Digital & Data Communication (4343201) - Summer 2024 Solution

Question 1(a) [3 marks]

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Define: (1) Bit rate, (2) Baud rate, and (3) Bandwidth

Answer:

Mnemonic: “BBB - Bits move By Bands”

Question 1(b) [4 marks]

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A signal has a bit rate of 8000bps and baud rate of 1000 baud. How many data element is carry by each signal? How many signals element do we need?

Answer:

Table: Signal Calculation

Diagram: Signal Element Representation

graph LR
    A[1000 Signals per second] -->|Each signal carries| B[8 bits of data]
    B -->|Requires| C[256 different signal elements]

Mnemonic: “Divide to Decide” - Divide bit rate by baud rate to decide how many bits per signal.

Question 1(c) [7 marks]

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Describe Elements of digital communication system with its block diagram

Answer:

Diagram: Digital Communication System

graph LR
    A[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]

Key Elements:

Mnemonic: “Send Messages Carefully; Destination Must Comprehend Signals Deeply”

Question 1(c OR) [7 marks]

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What is fundamental limitation of digital communication system? What are the advantages and disadvantages of digital communication system?

Answer:

Fundamental Limitations:

Advantages vs Disadvantages:

Mnemonic: “NEEDS” - Noise, Equipment, and Environment Determine Success

Question 2(a) [3 marks]

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Describe QPSK Modulator with block diagram

Answer:

Diagram: QPSK Modulator

Key Components:

• Serial-to-Parallel Converter: Splits data into 2-bit groups
• Cosine Carrier: Modulates first bit (I-channel)
• Sine Carrier: Modulates second bit (Q-channel)

Mnemonic: “Split Pair, Carrier Square” - data split into pairs, carried by squared signals

Question 2(b) [4 marks]

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Describe ASK Modulator with block diagram

Answer:

Diagram: ASK Modulator

ASK Modulation Process:

Mnemonic: “Amplify Signal when Keen” - carrier amplitude changes when signal is high

Question 2(c) [7 marks]

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Compare ASK, FSK and PSK and Draw the wave form of ASK, FSK and PSK for the input digital signal 100101000101

Answer:

Comparison Table:

Waveforms for input 100101000101:

Mnemonic: “AFP - Alter Frequencies or Phases” to remember modulation types

Question 2(a OR) [3 marks]

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Describe QPSK Demodulator with block diagram

Answer:

Diagram: QPSK Demodulator

Key Components:

• BPF (Bandpass Filter): Removes noise outside signal bandwidth
• Product Detectors: Multiply with carrier signals (cos & sin)
• LPF (Lowpass Filters): Extract original data bits

Mnemonic: “Filtered Pairs Deliver Data” - filters and paired carriers recover data

Question 2(b OR) [4 marks]

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Draw the Constellation diagram of ASK, BPSK and QPSK

Answer:

Constellation Diagrams:

Table: Constellation Characteristics

Mnemonic: “Points Double When Phases Double” - BPSK has 2 points, QPSK has 4 points

Question 2(c OR) [7 marks]

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Describe FSK Modulator and demodulator with block diagram and output wave form

Answer:

FSK Modulator Diagram:

FSK Demodulator Diagram:

FSK Waveform:

Key Components:

Mnemonic: “Frequency Shift Key - Two Tones Tell Truth”

Question 3(a) [3 marks]

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State the significance of probability in communication

Answer:

Mnemonic: “ICE - Information, Capacity, Errors” need probability

Question 3(b) [4 marks]

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State channel capacity in terms of SNR and explain its importance

Answer:

Shannon’s Channel Capacity Formula:

C = B × log₂(1 + SNR)

Where:

• C = Channel capacity (bits/second)
• B = Bandwidth (Hz)
• SNR = Signal-to-Noise Ratio

Importance:

Mnemonic: “BEST” - Bandwidth and Error-free Signal Transmission

Question 3(c) [7 marks]

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Discuss classification of line codes with suitable example

Answer:

Diagram: Line Code Classification

graph TD
    A[Line Codes] --> B[Unipolar]
    A --> C[Polar]
    A --> D[Bipolar]
    B --> B1[NRZ]
    B --> B2[RZ]
    C --> C1[NRZ]
    C --> C2[RZ]
    D --> D1[AMI]
    D --> D2[Pseudoternary]

Line Code Examples:

graph TD
    subgraph "Digital Data"
    D["1  0  1  1  0  1  0  0"]
    end

    subgraph "Unipolar NRZ"
    U["High  Low  High  High  Low  High  Low  Low"]
    end
    
    subgraph "Polar NRZ"
    P["+V   -V   +V   +V   -V   +V   -V   -V"]
    end
    
    subgraph "Bipolar AMI"
    B["+V   0   -V   +V   0   -V   0    0"]
    end

Waveform Visualization:

Comparison Table:

Mnemonic: “UPB - Use Proper Bits” for Unipolar, Polar, Bipolar

Question 3(a OR) [3 marks]

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Discuss conditional probability

Answer:

Conditional Probability Definition:

P(A|B) = P(A∩B) / P(B)

Table: Conditional Probability in Communication

Mnemonic: “CEaD” - Calculate Events after Data

Question 3(b OR) [4 marks]

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Define Entropy and Information. Discuss its physical significance

Answer:

Definitions:

Physical Significance:

