Question 1(a) [3 marks]

Explain umbrella cell.

Answer: Umbrella cell is a large coverage area cell that overlays smaller cells to provide continuous coverage and handle overflow traffic.

Table: Umbrella Cell Characteristics

Feature	Description
Coverage	Large geographic area
Purpose	Handle overflow traffic from microcells
Antenna	High-power, elevated position
Users	Fast-moving vehicles, emergency calls

Large coverage: Covers wide geographical area with high-power base station
Traffic management: Handles calls when smaller cells are congested
Mobility support: Serves fast-moving users crossing multiple cell boundaries

Mnemonic: "Umbrella Covers Large Areas"

Question 1(b) [4 marks]

Define cell and cluster.

Answer: Cell and cluster are fundamental concepts in cellular communication systems.

Table: Cell vs Cluster Comparison

Parameter	Cell	Cluster
Definition	Single coverage area served by one base station	Group of cells using different frequencies
Size	Limited by antenna power and interference	Contains N cells (typically 3, 4, 7, 12)
Frequency	Uses specific frequency set	Uses all available frequencies once
Purpose	Provide coverage to specific area	Enable frequency reuse pattern

Cell: Geographic area served by single base station with specific frequency allocation
Cluster: Group of adjacent cells that collectively use entire frequency spectrum
Frequency reuse: Same frequencies can be reused in different clusters
Pattern repetition: Cluster pattern repeats throughout coverage area

Mnemonic: "Cells Cluster for Complete Coverage"

Question 1(c) [7 marks]

Describe fundamental concept behind cellular communication systems.

Answer: Cellular communication divides service area into small cells to maximize spectrum efficiency and capacity.

Diagram:

    +-------+-------+-------+
    |   A   |   B   |   C   |
    |  f1   |  f2   |  f3   |
    +-------+-------+-------+
    |   D   |   E   |   F   |
    |  f4   |  f5   |  f6   |
    +-------+-------+-------+
    |   G   |   H   |   I   |
    |  f7   |  f1   |  f2   |
    +-------+-------+-------+

Table: Cellular System Benefits

Concept	Advantage
Frequency Reuse	Same frequencies used multiple times
Cell Division	Smaller coverage areas, more capacity
Handoff	Seamless call transfer between cells
Power Control	Reduced interference, longer battery life

Small cell concept: Service area divided into hexagonal cells for efficient coverage
Frequency reuse: Limited spectrum used multiple times with adequate separation
Base station control: Each cell served by low-power base station
Capacity improvement: More users supported compared to single large coverage area
Interference management: Co-channel interference controlled through proper cell planning

Mnemonic: "Small Cells Support Spectrum Sharing Successfully"

Question 1(c OR) [7 marks]

Explain co-channel interference in cellular communication.

Answer: Co-channel interference occurs when cells using same frequencies are too close, causing signal degradation.

graph TD
    A[Cell A - f1] --> B[Interference Zone]
    C[Cell C - f1] --> B
    B --> D[Degraded Signal Quality]
    E[Distance D] --> F[Reduced Interference]

Table: Co-channel Interference Parameters

Parameter	Description	Impact
Reuse Distance	Distance between co-channel cells	Higher distance = Less interference
C/I Ratio	Carrier to Interference ratio	Must be ≥ 18 dB for good quality
Cluster Size	Number of cells in cluster	Larger cluster = More separation

Signal overlap: Same frequency signals from different cells interfere
Quality degradation: Causes call drops and poor voice quality
Distance factor: Interference reduces with square of distance
Mitigation methods: Proper cell planning, power control, antenna design

Mnemonic: "Co-channel Causes Call Quality Concerns"

Question 2(a) [3 marks]

Explain cell splitting.

Answer: Cell splitting divides congested cells into smaller cells to increase system capacity.

Diagram:

Original Large Cell          After Cell Splitting
    +-------+                   +---+---+
    |       |                   | A | B |
    |   X   |        →          +---+---+
    |       |                   | C | D |
    +-------+                   +---+---+

Capacity increase: Each new cell handles fewer users with better service quality
Power reduction: New base stations use lower power to cover smaller areas
Frequency management: Original frequencies distributed among new smaller cells

Mnemonic: "Split Cells Serve Subscribers Successfully"

Question 2(b) [4 marks]

Explain channel assignment strategies.

