Mobile & Wireless Communication (4351104) - Summer 2025 Solution

Question 1(a) [3 marks]

#

Write key features of 4G and 5G system.

Answer:

Table: Key Features Comparison

Key Points:

• 4G: Uses LTE technology with OFDM modulation for high-speed data
• 5G: Ultra-low latency enables real-time applications like autonomous vehicles
• Network Slicing: 5G allows virtual networks for specific applications

Mnemonic: “4G Fast, 5G Super-Fast”

Question 1(b) [4 marks]

#

Explain concept of frequency reuse in cellular mobile system.

Answer:

Diagram:

Key Points:

• Frequency Reuse: Same frequencies used in non-adjacent cells to increase capacity
• Co-channel Distance: Minimum distance between cells using same frequency
• Cluster Size: Group of cells using different frequencies (typically 3, 4, 7, 12)
• Capacity Improvement: More users served with limited spectrum

Mnemonic: “Same Frequency, Different Places”

Question 1(c) [7 marks]

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If a total of 33 MHz of bandwidth is allocated to a particular FDD cellular telephone system which uses two 25 kHz simplex channels to provide full duplex communication. If 1 MHz of the allocated spectrum is dedicated to control channels, determine an equitable distribution of control channels and voice channels for cluster size of 7.

Answer:

Given Data:

• Total bandwidth = 33 MHz
• Channel bandwidth = 25 kHz (simplex)
• Control spectrum = 1 MHz
• Cluster size = 7

Calculations:

Step 1: Available spectrum for traffic Traffic spectrum = 33 - 1 = 32 MHz

Step 2: Total duplex channels Each duplex channel needs 2 × 25 kHz = 50 kHz Total channels = 32 MHz ÷ 50 kHz = 640 channels

Step 3: Control channels Control channels = 1 MHz ÷ 25 kHz = 40 channels

Step 4: Distribution per cell

• Voice channels per cell = 640 ÷ 7 ≈ 91 channels
• Control channels per cell = 40 ÷ 7 ≈ 6 channels

Final Distribution Table:

Mnemonic: “Divide Total by Cluster”

Question 1(c OR) [7 marks]

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List out types of cells and explain each.

Answer:

Table: Types of Cells

Detailed Explanation:

Macro Cells:

• Coverage: Large geographical areas (1-30 km radius)
• Power: High transmission power (up to 40W)
• Usage: Rural and suburban areas with low user density

Micro Cells:

• Coverage: Medium areas (100m to 1km radius)
• Power: Medium transmission power (1-10W)
• Usage: Urban areas, highway coverage

Pico Cells:

• Coverage: Small indoor/outdoor areas (10-100m)
• Power: Low transmission power (100mW-1W)
• Usage: Shopping malls, airports, offices

Umbrella Cells:

• Special Type: Covers multiple smaller cells
• Purpose: Handles high-speed mobile users
• Advantage: Reduces handoffs for fast-moving users

Mnemonic: “Macro-Micro-Pico-Femto = Big to Small”

Question 2(a) [3 marks]

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Define cell and cluster.

Answer:

Definitions:

Cell:

• Definition: Geographical area covered by one base station
• Shape: Typically hexagonal for planning purposes
• Function: Serves mobile users within its coverage area

Cluster:

• Definition: Group of cells using different frequency sets
• Purpose: Enables frequency reuse pattern
• Common Sizes: 3, 4, 7, 12 cells per cluster

Table: Cell vs Cluster

Mnemonic: “Cell = One Area, Cluster = Group Areas”

Question 2(b) [4 marks]

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Explain effect of cluster size on capacity and interference.

Answer:

Effects Table:

Key Effects:

On Capacity:

• Smaller Cluster: More channels per cell, higher capacity
• Larger Cluster: Fewer channels per cell, lower capacity
• Formula: Channels per cell = Total channels ÷ Cluster size

On Interference:

• Smaller Cluster: Higher co-channel interference
• Larger Cluster: Lower co-channel interference
• Trade-off: Capacity vs. Quality

Co-channel Distance:

• Relationship: D = R√(3N) where N = cluster size
• Effect: Larger N means larger distance between co-channel cells

Mnemonic: “Small Cluster = More Capacity, More Interference”

Question 2(c) [7 marks]

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Write key features of IS-95, CDMA2000 and WCDMA.

