Wireless Transmission and Services

1
Wireless Transmission and Services

• Chapter 9

2
Objectives

• Associate electromagnetic waves at different
  points on the wireless spectrum with their
  wireless services
• Identify characteristics that distinguish
  wireless transmission from wire-bound
  transmission
• Explain the architecture and access methods used
  in cellular net-works and services
• Understand the differences between wireless and
  wireline local loops
• Describe the most popular WLAN standards,
  including their advantages, disadvantages, and
  uses
• Identify the major satellite positioning schemes
  and list several telecommunications services that
  rely on satellite transmission

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The Wireless Spectrum
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The Wireless Spectrum
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The Wireless Spectrum
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Characteristics of Wireless Transmission
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Antennas

• Radiation pattern - the relative strength over a
  three dimensional area of all the electromagnetic
  energy the antenna sends or receives.
• Directional antenna - issues wireless signals
  along a single direction

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Antennas

• Omni-directional antenna - issues and receives
  wireless signals with equal strength and clarity
  in all directions.

9
Signal Propagation

• Reflection - the wave encounters an obstacle and
  bounces back towards its source.
• Diffraction - a wireless signal splits into
  secondary waves when it encounters an
  obstruction.
• Scattering - the diffusion, or the reflection in
  multiple different directions of a signal.

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Signal Propagation
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Signal Propagation

• Fading and Delay
• Fading a change in signal strength as result of
  some of the electromagnetic energy being
  scattered, reflected, or diffracted after being
  issued by the transmitter.
• Diversity - the use of multiple antennas or
  multiple signal transmissions to compensate for
  fading and delay.

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Signal Propagation

• Attenuation - after a signal has been
  transmitted, the farther it moves away from the
  transmission antenna, the more it weakens.
• Interference - because wireless signals are a
  form of electromagnetic activity, they can be
  hampered by other electromagnetic energy,
  resulting in interference.

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Narrowband, Broadband, and Spread Spectrum Signals

• Narrowband - a transmitter concentrates the
  signal energy at a single frequency or in a very
  small range of frequencies.
• Broadband - a type of signaling that uses a
  relatively wide band of the wireless spectrum.
• Spread spectrum - the use of multiple frequencies
  to transmit a signal.

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Fixed vs. Mobile
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Fixed vs. Mobile
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Cellular Communications

• Mobile telephone service - a system for providing
  telephone services to multiple, mobile receivers
  using two-way radio communication over a limited
  number of frequencies.
• Mobile wireless evolution
• First generation
• Second generation
• Third generation

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Principles of Cellular Technology
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Cells
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Cellular Call Completion

• Components of a signal
• Mobile Identification Number (MIN) - an enclosed
  representation of the mobile telephones 10-digit
  telephone number.
• Electronic Serial Number (ESN) - a fixed number
  assigned to the telephone by the manufacturer.
• System Identification Number (SID) - a number
  assigned to the particular wireless carrier to
  which the telephones user has subscribed.

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Cellular Call Completion
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Call Completion
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Advanced Mobile Pone Service (AMPS)

• A first generation cellular technology that
  encodes and transmits speech as analog signals.

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Time Division Multiple Access (TDMA)
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Code Division Multiple Access (CDMA)

• Each voice signal is digitized and assigned a
  unique code, and then small components of the
  signal are issued over multiple frequencies using
  the spread spectrum technique.

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Global System for Mobile Communications (GSM)

• A version of time division multiple access (TDMA)
  technology, because it divides frequency bands
  into channels and assigns signals time slots
  within each channel.
• Makes more efficient use of limited bandwidth
  than the IS-136 TDMA standard common in the
  United States.
• Makes use of silences in a phone call to increase
  its signal compression, leaving more open time
  slots in the channel.

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Emerging Third Generation (3G) Technologies

• The promise of these technologies is that a user
  can access all her telecommunication services
  from one mobile phone.
• CDMA2000 - a packet switched version of CDMA.
• Wideband CDMA (W-CDMA) - based on technology
  developed by Ericson, is also packet-based and
  its maximum throughput is also 2.4 Mbps.

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Wireless Local Loop (WLL)

• A generic term that describes a wireless link
  used in the PSTN to connect LEC central offices
  with subscribers.
• Acts the same as a copper local loop.
• Used to transmit both voice and data signals.

