Wireless Media, Protocols and Networks

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Wireless Media, Protocols and Networks

• COE 353 Fundamentals of Data Communications
• Nizar Mabroukeh, 2004

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Wireless Media

• (unguided media)

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Unguided Media

• Air, Water and vacuum of space are all type of
  unguided media.
• The forms of transmission that use this media
  are
• Broadcast radio
• Terrestrial and Satellite Microwave
• Cellular Radio
• Spread Spectrum Radio
• Infra Red

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Broadcast Radio
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Broadcast Radio

• It includes
• AM/FM/SW
• Citizen Band / CB Radio
• VHF\UHF Television Transmission
• HDTV and DTV

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Antenna Used

• Most forms of radio broadcast are
  omnidirectional, so the antenna does not have to
  be pointed or positioned in a specific direction
• TV transmission requires a Yagi antenna.
• Some broadcast radio produce elliptical
  transmission pattern that is designed to reduce
  interference with other surrounding signals

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AM \ FM \ SW Radio

• AM has lower frequency than FM, thus it can
  transmit further.
• Because of the low frequency it is more
  susceptible to interrupts and interference caused
  by atmospheric changes
• Shortwave Radio (SW) transmits in frequencies
  between AM and FM, it is used in
• International Radio Broadcasts,
• Military Communications,
• oceanic marine communications,
• and amateur radio

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UHF \ VHF TV broadcast

• Higher frequency than Radio transmission.
• The higher frequency is needed to transmit
  pictures beside sound.
• VHF (Very High Frequency) uses lower frequencies
  than UHF (Ultra High Frequency)

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HDTV

• High Definition Television delivers higher
  quality picture (higher resolution 720 X 1080)
  than standard TV along with CD-quality sound
• While standard TV is carried on analog signals,
  HDTV is broadcast digitally to accommodate the
  increased video and audio.
• One digital channel can carry several programs at
  once.
• Disadvantages of HDTV
• Standard and regular television cannot receive
  HDTV signals
• Televisions that have this digital HDTV
  capability are more expensive than analog
  television sets

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DTV

• Digital Television (DTV) is the technology that
  is used for HDTV
• It also includes devices such as camera and DVD
  recorders
• In DTV, broadcast companies send their signals
  digitally to viewers. In the viewers home, the
  decoder built into the DTV receives the signal
  and uses it in its digital form to derive the
  digital TV set.
• Advanced Television System Committee (ATSC) is
  the standard-making organization that develops
  standards for DTV and HDTV

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Digital Radio

• Approved for use by FCC in 2002 and is another
  form of digital broadcasting
• It provides CD-quality sound and a layer of data
  that is transmitted with sound and can contain
  information such as sport scores and traffic
  reports.

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Microwave
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Microwave

• Transmits super-high frequency signals (3-30 GHz)
  that have a very short wavelength (micro)
• Because of high frequency, microwave can carry
  large amounts of data, also they can be affected
  by weather and obstacles
• Unlike radio signals, microwave is focused and
  unidirectional using line-of-sight transmission
  (which can be blocked by earths curvature)

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Terrestrial Microwave

• Sent between two Earth Stations, using a
  parabolic dish or antenna
• The antenna focuses the microwaves into a beam
  and send it in a straight line to the next
  station.
• It is the most common form of long-distance
  communications today. Example used by major
  long-distance telephone carriers.

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Satellite Microwave

• Sending microwave signals between two or more
  Earth Stations and an orbiting satellite
• A transponder receives the uplink transmission,
  amplifies the signal to improve its quality and
  transmit it back to Earth over the downlink on a
  separate frequency (why?)
• Because of line-of-sight transmission, we have
  what is called a Footprint

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Satellites

• Geosynchronous Earth Orbiting Satellites (GEOS)
• Low Earth Orbiting Satellites (LEOS)
• Medium Earth Orbiting Satellites (MEOS)

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Geosynchronous Satellites (GEOS)

• Placed 22,300 miles over the equator
• revolve in orbit at the same rate the Earth
  rotates, so they appear in a fixed position
• Because of their high position, only three
  satellites are required to cover all the Earth
• Because of they high position also they
  experience what is called a Propagation Delay
  (PD).
• PD for GEOS can range from 1.5 sec for data
  transmission to 3 sec for voice or television
  transmission

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Low Earth Orbiting Satellites (LEOS)

• Revolve faster than earth rotation and so dont
  remain in a fixed position, while the devices to
  which they communication remain relatively
  Stationary.
• Advantages of LEOS over GEOS
• Less propagation delay,
• Shorter transmission time
• Better global coverage
• 12 LEOSs are required to cover the entire Earth.

