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ENEX 351Bachelor in Electronics, Communication and Information Engineering · Semester 61 Paper Available

Communication Systems

Past examination question papers and complete curriculum syllabus for Communication Systems (ENEX 351), Bachelor in Electronics, Communication and Information Engineering Semester 6 under Institute of Engineering (IOE), Tribhuvan University.

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Most Frequently Asked Questions

Top recurring IOE board exam questions for Communication Systems with verified mark schemes, formula notation, and recurrence frequency.

Showing 30 of 30 top repeated questions

Introduction

1 Question
#1Repeated 3 Times[8 Marks]Introduction
Sketch and describe the functional block diagram of a digital communication system operating in duplex mode. Contrast it with an analog communication system and discuss channel impairments (attenuation, distortion, noise, interference).
Appeared in:2082 Kartik2081 Chaitra2079 Chaitra

Amplitude Modulation

5 Questions
#1Repeated 4 Times[8 Marks]Amplitude Modulation
Derive the mathematical expression for Standard Amplitude Modulated (DSB-FC) wave. Calculate modulation index $\mu$, total transmitted power $P_t = P_c(1 + \frac{\mu^2}{2})$, and modulation efficiency $\eta$. Why does standard AM waste over $66.7\%$ of transmitted power in the carrier?
Appeared in:2082 Kartik2080 Chaitra2078 Kartik2075 Chaitra
#2Repeated 4 Times[8 Marks]Amplitude Modulation
Derive the time-domain equation and frequency spectrum for Frequency Modulated (FM) signal with single-tone sinusoidal modulation. Explain Carson's Rule for FM bandwidth $B_T = 2(\Delta f + f_m)$ and frequency demodulation using Phase Locked Loop (PLL).
Appeared in:2082 Kartik2081 Chaitra2079 Chaitra2076 Chaitra
#3Repeated 3 Times[8 Marks]Amplitude Modulation
Derive the mathematical expression for double-tone Amplitude Modulation (AM). Calculate the percentage of total transmitted power saved in DSB-SC and SSB-SC as compared to standard AM with modulation index $\mu = 1$.
Appeared in:2080 Ashwin2079 Ashwin2079 Chaitra
#4Repeated 2 Times[8 Marks]Amplitude Modulation
Explain the operation of a Superheterodyne Receiver with a block diagram. Explain RF amplifier, mixer, Intermediate Frequency (IF), Automatic Gain Control (AGC), and Image Frequency Rejection Ratio (IFRR).
Appeared in:2079 Ashwin2078 Chaitra
#5Repeated 2 Times[6 Marks]Amplitude Modulation
What is the Hilbert Transform? State its essential properties. Explain how the Hilbert transform is used to generate Single Sideband Suppressed Carrier (SSB-SC) modulated signals using the phase-shift method.
Appeared in:2081 Chaitra2079 Chaitra

Angle Modulation

1 Question
#1Repeated 2 Times[8 Marks]Angle Modulation
Explain Armstrong's indirect method for generating Wideband Frequency Modulation (WBFM) from Narrowband FM using frequency multipliers and mixers. Why are Pre-emphasis and De-emphasis filtering circuits used in FM broadcast?
Appeared in:2081 Chaitra2079 Ashwin

Pulse Modulation

2 Questions
#1Repeated 2 Times[8 Marks]Pulse Modulation
Why is non-uniform quantization required in telephony? Explain $\mu$-law and A-law logarithmic companding curves. Prove that for a standard voice channel ($300\text{ Hz} - 3.4\text{ kHz}$), 8-bit PCM sampled at $8\text{ kHz}$ yields a bit rate of $64\text{ kbps}$.
Appeared in:2080 Ashwin2079 Chaitra
#2Repeated 2 Times[8 Marks]Pulse Modulation
Compare Pulse Code Modulation (PCM), Differential Pulse Code Modulation (DPCM), and Delta Modulation (DM). Explain slope overload distortion and granular noise in Delta Modulation and how Adaptive Delta Modulation (ADM) solves them.
Appeared in:2081 Chaitra2079 Chaitra

Multiplexing Techniques

3 Questions
#1Repeated 4 Times[8 Marks]Multiplexing Techniques
Compare Time Division Multiplexing (TDM) with Frequency Division Multiplexing (FDM). Compare T1 ($1.544\text{ Mbps}$, 24 channels) and E1 ($2.048\text{ Mbps}$, 32 channels) digital PCM transmission hierarchies with frame structures.
Appeared in:2082 Kartik2081 Chaitra2079 Chaitra2078 Chaitra
#2Repeated 4 Times[8 Marks]Multiplexing Techniques
Explain Spread Spectrum Communication principles. Compare Direct Sequence Spread Spectrum (DSSS) and Frequency Hopping Spread Spectrum (FHSS). Define Pseudo-Noise (PN) sequence properties and calculate Processing Gain ($PG = B_{ss}/B$).
Appeared in:2082 Kartik2081 Chaitra2079 Chaitra2077 Magh
#3Repeated 4 Times[8 Marks]Multiplexing Techniques
Compare Frequency Division Multiple Access (FDMA), Time Division Multiple Access (TDMA), and Code Division Multiple Access (CDMA) in terms of spectrum allocation, synchronization requirements, and the near-far effect.
Appeared in:2082 Kartik2080 Chaitra2078 Kartik2075 Chaitra

