This document discusses mobile computing and mobile communication devices. It introduces the concepts of user mobility, where a person can access resources from different locations, and system mobility, where a system can be carried along with a user without interrupting tasks. It also describes characteristics of communication devices and applications of mobile computing like in vehicles, emergencies, business, and more. The document then covers multiplexing techniques used in mobile communication, including space, time, frequency, and code division multiplexing.

1. Mobile Computing
CS 8601

2. TEXT BOOK
• Jochen Schiller, “Mobile Communications”, PHI, Second
Edition, 2003.

3. UNIT - I
INTRODUCTION

4. Introduction to Mobile Computing
• What will computers look like in ten years?
• Computers are becoming portable.
• Aircraft Example
Two different kinds of Mobility:
- User Mobility
- Device Portability

5. Introduction (Contd.,)
User Mobility:
- Person accessing his / her resource at different locations.
Example: Mail access
System Mobility:
- System being carried along with the user without interrupting the
tasks.
Example: Mobile Phone

6. Characteristics of Communication device
• Fixed and wired – Desktop computer in office.
• Mobile and wired – Laptop with office internet.
• Fixed and wireless – In historical buildings.
• Mobile and wireless - GSM

7. Applications
Vehicles:
- Music, news, weather and other broadcast information are received
via digital audio broadcasting (DAB).
- Personal communication using UMTS (Universal mobile
telecommunications system)
- Satellite communication (For remote areas)
- GPS (Global positioning system – Current Location of vehicle)
- Local ad-hoc network for fast exchange of information

9. Applications (Contd.,)
Emergencies:
- Ambulance with high quality wireless connection to the
hospital.
- Vital information about the injured passed to hospital.
- Preliminary arrangements can be made at the hospital.
- During natural disasters, only ad-hoc network / wireless
network helps!

10. Applications (Contd.,)
Business:
- Company people may need instant access to company’s database.

11. Applications (Contd.,)
Replacement of wired networks:
- In some cases, wired networks to be replaced by wireless.
- Ex.: Historic buildings, remote sensors for weather forecasting..
- Wireless connection via satellite communication can help this.
- Wireless access point in a corner of a place can be a solution !

12. Applications (Contd.,)
Infotainment and more:
- Travel guide gives information about historic buildings.
- GPS.
- Concert booking.
- Payment via electronic cash.

13. Applications (Contd.,)
Location Dependent Services:
• Follow-on Services – Call forwarding
• Location aware services – Printing in new location
• Privacy
• Information Services – Google Map
• Support Services – Additional mechanisms integrated to support mobile
device.

14. Applications (Contd.,)
Mobile and Wireless Devices:
- Sensor
- Embedded Controllers
- Pager
- Mobile Phones
- Personal digital assistant (PDAs)
- Pocket Computer
- Notebook / Laptop

15. Multiplexing
• Several users share a medium with minimum or no interference.
• Ex.: Highway lane (Many vehicles share the same medium)
• How it is possible?
• Several lanes separated by space (Space division multiplexing)
• Different cars in same lane but at different points (Time division)
• The above are general.

16. Multiplexing (Contd.,)
•Multiplexing in four dimensions
1. Space
2. Time
3. Frequency
4.Code

17. Space Division Multiplexing
• Communication Channel – Association of sender and receiver.
• Guard Space – Space between channels to prevent interference.
• Ex.: FM radio (Same frequency for different radio in different
ranges)
• Ex.: Highway lane
• Problem: If several stations want to send data in the same
location.
• Solution: Frequency, Time and Code.

18. Space Division Multiplexing

19. Frequency division multiplexing
• Divides frequency dimension into several non-overlapping frequency bands.
• Senders using same frequency band can use this band continuously.
• Guard Spaces – To avoid frequency overlapping.
• No complex co-ordination between sender and receiver.
• Receiver needs to tune into the particular frequency.
Problem:
- Limits senders.
- Waste of resources.

20. Time division multiplexing
• Whole bandwidth allotted for a particular period of time.
• Guard Spaces – Represent time gaps.
• Ex.: Highway Lane – Same lane but with intervals.
Problem:
- Precise timing needed for synchronization.
- Co-ordination required between sender and receiver.

21. Code Division Multiple Access
• New scheme in commercial communication.
• First used in military applications for security.
• Separation achieved by assigning each channel its own code.
• Ex.: Language (Others are noise and separated)
Advantage:
- Strong against tapping and interference.
Problem:
- Receiver must know the code.