Answer: Channel assignment strategies determine how frequencies are allocated to cells for optimal performance.

Table: Channel Assignment Strategies

Strategy	Description	Advantages	Disadvantages
Fixed	Channels permanently assigned to cells	Simple, predictable	Inefficient during low traffic
Dynamic	Channels assigned based on demand	Efficient spectrum use	Complex implementation
Hybrid	Combination of fixed and dynamic	Balanced approach	Moderate complexity

Fixed assignment: Each cell has predetermined set of channels
Dynamic assignment: Channels allocated in real-time based on traffic demand
Load balancing: Distributes traffic evenly across available channels
Interference avoidance: Considers co-channel interference in assignment decisions

Mnemonic: "Dynamic Distribution Delivers Optimal Performance"

Question 2(c) [7 marks]

Calculate voice and control channels per cell for 33MHz bandwidth, 25KHz simplex channels, 7-cell reuse, 1MHz for control.

Answer: Calculation for channel allocation in cellular system.

Given Data:

Total bandwidth = 33 MHz
Channel bandwidth = 25 KHz (simplex)
Full duplex requires = 2 × 25 KHz = 50 KHz
Control spectrum = 1 MHz
Cluster size = 7 cells

Calculations:

Step 1: Total available channels Total channels = 33 MHz ÷ 25 KHz = 1320 channels

Step 2: Control channels Control channels = 1 MHz ÷ 25 KHz = 40 channels

Step 3: Voice channels Voice channels = 1320 - 40 = 1280 channels

Step 4: Duplex voice channels Duplex voice channels = 1280 ÷ 2 = 640 channels

Step 5: Channels per cell Voice channels per cell = 640 ÷ 7 ≈ 91 channels Control channels per cell = 40 ÷ 7 ≈ 6 channels

Final Answer:

Voice channels per cell: 91
Control channels per cell: 6

Mnemonic: "Calculate Carefully for Channel Count"

Question 2(a OR) [3 marks]

Write functions of FCCH and SCH in GSM.

Answer: FCCH and SCH are essential control channels in GSM system for synchronization.

Table: FCCH and SCH Functions

Channel	Full Form	Function
FCCH	Frequency Correction Channel	Provides frequency reference to mobile
SCH	Synchronization Channel	Provides timing and cell identity

FCCH function: Enables mobile to synchronize with base station frequency
SCH function: Carries BSIC (Base Station Identity Code) and frame number
Timing correction: Both channels help mobile achieve proper timing synchronization

Mnemonic: "FCCH Fixes Frequency, SCH Synchronizes System"

Question 2(b OR) [4 marks]

Write GSM 900 specifications.

Answer: GSM 900 operates in 900 MHz frequency band with specific technical parameters.

Table: GSM 900 Specifications

Parameter	Specification
Uplink Frequency	890-915 MHz
Downlink Frequency	935-960 MHz
Duplex Separation	45 MHz
Channel Spacing	200 KHz
Total Channels	124 channels
Access Method	TDMA/FDMA
Modulation	GMSK
Power Classes	2W, 8W, 20W

Frequency bands: Separate uplink and downlink frequencies for full duplex operation
TDMA structure: 8 time slots per carrier frequency

Mnemonic: "GSM 900 Gives Great Global Coverage"

Question 2(c OR) [7 marks]

Draw and explain GSM architecture.

Answer: GSM architecture consists of three main subsystems working together for mobile communication.

graph TB
    MS[Mobile Station] --> BSS[Base Station Subsystem]
    BSS --> NSS[Network Switching Subsystem]
    BSS --> BTS[Base Transceiver Station]
    BSS --> BSC[Base Station Controller]
    NSS --> MSC[Mobile Switching Center]
    NSS --> HLR[Home Location Register]
    NSS --> VLR[Visitor Location Register]
    NSS --> AuC[Authentication Center]
    MSC --> PSTN[Public Switched Telephone Network]

Table: GSM Architecture Components

Subsystem	Components	Function
Mobile Station	Mobile Equipment + SIM	User interface and identity
BSS	BTS + BSC	Radio interface and control
NSS	MSC, HLR, VLR, AuC	Switching and database management

Mobile Station: Consists of mobile equipment and SIM card for user identification
Base Station Subsystem: Handles radio communication and resource management
Network Switching Subsystem: Manages call switching, routing, and subscriber databases
Interfaces: A-bis (BTS-BSC), A (BSC-MSC) interfaces connect subsystems

Mnemonic: "Mobile Base Network - Complete Communication Chain"

Question 3(a) [3 marks]

Draw block diagram of signal processing in GSM.

