Mobile & Wireless Communication (4351104) - Summer 2024 Solution

Question 1(a) [3 marks]

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Explain selective cell.

Answer:

Table: Selective Cell Characteristics

• Selective coverage: Targets specific geographical areas needing signal
• Indoor solution: Primarily used for building coverage enhancement
• Directional transmission: Uses focused beam patterns for efficiency

Mnemonic: “Select Special Spots”

Question 1(b) [4 marks]

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Draw and explain umbrella cell.

Answer:

Table: Umbrella Cell Features

• Large coverage: Provides wide area signal coverage over smaller cells
• Traffic management: Handles overflow from micro and pico cells
• Seamless handoff: Ensures continuous communication during movement

Mnemonic: “Umbrella Covers All”

Question 1(c) [7 marks]

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What is the cell? Explain frequency reuse.

Answer:

Table: Cell and Frequency Reuse Concepts

graph TD
    A[Cell Concept] --> B[Hexagonal Shape]
    A --> C[Base Station Coverage]
    D[Frequency Reuse] --> E[Cluster Pattern]
    D --> F[Co-channel Reuse]
    E --> G[N=4,7,12 patterns]

• Cell definition: Geographical area covered by one base station antenna
• Hexagonal pattern: Most efficient shape for coverage without gaps
• Frequency reuse: Same frequencies used in non-adjacent cells for capacity
• Cluster size: Determines frequency reuse pattern (N=4,7,12)
• Co-channel interference: Controlled by minimum reuse distance

Mnemonic: “Cells Reuse Frequencies Efficiently”

Question 1(c) OR [7 marks]

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Explain cellular concept in detail.

Answer:

Table: Cellular System Components

graph LR
    A[Large Coverage Area] --> B[Cell Division]
    B --> C[Multiple Base Stations]
    C --> D[Frequency Reuse]
    D --> E[High Capacity System]

• Area division: Large service area divided into smaller hexagonal cells
• Power control: Low power transmitters reduce interference
• Frequency efficiency: Same frequencies reused in distant cells
• Capacity increase: More simultaneous users served
• Seamless coverage: Continuous service across all cells

Mnemonic: “Divide Area For Better Service”

Question 2(a) [3 marks]

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Define full forms: (i) IMEI (ii) LTE (iii) GSM

Answer:

Table: Full Forms

Mnemonic: “Identity, Long-term, Global”

Question 2(b) [4 marks]

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Explain MAHO in detail.

Answer:

Table: MAHO Characteristics

sequenceDiagram
    Mobile->>Base Station: Signal strength report
    Base Station->>MSC: Handoff request
    MSC->>Target BS: Prepare handoff
    Target BS->>MSC: Ready confirmation
    MSC->>Mobile: Handoff command

• Mobile assistance: Mobile unit measures neighboring cell signals
• Signal reporting: Continuous measurement reports sent to network
• Decision support: Network uses mobile data for handoff decisions
• Quality improvement: Better handoff decisions with mobile input

Mnemonic: “Mobile Assists Network Decisions”

Question 2(c) [7 marks]

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Explain GSM architecture with diagram

Answer:

graph TB
    A[Mobile Station] --> B[Base Transceiver Station]
    B --> C[Base Station Controller]
    C --> D[Mobile Switching Center]
    D --> E[Home Location Register]
    D --> F[Visitor Location Register]
    D --> G[Authentication Center]
    D --> H[PSTN/ISDN]

Table: GSM Architecture Components

• Radio subsystem: BTS and BSC handle radio communications
• Network subsystem: MSC, HLR, VLR manage calls and mobility
• Database management: HLR stores permanent, VLR stores temporary data
• Authentication: AuC provides security functions

Mnemonic: “Mobile Base Network Database”

Question 2(a) OR [3 marks]

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Explain cell splitting.

Answer:

Table: Cell Splitting Process

• Power reduction: Original cell power decreased to shrink coverage
• New cells: Additional base stations installed in coverage gaps
• Capacity gain: More cells mean higher user capacity in same area

Mnemonic: “Split Cells Double Capacity”

Question 2(b) OR [4 marks]

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What is handoff? Explain soft and hard handoffs.

