VARDHAMAN COLLEGE OF ENGINEERING
(AUTONOMOUS)
Affiliated to JNTUH, Approved by AICTE, Accredited by NAAC with A++ Grade, ISO 9001:2015 Certified
Kacharam, Shamshabad, Hyderabad – 501218, Telangana, India
A8422 - Digital Communications
Question Bank
Module 1:
1. Draw the block diagram of Digital Communication System and mention its
advantages?
2. Draw the block diagram of Pulse Code Modulation system and discuss each block.
3. Derive the expression for signal to quantization noise ratio for PCM System that
employs linear quantization technique. Assume that the input to the PCM system is a
sinusoidal signal.
4. Draw the block diagram and explain in detail about Regenerative Repeater.
5. Draw the NRZ, RZ, Differential encoding, Manchester encoding techniques for the
given binary data 100101.
6. Sketch the characteristics of Mid-Rise and Mid-Tread Quantization?
7. How is differential PCM advantageous over PCM? Give the block diagrams of DPCM
transmitter and receiver and analyze its parameters.
8. An analog signal is sampled at 36KHz and quantized into 256 levels. Find the time
duration of a bit of the binary coded signal?
9. If the Nyquist samples are quantized to L = 65, 536 levels and then binary coded,
determine the number of bits required to encode a sample.
10. In a PCM System the number of quantization levels are 16 and the maximum signal
frequency is 4KHz, the bit transmission rate is?
11. A PCM system uses uniform quantizer followed by 5 bit encoder. The bit rate of the
system is 50Mbps.What is the maximum message bandwidth at which the system
operates satisfactorily. Assume the amplitude of the signal is 2V.
a) Find maximum quantization error.
b) Find the signal to noise ratio.
c) Quantization error.
12. The bandwidth of a signal input to the PCM is restricted to 4 KHz. The input varies
from -3.8 V to +3.8 V and has the average power of 30 mw. The required signal to
noise ratio is 20db and the modulator produces binary output. Assume uniform
quantization. Calculate the number of bits required per sample.
13. Consider an audio signal with spectral components limited to the frequency band of
300Hz to 3300Hz. A PCM signal is generated with a sampling rate of 8000
samples/sec. The required output-signal-to-quantizing-noise ratio is 30dB. i) What is
the minimum number of uniform quantization levels needed ii) what is the minimum
number of bits per sample needed? iii) Calculate the minimum system bandwidth
required.
14. In a Pulse code modulated system, the number of bits is increased from 7 to 8 bits,
the improvement in the signal to quantization noise will be?
15. With the help of neat block diagram explain Differential Pulse Code Modulation
(DPCM) system.
16. Draw the block diagram of Delta Modulation and explain each block in detail?
17. Derive the expression for Signal to Quantization noise ratio of Delta Modulation
system?
18. How to avoid slope overload error in Delta Modulation system.
19. What is slope overload distortion and granular noise in Delta Modulation? How is it
removed in ADM?
20. A voice frequency signal band limited to 3kHz is transmitted with the use of the DM
system. The pulse repetition frequency is 30,000 pulses per second, and the step size
is 40mV. Determine the permissible speech signal amplitude to avoid slope overload.
21. The input to the delta modulator is m(t)=5t and sampling rate is 5000 samples/sec.
Determine the step size.
22. A speech signal of maximum frequency 3.4 KHz is applied to a delta modulator
whose bit rate is 20 Kbps. Determine minimum step size for the delta modulation so
that there is no slope overload.
23. A Delta modulation is tested with a 10KHz sinusoidal signal with 1V Peak to peak at
the input. It is sampled at 10 times the Nyquist rate.
(i) What is the step size required to prevent slope over load?
(ii) What is the corresponding SNR?