Mnemonic: “UCOR” - Uncertainty Correlates with Optimal Resources

Question 3(c OR) [7 marks]

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Describe Huffman code with suitable example

Answer:

Huffman Coding: Variable-length prefix code for lossless data compression

Example: Encoding symbols {A, B, C, D, E}

Step 1: Calculate probabilities

Step 2: Build Huffman Tree

graph LR
    A["1.0"] --> B["0.6"]
    A --> C["0.4 (A)"]
    C --> C1["0"]
    B --> D["0.3"]
    B --> E["0.3"]
    D --> F["0.2 (B)"]
    D --> G["0.1 (E)"]
    F --> F1["0"]
    G --> G1["1"]
    E --> H["0.1 (D)"]
    E --> I["0.2 (C)"]
    H --> H1["1"]
    I --> I1["0"]

Step 3: Assign codes

Average code length: (0.4×1) + (0.2×2) + (0.2×2) + (0.1×3) + (0.1×3) = 1.8 bits/symbol

Mnemonic: “HIGH PROB, LOW BITS” - Higher probability symbols get shorter codes

Question 4(a) [3 marks]

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List Data transmission techniques

Answer:

Table: Data Transmission Techniques

Mnemonic: “SPASH-F” - Serial, Parallel, Asynchronous, Synchronous, Half/Full

Question 4(b) [4 marks]

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Explain needs of multimedia processing for communication

Answer:

Multimedia Processing Needs:

Diagram: Multimedia Processing Flow

graph LR
    A[Raw Media] --> B[Compression]
    B --> C[Format Conversion]
    C --> D[Error Protection]
    D --> E[Transmission]
    E --> F[Error Correction]
    F --> G[Decompression]
    G --> H[Playback]

Mnemonic: “CQSEF” - Compress Quality, Standardize and Ensure Fidelity

Question 4(c) [7 marks]

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Explain data transmission mode

Answer:

Table: Data Transmission Modes

Diagram: Data Transmission Modes

Comparison:

Mnemonic: “SHF - Speed and Handling Factors” for Simplex, Half-duplex, Full-duplex

Question 4(a OR) [3 marks]

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List Important characteristics of data communication

Answer:

Key Data Communication Characteristics:

Mnemonic: “DATJSR” - Delivery, Accuracy, Timeliness, Jitter, Security, Reliability

Question 4(b OR) [4 marks]

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Discuss the standards for data communication

Answer:

Table: Key Data Communication Standards

Standards Organizations:

Mnemonic: “PITS” - Protocols, Interfaces, Transmission and Standards

Question 4(c OR) [7 marks]

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Explain model of Multimedia communications and elements of Multimedia system

Answer:

Multimedia Communication Model:

graph LR
    A[Content Creation] --> B[Compression]
    B --> C[Storage]
    C --> D[Distribution]
    D --> E[Decompression]
    E --> F[Presentation]

Multimedia System Elements:

Media Types:

Mnemonic: “CNIS-OS” - Capture, Network, Input-output, Storage, Output, Software

Question 5(a) [3 marks]

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Explain important elements of 5G technology

Answer:

Key 5G Elements:

Mnemonic: “MMBN-E” - Millimeter, MIMO, Beamforming, Network, Edge

Question 5(b) [4 marks]

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Describe Spread spectrum communication

Answer:

Spread Spectrum Definition: Technique where signal is spread over a wide frequency band, much wider than the minimum bandwidth required.

Types of Spread Spectrum:

Diagram: DSSS Process

Mnemonic: “DFT - Difficult For Trackers” - Direct, Frequency, Time Hopping

Question 5(c) [7 marks]

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Explain block diagram of satellite communication

Answer:

Satellite Communication Block Diagram:

graph LR
    A["Satellite Transponder"] --- B["Uplink"]
    A --- C["Downlink"]
    B --- D["Earth Station Tx"]
    C --- E["Earth Station Rx"]

    classDef satellite fill:#f9f,stroke:#333,stroke-width:2px;
    classDef earth fill:#9cf,stroke:#333,stroke-width:2px;
    classDef link stroke-dasharray: 5 5;
    
    class A satellite;
    class D,E earth;
    class B,C link;

Key Components:

Frequency Bands:

Mnemonic: “STUDER” - Station Transmits Uplink, Downlink to Earth Receiver

Question 5(a OR) [3 marks]

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Explain features and advantages of 5G technology

Answer:

5G Features and Advantages:

Mnemonic: “HUMNER” - High-speed, Ultra-low latency, Massive connectivity, Network slicing, Enhanced reliability

Question 5(b OR) [4 marks]

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Describe Edge Computing

Answer:

Edge Computing Definition: Computing paradigm that brings data processing closer to the source of data generation.

Diagram: Edge Computing Architecture

graph LR
    A[IoT Devices] --> B[Edge Devices]
    B --> C[Edge Servers]
    C --> D[Cloud Data Centers]

Key Characteristics:

Mnemonic: “PDRBD” - Process Data Rapidly By Distributing

Question 5(c OR) [7 marks]

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Explain importance of block chain in Communication Security

Answer:

Blockchain in Communication Security:

graph LR
    A[Transaction Request] --> B[Block Creation]
    B --> C[Block Verification]
    C --> D[Block Addition to Chain]
    D --> E[Chain Distribution]

Security Benefits:

Communication Applications:

Mnemonic: “DTCSCI” - Decentralized Transparent Cryptographic System Creates Immutability