Answer: Signal processing in GSM involves multiple stages for voice and data transmission.

Diagram:

Speech → Speech → Channel → Interleaving → Burst → RF
Input    Coding    Coding              Formatting  Processing
  ↓        ↓         ↓         ↓           ↓         ↓
13kbps → 22.8kbps → Error → Reordering → Time → Modulation
                  Protection              Slot    & Transmission

Speech coding: Converts analog speech to 13 kbps digital data using RPE-LTP
Channel coding: Adds error correction bits increasing rate to 22.8 kbps
Interleaving: Reorders data to combat burst errors from fading

Mnemonic: "Speech Signals Systematically Processed Successfully"

Question 3(b) [4 marks]

Write functions of Common Control Channels in GSM.

Answer: Common Control Channels manage system information and access procedures in GSM.

Table: Common Control Channels Functions

Channel	Function
FCCH	Frequency correction and synchronization
SCH	Frame synchronization and cell identification
BCCH	Broadcasts system information and cell parameters
RACH	Random access for call initiation by mobile
AGCH	Assigns dedicated channels to mobiles
PCH	Pages mobiles for incoming calls

Broadcast function: BCCH continuously transmits system information
Access management: RACH allows mobiles to request service
Channel assignment: AGCH allocates resources for active calls
Paging service: PCH notifies mobiles of incoming calls

Mnemonic: "Common Channels Control Communication Completely"

Question 3(c) [7 marks]

Explain GSM identifiers.

Answer: GSM identifiers uniquely identify subscribers, equipment, and network elements.

Table: GSM Identifiers

Identifier	Full Form	Purpose	Format
IMSI	International Mobile Subscriber Identity	Unique subscriber ID	15 digits
IMEI	International Mobile Equipment Identity	Unique equipment ID	15 digits
MSISDN	Mobile Station ISDN Number	Phone number	Variable length
TMSI	Temporary Mobile Subscriber Identity	Temporary ID for security	32 bits
LAI	Location Area Identity	Geographic area identification	MCC+MNC+LAC
BSIC	Base Station Identity Code	Cell identification	6 bits

IMSI structure: MCC (3) + MNC (2-3) + MSIN (9-10 digits)
Security purpose: TMSI protects subscriber identity over radio interface
Location management: LAI helps in efficient paging and location updates
Network planning: BSIC prevents confusion between adjacent cells

Mnemonic: "Important Mobile System Identifiers Ensure Security"

Question 3(a OR) [3 marks]

Compare Fast and Slow frequency hopping.

Answer: Frequency hopping techniques differ in hopping rate relative to symbol rate.

Table: Fast vs Slow Frequency Hopping

Parameter	Fast Hopping	Slow Hopping
Hopping Rate	> Symbol rate	< Symbol rate
Symbols per Hop	< 1	> 1
Complexity	High	Low
Applications	Military, Bluetooth	GSM, CDMA

Fast hopping: Multiple hops per symbol, better security but more complex
Slow hopping: Multiple symbols per hop, simpler implementation

Mnemonic: "Fast Frequently Flips, Slow Stays Stable"

Question 3(b OR) [4 marks]

Calculate number of users in GSM 900 band without frequency reuse.

Answer: Calculation for maximum users in GSM 900 without frequency reuse.

