Mumbai University > Electronics Engineering > Sem4 > Fundamentals of Communication Engineering

Marks: 10M

Year: Dec 2015

1. Quantization is a process of approximating or rounding off. The sampled signal in PCM transmitted is applied to the quantizer block
2. Quantizer converts the sampled signal into an approximate quantized signal which consists of only finite number of predicted voltage levels
3. Each sampled value at the input of the quantizer is approximated or rounded off to the nearest standard predicted voltage level
4. These standard levels are called as quantization levels
5. The quantized signal xq (t) is the approximation of x(t). The difference between them is called as quantization error or as quantization noise
6. This error should be small as possible
7. To minimize the quantization error, we need to reduce the step size ‘s’ by increasing the number of quantization levels Q.
8. If we do not use the quantizer block in the PCM transmitter, then we will have to convert each and every sampled value into a unique digital word
9. This will need a large number of bits per word (N). This will increase the bit rate and hence the bandwidth requirement of the channel.
10. The difference between the instantaneous values of the quantized signals and the input signal is called as quantization error or as quantization noise.
11. The mean square value of the quantization error= $\frac{s^2}{12}$

Adaptive Delta Modulation

Advantages of ADM over DM

1. Reduction in slope overload distortion and granular noise
2. Improvement in signal to noise ratio+
3. Wide dynamic range due to variable step size
4. Better utilization bandwidth as compared to delta modulation
5. Low signalling rate
6. Simplicity of implantations