Download - Mobile Computing - Basics
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