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Satellites

• Together, LEOSs, MEOSs and GEOSs are used to
  support Mobile Satellite Services (MSS)
• MSS is any two-way voice and data communication
  via handheld devices in which the link is
  provided by satellite communication.

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GPS

• An example of satellite communication is the
  Global Positioning System (GPS)
• The US GPS has 24 satellites placed in an orbit
  at a cost of 12 billion
• This system uses a triangulation method to
  determine a vehicles exact location on earth
• A signal is sent from a GPS device to a
  satellite, which then sends the signal to a known
  spot on earth
• By calculating the distance between the known
  spot and the GPS device, the satellite can
  provide the exact coordinate and precise location
  of the GPS device.

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Cellular Radio
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Cellular Radio

• Cellular radio is a form of broadcast radio with
  restrictions on how far the signal is transmitted
• The broadcast area is divided into cells, each
  has its own transmitting antenna, all
  transmitting in the same frequency
• Transmitters have very low power so they dont
  interfere with transmitters in adjacent cells

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Cellular Phone

• As a person with a mobile phone moves from cell
  to cell, the signal is transferred from the
  transmitter in one cell to the transmitter in the
  next cell.
• This handover in transmitters will occasionally
  cause interruption or even loss of signal

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Problems of Cellular Phone

• Transmission on cellular phones can be easily
  intercepted, because it uses simple radio
  transmission.
• To solve this problem one needs to take a
  security precaution, may be encryption.
• Another problem is cloning, which involves
  stealing someones access code and thus being
  able to use his phone number and make phone calls
  on his expense.
• To eliminate this problem most mobile phones now
  use a Personal Identification Number (PIN)
• This number should be provided each time you want
  to make a phone call, like the PIN number of your
  ATM card

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Spread Spectrum Radio(SSR)
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SSR

• Involves the transmission of radio signals across
  a wide range of the spectrum, avoiding a
  concentration of power in a single narrow
  frequency band
• It was developed initially by the military to
  provide reliable radio communications in
  environments susceptible to eavesdropping and
  jamming of radio signals
• Today it is most widely used for wireless LANs

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Type of SSR

• There are two main methods used to send SSR
  signals
• Frequency-Hopping Spread Spectrum (FHSS)
• Direct Sequence Spread Spectrum (DSSS)

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FHSS

• Broadcasting a signal over a random series of
  radio frequencies (hopping from frequency to
  frequency)
• The source and the destination must be
  synchronized so they are on the same frequency at
  the same time.
• Because only the intended receiver knows the
  transmitters hopping sequence, only that
  receiver can receive all the data successfully.

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DSSS

• The signal will be transmitted over several
  frequencies at the same time along with another
  signal (additional bits) called The Chips
• It will appear as if there is interference and
  the original signal is incomprehensible
• The receiver will identify the chips and subtract
  them, leaving only the useful signal
• This procedure allows several signals to be sent
  over the same channel. Each useful signal is
  differentiated by a special chip

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FHSS Vs. DSSS

• Most wireless spread spectrum LANs use DSSS
• FHSS uses less power and cost less than DSSS
• DSSS has faster transmission rate, more immune to
  interference and can transmit to longer distance

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Infrared Transmission
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Infrared (IR)

• Sending electromagnetic light signals at a
  frequency between visible light and radio waves
• Because it uses light waves, it is a
  line-of-sight technology
• LANs using IR must be configured so that signals
  can be transmitted directly or reflected off a
  surface
• IR has a maximum coverage of 30 to 80 feet and
  can carry high-bandwidth transmissions.

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IrDA

• Infrared Data Association (IrDA) is the
  standard-making organization for IR
• An example of IrDA ports is the wireless mouse.
• IrDA ports have transmission rate similar to
  parallel ports, but require that the two devices
  be within a few feet of each other and have a
  clear line of sight.
• IrDA is also used as a wireless protocol in LANs,
  in this case CRC is used for error detection and
  each host device can communicate with up to 8
  devices.