B.TECH - Semester 6 digital communication Question Paper 2021 (dec)
Practice authentic previous year university questions for better exam preparation.
Sample Questions
- State the sampling theorem for low pass and bandpass signals with necessary mathematical expressions.
- Derive an expression for SNR in PCM system due to quantisation noise.
- Explain the role of an equaliser in a communication system.
- State Nyquist criterion for zero ISI and derive Nyquist pulse shape for minimum bandwidth utilization.
- Give the steps in Gram Schmidt orthogonalization.
- Explain the parameters to be considered while choosing a digital modulation scheme for an application.
- With a neat sketch, explain the method of generation of BPSK signal.
- Define the terms : (a) Coherence Bandwidth
- Define the terms : (b) Coherence Time
- Define the terms : (c) Delay Spread
- Define the terms : (d) Doppler Spread
- Derive an expression for average SNR at the output of selection combiner for i.i.d. Rayleigh fading on each arm. With necessary sketches explain how increasing diversity order results in diminishing returns.
- Briefly explain the concept of frequency selective and time selective fading. For a small scale fading channel, the rms delay spread is seen to be $0.01 \mu \mathrm{~s}$ and Doppler frequency spread is 400 Hz . Find the range of values of bit rate fo...
- Explain briefly PCM and DPCM methods of waveform coding. Explain how DPCM is different from delta modulation.
- Explain partial response signaling. Compare this scheme with Nyquist pulse signalling scheme by giving the pulse shapes and bandwidth requirement. What is the need for precoding? A binary data 1101001 is applied to the input of a duo-binary coder. Sk...
- Show that a matched filter can be realized using product integrator structure. Determine the impulse response of a filter matched to the signal shown above and sketch it as a function of time. Plot the matched filter output as a function of time.
- What is MAP rule for digital detection? With necessary statistics, explain the structure of a MAP detector?
- With necessary sketches, explain the method of differential phase shift keying. Compare it with BPSK and BFSK schemes.
- Derive the error probability $\mathrm{of} \leq \mathrm{BPS}$ and BASK schemes, considering optimal detector structure. Consare trans terms of energy efficiency.
- How a Direct sequence spread spectrum system can provide protection against single-tone jamming? The data rate of a DS-CDMA system using BPSK modulation is $10 \mathrm{~kb} / \mathrm{s}$ and the chip rate is $10 \mathrm{mb} / \mathrm{s}$. What is the...
- What is level crossing rate? A flat Rayleigh fading signal at 6 GHz is received by a mobile traveling at $80 \mathrm{~km} / \mathrm{hr}$. (a) Determine the number of positive going zero crossings about the rms value that occur over 5 sec . interval
- What is level crossing rate? A flat Rayleigh fading signal at 6 GHz is received by a mobile traveling at $80 \mathrm{~km} / \mathrm{hr}$. (b) Determine the average duration of a fade below the rms level
- What is level crossing rate? A flat Rayleigh fading signal at 6 GHz is received by a mobile traveling at $80 \mathrm{~km} / \mathrm{hr}$. (c) Determine the average duration of a fade at a level of 20 dB below the rms level.
- What are the benefits of diversity techniques in wireless communication? Give one example of time, frequency and space diversity as applied to modern wireless systems. $$ (6 \times 10=60 \text { Marks }) $$