Answer:

Table: Handoff Types Comparison

graph LR
    A[Mobile Moving] --> B{Handoff Type}
    B -->|Hard| C[Disconnect old, Connect new]
    B -->|Soft| D[Connect new, then disconnect old]

• Handoff definition: Process of transferring call from one cell to another
• Hard handoff: Connection broken before establishing new connection
• Soft handoff: New connection established before breaking old one
• Quality difference: Soft handoff provides better call quality

Mnemonic: “Hard Breaks, Soft Connects”

Question 2(c) OR [7 marks]

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Explain GSM signal processing with diagram

Answer:

graph LR
    A[Voice Input] --> B[Speech Codec]
    B --> C[Channel Coding]
    C --> D[Interleaving]
    D --> E[Encryption]
    E --> F[Burst Formatting]
    F --> G[Modulation]
    G --> H[RF Transmission]

Table: GSM Signal Processing Stages

• Speech processing: Voice compressed using RPE-LTP codec
• Error protection: Convolutional coding adds redundancy
• Security layer: A5 algorithm encrypts data
• Burst structure: Data organized in time slots
• Modulation: GMSK modulation for RF transmission

Mnemonic: “Voice Coded Interleaved Encrypted Modulated”

Question 3(a) [3 marks]

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Explain cell sectoring.

Answer:

Table: Cell Sectoring Benefits

• Directional antennas: Replace omnidirectional with sector antennas
• Capacity multiplication: Each sector treated as separate cell
• Interference reduction: Directional pattern reduces interference

Mnemonic: “Sector Antennas Triple Capacity”

Question 3(b) [4 marks]

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Explain GSM call procedure.

Answer:

sequenceDiagram
    Mobile->>BTS: Call request
    BTS->>BSC: Forward request
    BSC->>MSC: Route call
    MSC->>HLR: Authenticate user
    HLR->>MSC: Authentication OK
    MSC->>PSTN: Establish connection

Table: Call Setup Steps

• Authentication: Network verifies subscriber identity
• Resource allocation: Traffic channel assigned to call
• Routing: Call path determined through network
• Connection: End-to-end communication established

Mnemonic: “Authenticate Allocate Route Connect”

Question 3(c) [7 marks]

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Explain GPRS.

Answer:

Table: GPRS Features

graph TB
    A[GPRS Network] --> B[SGSN]
    A --> C[GGSN]
    B --> D[Packet Data]
    C --> E[Internet Gateway]
    F[Mobile] --> B
    C --> G[External Networks]

• Packet switching: Data transmitted in packets, not circuits
• Always-on connection: No dial-up required for data access
• Higher speeds: Significant improvement over circuit-switched data
• New nodes: SGSN and GGSN added to GSM architecture
• Internet access: Direct connection to IP networks

Mnemonic: “General Packet Radio Service”

Question 3(a) OR [3 marks]

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Explain advantage of CDMA

Answer:

Table: CDMA Advantages

• Increased capacity: More users per frequency band
• Enhanced security: Spread spectrum provides natural encryption
• Soft handoff: Better call quality during handoffs

Mnemonic: “Capacity Security Quality”

Question 3(b) OR [4 marks]

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Explain frequency hopping techniques.

Answer:

Table: Frequency Hopping Types

graph LR
    A[Data] --> B[Spread Spectrum]
    B --> C[Frequency Synthesizer]
    C --> D[Hop Sequence]
    D --> E[RF Transmission]

• Frequency hopping: Carrier frequency changes according to pattern
• Interference resistance: Reduces effect of narrowband interference
• Security enhancement: Difficult to intercept hopping signals
• GSM implementation: Slow frequency hopping used for quality

Mnemonic: “Frequency Hops For Security”

Question 3(c) OR [7 marks]

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Explain EDGE.

Answer:

Table: EDGE Specifications

graph TB
    A[EDGE Enhancement] --> B[8-PSK Modulation]
    A --> C[Link Adaptation]
    A --> D[Incremental Redundancy]
    B --> E[Higher Data Rate]
    C --> F[Better Quality]
    D --> G[Error Correction]

• Enhanced modulation: 8-PSK instead of GMSK increases data rate
• Link adaptation: Modulation scheme adapts to channel conditions
• Incremental redundancy: Improved error correction mechanism
• Backward compatibility: Works with existing GSM/GPRS infrastructure
• 3G stepping stone: Bridge between 2G and 3G technologies

Mnemonic: “Enhanced Data Gets Excellence”

Question 4(a) [3 marks]

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Draw FHSS transmitter block diagram

Answer:

Table: FHSS Components

Mnemonic: “Data Modulated Frequency Hops”

Question 4(b) [4 marks]

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Explain call processing in CDMA

Answer:

Table: CDMA Call Processing

• System access: Mobile acquires pilot channel and synchronizes
• Authentication: Network verifies subscriber credentials
• Traffic state: Active communication with power control
• Call release: Resources freed when call ends

Mnemonic: “Access Authenticate Transfer Release”

Question 4(c) [7 marks]

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Draw OFDM receiver and explain its working

Answer:

Table: OFDM Receiver Functions

• RF processing: Converts received RF signal to baseband
• Digital conversion: ADC samples the analog signal
• Prefix removal: Cyclic prefix removed to eliminate ISI
• FFT processing: Separates orthogonal subcarriers
• Data recovery: Channel decoding recovers original data

Mnemonic: “Receive Convert Remove Transform Decode”

Question 4(a) OR [3 marks]

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Explain radiation hazard due to mobile.