Answer:

Comparison Table:

IS-95 Features:

• Technology: First commercial CDMA system
• Voice Quality: Better than GSM in some conditions
• Soft Handoff: Maintains multiple connections during handoff
• Power Control: Precise power control reduces interference

CDMA2000 Features:

• Backward Compatibility: Works with IS-95 networks
• High Data Rate: Up to 2 Mbps for 1xEV-DO
• Multimedia: Supports voice, data, and video
• Efficiency: Better spectrum efficiency than IS-95

WCDMA Features:

• Global Standard: Used worldwide for 3G
• High Capacity: Supports more simultaneous users
• QoS Support: Different service classes for applications
• International Roaming: Global compatibility

Mnemonic: “IS-95 First, CDMA2000 Faster, WCDMA Global”

Question 2(a OR) [3 marks]

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Explain cell splitting.

Answer:

Definition: Cell splitting is a technique to increase system capacity by subdividing congested cells into smaller cells.

graph TD
    A[Original Large Cell] --> B[Split into 4 Smaller Cells]
    B --> C[Cell 1]
    B --> D[Cell 2]
    B --> E[Cell 3]
    B --> F[Cell 4]

Process:

• Step 1: Identify congested cell with high traffic
• Step 2: Install new base stations with lower power
• Step 3: Reduce original base station power
• Step 4: Create multiple smaller coverage areas

Benefits:

• Capacity Increase: More channels available in same area
• Better Signal Quality: Shorter distances improve signal strength

Mnemonic: “Split Big Cell into Small Cells”

Question 2(b OR) [4 marks]

#

Write functions of HLR and VLR in GSM.

Answer:

Functions Table:

HLR Functions:

• Subscriber Profile: Stores permanent subscriber information (IMSI, services)
• Location Tracking: Maintains current location area of subscriber
• Authentication: Provides authentication keys for security
• Service Management: Controls subscribed services and restrictions

VLR Functions:

• Temporary Storage: Stores visiting subscriber data temporarily
• Local Services: Enables services for roaming subscribers
• Call Routing: Assists in routing calls to visiting subscribers
• Authentication Copy: Maintains copy of authentication data from HLR

Interaction:

• HLR updates VLR when subscriber roams to new area
• VLR requests subscriber data from HLR during registration

Mnemonic: “HLR = Home Data, VLR = Visitor Data”

Question 2(c OR) [7 marks]

#

Describe RFID technology.

Answer:

RFID Overview: Radio Frequency Identification uses electromagnetic fields to identify and track tags attached to objects.

System Components:

graph LR
    A[RFID Reader] --> B[Radio Waves]
    B --> C[RFID Tag]
    C --> D[Stored Data]
    C --> B
    B --> A

Types Table:

Key Features:

• No Line of Sight: Works without direct visual contact
• Multiple Reading: Can read multiple tags simultaneously
• Data Storage: Can store and update information
• Durability: Resistant to environmental conditions

Applications:

• Inventory Management: Warehouse and retail tracking
• Access Control: Building and vehicle access
• Payment Systems: Contactless payment cards
• Supply Chain: Product tracking from manufacturing to sale

Advantages:

• Fast Reading: Instant identification without scanning
• Automation: Reduces manual data entry errors
• Real-time Tracking: Continuous monitoring of assets

Mnemonic: “Radio Frequency Identifies Everything”

Question 3(a) [3 marks]

#

Draw GSM architecture.

Answer:

graph TD
    A[Mobile Station] --> B[BTS - Base Transceiver Station]
    B --> C[BSC - Base Station Controller]
    C --> D[MSC - Mobile Switching Center]
    D --> E[HLR - Home Location Register]
    D --> F[VLR - Visitor Location Register]
    D --> G[PSTN/ISDN]

    H[Authentication Center] --> D
    I[Equipment Identity Register] --> D

Components:

• MS: Mobile Station (handset + SIM)
• BTS: Radio interface with mobile
• BSC: Controls multiple BTS, handles handoffs
• MSC: Switching and call control
• HLR/VLR: Database for subscriber information

Mnemonic: “Mobile Talks Through BTS-BSC-MSC”

Question 3(b) [4 marks]

#

Write GSM 900 specifications.