Given GSM 900 Parameters:

Uplink: 890-915 MHz (25 MHz)
Downlink: 935-960 MHz (25 MHz)
Channel spacing: 200 KHz
Time slots per channel: 8

Calculations:

Step 1: Available channels Total channels = 25 MHz ÷ 200 KHz = 125 channels

Step 2: Usable channels Guard channels removed ≈ 124 channels

Step 3: Simultaneous users Users per channel = 8 time slots Total users = 124 × 8 = 992 users

Answer: 992 users can talk simultaneously

Mnemonic: "Calculate Channels Times Time-slots"

Question 3(c OR) [7 marks]

Draw and explain general block diagram of mobile handset.

Answer: Mobile handset consists of several functional blocks working together.

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

Table: Mobile Handset Blocks

Block	Function
RF Section	Signal transmission and reception
Baseband	Digital signal processing
Audio	Voice input/output processing
Power Management	Battery and power control
User Interface	Display, keypad, speaker, microphone

RF processing: Handles radio frequency transmission and reception
Digital processing: Baseband performs channel coding, speech processing
User interface: Provides interaction through display, keypad, audio
Power control: Manages battery usage and charging functions

Mnemonic: "Mobile Manages Multiple Modules Simultaneously"

Question 4(a) [3 marks]

Write radiation hazards due to mobile.

Answer: Radiation hazards from mobile phones are a health concern due to RF energy exposure.

Table: Mobile Radiation Hazards

Hazard	Effect	Prevention
SAR Exposure	Tissue heating	Use hands-free devices
Brain Effects	Memory, sleep issues	Limit call duration
Cancer Risk	Potential tumor risk	Keep phone away from body

SAR (Specific Absorption Rate): Measures RF energy absorbed by body tissue
Thermal effects: RF energy can cause localized heating of tissues
Non-thermal effects: Possible impacts on cellular functions and DNA

Mnemonic: "Safety Awareness Reduces Radiation Risk"

Question 4(b) [4 marks]

Explain working of baseband section in mobile handset.

Answer: Baseband section performs digital signal processing functions in mobile handset.

Table: Baseband Section Functions

Function	Description
Speech Processing	Encode/decode voice using vocoder
Channel Coding	Add error correction and detection
Modulation	Convert digital data to analog signals
Protocol Processing	Handle signaling and call control

Digital signal processor: Executes speech coding algorithms (GSM: RPE-LTP)
Error correction: Implements convolutional coding for reliable transmission
Control functions: Manages call setup, handoff, and power control
Interface: Connects RF section with user interface components

Mnemonic: "Baseband Brings Better Communication Control"

Question 4(c) [7 marks]

Explain working of DSSS transmitter and receiver.

Answer: DSSS (Direct Sequence Spread Spectrum) spreads signal bandwidth using pseudorandom codes.

Transmitter Diagram:

graph LR
    A[Data Input] --> B[PN Code Generator]
    A --> C[XOR Gate]
    B --> C
    C --> D[Modulator]
    D --> E[RF Output]

Receiver Diagram:

graph LR
    F[RF Input] --> G[Demodulator]
    G --> H[XOR Gate]
    I[PN Code Generator] --> H
    H --> J[Data Output]

Table: DSSS Process

Stage	Transmitter	Receiver
Spreading	Data XOR with PN code	Received signal XOR with PN
Modulation	Spread signal modulated	Demodulate received signal
Processing	Bandwidth increased	Original data recovered

Spreading process: Original data XORed with high-rate pseudorandom sequence
Bandwidth expansion: Signal bandwidth increased by processing gain factor
Despreading: Receiver uses same PN code to recover original data
Interference rejection: Spread spectrum provides resistance to jamming

Mnemonic: "Direct Sequence Spreads Signals Successfully"

Question 4(a OR) [3 marks]

Calculate processing gain for DSSS system with 10 Mcps chip rate and 1 Mbps data rate.

Answer: Processing gain determines spread spectrum system's performance improvement.

Given:

Chip rate (Rc) = 10 million chips per second = 10 × 10⁶ cps
Data rate (Rd) = 1 Mbps = 1 × 10⁶ bps

Calculation: Processing Gain (Gp) = Chip rate ÷ Data rate Gp = Rc ÷ Rd = (10 × 10⁶) ÷ (1 × 10⁶) = 10

In dB: Gp (dB) = 10 log₁₀(10) = 10 × 1 = 10 dB

Answer: Processing Gain = 10 or 10 dB

Mnemonic: "Processing Power Provides Protection"

Question 4(b OR) [4 marks]

Explain how data rate is improved in EDGE.

