Mobile Computing

Basics

Why Mobile Computing ?

People are mobile

Devices are mobile

Definition of Mobile and Wireless

Mobile is the ability to be on the move. A mobile device is anything that can be used on the move, ranging from laptops to mobile phones. As long as location is not fixed, it is considered mobile.

Wireless refers to the transmission of voice and data over radio waves. Wireless devices include anything that uses a wireless network to either send or receive data.

Relationship between mobile and wireless.

Relationship between mobile and wireless. Not all the wireless communications

are mobile. E.g. lasers

Mobile computing does not necessarily require wireless communication. E.g. sending data from a laptop to a

central database over temporary dial-up connection.

Mobile Computing: Advantages

Convenience Communicate with others

anywhere, anytime Access to electronic

information Increasing responsiveness

and customer satisfaction

Limitations Expensive Battery life Small screen display Slow Internet speed

Mobile Computing A technology that allows transmission of

data without having to be connected to a fixed physical link.

Computing environment over physical mobility.

The user of a mobile computing environment will be able to access data, information or other logical objects from any device in any network while on the move.

Mobile Computing Nomadic computing, another name for

mobile computing, is the use of portable computing devices (such as laptop and handheld computers) in conjunction with mobile communications technologies to enable users to access the Internet and data on their home or work computers from anywhere in the world. People using such a system are sometimes referred to as technomads, and their ability to use that system as nomadicity.

Challenges Reliable communication

Radio collisions Transmission range Asymmetric communication Intermediate nodes dropping packets or being

unavailable Voluntary disconnection, e.g., for network cost

or battery conservation Quality of Service

Sufficient communication for task Predicting QoS

Challenges (cont..) Limited resources

Smaller screen Limited audio RAM Persistent storage Processor Battery

Other challenges Secure communication and privacy Device and protocol heterogeneity Transparency - hidden

Mobile Computing Functions:

User with Device Network Gateway Middleware Content

What is Mobility? A person who moves

Between different geographical locations Between different networks Between different communication devices Between different applications

A device that moves Between different geographical locations Between different networks

Types of Mobility User Network Bearer Device Session Agent Host

SOC and AOC Clients Sometimes On Connectivity (SOC)

Stores large amount of data on mobile devices

Provides complete application solution without wireless or wired connection.

Always On Connectivity (AOC) Small amounts of data on devices Requires connection all the time.

3 generations of wireless technology 1G (analog technology)

AMPS (Advanced Mobile Phone Services) 2G

CDMA (Code Division Multiple Access) CDPD (Cellular Digital Packet Data) TDMA (Time Division Multiple Access) GSM (Global System for Mobile Communication) PDC (Personal Digital Cellular)

3G W-CDMA (Wideband Code Division Multiple Access) UMTS (Universal Mobile Telephone Standard) Wireless Voice over IP

Introduction to Handoff

What is handoff? The process of transferring a mobile from one

channel or base-station to another is called handoff When a mobile moves into a different cell while a

conversation is in progress, the MSC(Mobile Switch Center) automatically transfers the call to a new channel belonging to the new base-station

Roaming: from one network to another network.

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Handoff

Purpose of handoff Rescue handoff : To rescue the connection

with poor quality If quality of a communication has become

worse than a threshold, a decision of handoff is made for rescuing this connection

Confinement handoff : To minimize interference

When the mobile can employ lower transmission power in another cell than in current one, a handoff can be triggered to confine the transmission power

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Purpose of handoff

Traffic handoff(Load sharing) : It takes account of capacity and load.

If a new call set-up occurs, a traffic handoff will be triggered owing to the congestion in current cell.

A certain established call in the congested cell will be handed over to another cell so that the new call can be set up.

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Handoff Types By destination base-station

Intercell handoff : Call is handed off to another base-station of different cell.

Intracell handoff : Call is handed off to another base-station of same cell.

By connection method Soft handoff : The connection is never

suspended Hard handoff : The connection is suspended

at first and then recovered at the destination base-station

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Global Positioning System (GPS) Gives the exact position on earth. NAVSTAR GPS

Navigation Satellite Timing and Ranging Global Positioning System

Funded and controlled by U. S. Departmentof Defense.

Three segments Space segment User segment Control segment

Control Segment

Space Segment

User Segment

Three Segments of the GPSThree Segments of the GPS

Monitor Stations

GroundAntennas

Master Station

Space Segment

Kwajalein Atoll

US Space Command

Control SegmentControl Segment

Hawaii

Ascension Is.

Diego Garcia

Cape Canaveral

Ground AntennaMaster Control Station Monitor Station

Military. Search and rescue. Disaster relief. Surveying. Marine, aeronautical and terrestrial navigation. Remote controlled vehicle and robot guidance. Satellite positioning and tracking. Shipping. Geographic Information Systems (GIS). Recreation.

User Segment

GPS System Review

Position and coordinates.

Travel progress reports.

Accurate time measurement.

Basic Functions of GPS

Position is Based on TimePosition is Based on Time

T + 3

Distance between satellite and receiver = “3 times the speed of light”

T

Signal leaves satellite at time “T”

Signal is picked up by the receiver at time “T + 3”

What Time is It?What Time is It?

Zulu Time

Military Time(local time on a 24 hour clock)

Universal Coordinated Time

Greenwich Mean Time

Local Time: AM and PM (adjusted for local time zone)

GPS Time + 13*

* GPS Time is ahead of UTC by approximately 13 seconds

Trilateration Global Positioning System (GPS) navigators use the

mathematical technique of trilateration to determine user position, speed, and elevation. GPS navigators constantly receive and analyze radio signals from GPS satellites, calculating precise distance (range) to each satellite being tracked.

Data from a single satellite narrows position down to a large area of the earth's surface. Adding data from a second satellite narrows position down to the region where two spheres overlap. Adding data from a third satellite (see illustration) provides relatively accurate position. Data from a fourth satellite (or more) enhances precision and also the ability to determine accurate elevation or altitude (in the case of aircraft).

Signal From One SatelliteSignal From One Satellite

The receiver is somewhere on this sphere.

Signals From Two SatellitesSignals From Two Satellites

Three Satellites (2D Positioning)Three Satellites (2D Positioning)

Triangulating Correct Position Triangulating Correct Position

Three Dimensional (3D) PositioningThree Dimensional (3D) Positioning