This document contains the complete B.Tech Semester IV – Theory Examination 2024–25 question paper for Communication Engineering (BEC401). The paper spans two printed pages, carries a total of 70 marks, and evaluates a student’s understanding of analog and digital communication systems, modulation techniques, noise analysis, sampling, signal representation, digital modulation schemes, and communication system performance.
Section A – Short Conceptual Questions (14 Marks)
This section contains seven 2-mark questions, each designed to test essential communication theory fundamentals. Concepts include:
Frequency-domain representation of δ(t) and sin(at) (Page 1)
Need for modulation in communication systems
Carson’s Rule for estimating FM bandwidth
Meaning of Figure of Merit (FOM)
Definition of white noise
Basic working of PAM (Pulse Amplitude Modulation)
Short explanation of QPSK (Quadrature Phase Shift Keying)
These questions check foundational knowledge of analog/digital modulation and signal properties.
Section B – Medium-Difficulty Analytical Questions (21 Marks)
Students attempt any three out of five. Topics include:
SSB-SC Modulation
Explanation, difference from standard AM, full derivation of SSB-SC signal, and benefits in power and bandwidth.
FM and PM Signal Expressions
Given a message signal m(t)=5cos(1000πt) and a carrier signal c(t)=10cos(2π×10⁵t) with FM and PM constants, students compute:
Mathematical expression of FM and PM signals
Comparison of bandwidths
Random Processes & Noise Characteristics
Short notes on:
Random processes
Autocorrelation
Power spectral density of WGN
PDF & CDF definitions
Sampling Theorem
Explanation of Nyquist rate and consequences of sampling below Nyquist (aliasing).
QAM (Quadrature Amplitude Modulation)
Detailed discussion of combined amplitude and phase modulation.
These questions test conceptual clarity, mathematical derivation, and system understanding.
Section C – Long Numerical & Advanced Questions (35 Marks)
Students must attempt one part from each question (Q3 to Q7).
Q3 – AM System Calculations / DSB-SC
Full numerical problem involving modulation index, AM equation, powers, bandwidth, and efficiency (Page 1)
OR explanation of DSB-SC modulator and demodulator
Q4 – NBFM vs WBFM / Angle Modulation
Differences in spectrum, mathematical form, and bandwidth
OR comparison of FM vs PM, including FOM and practical aspects (Page 2)
Q5 – Noise in AM / FM Pre-emphasis
Derivation of SNR in coherent AM receiver
OR role of pre-emphasis & de-emphasis circuits in improving SNR for FM systems
Q6 – PCM & SNR / Delta Modulation
Block diagram of PCM, quantization and SNR explanation
OR definitions of Delta Modulation and TDM
Q7 – Digital Modulation Techniques
Explanation and waveforms of PSK & FSK, including working principles
OR detailed explanation of MSK (Minimum Shift Keying)
This section deeply evaluates proficiency in analog/digital modulation, noise, PCM, multiplexing, and system-level communication engineering concepts.
