(SEM IV) THEORY EXAMINATION 2022-23 COMMUNICATION ENGINEERING

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.