Baseband Digital Data Transmission

5 Questions
#1Repeated 6 Times[8 Marks]Baseband Digital Data Transmission
For a given binary sequence (e.g. 100000000001101 or 110011000001), draw the resulting waveforms for: Unipolar RZ, Polar NRZ, Bipolar AMI, Manchester, and HDB3 / B8ZS scrambling line codes. Discuss DC component, clock recovery, and bandwidth requirements.
Appeared in:2082 Kartik2081 Chaitra2080 Ashwin2079 Ashwin2079 Chaitra2078 Chaitra
#2Repeated 4 Times[8 Marks]Baseband Digital Data Transmission
Explain Pulse Code Modulation (PCM). Detail the processes of Sampling, Uniform vs Non-uniform Quantization, and Encoding. Derive the signal-to-quantization noise ratio formula $(S/N_q) = 1.8 + 6n \text{ dB}$ for an $n$-bit quantizer. Compare $\mu$-law and A-law companding.
Appeared in:2082 Kartik2081 Chaitra2080 Chaitra2077 Magh
#3Repeated 4 Times[8 Marks]Baseband Digital Data Transmission
State the Nyquist Criterion for Zero Intersymbol Interference (ISI). Derive the condition on transfer function $H(f)$ for distortionless baseband pulse transmission. Explain the Raised Cosine roll-off filter and the concept of excess bandwidth factor ($\alpha$).
Appeared in:2082 Kartik2080 Chaitra2078 Bhadra2075 Chaitra
#4Repeated 4 Times[8 Marks]Baseband Digital Data Transmission
Explain the working of Delta Modulation (DM) system. Describe the causes and waveforms of Slope Overload Distortion and Granular Noise. How does Adaptive Delta Modulation (ADM) overcome these limitations?
Appeared in:2082 Kartik2079 Chaitra2077 Magh2073 Chaitra
#5Repeated 4 Times[6 Marks]Baseband Digital Data Transmission
What is an Eye Pattern (Eye Diagram)? Explain how an eye pattern is generated on an oscilloscope and how it is used to measure ISI, optimum sampling instant, timing jitter, sensitivity to timing error, and noise margin in digital communication systems.
Appeared in:2081 Chaitra2080 Chaitra2078 Kartik2075 Chaitra

Digital Modulation Techniques

5 Questions
#1Repeated 4 Times[8 Marks]Digital Modulation Techniques
Explain Binary Phase Shift Keying (BPSK) and Quadrature Phase Shift Keying (QPSK). Draw transmitter and receiver block diagrams, signal constellations, and derive the probability of bit error $P_b = Q\left(\sqrt{\frac{2E_b}{N_0}}\right)$ for coherent BPSK.
Appeared in:2082 Kartik2081 Chaitra2079 Chaitra2076 Ashwin
#2Repeated 4 Times[6 Marks]Digital Modulation Techniques
State the Shannon-Hartley Channel Capacity Theorem $C = B \log_2\left(1 + \frac{S}{N}\right)$. Prove that as bandwidth $B \to \infty$, the channel capacity approaches the Shannon Limit $C_{\infty} = \frac{S}{N_0 \ln 2} \approx 1.44 \frac{S}{N_0}$ and determine the minimum $E_b/N_0 = -1.59 \text{ dB}$.
Appeared in:2082 Kartik2080 Chaitra2078 Kartik2074 Chaitra
#3Repeated 3 Times[8 Marks]Digital Modulation Techniques
What is the aim of source coding? For a given message string with character frequencies, construct the Huffman code tree, generate binary codewords, and calculate source entropy $H(X)$, average codeword length $L$, coding efficiency $\eta = \frac{H(X)}{L}$, and redundancy.
Appeared in:2081 Chaitra2080 Ashwin2079 Chaitra
#4Repeated 3 Times[8 Marks]Digital Modulation Techniques
Draw and explain the constellation diagram of 16-QAM and 32-QAM. Compare QAM with QPSK and Minimum Shift Keying (MSK) in terms of bandwidth efficiency, bit error rate, and constant envelope property.
Appeared in:2082 Kartik2081 Chaitra2078 Chaitra
#5Repeated 2 Times[6 Marks]Digital Modulation Techniques
State the Shannon-Hartley Channel Capacity Theorem: $C = B \log_2\left(1 + \frac{S}{N}\right)$. Discuss the trade-off between bandwidth and signal-to-noise ratio, and prove the Shannon capacity limit: $\frac{E_b}{N_0} \ge \ln 2 = -1.59\text{ dB}$ as channel bandwidth approaches infinity.
Appeared in:2082 Kartik2080 Ashwin

