Wireless Networks

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Wireless Networks

• Team 13
• Jim McGinnis
• Don Braden
• John Gruman
• Heather Harrison
• Brandon Lawson

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Wireless Networks

• Wireless Communications
• Mobile Telephony
• Global System for Mobile Communications and
  Multiple Access
• Third Generation Wireless Communication
• Satellite Communication
• ALOHANET
• Wireless Network Hardware

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Wireless Communications

• Advantages
• Ease of use in difficult terrain.
• Quick to deploy.
• Low initial cost of installation.
• Broadcasts same information to many locations.

• Disadvantages
• Security
• Interference
• Noise
• Signal loss
• Lower data transfer rates
• Frequency reuse more difficult than with guided
  media

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Mobile Telephony

• Advanced Mobile Phone System (AMPS)
• Spectrum and Spacial allocation
• Mobile Devices
• Operation

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AMPS

• Developed in early 1980s by ATT
• Most common mobile system in North America, South
  America, Australia, and China.
• Forerunner to Global System for Mobile
  communications (GSM)

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Spectral and Spacial Allocation

• Frequency allocation
• Two 25MHz bands
• 869-894 MHz
• 824-849 MHz
• Frequency division
• Frequency reuse

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Mobile Devices

• Mobile units
• Mobile
• Hand held (portable)
• Base transceiver
• Mobile Switching Center (MSC)
• Performs switching functions
• Coordinates backup
• Collects data for billing
• Tests and monitors system
• Connections to wired public phone system

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Operation

• Log on
• Control channels and conversation channels
• Monitoring
• Calls
• Power level
• Handling calls
• Handoffs
• Necessary for cell to cell movement

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Global System For Mobile Communications (GSM)

• GSM
• First appeared in Europe in 1991
• Similar standards have been implemented in North
  and South America, Asia, North Africa, the Middle
  East and Australia.
• Many features of GSM are based on
  first-generation systems and share most of the
  same characteristics.

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GSM

• Features
• Subscriber Identity Model (SIM)
• A portable device similar to a smart card or
  plug-in module that stores the subscribers id
  number, authorization of network usage,
  encryption keys, and other subscriber specific
  information
• GSM transmission is encrypted
• AMPS transmissions can easily be monitored

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4 Major Elements subscriber, base transceiver,
base station controllers, and mobile services
switching center
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• HLR or home location register database stores
  information, both permanent and temporary, about
  each of the subscribers that belong to it, such
  as the telephone number associated with the
  switching center.
• VLR or visitor location register database
  determines the location of the subscriber. This
  temporarily registers the subscribers physical
  location within the region covered by the
  switching center.
• AuC or authentication center database is used for
  authentication activities of the system such as
  the authentication and encryption keys for all
  the subscribers in both the home and visitor
  location centers. It also controls access to
  user data.
• EIR or equipment identity register database keeps
  track of the type of equipment that exists at the
  mobile station. It also plays a role in security
  by blocking calls from stolen mobile stations and
  preventing the use of network by unapproved
  stations.

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Code-Division Multiplexing

• Using a signal that is D bits per second and
  converting it for transmission into a longer
  message. Transmit it at a higher rate say, kD,
  where k is the spreading factor. Approximately
  100. Several things can be gained by this
  apparent waste of spectrum. For example, gaining
  immunity from various kinds of noise and
  multipath distortion.

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Which Access Method To Use?

• Besides the pure forms of splitting the channel
  hybrids are also possible.
• For example, GSM uses FDM to divide the allotted
  spectrum into 124 carriers. Each carrier is then
  split into 8 parts using TDM.

• This would cause the potential of users in one
  cell to be enormous.
• The problem is determining which users are active
  in a cell and how to assign them to vacant
  subchannels.

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ALOHA Is The Answer!

• Since the message from a mobile/subscriber
  announcing its presence is short and infrequent,
  the poor utilization that is characteristic of
  ALOHA channels is not a problem. ALOHANET is
  discussed further later in the presentation.

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Random Access Scheme

• When a random access scheme such as ALOHA is
  added to the multiplexing methods FDM, TDM, CDM,
  SDM to dynamically assign subchannels to users,
  the resulting system is called a Random Access
  Method.
• FDMA corresponds to FDM
• TDMA corresponds to TDM
• CDMA corresponds to CDM
• SDMA corresponds to SDM

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ITUs view of third-generation capabilities

• Voice quality comparable to the public switched
  telephone network
• 144 kbps data rate available to users in high
  speed motor vehicles over large areas
• 384 kbps available to pedestrians standing or
  moving slowly over small areas
• Support for 2.048 mbps for office use
• Support for both packet switched and circuit
  switched data services
• An adaptive interface to the internet to reflect
  efficiently the common asymmetry between inbound
  and outbound traffic
• More efficient use of the available spectrum in
  general
• Support for a wide variety of mobile equipment
• Flexibility to allow the introduction of new
  services and technologies