Answer:

GSM 900 Specifications Table:

Key Features:

• Digital Transmission: Superior voice quality compared to analog
• International Roaming: Global compatibility standard
• Security: Encryption and authentication built-in
• SMS Support: Short message service capability

Coverage:

• Cell Radius: Up to 35 km (rural areas)
• Power Classes: 5 classes from 0.8W to 20W

Mnemonic: “900 MHz, 200 kHz spacing, 8 time slots”

Question 3(c) [7 marks]

#

Explain mobile to landline and landline to mobile call procedure in GSM.

Answer:

Mobile to Landline Call Procedure:

sequenceDiagram
    participant MS as Mobile Station
    participant BTS as BTS/BSC
    participant MSC as MSC
    participant PSTN as PSTN/Landline

    MS->>BTS: Call Request
    BTS->>MSC: Forward Request
    MSC->>MSC: Authenticate User
    MSC->>PSTN: Route Call
    PSTN->>MSC: Ring Response
    MSC->>BTS: Ring Indication
    BTS->>MS: Ring Back Tone
    PSTN->>MSC: Call Answered
    MSC->>MS: Connect Call

Steps:

1. Call Initiation: Mobile dials landline number
2. Channel Assignment: BSC assigns traffic channel
3. Authentication: MSC verifies subscriber
4. Routing: MSC routes call to PSTN gateway
5. Connection: End-to-end connection established

Landline to Mobile Call Procedure:

sequenceDiagram
    participant PSTN as PSTN/Landline
    participant MSC as Gateway MSC
    participant HLR as HLR
    participant VMSC as Visited MSC
    participant MS as Mobile Station

    PSTN->>MSC: Call to Mobile
    MSC->>HLR: Location Request
    HLR->>VMSC: Get Routing Number
    VMSC->>MSC: Return Routing Number
    MSC->>VMSC: Route Call
    VMSC->>MS: Page Mobile
    MS->>VMSC: Page Response
    VMSC->>MS: Ring Mobile

Steps:

1. Call Reception: PSTN receives call to mobile number
2. HLR Query: Gateway MSC queries HLR for location
3. Location Update: HLR provides current MSC information
4. Paging: Visited MSC pages mobile in location area
5. Connection: Mobile responds and call is connected

Key Differences:

• Mobile Originating: Direct routing through serving MSC
• Mobile Terminating: Requires location lookup through HLR

Mnemonic: “Mobile Out = Direct, Mobile In = Find First”

Question 3(a OR) [3 marks]

#

Explain fast and slow frequency hopping.

Answer:

Frequency Hopping Types:

Table: Fast vs Slow Hopping

Fast Frequency Hopping:

• Definition: Frequency changes multiple times per symbol
• Characteristics: Very high hop rate, complex implementation
• Advantage: Excellent interference resistance

Slow Frequency Hopping:

• Definition: Multiple symbols transmitted per frequency
• GSM Implementation: 217 hops per second
• Advantage: Simple to implement, effective interference averaging

Mnemonic: “Fast = Many hops per symbol, Slow = Many symbols per hop”

Question 3(b OR) [4 marks]

#

Explain authentication process in GSM.

Answer:

Authentication Process:

sequenceDiagram
    participant MS as Mobile Station
    participant MSC as MSC/VLR
    participant HLR as HLR/AuC

    MS->>MSC: Location Update Request
    MSC->>HLR: Send IMSI
    HLR->>HLR: Generate RAND, SRES, Kc
    HLR->>MSC: Return Triplet (RAND, SRES, Kc)
    MSC->>MS: Authentication Request (RAND)
    MS->>MS: Calculate SRES using A3 algorithm
    MS->>MSC: Authentication Response (SRES)
    MSC->>MSC: Compare SRES values
    MSC->>MS: Accept/Reject

Key Components:

• RAND: Random number (128 bits)
• SRES: Signed response (32 bits)
• Kc: Cipher key (64 bits)
• Ki: Individual subscriber authentication key

Process Steps:

1. Challenge: Network sends random number (RAND)
2. Response: Mobile calculates SRES using Ki and RAND
3. Verification: Network compares received and expected SRES
4. Result: Authentication success or failure

Security Features:

• Mutual Authentication: Prevents fake base stations
• Unique Keys: Each subscriber has individual Ki
• Challenge-Response: Prevents replay attacks

Mnemonic: “Random Challenge, Signed Response, Compare and Accept”

Question 3(c OR) [7 marks]

#

Draw and explain block diagram of Signal processing in GSM.