Error Detection and Correction Coding

4 Questions
#1Repeated 4 Times[8 Marks]Error Detection and Correction Coding
Explain Cyclic Redundancy Check (CRC) codes. Given generator polynomial $G(X) = X^4 + X + 1$ and message bits $M = 1101011011$, compute the transmitted codeword using modulo-2 polynomial division. Show how the receiver detects an error if a bit flips during transmission.
Appeared in:2082 Kartik2081 Chaitra2079 Chaitra2075 Chaitra
#2Repeated 4 Times[8 Marks]Error Detection and Correction Coding
Describe Convolutional Encoding and Viterbi Decoding. For a rate $r = 1/2$ convolutional encoder with generator polynomials $g_1 = (1, 1, 1)$ and $g_2 = (1, 0, 1)$, draw the state transition diagram, tree diagram, and trellis diagram. Trace Viterbi decoding of a received bit stream.
Appeared in:2081 Chaitra2080 Chaitra2078 Bhadra2076 Chaitra
#3Repeated 2 Times[8 Marks]Error Detection and Correction Coding
A $(6, 3)$ linear block code has a specified parity check matrix $H$. (a) Determine the generator matrix $G$, (b) Generate the valid codeword for message vector $m = [1, 1, 0]$, (c) Compute the syndrome vector $S = r H^T$ for a received word $r$ and demonstrate single-bit error detection and correction.
Appeared in:2082 Kartik2081 Chaitra
#4Repeated 2 Times[8 Marks]Error Detection and Correction Coding
For a rate-1/2 convolutional encoder with given generator polynomials, draw the State Diagram, Tree Diagram, and Trellis Diagram. Explain how the Viterbi decoding algorithm performs maximum-likelihood path decoding.
Appeared in:2082 Kartik2081 Chaitra

Noise in Communication Systems

4 Questions
#1Repeated 4 Times[8 Marks]Noise in Communication Systems
Define Additive White Gaussian Noise (AWGN), Equivalent Noise Temperature ($T_e$), and Noise Figure ($F$). Derive Friis' formula for the overall noise factor of a multi-stage cascaded amplifier: $F = F_1 + \frac{F_2 - 1}{G_1} + \frac{F_3 - 1}{G_1 G_2}$.
Appeared in:2081 Chaitra2080 Chaitra2078 Bhadra2074 Chaitra
#2Repeated 2 Times[8 Marks]Noise in Communication Systems
Derive the impulse response $h(t) = s(T-t)$ and maximum output signal-to-noise ratio ($SNR = \frac{2E}{N_0}$) of a Matched Filter receiver operating in an Additive White Gaussian Noise (AWGN) channel.
Appeared in:2082 Kartik2081 Chaitra
#3Repeated 2 Times[8 Marks]Noise in Communication Systems
Define Noise Figure ($F$), Equivalent Noise Temperature ($T_e$), and Noise Factor in cascaded stages (Friis formula for noise). Derive the Figure of Merit $(\gamma = \frac{SNR_o}{SNR_c})$ for SSB, DSB-SC, and AM receivers.
Appeared in:2081 Chaitra2080 Ashwin
#4Repeated 2 Times[6 Marks]Noise in Communication Systems
Define Auto-correlation and Cross-correlation for energy and power signals. State and prove the Wiener-Khinchin theorem relating the autocorrelation function and the Power Spectral Density (PSD).
Appeared in:2082 Kartik2079 Ashwin

Curriculum Syllabus & Course Topics

Chapter-wise Units & Micro-Syllabus Topics (9 Units)

  1. 1. Introduction

    • 1.1Review of signals and systems
    • 1.2Block diagram of analog and digital communication systems
    • 1.3System needs and requirements
    • 1.4Noise, attenuation, and interference

  2. 2. Amplitude Modulation

    • 2.1Time domain expressions, frequency domain representation, modulation index, signal bandwidth of amplitude modulated signal
    • 2.2AM for single and double tone message, carrier and sideband components, power in carrier and sideband components, bandwidth and power efficiency, Hilbert transform
    • 2.3Double sideband AM (DSB-FC), generation (Square law), detection (Envelope and square law method)
    • 2.4Double sideband suppress carrier (DSB-SC), Generation (Linear modulator, balance modulator), Synchronous detection method
    • 2.5Overview of SSB, VSB, and ISB modulations
    • 2.6Phase locked loop (PLL), demodulation of AM using PLL
    • 2.7Super-heterodyne AM receiver

