IT101 Section 001

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IT-101Section 001
Introduction to Information Technology

• Lecture 11

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• Overview

• Finish chapter 13
• Generations of cellular systems
• Satellite telephones
• Chapter 16
• Radio-Frequency and Satellite Systems
• -Satellite systems
• -GPS

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Generations of Cellular Systems

• Generations of cellular systems include
• AMPS 1st generation
• GSM 2nd generation
• W-CDMA 3rd generation
• Cellular systems operate based on various
  protocols, and use RF (radio frequency) waves
  that propagate through the air for transmission
  of information. These systems typically use the
  800-900 MHz or 1800-1900 MHz frequency band of
  the radio spectrum.
• But what is the radio spectrum?

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The Radio Spectrum

• The Radio spectrum is composed of many frequency
  bands
• Communication systems have the liberty to
  transmit signals at various frequencies, and the
  FCC (Federal Communications Commission) regulates
  which frequencies to use

Sourcehttp//howstuffworks.lycoszone.com/radio-sp
ectrum1.htm
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Radio Spectrum Bands
Low Frequencylarge period
High Frequencysmall period
400-2400 MHz frequency range

• VHF
• Television
• FM radio
• Aviation

• UHF/SHF
• Satellite
• Television
• Cell Phones
• Microwave

• EHF
• Astronomy

• MF
• AM Radio
• Maritime

• HF
• Maritime
• Amateur Radio

FM radio stations between 88-108 MHz
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1st generation

• AMPS Advanced Mobile Phone System
• The only system available in the United States
  until about 1997
• The first system used for cellular telephony- is
  analog
• Uses the 800 MHz frequency band of the spectrum
• Is still being used widely - The number of
  subscribers began to decrease in 1999 due to
  migration to digital
• Utilizes FDMA (Frequency division multiple
  access) to separate users
• In FDMA, users are separated in frequency. i.e.
  mobile phones communicate at different
  frequencies than the others within each cell. The
  radio spectrum is shared among users

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2nd generation

• GSM Originally Group Special Mobile, now
  Global System for Mobile Communications
• Is the most popular system worldwide
• Originally developed in Europe
• Was later introduced into the United States
• Is a digital system for both voice and data
  transmission
• Uses the 900 and 1800 MHz frequency bands
• Utilizes TDMA (Time division multiple access)
• In TDMA, users are separated in time. i.e. mobile
  phones communicate in a different time slot than
  the others within each cell. Time is shared among
  the users

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3rd generation

• W-CDMA Wideband code division multiple access
• Provides much higher data rates
• Supports a larger number of users
• Enables features such as video, internet access,
  web browsing and complete worldwide operability
• Widespread introduction expected to begin by 2005
• Utilizes CDMA (Code division multiple access)
• In CDMA, users are separated by a unique code
  assigned to them. i.e. each mobile phone can
  utilize the entire chunk of spectrum, and the
  unique code of each user is used to encode and
  decode the information during transmission

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Satellite Telephones

• Satellite telephones are utilized in
  circumstances where there is no access to a
  telephone or cellular network
• Examples include ships at sea
• Previously, these remote users would communicate
  via High frequency (HF) systems. A licensed radio
  operator would need to be present on board to
  operate these systems, and would need to know
  morse code
• Using radio waves in the HF range of the
  spectrum, communication could be realized between
  any two points on the earth

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• This was possible due to the unique property of
  HF waves to travel all the way around the world
• Under appropriate conditions, HF waves can travel
  around the world by reflection between the earths
  surface and the ionosphere (the ionospheric
  reflection is analogous to the internal
  reflection that occurs in optical fibers-we will
  learn about fibers in chapter 15 )

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• This method of communication however is
  unreliable, and currently satellites are utilized
  for communication in remote places
• Using satellites, a ship at sea is easily
  reachable as any point on land
• INMARSAT is one of the main providers of
  satellite radio communications for remote users
• A Satellite based system called the Iridium
  system, conceived by Motorola corp. was proposed
  as an alternative to the conventional cellular
  systems
• In the Iridium system, 66 low earth orbiting
  satellites are used for relaying information,
  analogous to a switching center in conventional
  cellular and telephone systems
• The call does not pass through land lines,
  increasing the efficiency over other cellular
  systems

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• The cell sites in the Iridium system are overhead
  and are in constant motion
• Let us see how iridium works http//www2.sis.pitt
  .edu/jkabara/tele-2100/iridium/iridium_final.html
  

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• The Iridium system began operations in 1999, and
  presented the first generally available global
  system
• However, the relatively high cost of service
  (around 3 per minute) and the relatively large
  size of the handsets drove the system to
  bankruptcy
• Iridium failed to attract a sufficient amount of
  customers in competition with the rapidly
  spreading cellular systems across the globe
• Shortly after this failure, a group of investors
  bought the system for 25 million, which had
  actually cost Motorola more than 5 billion
  to build
• The system is expected to be profitable within a
  couple of years

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Satellite Systems

• Communication satellites provided the first
  long-distance, wide-bandwidth communication
  service
• Testar 1 was the first commercial communications
  satellite to be launched into orbit
• Satellites can be distinguished into 3 primary
  categories, depending on the type of orbit they
  reside on
• LEO
• MEO
• GEO

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• LEO Low Earth Orbit satellites have a small area
  of coverage. They are positioned in an orbit
  approximately 3000km from the surface of the
  earth
• They complete one orbit every 90 minutes
• The large majority of satellites are in low earth
  orbit
• The Iridium system utilizes LEO satellites
• The satellite in LEO orbit is visible to a point
  on the earth for a very short time
• MEO Medium Earth Orbit satellites have orbital
  altitudes between 3,000 and 30,000 km.
• They are commonly used used in navigation systems
  such as GPS

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• GEO Geosynchronous (Geostationary) Earth Orbit
  satellites are positioned over the equator. The
  orbital altitude is around 30,000-40,000 km
• They complete one orbit every 24 hours. This
  causes the satellite to appear stationary with
  respect to a point on the earth, allowing one
  satellite to provide continual coverage to a
  given area on the earth's surface
• One GEO satellite can cover approximately 1/3 of
  the worlds surface
• They are commonly used in communication systems
• Lets look at a GEO animation
• http//www.jpl.nasa.gov/basics/bsf5-1.htm

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The Global Positioning System

• GPS is funded and controlled by the Department of
  Defense (DOD).
• Although there are many thousands of civil users
  of GPS worldwide, the system was originally
  designed for the U. S. military
• GPS provides special satellite signals that can
  be processed in a GPS receiver, enabling the
  receiver to compute position and velocity
• Four GPS satellite signals are used to compute
  positions in three dimensions and the time offset
  in the receiver
• For around 100, you can get a hand held gadget
  that will tell you exactly what point you are on
  the earth

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Sourcehttp//www.colorado.edu/geography/gcraft/no
tes/gps/gps_f.html
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• The orbital period of the GPS satellites is
  around 12 hours
• The satellites move with respect to the receivers
  on the earth, but at a slower speed compared to
  LEOs
• Typical civilian accuracy is around 100 ft, with
  occasional errors of up to 300 ft
• For applications requiring higher accuracy such
  as aircraft landing etc., enhancements in the
  systems are made that can reduce the error to
  around 1 cm
• Some applications of GPS include
• Aircraft navigation
• Marine navigation
• Driving
• Surveying
• Farming