Answer:

GSM Signal Processing Block Diagram:

graph TD
    A[Speech Input] --> B[Speech Coder]
    B --> C[Channel Coder]
    C --> D[Interleaver]
    D --> E[Burst Formatter]
    E --> F[Modulator]
    F --> G[RF Section]
    G --> H[Antenna]

    I[Antenna] --> J[RF Section]
    J --> K[Demodulator]
    K --> L[Burst Detector]
    L --> M[De-interleaver]
    M --> N[Channel Decoder]
    N --> O[Speech Decoder]
    O --> P[Speech Output]

Transmitter Processing:

Speech Coding:

• Function: Converts analog speech to 13 kbps digital
• Algorithm: RPE-LTP (Regular Pulse Excitation - Long Term Prediction)
• Frame Size: 20 ms speech frames

Channel Coding:

• Purpose: Adds redundancy for error correction
• Types: Convolutional coding, block coding
• Output: Protected 22.8 kbps data stream

Interleaving:

• Function: Spreads coded bits across multiple time slots
• Benefit: Combats burst errors from fading
• Types: Block interleaving over 8 time slots

Burst Formatting:

• Process: Organizes data into GSM burst structure
• Components: Training sequence, guard bits, data bits
• Types: Normal burst, access burst, sync burst

Modulation:

• Technique: GMSK (Gaussian Minimum Shift Keying)
• Bandwidth: 200 kHz channel spacing
• Symbol Rate: 270.833 kbps

Receiver Processing:

• Demodulation: Recovers digital bits from RF signal
• Equalization: Compensates for multipath distortion
• Error Correction: Uses channel coding redundancy
• Speech Decoding: Reconstructs original speech

Key Features:

• Digital Processing: All operations in digital domain
• Error Protection: Multiple levels of error correction
• Adaptive: Parameters adjust to channel conditions

Mnemonic: “Speech-Code-Interleave-Burst-Modulate-Transmit”

Question 4(a) [3 marks]

#

Draw block diagram of baseband section.

Answer:

Baseband Section Block Diagram:

graph TD
    A[DSP Processor] --> B[Audio Codec]
    B --> C[Speaker]
    D[Microphone] --> B
    A --> E[Memory Interface]
    E --> F[Flash Memory]
    E --> G[RAM]
    A --> H[Control Interface]
    H --> I[Keypad]
    H --> J[Display]
    A --> K[RF Interface]
    A --> L[SIM Interface]

Components:

• DSP: Digital signal processing for speech and data
• Audio Codec: Analog-to-digital conversion
• Memory: Program storage (Flash) and working memory (RAM)
• Control: User interface management
• Interfaces: RF section, SIM card connections

Functions:

• Signal Processing: Speech coding, echo cancellation
• Protocol Stack: GSM layer 1, 2, 3 protocols
• User Interface: Display, keypad, audio management

Mnemonic: “DSP Controls Audio, Memory, Display, RF”

Question 4(b) [4 marks]

#

Explain EDGE.

Answer:

EDGE Overview: Enhanced Data rates for GSM Evolution - improves data transmission in GSM networks.

Key Features Table:

Technical Improvements:

• Advanced Modulation: 8-PSK carries 3 bits per symbol vs 1 bit in GMSK
• Link Adaptation: Automatically switches between GMSK and 8-PSK
• Enhanced Coding: Better error correction schemes
• Incremental Redundancy: Improved retransmission strategy

Benefits:

• Higher Data Rates: 3x faster than GPRS
• Backward Compatibility: Works with existing GSM infrastructure
• Cost Effective: Software upgrade to existing networks
• Multimedia Support: Enables better mobile internet experience

Applications:

• Mobile Internet: Faster web browsing
• Email: Quick email with attachments
• Multimedia Messaging: MMS support
• Video Calls: Basic video communication

Mnemonic: “EDGE = Enhanced Data rates for GSM Evolution”

Question 4(c) [7 marks]

#

Draw and explain block diagram of mobile handset.

