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Connections Without Wires - Practices

This first chapter from the book Linux Unwired by Roger Weeks et al. introduces radio waves, antennas, connections without wires, Bluetooth, cellular data and infrared. (O'Reilly Media, ISBN: 0596005830, 2004.)

TABLE OF CONTENTS:
  1. Introduction to Wireless
  2. Radio Wave Behavior
  3. Connections Without Wires
  4. Operating Modes
  5. Wi-Fi Hardware
  6. Antennas
  7. Bluetooth, Cellular Data and Infrared
By: O'Reilly Media
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August 09, 2004

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There are many types of wireless networks, such as Cellular (wide-area wireless networking), Wi-Fi (local and wide area wireless networking), and Blue-tooth (cable-replacement and short-range wireless networking). All of these networks run with Linux. Here is a list of tasks you can complete with Linux and wireless networks:

Build your own wireless access point. At home, use a Linux box as your wireless access point and secure firewall for a broadband connection, and use a Linux notebook as a wireless client. To control who uses your access point, build a captive portal. It’s also possible that your broadband connection is wireless and uses a point-to-point directional wireless network.

Synchronize your contacts. At the office, keep your contacts list from your Linux desktop synchronized with your cell phone using Bluetooth or an infrared port.

Use a cellular network and GPS for the ultimate road warrior experience. On the road, use your Linux-powered PDA to check email from a wireless hotspot. Connect your cell phone and laptop, and use a high-speed data network where there is a digital cell signal. Hook a GPS receiver to your laptop and find that out-of-the-way hotel.

Wireless Alphabet Soup

While it is not the sole focus of this book, there are several chapters that deal entirely with “Wi-Fi,” or Wireless Fidelity. This phrase is trademarked by the Wi-Fi Alliance, a group that consists of nearly all 802.11 manufacturers. The Wi-Fi Alliance does product testing and certification for interoperability.

802.11 was defined as a protocol by the Institute of Electrical and Electron ics Engineers (IEEE) in 1997. This protocol specification allowed for 1 and 2 Mbps transfer rates using the 2.4 GHz ISM (Industrial, Scientific, and Medical) band, which is open to unlicensed public use. Prior to the adoption of this standard, there were various wireless network vendors manufacturing proprietary equipment using both the 2.4 GHz and the 900 MHz bands. The early adopters of the proprietary technologies and 802.11 were primarily the manufacturing and health care industries, which rapidly benefited from their employees’ mobile access to data. The 802.11 standard uses spread spectrum modulation to achieve high data rates. Two types of modulation were specified: Frequency Hopping and Direct Sequence. 802.11 also uses the Carrier Sense Multiple Access (CSMA), which was developed for Ethernet in 1975 with the addition of Collision Avoidance (CA)— referred to as CSMA-CA.

In 1999, the IEEE adopted two supplements to the 802.11 standard: 802.11a and 802.11b. The 802.11b standard is also referred to as High Rate DS and is an extension of the Direct Sequence Spread Spectrum type of modulation specified in 802.11. 802.11b uses 14 overlapping, staggered channels, each channel occupying 22 MHz of the spectrum. This standard’s primary benefit is that it offers data rates of 5.5 and 11 Mbps in addition to the 12 megabits provided by 802.11. 802.11b has been widely adopted around the world, and its products have been readily available since 1999.

However, 802.11a products did not begin shipping until 2001. 802.11a utilizes a range in the 5 GHz frequency and operates with a theoretical maximum throughput of 54 Mbps. It provides for 12 nonoverlapping channels.

Products based on this protocol have not seen the adoption rate of 802.11b products for several reasons. At higher frequencies, more power is needed to transmit. The power of 802.11 radio types is limited; therefore, 802.11 and 802.11b have longer range transmission and reception characteristics than 802.11a. Because of its higher frequency, 802.11a is absorbed more readily by obstacles, reducing range and throughput.

In June of 2003, the IEEE ratified a third supplement to the 802.11 standard: 802.11g. This standard continues to operate in the 2.4 GHz band with backward compatibility to 802.11b, but it raises the theoretical maximum throughput to 54 Mbps. In early 2003, there were many products released prior to the ratification of the standard. The standard was delayed several times as the subcommittees in the IEEE worked out interoperability issues between 802.11b and 802.11g.  

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