Chapter 8
Low Earth Orbit (LEO)
400 - 700 miles Many Telephone, Internet Satellites move rapidly relative to point on Earth Large number needed for global coverage Requires only low-power transmitters Negligible transmission delay Least expensive to build and launch Shortest orbital life (as low as 5 years)
Middle Earth Orbit (MEO)
6,434 miles 10 - 12 Global Positioning Systems (GPS) Satellites move relative to point on Earth Moderate number needed for global coverage Requires medium-powered transmitters Negligible transmission delay Less expensive to build and launch Moderate orbital life (6-12 years)
Versus bar codes
A typical bar code, known as the Universal Product Code (UPC), is made up of 12 digits that are batched in various groups. The first digit identifies the item type, the next 5 digits identify the manufacturer, and the next 5 identify the product. The last digit is a check digit for error detection.
hotspot
A wireless access point provides service to a number of users within a small geographical perimeter (up to a couple of hundred feet)
Wireless Local Area Networks (WLAN)
In a typical configuration, a transmitter with an antenna, called a wireless access point connects to a wired LAN or to satellite dishes that provide an Internet connection.
pervasive computing
Invisible "everywhere computing" that is embedded in the objects around us
Satellite radio
Most radio signals can travel only 30 to 40 miles from their source offers uninterrupted, near CD-quality transmission that is beamed to your radio, either at home or in your car, from space.
Wireless Sensor Networks
Networks of interconnected, battery powered, wireless sensors called motes that are placed into the physical environment.
Versus Quick Response (QR) codes
QR codes can store much more information than bar codes. Data types stored in QR codes include numbers, text, URLs, and even Japanese characters. The size of QR codes is small because these codes store information horizontally and vertically. QR codes are more resistant to damage than bar codes. QR codes can be read from any direction or angle, so they are less likely to be misread.
Three factors are preventing the commercial Wi-Fi market from expanding even further:
Roaming Security Cost
Wi-Fi Direct
Wi-Fi Direct enables peer-to-peer communications, so devices can connect directly. It allows users to transfer content among devices without having to rely on a wireless antenna. It can connect pairs or groups of devices at Wi-Fi speeds of up to 250 Mbps and at distances of up to 800 feet
MiFi
a small, portable wireless device that provides users with a permanent Wi-Fi hotspot wherever they go
personal area network
computer network used for communication among computer devices—for example, telephones, personal digital assistants, and smartphones—located close to one person.
bluetooth
is an industry specification used to create small personal area networks.
Geostationary Earth Orbit (GEO)
22,300 miles 8 TV Signal, Internet Satellites stationary relative to point on Earth Few satellites needed for global coverage Transmission delay (approximately .25 second) Most expensive to build and launch Longest orbital life (many years)
Global Positioning Systems (GPS)
A wireless system that utilizes satellites to enable users to determine their position anywhere on Earth.
Two types of RFID tags:
Active RFID tags use internal batteries for power and they broadcast radio waves to a reader Passive RFID tags rely entirely on readers for their power
Near-Field Communications (NFC)
has the smallest range of any short-range wireless networks it is designed to be embedded in mobile devices such as cell phones and credit cards
Ultra-Wideband (UWB)
high speed