Answer:

Table: Mobile Radiation Effects

• SAR measurement: Specific Absorption Rate measures energy absorption
• Thermal effects: High SAR can cause tissue heating
• Safety limits: International standards limit SAR values

Mnemonic: “SAR Safety Absorption Rate”

Question 4(b) OR [4 marks]

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Explain Li-Po type batteries used in mobile handset.

Answer:

Table: Li-Po Battery Characteristics

• Polymer electrolyte: Uses polymer instead of liquid electrolyte
• Flexible packaging: Can be shaped to fit device design
• High energy density: More capacity in smaller size
• Fast charging: Supports rapid charging protocols

Mnemonic: “Lithium Polymer Power”

Question 4(c) OR [7 marks]

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Explain mobile handset block diagram.

Answer:

graph TB
    A[Antenna] --> B[RF Section]
    B --> C[Baseband Processor]
    C --> D[Audio Codec]
    C --> E[Display Controller]
    C --> F[Keypad Interface]
    G[Battery] --> H[Power Management]
    H --> B
    H --> C
    I[SIM Interface] --> C

Table: Mobile Handset Components

• RF section: Handles transmission and reception of radio signals
• Baseband processor: Implements communication protocols
• Audio subsystem: Processes voice and audio signals
• Power management: Controls battery usage and charging
• User interface: Display, keypad, and user interaction

Mnemonic: “Radio Baseband Audio Power Interface”

Question 5(a) [3 marks]

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Compare CDMA and GSM

Answer:

Table: CDMA vs GSM Comparison

Mnemonic: “Code vs Time Division”

Question 5(b) [4 marks]

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Explain HSDPA.

Answer:

Table: HSDPA Features

• 3.5G technology: Enhancement to 3G UMTS system
• High speed downlink: Optimized for download applications
• Adaptive modulation: QPSK to 16-QAM based on channel
• Fast scheduling: 2ms scheduling intervals

Mnemonic: “High Speed Download Access”

Question 5(c) [7 marks]

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Explain architecture, features and advantage of Bluetooth.

Answer:

graph TB
    A[Application Layer] --> B[L2CAP]
    B --> C[HCI]
    C --> D[Link Manager]
    D --> E[Baseband]
    E --> F[Radio Layer]

Table: Bluetooth Features

Table: Bluetooth Applications

• Short range: Designed for personal area networks
• Low power: Optimized for battery-powered devices
• Frequency hopping: 79 channels for interference resistance
• Master-slave: One master can connect to 7 slaves
• Applications: Audio, data transfer, input devices

Mnemonic: “Blue Personal Area Network”

Question 5(a) OR [3 marks]

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Explain basic concept of RFID.

Answer:

Table: RFID Components

• Radio frequency identification: Uses RF waves for identification
• Contactless operation: No physical contact required
• Automatic identification: Reads tags automatically in range

Mnemonic: “Radio Frequency Identifies”

Question 5(b) OR [4 marks]

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Explain architecture of 5G system.

Answer:

Table: 5G Architecture Components

• Service-based architecture: Modular network functions
• Network slicing: Virtual networks for different services
• Edge computing: Processing closer to users
• Massive MIMO: Multiple antenna technology

Mnemonic: “Service Based Network Slicing”

Question 5(c) OR [7 marks]

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Explain MANET in detail.

Answer:

Table: MANET Characteristics

graph TD
    A[Node A] --> B[Node B]
    B --> C[Node C]
    A --> D[Node D]
    C --> E[Node E]
    D --> E
    B --> E

Table: MANET vs Cellular Network

• Mobile Ad-hoc Network: Self-configuring network of mobile devices
• No infrastructure: Nodes communicate directly without base stations
• Dynamic routing: Routes change as nodes move
• Multi-hop communication: Messages relay through intermediate nodes
• Applications: Military, disaster recovery, sensor networks

Mnemonic: “Mobile Adhoc Network”