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Local Multipoint Distribution Service (LMDS)

• A point-to-multipoint, fixed wireless technology
  that was conceived to supply wireless local loop
  service in densely populated urban areas and
  later on a trial basis to issue television
  signals.
• A disadvantage is that its use of very high
  frequencies limits its signals transmission
  distance to no more than 4km between antennas.

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Multipoint Multichannel Distribution System (MMDS)

• Uses microwaves with frequencies in the 2.1 to
  2.7 GHz range of the wireless spectrum.
• One advantage is that because of its lower
  frequency range, MMDS is less susceptible to
  interference.
• MMDS does not require a line-of-sight path
  between the transmitter and receiver.

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WLAN Architecture
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WLAN Architecture
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WLAN Architecture
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Wireless Networking Standards

• 802.11 - IEEEs Radio Frequency Wireless
  networking standard committee.
• 802.11b - uses direct sequence spread spectrum
  (DSSS) signaling. Also used the 2.4 - 2.4835 GHz
  frequency range and separates it into 14
  overlapping 22-MHz channels.
• 802.11g - designed to be just as affordable as
  802.11b while increasing its maximum capacity
  from 11 Mbps to 54 Mbps through different
  encoding techniques.
• 802.11a - uses multiple frequency bands in the 5
  GHz range. Like 802.11g, 802.11a provides a
  maximum throughput of 54 Mbps.

34
Bluetooth

• A mobile wireless networking standard that uses
  direct sequence spread spectrum (DSS) signaling
  in the 2.4 GHz band to achieve a maximum
  throughput of less than 1 Mbps. Access points
  and receivers are to be spaced no farther than 10
  meters apart.
• Designed to be used on small networks composed of
  personal communications devices, also known as
  personal area networks also used with cordless
  telephones and pagers in a home.
• IEEE has released 802.15.1 designed to be fully
  compatible with the latest version of Bluetooth.

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Personal Area Networks
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HomeRF

• Wireless networking specification that also uses
  DSSS n the 2.4 GHz frequency band to achieve a
  maximum of 10 Mbps throughput.
• Allowed both voice and data signals to be
  exchanged on the same wireless network for home
  or small offices.
• Differs from Bluetooth in that its nodes can
  travel within a 50 meter range of an access point
  and remain connected to the PAN.

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Satellite Positioning

• The original method for positioning satellites
  above the earth was in geosynchronous orbit.
• Geosynchronous satellites are positioned
  approximately 35,800 km (22,300 miles) above the
  earths equator. These are power heavy and
  experience a .25 second delay from earth to
  satellite and back again.
• An alternative to GEO satellites are low earth
  orbiting (LEO) satellites. Positioned between 700
  and 1400 kilometers above the equator. These are
  less power intensive and take less time for
  signal to travel between transmitter and
  receiver.
• Medium earth orbiting satellites (MEO). Orbit
  between 10,350 and 10,390 km above the earth,
  less power intensive and less signal delay than
  GEO satellites.

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Satellite Positioning
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Satellite Services

• Digital broadcasting - To deliver content to
  subscribers, networks (or other multimedia
  providers) uplink their audio and video signals
  to a satellite, which then downlinks the signals,
  in a broadcast fashion, to earth.
• Analog broadcasting - Traditional analog
  television and radio signals can be issued from a
  terrestrial transmitter to a satellite and then
  downlinked to another terrestrial location within
  seconds.
• Mobile Wireless - Services such as cellular
  telephone, paging, and other PCS applications are
  well suited to LEO or MEO satellite transmission.

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Satellite Services

• Tracking and monitoring - Two-way satellite
  communications can be used to monitor the
  whereabouts and condition of wildlife, mobile
  weather sensors, marine vessels, and so on
  anywhere in the world.
• Global positioning service (GPS) - A service that
  expands on remote monitoring functions, GPS
  allows a mobile station on earth to exchange
  signals with a satellite to determine its precise
  location.
• Wide area networks - Private companies use
  satellite transmission to connect multiple
  locations on their WANs.

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Summary

• The wireless spectrum, the range of frequencies
  within the electromagnetic spectrum that are used
  for telecommunications services, starts at 9 KHz
  and ends at 300 GHz.
• Cellular telephone service is distinguished from
  other mobile two-way radio services by its use of
  cells to reuse limited frequencies within a
  certain geographical area.
• Wireless LANs (WLANs) use the same protocols and
  a similar architecture as wire-bound LANs.