Answer: EDGE (Enhanced Data rates for GSM Evolution) improves data rates through advanced modulation.

Table: EDGE Improvements

Parameter	GSM	EDGE	Improvement
Modulation	GMSK	8-PSK	3 bits per symbol vs 1 bit
Data Rate	9.6 kbps	43.2 kbps per slot	~4.5x increase
Coding	Fixed	Adaptive	Link adaptation
Applications	Voice, SMS	Multimedia, Internet	Enhanced services

8-PSK modulation: Transmits 3 bits per symbol instead of 1 bit in GMSK
Link adaptation: Dynamically selects coding scheme based on channel quality
Backward compatibility: Works with existing GSM infrastructure
Enhanced applications: Supports multimedia and higher data rate services

Mnemonic: "EDGE Enhances Exchange Efficiently"

Question 4(c OR) [7 marks]

Explain call processing in CDMA.

Answer: CDMA call processing involves unique procedures for code-based multiple access.

graph LR
    A[Mobile Power On] --> B[Pilot Channel Search]
    B --> C[Sync Channel Read]
    C --> D[Paging Channel Monitor]
    D --> E[Access Channel Request]
    E --> F[Traffic Channel Assignment]
    F --> G[Active Call State]
    G --> H[Soft Handoff]

Table: CDMA Call Processing Stages

Stage	Process	Function
Initialization	Pilot acquisition	Find strongest base station
Idle State	Monitor paging	Listen for incoming calls
Access	Random access	Request service from network
Traffic	Dedicated channel	Active communication
Handoff	Soft handoff	Seamless cell transition

Pilot channel: Provides timing reference and system identification
Rake receiver: Combines multipath signals for improved performance
Power control: Maintains optimal signal levels for all users
Soft handoff: Mobile communicates with multiple base stations simultaneously
Code assignment: Each user assigned unique spreading code

Mnemonic: "CDMA Calls Connect Carefully and Clearly"

Question 5(a) [3 marks]

Compare CDMA and GSM.

Answer: CDMA and GSM represent different approaches to cellular communication.

Table: CDMA vs GSM Comparison

Parameter	CDMA	GSM
Access Method	Code Division	Time/Frequency Division
Capacity	Higher	Lower
Handoff	Soft handoff	Hard handoff
Security	Better (spreading codes)	Good (encryption)
Global Usage	Limited	Widespread
Power Control	Continuous	Periodic

Multiple access: CDMA uses unique codes, GSM uses time slots
Call quality: CDMA provides soft handoff, GSM has hard handoff

Mnemonic: "Choose CDMA or GSM Carefully"

Question 5(b) [4 marks]

Write advantages of CDMA.

Answer: CDMA advantages make it suitable for high-capacity cellular systems.

Table: CDMA Advantages

Advantage	Benefit
High Capacity	More users per spectrum
Soft Handoff	Seamless call transfer
Variable Rate	Adapts to speech patterns
Privacy	Inherent security through spreading
Multipath Resistance	Uses rake receiver
Power Control	Optimizes battery life
Frequency Planning	Same frequency in all cells

Spectrum efficiency: Higher capacity compared to FDMA/TDMA systems
Quality advantage: Soft handoff eliminates call drops during cell transitions
Security benefit: Spread spectrum provides inherent privacy protection
Simplified planning: No frequency reuse planning required

Mnemonic: "CDMA Creates Considerable Communication Capacity"

Question 5(c) [7 marks]

Explain MANET in brief and write its applications.

