Wireless Transmission

1
Wireless Transmission

• Directional
• Focuses electromagnetic beam in direction of
  receiver
• Terrestrial microwave
• Satellite microwave
• Omni directional
• Spreads the electromagnetic signal in all
  directions
• AM and FM radio
• 3G networks
• Smart watches

2
Terrestrial Microwave

• Parabolic dish antenna sends signal to receiving
  dish
• Line-of-sight
• Typically on towers to avoid obstacles
• Frequencies in the gigahertz range

3
Global Satellite Services

• GEO, MEO and LEO Satellites, IntelSat, and Global
  Positioning Systems

4
Telecommunications satellites

• Space-based cluster of radio repeaters (called
  transponders)
• Link
• terrestrial radio transmitters to satellite
  receiver (uplink)
• Satellite transmitters to terrestrial receivers
  (downlink)

5
Orbits

• Mostly geostationary (GEO)
• Circular orbit
• 22,235 miles above earth
• Fixed point above surface
• Almost always a point on Equator
• Must be separated by at least 4 degrees

6
Satellite services

• Wide Area Broadcasting
• Single transmitter to multiple receivers
• Wide Area Report-Back
• Multiple transmitters to a single receiver
• Example VSATs (very small aperture terminals)
• Also have microwave transmitters and receivers
• Allows for spot-beam transmission (point-
  to-point data communications)
• Can switch between beams upon request (Demand
  Assigned Multiple Access DAMA)
• Multi-beam satellites link widely dispersed
  mobile and fixed point users

7
Earth-based equipment

• Original microwave transmitters and receivers
  were large installations
• Dishes measuring 100 feet in diameter
• Modern antennas about 3 feet in diameter

8
A Modern GEO satellite (IntelSat 900 series)

• May have more than 72 separate microwave
  transponders
• Each transponder handles multiple simultaneous
  users (protocol called Time Division Multiple
  Access)
• Transponder consists of
• Receiver tuned to frequency of uplink
• Frequency shifter (to lower frequency to that of
  transmitter)
• Power amplifier

9
Frequency ranges

• Most transponders operate in 36MHz bandwidth
• Use this bandwidth for
• voice telephony (400 2-way channels/transponder)
• Data communication (120Mbs)
• TV and FM Radio

10
C-band, Ku-band, Ka-band

• Most GEO satellites operate in the C-Band
  frequencies
• Uplink at 6 GHz
• Downlink at 4 GHz
• Ku-band also used
• Uplink at 14 GHz
• Downlink at 11 GHz
• Above bands best suited for minimal atmospheric
  attenuation
• Few slots left forcing companies to look at Ka
  band (uplink30 GHZ , downlink 20 GHz)

11
Intelsat

• Began as an inter-governmental consortium in 1964
• Launched worlds first commercial communication
  satellite in 1965
• By 1969, had a fleet
• Broadcast live Neil Armstrongs first steps on
  the moon
• In 1974, establish the hot-line between the
  Kremlin and the White House
• In mid-1980s, developed more powerful satellites
  allowed smaller ground equipment for live
  broadcasts
• In 1997, introduced pay-as-you-go, shared access
  satellite coverage for low demand, rural areas.
• 2001 became a private company providing turnkey
  connectivity solutions

12
Intelsats fleet

• 20 Geosynchronous satellites
• Cover 200 countries
• 4 nines reliability (99.997)
• 18000 earth stations, and millions of VSATs
• Offer
• Bandwidth-on-demand
• Point-to-point
• Point-to-multipoint
• C- and Ku-band capacity

13
Latest Satellites launched

• Last of the Intelsat IX series launched Feb 15,
  2003 (went live in March)
• Offers more powerful C-band coverage for
• Europe
• Africa
• The Americas
• Ku spot beam coverage for Europe and Africa

14
Global Positioning Satellites

• 24 MEO satellites owned by US DoD (last launched
  in 1994)
• 21 active, 3 spare
• 11,000 miles above earth
• Five control stations around the world make sure
  satellites operating correctly
• Can tell your position within 300 feet
• Possible to get as accurate as 3 feet using
  special calculations.

15
How GPS works

• 24 satellites, each takes 12 hours to orbit the
  earth
• You can receive signals from 6 from any point on
  earth
• Satellites have up to 4 cesium and rubidium
  clocks (accurate to 3 billionths of a second)

16
The signals

• GPS satellites transmit 2 low power radio signals
  L1 and L2 (civilians can only use L1)
• 25-50 watts (compare to 100,000 watts for an FM
  radio station)
• L1 sends 3 pieces of data
• Pseudorandom code (ID of transmitting satellite)
• Ephemeris data (tells current data and time)
• Almanac data (tells GPS receiver where every
  satellite should be at any time of day)
• The data indicates when the signal was
  transmitted from the satellite
• The receiver indicates when it was received.
• It is now possible to calculate distance from
  satellite
• Three more such signals and you can be pinpointed.

17
Galileo

• The EU wants to compete
• Galileo will be under civilian control
• 30 satellites (273 spare)
• Inter-operable with GPS
• Dual frequency design allows positioning within 1
  meter.

18
Then there was LEO

• Iridium project
• Initially began as a plan for 77 LEO satellites
  (atomic number 77 Iridium)
• Scaled down to 66 (should be called Dysporium)
• Cost 5billion (Mostly Motorola)
• Sold 3 years ago for 25 million

19
What is the Internet?

• Internet Infrastructure
• The backbone
• Routers
• Points of Presence (POP)
• Servers
• Client (or user) computers

20
Backbone

• Collection of high-speed telecommunication lines
• Typically fiber optic cables
• Fiber has bandwidth
• Lines are connected by fast computers called
  digital switches

21
Routers

• Digital switches are fast computers that move
  traffic along backbone lines
• Some switches actually direct or route this data
  to particular lines
• Routers forward traffic from one line to another
  depending on the ultimate destination

22
Points of Presence

• To gain access to the backbone, we need a point
  of presence (POP)
• May be through a simple dial-up connection to an
  Internet Service Provider (individuals and SMEs)
• May be through a server connected to a local area
  network (larger enterprises)

23
Servers

• A program that provides services to other
  computers in a network
• Also used to refer to the computer on which
  program resides
• Web servers serves web page files to requesting
  client computers
• Every computer on the internet that hosts web
  sites must have a web server program
• Apache, IIS, Netware servers, Lotus Domino

24
Clients

• Client is a program housed on a users computer
  that requests web files from a server.
• A web browser acts as a client when requesting
  pages
• This client/server relationship is key to most
  networks, including the internet

25
Putting the pieces together
Individual user
SME user
backbone
Web server
routers
Individual user
LAN gateway server
26
Can we track the route we take?

• Tracert
• VisualRoute by VisualWare
• http//www.visualware.com

27
The Internet A Formal Resolution

• The Federal Networking Council (FNC) agrees that
  the following language reflects our definition of
  the term Internet
• Internet refers to a global information system
  that
• Is logically linked together by a globally unique
  address space based on the Internet Protocol (IP)
  or its subsequent extensions/follow-ons
• Is able to support communications using the
  Transmission Control Protocol/Internet Protocol
  (TCP/IP) suite and
• Provides, uses or makes accessible, either
  publicly or privately, high-level services
  layered on the communications and related
  infrastructure described herein
• October, 1995

28
Three Important Concepts

• Packet Switching
• TCP/IP
• Client/Server Computing
• We will deal with these over the next few classes