ADMS 2511 Chapter Notes -Tellme Networks, Mobile Commerce, Qwerty

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Published on 9 Nov 2011
Wireless: telecommunication in which electromagnetic waves – in the form of wire or cable, carry
signal between communicating devices.
Wireless Mobile
Without wires. Can be mobile or fixed. Changes location over time.
Traditional- fixed computer ineffective or inefficient.
Wireless technologies- mobile computing, mobile commerce, and pervasive computing.
Mobile computing: real time, wireless connection between a mobile device and other computing
environments such as intranet/extranet.
Mobile commerce/m-commerce: EC transactions conducted in a wireless environment, especially
via internet.
Pervasive computing/ubiquitous computing: means that virtually every object has processing
power with wireless or wired connections to a global network.
Wireless devices: advantages:
Saves time that can be used effectively for some useful purpose
Mobile- makes it flexible for a person to go anywhere with the devices.
Allocate working time between personal and professional obligations.
WAP: wireless application protocol (WAP) is the standard that enables wireless devices to access
web-based information and services.
Micro browsers: internet browsers with a small file size that can work within the confines of
small screen sizes on wireless devices and relatively low bandwidths of wireless networks. Eg.
Apple iphone- safari browser.
Smart phones- cellular telephony, Bluetooth, Wi-Fi, a digital camera, global positioning
system(GPS), an organizer, a scheduler, an address book, calculator, access to e-mail, Short
message service(SMS), instant messaging, text messaging, mp3 music player, video player,
internet access with full function browser, QWERTY keyboard.
Lack of privacy- user can copy and pass confidential information.
Jamming devices- jam signals from phones when they enter specific locations.
Wireless transmission media: wireless media/broadcast media transmit signals
without wires over the air or space.
Channel Advantages disadvantages
microwave transmission
High bandwidth
Relatively inexpensive
Must have unobstructed line of
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systems – high volume, long
distance, line-of-sight
Susceptible to environmental
interference, severe weather
Satellite transmission systems
make use of communication
High bandwidth
Large coverage area
Must have unobstructed line of
sight signals experience
propagation delay
Must use encryption for
Radio High bandwidth
Signals pass through walls
Inexpensive and easy to install
Creates electrical interference
Susceptible to snooping unless
Infrared Low to medium bandwidth
Used only for short distances
Must have unobstructed line of
Microwave: towers cannot be spaced more than 50km apart.
Satellite: 3 basic types of satellites-
Type Characteristics Orbit Numb
Satellites remain stationary relative to point
on earth
Few satellites needed for global coverage*
Transmission delay (approx. 0.25sec-also
called propagation delay)
Most expensive to build and launch
Longest orbital life(many years)*
35900km 8 TV
earth orbit
Satellites move relative to the point on earth
Moderate no. Needed for global coverage
Requires medium-powered transmitters
Negligible transmission delay*
Less expensive to build and launch*
Moderate orbital life ( 6-12years)
10354km 10-12 GPS
Low earth
Satellites move rapidly relative to point on
Large number needed for global coverage
Requires only low-power transmitters
Negligible transmission delay*
Least expensive to build and launch*
Shortest orbital life( as low as 5 years)
Many telepho
Geo satellite orbit has a fixed position right above the earth’s equator, thus its orbital period
matches 24hrs rotation of the earth.
Leo has the ability to pick up weak transmissions-satellite telephone to operate.
A single organization often produces multiple Leo satellites- known as LEO constellations.
Eg. Iridium has Leo constellations in orbit that consist of 66 satellites and 12 in-orbit square
Two major satellite applications-
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1) Global positioning system (GPS): wireless system that uses satellites to enable users to
determine their position anywhere on earth. Has 24MEO satellites shared worldwide.
Known speed of signals and distance between various signals- locates position and finds
user/ receiving station within 3 metres. Converts user’s latitude longitude to electronic
map for driving directions.
Russian GPS- GLONASS by 1995 but failed.
European Union GPS- Galileo by 2013
China GPS- Beidou by 2015
2) Internet transmission via satellites (IoS): installing necessary cables are expensive /
physically impossible).
Enables users to have access to GEO satellite internet using a dish mounted on the side of
their homes.
Disadvantage is disruption due to propagation delay and weather conditions.
Microwave transmission- within line of sight. But earth has a huge footprint: area of earth’s
surface reached by a satellite’s transmission.
“Basic Rule: Higher the satellite orbits, larger the footprint.”
Broadcast transmission: sends signals to many receivers at the same time. Satellite is high
enough to reach many.
Radio transmission: uses radio-wave frequencies to send and receive data directly
between transmitters and receivers.
I. Easily travel through normal office walls.
II. Fairly inexpensive, easy to install
III. Transmit data at high speed
Often used to connect computers to peripheral equipment and LAN
I. Create electrical interference problems
II. Susceptible to snooping by outsider with similar equipment.
Satellite radio/digital radio: overcomes the problem of traditional satellite which requires
the transmitter and receiver to be at a min distance of 50-65km from each other.
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