  3. 3. Angle Modulation

    • 3.1Basic definition, time domain expression for frequency modulation (FM) and phase modulation (PM)
    • 3.2Time domain expression for single tone, modulated FM signals, spectral representation
    • 3.3Bandwidth of FM, Carson’s rule, narrow and wideband FM
    • 3.4Generation of FM: Direct and indirect
    • 3.5Demodulation of FM signals: Non-synchronous (Limiter discriminator) and synchronous (PLL)
    • 3.6Stereo FM, spectral details, pre-emphasis and de-emphasis network
    • 3.7Super-heterodyne Radio receiver for FM

  4. 4. Pulse Modulation

    • 4.1Sampling theorem, ideal sampling, practical sampling, aliasing effect, aperture effect, signal reconstruction
    • 4.2Fundamentals of PAM, PWM, and PPM, time domain representation
    • 4.3Pulse coded modulation (PCM), quantization, quantization error, quantization noise
    • 4.4Signal to quantization noise ratio (SQNR) in uniform quantization, SQNR improvements, non-uniform quantization, companding techniques (A-law, µ-Law)
    • 4.5DPCM, DM: Encoder, decoder, advantage, disadvantage, noise in DM

  5. 5. Multiplexing Techniques

    • 5.1Multiplexing fundamentals: FDM, TDM, WDM and applications
    • 5.2T1 and E1 TDM PCM telephony hierarchy
    • 5.3Multiple access fundamentals: FDMA, TDMA, CDMA, SDMA

  6. 6. Baseband Digital Data Transmission

    • 6.1Information theory, measurement of information, entropy, symbol rates and data rates
    • 6.2Shannon Hartley channel capacity theorem, implication of theorem, and theoretical limits
    • 6.3Compression techniques: Shannon-Fano, Huffman codes
    • 6.4Line coding schemes: Unipolar, polar, bipolar
    • 6.5RZ, NRZ, AMI, Manchester, differential Manchester, B8ZS, HDB3 for digital data transmission
    • 6.6ISI, Nyquist criteria, pulse shaping for zero ISI

  7. 7. Digital Modulation Techniques

    • 7.1Binary digital modulation (ASK, FSK, PSK), generation, properties, constellation diagram and detections
    • 7.2QPSK generation, properties, constellation diagram, and detections
    • 7.3M-ARY modulation techniques, M-PSK versus M-QAM

  8. 8. Error Detection and Correction Coding

    • 8.1Hamming weight, hamming distance, code vectors, constraint length, code rate, syndromes
    • 8.2Error detection and correction
    • 8.2.1Error detection codes: Checksum, CRC
    • 8.2.2Error correction codes: Linear block codes, hamming codes
    • 8.3Cyclic codes (Generator polynomial, parity-check polynomial)

  9. 9. Noise in Communication Systems

    • 9.1Definition, white noise, AWGN channel, PSDF, and AC function of white noise
    • 9.2Ideal low-pass and RC filtering of white noise, noise equivalent bandwidth of a filter
    • 9.3Optimum detection of a pulse in additive white noise, the matched filter, realization of matched filters (Time correlators), the matched filter for a rectangular pulse
    • 9.4Overview of error probability function in digital communication (ASK, FSK, and PSK)

Examination Scheme & Marks Distribution

Evaluation Structure

  • Final Board Theory Exam: 60 Marks (Pass mark: 24)
  • Internal Assessment: 40 Marks (Pass mark: 16)
  • Practical / Lab Exam: 25 or 50 Marks (Continuous lab evaluation + viva, where applicable)

* This is the general current IOE 60/40 scheme; verify course-specific details in the syllabus above.

Exam Preparation Guidelines

  • Review the available past examination paper to understand question styling, typical derivation topics, and marks allocation.
  • Cross-reference key answers with official syllabus units, standard textbooks, and lecture notes.
  • Structure answers with labeled diagrams, concise bullet points, and highlight final answers in numerical solutions.

Frequently Asked Questions (Communication Systems)

Q: How can I download Communication Systems past question papers?

You can preview or download the Communication Systems question papers (PDF) directly using the built-in viewer on this page with zero redirects or paywalls.

Q: What is the pass mark for Communication Systems?

The general current scheme is a 60-mark final theory exam and a 40-mark internal assessment, with pass marks of 24 and 16. Verify the course-specific syllabus above.

Q: Where can I find the complete syllabus for this subject?

The available chapter-wise syllabus and topic breakdown is indexed in the Syllabus section above, with links to the curriculum PDF source.

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