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Wireless Application Protocol (WAP)

• A universal, open standard that provides mobile
  users of wireless phones and other wireless
  terminals access to telephony and information
  services.
• WAP deals with many challenges

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-A programming model based on WWW Programmng
Model-A markup language, the Wireless language,
adhering to XML-Specification of a small browser
suitable for a mobile, wireless
terminal-Lightweight communications protocol
stack-Framework for wireless telephony
applications (WTAs)
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WAP Programming Model

• Based on three elements client, gateway, and
  original server
• Wireless Markup Language(WML)
• Subdivided into small units called cards. Users
  navigate by moving back and forth between cards.
• Communications Protocol Stack
• Adapts the standard web protocols for the
  demanding environment of wireless communications.
• It translates plain text headers into binary,
  reducing amount of data that is sent.

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Wireless Telephony Applications (WTAs)

• Provide an interface to the local and network
  telephone systems.
• Gives applications developers the use of
  microbrowsers to originate phone calls and
  respond to events from the telephone network.

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Satellite Communication LEOS, MEOS, and GEOS

• Satellites are categorized by the orbits they
  keep
• GEOS are geosynchronous earth orbit satellites
• MEOS are medium earth orbit satellites
• LEOS are low earth orbit satellites

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Geostationary Satellites

• Circular orbit 35,838 km above the earth
• Rotates in the equatorial plane
• Can communicate with roughly a fourth of the
  earth
• Delay in communications is (2 X 35,838) / 300,000
  .24 seconds

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Medium Earth Orbiting Satellites

• Orbits at 8,000 to 12,000 km above the earth
• Rotate at various angles (one proposal was for 45
  degrees)
• Approximate delay in communications is (2 X
  10,000) / 300,000 .067 seconds

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Big and Little LEOS

• Little LEOS operate in the frequencies below 1
  GHz using no more than 5 MHz and orbit at 320 to
  1100 above the earth
• Orbcom used to track trailers, railcars, heavy
  equipment and other remote and mobile assets
• Big LEOS operate in frequencies above 1 GHz
• Globalstar used for mobile phone applications

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Iridium

• A flock of inexpensive LEOS
• Global network of 66 LEOS to provide voice and
  paging services
• Put in service in 1998

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Orbits

• The orbits are at an 86-degree tilt from the
  equatorial plane making them almost polar.
• They operate at 778 km above the earth

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Communications

• Users to satellites communicate in the L band
  between 1600 and 1700 MHz
• Phased-array antennas.
• Each antenna complex supports 48 interlaced spot
  beams (cells).

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Case StudyAlohaNet

• University of Hawaii
• Objective Provide terminals at all campuses
  interactive access to the computer resources of
  the main campus
• Problem type of communications/media

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Case StudyAlohaNet

• Land Lines not feasible!
• Leased Radio facilities Too expensive
• Sharing channels using Frequency or time-division
  multiplexing too bursty, especially considering
  the number of terminals

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Case StudyAlohaNet

• Solution Define a new protocol! AlohaNet
• Use two channels One in, one out _at_ 9600bps
• Next Problem How to determine who could get
  control of the inbound channel and how?
• Contention- by simply transmitting packets
  asynchronously and independently

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Case StudyAlohaNet

• Transmission if successful the Oahu
  station(main station) would acknowledge and the
  communications continued
• Unsuccessful Transmission If more than one
  station began transmitting at the same time
  Oahu would not acknowledge and the station would
  wait an appropriate timeout

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Case StudyAlohaNet

• Timeout It was important for the timeout to be
  different, usually random to avoid stations
  beginning to transmit simultaneously again
• Implementation began in June of 1971
• Issues
• why not frequency/ time-division?
• Polling

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Case StudyAlohaNet

• Instead of not being able to communicate with all
  stations, all stations could communicate how
  could the process be improved?
• Synchronization of the time slots?
• Adding Flexibility to the system Multiple
  access?

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Case StudyAlohaNet

• Recommended websites
• The CDMA Development Group
• The GSM Association
• Universal Wireless Communications Consortium
• Lloyd Woods Satellite web page

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Dons Question

• How is the Mobile Switching Center (MSC) able to
  identify if a call is made from outside the
  home area and therefore gather data for
  roaming charges?

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Heathers Question

• What are the three general types of control
  channels?

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Brandons question

• What are the specifications of the WAP include?

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Johns Question

• What are the approximate orbital altitudes of the
  three types of satellites?

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Jims Question

• How did the remote stations using AlohaNet know
  if they had control of the channel?