Answer:

Mobile Handset Block Diagram:

graph TD
    A[Antenna] --> B[Antenna Switch]
    B --> C[RF Transceiver]
    C --> D[Baseband Processor]
    D --> E[Audio Section]
    E --> F[Speaker/Microphone]

    D --> G[Display Controller]
    G --> H[LCD Display]
    
    D --> I[Keypad Interface]
    I --> J[Keypad]
    
    D --> K[Memory Controller]
    K --> L[Flash Memory]
    K --> M[RAM]
    
    D --> N[SIM Interface]
    N --> O[SIM Card]
    
    P[Battery] --> Q[Power Management]
    Q --> C
    Q --> D
    Q --> R[Charging Circuit]

Major Sections:

RF Section:

• Antenna: Transmits and receives radio signals
• Duplexer: Separates TX and RX signals
• RF Transceiver: Up/down conversion, amplification
• Frequency Synthesizer: Generates carrier frequencies

Baseband Section:

• DSP: Digital signal processing for speech and data
• Protocol Stack: Implements GSM protocols
• Control Unit: Manages all mobile functions
• Memory Interface: Controls program and data storage

Audio Section:

• Audio Codec: A/D and D/A conversion
• Audio Amplifier: Drives speaker
• Microphone Amplifier: Amplifies voice input
• Hands-free Support: External audio accessories

User Interface:

• Display: Shows information to user (LCD/OLED)
• Keypad: User input interface
• LED Indicators: Status indication
• Vibrator: Alert mechanism

Power Management:

• Battery: Energy storage (Li-ion typically)
• Charging Circuit: Battery charging control
• Power Regulation: Voltage regulation for all sections
• Power Saving: Sleep modes and power optimization

Memory System:

• Flash Memory: Program storage and user data
• RAM: Working memory for program execution
• SIM Interface: Secure element for subscriber identity

Interconnections:

• Control Bus: Command and control signals
• Data Bus: Information transfer
• Power Bus: Power distribution
• Audio Bus: Voice and audio signals

Operation:

1. Receive: Antenna → RF → Baseband → Audio → Speaker
2. Transmit: Microphone → Audio → Baseband → RF → Antenna
3. Control: User input → Baseband → Display output
4. Processing: All operations controlled by baseband processor

Mnemonic: “Antenna-RF-Baseband-Audio-Display-Power”

Question 4(a OR) [3 marks]

#

Explain radiation hazards due to mobile.

Answer:

Radiation Hazards:

SAR (Specific Absorption Rate):

• Definition: Rate of energy absorption by human body
• Unit: Watts per kilogram (W/kg)
• Limit: 2.0 W/kg (Europe), 1.6 W/kg (USA)

Health Concerns Table:

Prevention Measures:

• Distance: Keep phone away from body during calls
• Duration: Limit call duration
• Hands-free: Use headsets or speakerphone
• Low SAR: Choose phones with lower SAR values

Safety Guidelines:

• Avoid sleeping with phone near head
• Use airplane mode when not needed
• Keep calls short and use text when possible

Mnemonic: “SAR measures absorption rate”

Question 4(b OR) [4 marks]

#

Describe working of charging section in mobile handset.

Answer:

Charging Section Block Diagram:

graph TD
    A[AC Adapter] --> B[Rectifier]
    B --> C[Voltage Regulator]
    C --> D[Charging Controller]
    D --> E[Battery]
    D --> F[Current Monitor]
    F --> G[Protection Circuit]
    G --> H[Temperature Sensor]

Components & Functions:

Charging Controller:

• Function: Controls charging current and voltage
• Types: Linear and switching mode controllers
• Protection: Prevents overcharging and overheating

Charging Process:

1. Constant Current: Initial high current charging (fast charge)
2. Constant Voltage: Voltage maintained, current decreases
3. Trickle Charge: Low current maintenance charging
4. Cut-off: Charging stops when battery full

Protection Features:

• Over-voltage Protection: Prevents damage from high voltage
• Over-current Protection: Limits maximum charging current
• Temperature Monitoring: Stops charging if battery gets too hot
• Reverse Polarity: Prevents damage from wrong connection

Battery Management:

• Fuel Gauge: Monitors battery capacity
• Cell Balancing: Ensures equal charging of battery cells
• Health Monitoring: Tracks battery condition over time

Mnemonic: “Control Current, Voltage, Temperature, and Time”

Question 4(c OR) [7 marks]

#

Draw and explain block diagram of DSSS transmitter and receiver.

