This question paper belongs to B.Tech Semester IV – Communication Engineering (KEC-401).
It carries 100 marks and the duration is 3 hours.
The paper is divided into three major sections – A, B, and C, designed to test:
Theoretical understanding Mathematical derivations
Analytical skills
Practical applications in signal processing, modulation, sampling, and digital communication
Students are instructed to attempt all sections. Wherever required, they may assume suitable missing data.
2. Section A – Short & Conceptual Questions (20 Marks)
This section contains 10 brief questions, each of 2 marks, covering fundamental concepts of communication engineering.
The topics include:
● Modulation Basics
Explaining the need of modulation, its importance in long-distance communication, antenna size limitations, and multiplexing.
● Fourier Transform Property
Writing the time convolution property, essential for analysing LTI systems.
● Frequency Modulation
Definition of FM and drawing of its time-domain waveform.
● FM Bandwidth
Calculating bandwidth using Carson’s Rule with given deviation and message frequency.
● Noise Figure / Figure of Merit
Definition indicating performance of communication receivers.
● AWGN Characteristics
Sketching the Gaussian noise probability distribution curve.
● DPCM vs PCM
Describing how Differential PCM differs from standard PCM.
● Nyquist Rate & Interval
Computing sampling rate from highest frequency component in the given signals.
● Non-coherent Demodulation Issue
Why BPSK cannot be demodulated non-coherently.
● Types of Digital Modulation
Listing ASK, PSK, FSK, QAM, DPSK etc.
This section checks basic conceptual clarity.
3. Section B – Long Analytical Questions (30 Marks)
Students must attempt any three (3) out of five questions.
Each question is 10 marks and requires full explanation, mathematical expressions, block diagrams, or derivations.
The topics include:
● Fourier Transform of Rectangular Pulse
Deriving sinc-shaped spectrum and sketching magnitude.
● Narrowband FM
Mathematical representation, approximations for small modulation index, and phasor interpretation.
● Threshold Effect
Explaining noise behavior in angle modulation, plus relation between pre-emphasis and de-emphasis networks.
● Sampling Theorem
Statement, mathematical proof, and demonstration of signal reconstruction using LPF.
● QAM Transmitter & Receiver
Block diagram and working of Quadrature Amplitude Modulation.
This section evaluates analytical and problem-solving ability.
4. Section C – Application-Based Questions (50 Marks)
This section has five parts (Q3–Q7) and in each part, the student must attempt any one option.
Each part carries 10 marks.
Part 3: Analog Modulation Techniques
Choice between:
● DSB-SC Modulator & Demodulator
Drawing and explaining balanced modulator, switching modulator, coherent detector etc.
OR
● SSB-SC Mathematical Derivation
Deriving SSB using Hilbert transform, filters, or phase-shift method.
Part 4: Angle Modulation
Choice between:
● Wideband FM (WBFM) Spectrum expansion, Bessel components, and mathematical expression.
OR
● Phase Modulation Definition and relation between PM⇄FM conversion.
Part 5: Probability & Noise
Choice between:
● Probability of Error for BPSK Deriving Pe = Q(√(2Eb/N0))
OR
● PDF vs CDF Definitions, differences, and properties.
Part 6: Pulse Code Modulation
Choice between:
● Delta Modulation
Definition + bandwidth calculation for PCM with given parameters.
OR
● PCM System Block Diagram
Explaining transmitter, channel and receiver operations.
Part 7: Digital Modulation Schemes
Choice between:
● BPSK vs QPSK
Differences, constellation diagram, generation and detection.
OR
● BFSK System
Block diagram and explanation of binary frequency shift keying.
This entire section evaluates practical understanding and ability to apply concepts to real communication systems.
Final Summary of WHAT DESCRIPTION
This description explains:
What the paper contains
How many sections and what they test
Type of questions in each section
Expected depth of answers
Core communication engineering concepts covered
It is a complete, long, formal, section-wise description of the uploaded question paper.
