Digital & Data Communication (4343201) - Summer 2025 Solution

Question 1(a) [3 marks]

#

Define bit rate, baud rate and bandwidth

Answer:

• Bit rate: Actual data transmission speed
• Baud rate: Modulation rate or symbol rate
• Bandwidth: Channel capacity for frequency range

Mnemonic: “Bits Baud Bandwidth - BBB for communication”

Question 1(b) [4 marks]

#

Explain TDM with block diagram

Answer:

graph LR
    A[Input 1] --> MUX[Time Division Multiplexer]
    B[Input 2] --> MUX
    C[Input 3] --> MUX
    D[Input 4] --> MUX
    MUX --> E[Transmission Channel]
    E --> DEMUX[Time Division Demultiplexer]
    DEMUX --> F[Output 1]
    DEMUX --> G[Output 2]
    DEMUX --> H[Output 3]
    DEMUX --> I[Output 4]

• TDM principle: Multiple signals share single channel by time slots
• Time slots: Each input gets dedicated time period
• Synchronization: Transmitter and receiver must be synchronized
• Applications: Digital telephone systems, computer networks

Mnemonic: “Time Divided Multiple - TDM shares time”

Question 1(c) [7 marks]

#

Explain block diagram of digital communication system

Answer:

graph LR
    A[Information Source] --> B[Source Encoder]
    B --> C[Channel Encoder]
    C --> D[Digital Modulator]
    D --> E[Channel]
    E --> F[Digital Demodulator]
    F --> G[Channel Decoder]
    G --> H[Source Decoder]
    H --> I[Destination]
    J[Noise] --> E

Table: System Components

• Advantages: Noise immunity, error correction capability
• Processing: Digital signal processing techniques
• Reliability: Better performance over long distances

Mnemonic: “Source Channel Modulate Transmit Demodulate Decode - SCMTDD”

Question 1(c OR) [7 marks]

#

Explain different types of Communication channel

Answer:

Channel Types Table:

• Bandwidth: Different channels offer varying frequency ranges
• Noise characteristics: Each channel has specific noise properties
• Distance capability: Varies from local to global coverage
• Cost factors: Installation and maintenance costs differ

Mnemonic: “Telephone Coax Optical Wireless Satellite - TCOWS channels”

Question 2(a) [3 marks]

#

Draw the modulation waveform for ASK, FSK and BPSK for the digital sequence 11100110

Answer:

Mnemonic: “ASK Amplitude, FSK Frequency, BPSK Phase - AFP modulation”

Question 2(b) [4 marks]

#

Explain the basic principle and generation of frequency shift keying (FSK) signal

Answer:

FSK Generation Table:

graph LR
    A[Digital Data] --> B[Frequency Selector]
    C[Oscillator 1 - f1] --> B
    D[Oscillator 2 - f0] --> B
    B --> E[FSK Output]

• Principle: Binary data controls carrier frequency
• Two frequencies: f₁ for ‘1’ and f₀ for ‘0’
• Constant amplitude: Only frequency changes
• Detection: Frequency discrimination at receiver

Mnemonic: “Frequency Shifts Key - FSK frequency control”

Question 2(c) [7 marks]

#

Explain the working of QPSK modulator and Demodulator with block diagram and constellation diagram

Answer:

QPSK Modulator Block Diagram:

graph TD
    A[Serial Data] --> B[Serial to Parallel]
    B --> C[I Channel]
    B --> D[Q Channel]
    E[Carrier cos(ωt)] --> F[Multiplier 1]
    G[Carrier sin(ωt)] --> H[Multiplier 2]
    C --> F
    D --> H
    F --> I[Adder]
    H --> I
    I --> J[QPSK Output]

Constellation Diagram:

QPSK Truth Table:

• Four phases: 45°, 135°, 225°, 315°
• Two bits per symbol: Higher data rate
• Constant envelope: Amplitude remains constant
• Demodulation: Phase detection and parallel to serial conversion

Mnemonic: “Quadrature Phase Shift Key - QPSK four phases”

Question 2(a OR) [3 marks]

#

Draw the block diagram of ASK modulator and describe working of it

Answer:

graph LR
    A[Digital Data] --> B[Switch/Multiplier]
    C[Carrier Oscillator] --> B
    B --> D[ASK Output]

• Working principle: Digital data controls carrier amplitude
• Logic ‘1’: Carrier transmitted with full amplitude
• Logic ‘0’: No carrier transmitted (zero amplitude)
• Simple implementation: Uses analog switch or multiplier

Mnemonic: “Amplitude Shift Key - ASK amplitude control”

Question 2(b OR) [4 marks]

#

Explain the principal of 16-QAM and draw the constellation diagram

Answer:

16-QAM Constellation:

16-QAM Characteristics Table:

• Principle: Combines amplitude and phase modulation
• Higher data rate: 4 bits per symbol
• Complex modulation: Requires precise amplitude and phase control
• Applications: High-speed digital communication

Mnemonic: “16 Quadrature Amplitude Modulation - 16QAM complex signals”

Question 2(c OR) [7 marks]

