Introduction to Mobile Computing
Introduction to Mobile Computing
Mobile Computing is a technology that allows transmission of data, voice, and video via wireless devices (smartphones, laptops) without fixed physical connections.
Components
| Component | Description |
|---|---|
| Mobile Hardware | Devices like phones, tablets |
| Mobile Software | Apps, OS (Android, iOS) |
| Communication | Wireless networks |
Basic Architecture
Mobile Device → Base Station → Network → Internet/Server
Features
- Portability
- Connectivity
- Mobility
- Real-time communication
Issues in Mobile Computing
Major Issues
| Issue | Description |
|---|---|
| Limited Bandwidth | Slower than wired networks |
| Battery Power | Limited energy |
| Security | Risk of hacking |
| Mobility Management | Tracking moving users |
| Network Latency | Delay in communication |
Example
- Weak signal in remote areas
- Frequent disconnections
Overview of Wireless Telephony
Wireless telephony allows voice communication without wires using radio signals.
Types
- Cellular networks
- Satellite communication
- Wi-Fi calling
Working
Mobile → Radio Signal → Base Station → Switching Center → Receiver
Cellular Concept
Cellular system divides a large area into small regions called cells.
Cellular Structure
[Cell1] [Cell2] [Cell3]
\ | /
Base Stations
Advantages
- Efficient frequency reuse
- Better coverage
- Scalability
GSM (Global System for Mobile Communication)
A 2G digital cellular standard used for mobile communication.
GSM Air Interface
Diagram
Mobile Station ↔ Base Transceiver Station (BTS)
Key Features
- Digital communication
- SIM-based authentication
- Supports SMS & voice
GSM Channel Structure
Types of Channels
| Channel Type | Description |
|---|---|
| Traffic Channel (TCH) | Carries voice/data |
| Control Channel (CCH) | Carries signaling |
Control Channel Types
- Broadcast Channel (BCCH)
- Common Control Channel (CCCH)
- Dedicated Control Channel (DCCH)
Location Management
Tracking the location of mobile users.
Components
- HLR (Home Location Register): Stores permanent user data
- VLR (Visitor Location Register): Stores temporary data
HLR-VLR Architecture
HLR ↔ VLR ↔ Base Station ↔ Mobile
Hierarchical Location Management
- Multi-level location tracking
- Reduces signaling traffic
Handoff (Handover)
Transfer of active call from one cell to another.
Handoff Process
Cell A → Signal Weak → Switch → Cell B
Types
| Type | Description |
|---|---|
| Hard Handoff | Break before make |
| Soft Handoff | Make before break |
Channel Allocation in Cellular System
Assigning frequency channels to cells.
Types
| Type | Description |
|---|---|
| Fixed Allocation | Pre-assigned channels |
| Dynamic Allocation | Assigned based on demand |
CDMA (Code Division Multiple Access)
Multiple users share same frequency using unique codes.
Working
User1 → Code1
User2 → Code2
→ Combined Signal → Receiver separates
Advantages
- High capacity
- Better security
- Less interference
GPRS (General Packet Radio Service)
Packet-based data service on GSM (2.5G).
Features
- Internet access
- Email, MMS
- Always-on connectivity
Working
Mobile → Packet Data → Network → Internet
MAC (Medium Access Control) for Cellular Systems
Controls how multiple users access shared communication medium.
Functions
- Channel assignment
- Collision avoidance
- Scheduling
Techniques
| Technique | Description |
|---|---|
| TDMA | Time-based access |
| FDMA | Frequency-based |
| CDMA | Code-based |
MAC Layer Diagram
Users → MAC Layer → Shared Channel
Important Exam Questions
Short Questions
- Define GSM
- What is HLR and VLR?
- What is CDMA?
Long Question
- Explain cellular concept with diagram
- Describe GSM architecture and channels
- Explain location management and handoff
Case-Based Questions
- Explain how handoff works during a call
- Compare CDMA and GSM
- Discuss channel allocation strategies
Final Summary
- Mobile Computing → wireless communication system
- Cellular Concept → divide area into cells
- GSM → digital mobile standard
- HLR/VLR → location tracking
- CDMA → code-based access
- GPRS → packet data service
- MAC → controls channel access
Tags:
Mobile Computing