples.
Similar to DPCM, DM sends only the difference between present and previous samples. Note that 1-bit per sample is enough to transmit DM signal. In DM, only a single bit is transmitted, which indicate whether the present sample is larger or smaller than previous sample.
DM Algorithm
Note that the output of quantizer is represented by a single binary digit (1 or 0) depending on whether the difference is positive or negative. So, hardware required for modulation at transmitter and demodulation at receiver is much simpler.
If input signal changes fast, DM is good. If the changes in signal amplitudes are large, DM results in large errors. Note that DM suffers from following two quantization errors, which are left as home study.
- Granular noise
- Slope overload distortion