#

Explain working of BPSK modulator and demodulator with block diagram and waveform

Answer:

BPSK Modulator:

graph LR
    A[Digital Data] --> B[NRZ Encoder]
    B --> C[Balanced Modulator]
    D[Carrier Oscillator] --> C
    C --> E[BPSK Output]

BPSK Demodulator:

graph LR
    A[BPSK Input] --> B[Balanced Demodulator]
    C[Local Carrier] --> B
    B --> D[Low Pass Filter]
    D --> E[Decision Circuit]
    E --> F[Digital Output]

BPSK Waveforms:

• Phase shift: 180° between ‘1’ and ‘0’
• Coherent detection: Requires synchronized carrier
• Best performance: Lowest bit error rate
• Constant envelope: Amplitude remains constant

Mnemonic: “Binary Phase Shift Key - BPSK two phases”

Question 3(a) [3 marks]

#

Define Channel Capacity in terms of SNR and explain importance of it

Answer:

Shannon’s Channel Capacity Formula:

• Importance: Maximum theoretical data rate
• SNR effect: Higher SNR allows higher capacity
• Bandwidth trade-off: Can exchange bandwidth for SNR
• Design limit: Sets upper bound for system design

Mnemonic: “Channel Capacity Shannon’s Limit - CCSL”

Question 3(b) [4 marks]

#

Describe Asynchronous and synchronous serial data communication techniques

Answer:

Comparison Table:

• Synchronous: Clock synchronization required
• Asynchronous: Self-synchronizing with start/stop bits
• Applications: Synchronous for high-speed, Asynchronous for simple systems
• Efficiency: Synchronous more efficient, Asynchronous more flexible

Mnemonic: “Sync Clock, Async Start-Stop - SCSS”

Question 3(c) [7 marks]

#

Explain Huffman coding with help of suitable example

Answer:

Example: Characters A, B, C, D with probabilities 0.4, 0.3, 0.2, 0.1

Step-by-step Huffman Tree Construction:

Huffman Codes Table:

• Average code length: 0.4×1 + 0.3×2 + 0.2×3 + 0.1×3 = 1.9 bits
• Compression achieved: Reduces average bits per character
• Prefix property: No code is prefix of another

Mnemonic: “Huffman Minimum Average Length - HMAL”

Question 3(a OR) [3 marks]

#

State the significance of probability and entropy in communication

Answer:

Significance Table:

• Information content: I = log₂(1/P) bits
• Entropy formula: H = -Σ P(x) log₂ P(x)
• Channel design: Helps optimize communication systems
• Coding efficiency: Guides source coding design

Mnemonic: “Probability Entropy Information - PEI communication”

Question 3(b OR) [4 marks]

#

Explain simplex, half duplex and full duplex data transmission mode

Answer:

Transmission Modes Table:

• Simplex: Unidirectional communication
• Half duplex: Bidirectional but alternate
• Full duplex: Simultaneous bidirectional
• Bandwidth requirement: Full duplex needs twice the bandwidth

Mnemonic: “Simple Half Full - SHF transmission modes”

Question 3(c OR) [7 marks]

#

Explain Shannon Fano coding with help of suitable example

Answer:

Example: Characters A, B, C, D with probabilities 0.4, 0.3, 0.2, 0.1

Shannon-Fano Algorithm Steps:

Shannon-Fano Codes Table:

• Average length: Same as Huffman (1.9 bits)
• Top-down approach: Divides from root to leaves
• Not always optimal: Huffman is generally better

Mnemonic: “Shannon Fano Top-Down - SFTD coding”

Question 4(a) [3 marks]

#

Describe Ethical and Privacy Considerations in Data Communication

Answer:

Ethics and Privacy Table:

• Privacy rights: Users control over personal data
• Ethical use: Responsible data handling practices
• Legal compliance: Following data protection laws
• Security measures: Protecting against unauthorized access

Mnemonic: “Privacy Security Transparency - PST ethics”

Question 4(b) [4 marks]

#

Explain RS 232 standard with pin diagram

Answer:

RS-232 Pin Configuration (DB-9):

• Voltage levels: +3V to +25V for ‘0’, -3V to -25V for ‘1’
• Maximum distance: 50 feet at 19.2 kbps
• Applications: Serial communication between computers and modems

Mnemonic: “RS-232 Nine pins Serial - RNS communication”

Question 4(c) [7 marks]

#

Explain Hamming code with help of suitable example

Answer:

Example: 4-bit data 1011

Hamming Code Construction:

Parity Calculations:

• P1 (positions 1,3,5,7): P1 ⊕ 1 ⊕ 0 ⊕ 1 = 0, so P1 = 0
• P2 (positions 2,3,6,7): P2 ⊕ 1 ⊕ 1 ⊕ 1 = 1, so P2 = 1
• P4 (positions 4,5,6,7): P4 ⊕ 0 ⊕ 1 ⊕ 1 = 0, so P4 = 0

Final Hamming Code: 0110111

Error Detection Process:

• Calculate syndrome S = S4S2S1

• If S = 000, no error

• If S ≠ 000, error at position indicated by S

• Single error correction: Can correct one-bit errors

• Double error detection: Can detect two-bit errors

• Systematic approach: Organized parity bit placement

Mnemonic: “Hamming Single Error Correction - HSEC”

Question 4(a OR) [3 marks]

#

Define Edge Computing and explain feature of it

Answer:

Edge Computing Features:

• Definition: Computing at network edge, close to data sources
• Reduced latency: Faster response times
• Distributed processing: Reduces central server load
• Applications: IoT, autonomous vehicles, smart cities

Mnemonic: “Edge Low-latency Real-time - ELR computing”

Question 4(b OR) [4 marks]

#

Explain needs of multimedia processing for communication and various file formats of different data

Answer:

Multimedia File Formats Table:

• Processing needs: Compression, format conversion, quality optimization
• Bandwidth optimization: Reducing file sizes for transmission
• Quality preservation: Maintaining acceptable quality levels
• Compatibility: Supporting multiple devices and platforms

Mnemonic: “Audio Video Image Text - AVIT multimedia”

Question 4(c OR) [7 marks]

#

Explain different Line coding with help of waveform

Answer:

Line Coding Waveforms for data 1011:

Line Coding Comparison:

• NRZ: Non-Return-to-Zero, simple but has DC component
• RZ: Return-to-Zero, better synchronization
• Manchester: Self-synchronizing, no DC component
• Selection criteria: Bandwidth, synchronization, complexity

Mnemonic: “NRZ RZ Manchester - NRM line codes”

Question 5(a) [3 marks]

#

Explain concept of spread spectrum technology

Answer:

Spread Spectrum Characteristics:

• Principle: Spreads signal over much wider bandwidth than required
• Techniques: Direct Sequence (DS-SS), Frequency Hopping (FH-SS)
• Advantages: Security, interference resistance, multiple access
• Applications: GPS, CDMA, WiFi, Bluetooth

Mnemonic: “Spread Spectrum Security - SSS technology”

Question 5(b) [4 marks]

#

Explain block diagram of satellite communication

Answer:

graph TD
    A[Earth Station 1] --> B[Uplink]
    B --> C[Satellite Transponder]
    C --> D[Downlink]
    D --> E[Earth Station 2]
    F[Antenna] --> C
    C --> G[Antenna]

Satellite Communication Components:

• Frequency bands: C-band, Ku-band, Ka-band
• Coverage area: Large geographical coverage
• Applications: Broadcasting, telephony, internet
• Advantages: Wide coverage, long-distance communication

Mnemonic: “Earth Uplink Transponder Downlink - EUTD satellite”

Question 5(c) [7 marks]

#

Demonstrate model of Multimedia Communications and elements of Multimedia system

Answer:

Multimedia Communication Model:

graph LR
    A[Source] --> B[Encoder]
    B --> C[Multiplexer]
    C --> D[Network]
    D --> E[Demultiplexer]
    E --> F[Decoder]
    F --> G[Destination]
    H[Audio] --> B
    I[Video] --> B
    J[Text] --> B
    K[Graphics] --> B

Multimedia System Elements:

• Synchronization: Audio-video synchronization critical
• Compression: Reduces bandwidth requirements
• Quality of Service: Maintains acceptable quality
• Real-time constraints: Time-sensitive data delivery

Mnemonic: “Capture Store Process Communicate Present - CSPCP multimedia”

Question 5(a OR) [3 marks]

#

Explain importance of Block chain in Communication Security

Answer:

Blockchain Security Features:

• Cryptographic security: Hash functions and digital signatures
• Distributed ledger: Multiple copies prevent tampering
• Smart contracts: Automated security protocols
• Applications: Secure messaging, identity verification

Mnemonic: “Blockchain Distributed Immutable - BDI security”

Question 5(b OR) [4 marks]

#

Explain important elements, features and advantages of 5G technology

Answer:

5G Technology Elements:

Key Features:

• Enhanced Mobile Broadband: Ultra-high-speed internet
• Ultra-Reliable Low Latency: Critical applications
• Massive Machine Communication: IoT connectivity
• Network Slicing: Customized network services

Advantages:

• Higher capacity: More simultaneous users
• Energy efficiency: Better battery life for devices
• New applications: AR/VR, autonomous vehicles

Mnemonic: “5G Speed Latency Connections - SLC features”

Question 5(c OR) [7 marks]

#

Compare RS 232, RS 422 and RS 485 standard

Answer:

RS Standards Comparison Table:

Voltage Levels:

Applications:

• RS-232: Computer serial ports, modems
• RS-422: Industrial automation, long-distance
• RS-485: Building automation, industrial networks

Key Differences:

• Noise immunity: Differential signaling in RS-422/485 better than RS-232
• Distance capability: RS-422/485 much longer than RS-232
• Multi-drop capability: RS-485 supports multiple devices
• Cost: RS-232 cheapest, RS-485 most complex

Mnemonic: “RS-232 Simple, RS-422 Long, RS-485 Multi - SLM standards”