Answer:

DSSS Transmitter Block Diagram:

graph TD
    A[Data Input] --> B[Data Modulator]
    B --> C[Spreader/Mixer]
    D[PN Code Generator] --> C
    C --> E[RF Modulator]
    E --> F[Power Amplifier]
    F --> G[Antenna]

DSSS Receiver Block Diagram:

graph TD
    H[Antenna] --> I[RF Amplifier]
    I --> J[RF Demodulator]
    J --> K[Correlator/Despreader]
    L[PN Code Generator] --> K
    K --> M[Data Demodulator]
    M --> N[Data Output]
    K --> O[Synchronization]
    O --> L

Transmitter Operation:

Data Modulation:

• Input: Original data stream (low rate)
• Modulation: BPSK or QPSK modulation
• Output: Modulated narrowband signal

Spreading Process:

• PN Code: Pseudo-random binary sequence (high rate)
• Spreading: XOR operation between data and PN code
• Result: Wideband spread spectrum signal

RF Modulation:

• Carrier: High frequency carrier signal
• Modulation: Spread signal modulates RF carrier
• Transmission: Signal transmitted through antenna

Receiver Operation:

RF Processing:

• Reception: Antenna receives spread spectrum signal
• Amplification: Low noise amplifier boosts weak signal
• Demodulation: Recovers baseband spread signal

Despreading Process:

• Correlation: Received signal correlated with same PN code
• Synchronization: PN code timing synchronized with received signal
• Output: Original narrowband data signal recovered

Key Parameters:

• Processing Gain: Ratio of spread bandwidth to data bandwidth
• Chip Rate: Rate of PN code (higher than data rate)
• Spreading Factor: Processing gain value

Advantages:

• Interference Rejection: Resistant to narrowband interference
• Low Probability of Intercept: Difficult to detect and jam
• Multiple Access: Many users can share same frequency
• Multipath Resistance: Reduces fading effects

Applications:

• CDMA Cellular: IS-95, CDMA2000, WCDMA
• GPS: Global positioning system
• WiFi: 802.11b spread spectrum mode
• Military: Secure communications

Mnemonic: “Data Spreads with PN, Correlates to Recover”

Question 5(a) [3 marks]

#

Explain the concept of spread spectrum.

Answer:

Spread Spectrum Concept: A communication technique where the transmitted signal bandwidth is much wider than the minimum required bandwidth.

Basic Principle:

Key Characteristics:

• Bandwidth Expansion: Signal spread over wide frequency range
• Processing Gain: Improvement in signal-to-noise ratio
• Pseudo-random Sequence: Spreading code known only to intended receiver
• Security: Difficult for unauthorized users to intercept

Benefits:

• Jam Resistance: Immune to intentional interference
• Low Power Density: Coexists with narrowband systems
• Multiple Access: Many users share same spectrum
• Privacy: Encrypted-like transmission

Mnemonic: “Spread Wide, Gain Processing Power”

Question 5(b) [4 marks]

#

Write criteria of spread spectrum and its applications.

Answer:

Spread Spectrum Criteria:

Technical Criteria:

1. Bandwidth: Transmitted bandwidth » Information bandwidth
2. Processing Gain: Gp = Spread BW / Data BW ≥ 10 dB
3. Pseudo-random: Spreading sequence appears random
4. Synchronization: Receiver must sync with transmitter code

Performance Criteria Table:

Applications:

Military Communications:

• Anti-jam: Resistant to enemy jamming
• LPI/LPD: Low probability of intercept/detection
• Secure: Encrypted transmission

Cellular Systems:

• CDMA: IS-95, CDMA2000, WCDMA
• Capacity: Multiple users per frequency
• Quality: Reduced interference

Satellite Communications:

• GPS: Global positioning system
• Weather: Satellite data transmission
• Broadcasting: Satellite radio/TV

Wireless Networks:

• WiFi: 802.11b DSSS mode
• Bluetooth: Frequency hopping
• Cordless Phones: 2.4 GHz band

Mnemonic: “Military, Cellular, Satellite, Wireless use Spread Spectrum”

Question 5(c) [7 marks]

#

Explain call processing in CDMA.