Answer: MANET (Mobile Ad Hoc Network) is infrastructure-less network of mobile devices.

graph LR
    A[Mobile Node A] -.-> B[Mobile Node B]
    B -.-> C[Mobile Node C]
    C -.-> D[Mobile Node D]
    A -.-> C
    B -.-> D
    A -.-> D

    style A fill:#f9f
    style B fill:#9ff
    style C fill:#ff9
    style D fill:#9f9

Table: MANET Characteristics vs Applications

Characteristic	Feature	Applications
Self-organizing	No fixed infrastructure	Military communications
Dynamic topology	Nodes move freely	Emergency response
Multi-hop routing	Intermediate node relay	Disaster recovery
Distributed control	No central authority	Sensor networks
Resource constraints	Limited battery, bandwidth	Vehicular networks

Applications:

Military operations: Battlefield communications without infrastructure
Emergency services: Disaster response and rescue operations
Sensor networks: Environmental monitoring and data collection
Vehicular networks: Car-to-car communication for traffic management
Personal area networks: Device-to-device communication
Academic research: Collaborative computing environments

Advantages:

Rapid deployment: No infrastructure setup required
Self-healing: Automatic route reconfiguration when nodes fail
Cost effective: No base station installation costs

Disadvantages:

Limited bandwidth: Shared wireless medium
Security challenges: Vulnerable to attacks
Power constraints: Battery-dependent operation

Mnemonic: "Mobile Ad Hoc Networks Enable Everywhere"

Question 5(a OR) [3 marks]

Write key features of WCDMA.

Answer: WCDMA (Wideband CDMA) is the 3G standard offering enhanced capabilities.

Table: WCDMA Key Features

Feature	Specification
Chip Rate	3.84 Mcps
Bandwidth	5 MHz
Data Rates	Up to 2 Mbps
Spreading	Variable spreading factor
Power Control	Fast closed-loop
Handoff	Soft and softer handoff

Wideband operation: 5 MHz bandwidth provides high data rates
Variable spreading: Adapts to different service requirements

Mnemonic: "WCDMA Widens Communication Data Magnificently"

Question 5(b OR) [4 marks]

Enlist advantages of 5G.

Answer: 5G advantages represent significant improvements over previous generations.

Table: 5G Advantages

Advantage	Benefit
Ultra-high Speed	Up to 20 Gbps peak data rate
Low Latency	<1ms for critical applications
Massive IoT	1 million devices per km²
Network Slicing	Customized virtual networks
Enhanced Coverage	Better indoor and edge coverage
Energy Efficiency	100x more efficient than 4G
High Reliability	99.999% availability

Enhanced mobile broadband: Supports AR/VR and 4K/8K video streaming
Ultra-reliable communications: Enables autonomous vehicles and remote surgery
Massive machine communications: Supports smart cities and Industry 4.0
Flexible network architecture: Software-defined networking capabilities

Mnemonic: "5G Generates Great Gigabit Growth"

Question 5(c OR) [7 marks]

Explain working of OFDM with block diagram.

Answer: OFDM (Orthogonal Frequency Division Multiplexing) uses multiple subcarriers for high-speed data transmission.

OFDM Transmitter:

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

OFDM Receiver:

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

Table: OFDM Process Steps

Stage	Transmitter Function	Receiver Function
Data Conversion	Serial to parallel conversion	Parallel to serial reconstruction
Modulation	QAM mapping on subcarriers	QAM demapping
Transform	IFFT creates time domain signal	FFT recovers frequency domain
Guard Period	Cyclic prefix prevents ISI	Cyclic prefix removal

Key Features:

Orthogonal subcarriers: Multiple parallel low-rate data streams prevent interference
FFT/IFFT processing: Efficient digital implementation using fast transforms
Cyclic prefix: Guard interval prevents inter-symbol interference from multipath
Spectral efficiency: High data rates achieved in limited bandwidth
Multipath resistance: Individual subcarriers experience flat fading

Applications:

WiFi (802.11): Wireless LAN communications
LTE/4G: Mobile broadband networks
Digital TV: DVB-T terrestrial broadcasting
WiMAX: Broadband wireless access

Advantages:

High spectral efficiency: Optimal bandwidth utilization
Robustness: Resistant to frequency selective fading
Flexibility: Adaptive modulation per subcarrier
Implementation: Digital signal processing simplifies hardware

Table: OFDM Parameters

Parameter	Typical Values
Subcarriers	64, 128, 256, 512, 1024
Modulation	BPSK, QPSK, 16-QAM, 64-QAM
Cyclic Prefix	1/4, 1/8, 1/16 of symbol duration
Applications	WiFi, LTE, DVB, WiMAX

Mnemonic: "OFDM Offers Outstanding Data Multiplexing"