Answer:

CDMA Call Processing Sequence:

sequenceDiagram
    participant MS as Mobile Station
    participant BTS as Base Station
    participant BSC as Base Station Controller
    participant MSC as Mobile Switching Center

    Note over MS,MSC: Call Origination
    MS->>BTS: Access Request (Random Access)
    BTS->>MS: Access Grant (Assign Code)
    MS->>BTS: Call Setup Request
    BTS->>BSC: Forward Call Request
    BSC->>MSC: Route Call Setup
    MSC->>BSC: Assign Traffic Channel
    BSC->>BTS: Allocate Walsh Code
    BTS->>MS: Traffic Channel Assignment
    MS->>BTS: Confirm Assignment
    Note over MS,MSC: Call in Progress

Call Origination Process:

Step 1: System Access

• Random Access: Mobile sends access probe on access channel
• Power Control: Gradually increases power until acknowledged
• Code Assignment: Base station assigns unique spreading code

Step 2: Authentication

• Challenge: Network sends authentication challenge
• Response: Mobile responds with calculated authentication
• Validation: Network validates mobile identity

Step 3: Channel Assignment

• Walsh Code: Unique orthogonal code assigned for forward link
• PN Offset: Base station identified by PN sequence offset
• Power Level: Initial transmission power set

Step 4: Traffic Channel Setup

• Service Options: Voice, data, or multimedia service negotiated
• Rate Set: Transmission rate configured (Rate Set 1 or 2)
• Handoff Parameters: Neighboring cell information provided

Call Processing Features:

Soft Handoff:

• Multiple Connections: Mobile maintains links to multiple base stations
• Diversity: Improves call quality and reliability
• Make-before-Break: New connection established before old one dropped

Power Control:

• Closed Loop: Rapid power adjustments (800 Hz rate)
• Open Loop: Initial power estimation
• Purpose: Minimize interference, maximize capacity

Variable Rate Vocoder:

• Rate Adaptation: Transmission rate varies with speech activity
• Silence Detection: Lower rates during speech pauses
• Capacity: Increases system capacity

Call Termination Process:

sequenceDiagram
    participant PSTN as PSTN
    participant MSC as MSC
    participant HLR as HLR
    participant BSC as BSC/BTS
    participant MS as Mobile Station

    PSTN->>MSC: Incoming Call
    MSC->>HLR: Location Request
    HLR->>MSC: Routing Information
    MSC->>BSC: Page Mobile
    BSC->>MS: Paging Message
    MS->>BSC: Page Response
    BSC->>MSC: Page Response
    MSC->>BSC: Setup Traffic Channel
    BSC->>MS: Channel Assignment
    MS->>BSC: Assignment Complete
    Note over PSTN,MS: Call Connected

Key CDMA Features:

Rake Receiver:

• Multipath Combining: Combines multiple signal paths
• Diversity Gain: Improves signal quality
• Finger Assignment: Each finger tracks different path

Capacity Advantages:

• Frequency Reuse: Same frequency used in all cells
• Interference Limited: Capacity limited by interference, not frequency
• Voice Activity: Statistical multiplexing increases capacity

Quality Features:

• Error Correction: Forward error correction coding
• Interleaving: Protects against burst errors
• Adaptive Rates: Data rate adapts to channel conditions

Call States:

1. Idle: Mobile monitoring paging channel
2. Access: Attempting to access system
3. Traffic: Active call in progress
4. Handoff: Transitioning between base stations

Mnemonic: “Access-Authenticate-Assign-Traffic-Handoff”

Question 5(a OR) [3 marks]

#

Write features of Zigbee and advantages.

Answer:

Zigbee Features:

Technical Specifications Table:

Key Features:

• Mesh Network: Self-organizing and self-healing network
• Low Power: Battery life up to years
• Low Cost: Inexpensive hardware implementation
• Simple Protocol: Easy to implement and deploy

Advantages:

• Long Battery Life: Optimized for battery-powered devices
• Network Reliability: Multiple routing paths available
• Scalability: Supports thousands of nodes
• Interoperability: Standard ensures device compatibility

Applications:

• Home automation, Industrial monitoring, Smart lighting

Mnemonic: “Low Power, Mesh Network, Many Applications”

Question 5(b OR) [4 marks]

#

Explain OFDM with block diagram.

Answer:

OFDM Block Diagram:

graph TD
    A[Serial Data] --> B[Serial to Parallel]
    B --> C[QAM Modulator]
    C --> D[IFFT]
    D --> E[Add Cyclic Prefix]
    E --> F[Parallel to Serial]
    F --> G[RF Transmission]

    H[RF Reception] --> I[Serial to Parallel]
    I --> J[Remove Cyclic Prefix]
    J --> K[FFT]
    K --> L[QAM Demodulator]
    L --> M[Parallel to Serial]
    M --> N[Serial Data]

OFDM Principle: Orthogonal Frequency Division Multiplexing divides high-speed data into multiple parallel low-speed streams transmitted simultaneously on different frequencies.

Key Components:

IFFT/FFT:

• IFFT: Inverse Fast Fourier Transform creates orthogonal subcarriers
• FFT: Fast Fourier Transform recovers data at receiver
• Orthogonality: Subcarriers don’t interfere with each other

Cyclic Prefix:

• Function: Prevents inter-symbol interference
• Implementation: Copy of signal end added to beginning
• Length: Longer than channel delay spread

Advantages:

• Spectral Efficiency: High data rate in limited bandwidth
• Multipath Immunity: Resistant to fading channels
• Flexible: Easy to implement with DSP

Applications:

• 4G LTE: Mobile communication standard
• WiFi: 802.11a/g/n/ac standards
• Digital TV: DVB-T, ISDB-T standards

Mnemonic: “Orthogonal Frequencies Divide Multiplexed data”

Question 5(c OR) [7 marks]

#

Describe MANET.

Answer:

MANET Overview: Mobile Ad-hoc Network is a self-configuring network of mobile devices connected wirelessly without fixed infrastructure.

Network Topology:

Key Characteristics:

Architecture Table:

MANET Features:

Dynamic Topology:

• Mobile Nodes: All nodes can move freely
• Changing Links: Network connections change as nodes move
• Self-Organization: Network automatically reconfigures

Multi-hop Communication:

• Relay Function: Nodes act as routers for other nodes
• Path Discovery: Dynamic route finding to destination
• Distributed Control: No central coordination needed

Routing Protocols:

Proactive Protocols:

• DSDV: Destination Sequenced Distance Vector
• Characteristic: Maintain routing tables continuously
• Advantage: Routes available immediately
• Disadvantage: High overhead in mobile environment

Reactive Protocols:

• AODV: Ad-hoc On-demand Distance Vector
• DSR: Dynamic Source Routing
• Characteristic: Find routes only when needed
• Advantage: Lower overhead
• Disadvantage: Route discovery delay

Hybrid Protocols:

• ZRP: Zone Routing Protocol
• Combination: Proactive within zone, reactive between zones
• Balance: Overhead vs. delay optimization

Advantages:

• No Infrastructure: Quick deployment without base stations
• Flexibility: Network adapts to changing topology
• Cost Effective: Lower setup and maintenance costs
• Robustness: No single point of failure

Disadvantages:

• Limited Bandwidth: Shared wireless medium
• Power Consumption: Routing functions drain battery
• Security Issues: Vulnerable to attacks
• Scalability: Performance degrades with network size

Applications:

Military Operations:

• Battlefield Communications: Soldier-to-soldier communication
• Emergency Response: Disaster relief coordination
• Surveillance: Sensor network deployment

Commercial Applications:

• Vehicular Networks: Car-to-car communication
• Sensor Networks: Environmental monitoring
• Conference Networks: Temporary meeting networks
• Personal Area Networks: Device interconnection

Challenges:

Technical Challenges:

• Routing Overhead: Control message bandwidth consumption
• Quality of Service: Difficulty in guaranteeing service levels
• Power Management: Energy-efficient operation
• Interference: Co-channel interference from multiple hops

Security Challenges:

• Authentication: Verifying node identity
• Data Integrity: Ensuring message authenticity
• Privacy: Protecting user information
• Denial of Service: Preventing network attacks

Performance Metrics:

• Throughput: Data delivery rate
• Delay: End-to-end packet delivery time
• Packet Loss: Percentage of lost packets
• Energy Consumption: Battery life optimization

Future Trends:

• Integration: Combination with cellular and WiFi networks
• IoT Applications: Internet of Things device networks
• 5G Integration: Part of 5G network architecture
• AI-based Routing: Machine learning for optimal routing

Mnemonic: “Mobile Nodes, Ad-hoc Routing, No Infrastructure, Temporary Networks”