Wireless Networks | Research & Encyclopedia Articles

Wireless Networks

Wireless communication networks have been around for centuries: the use of smoke signals from mountain tops to alert tribal members of impending danger; waving lanterns at night to signal neighbors of the arrival of unexpected or uninvited visitors. Broadcast radio and television are more contemporary examples of wireless communication, as are cellular and cordless telephones, garage door openers, and automobile car locks. Some of these examples use radio frequencies (RF), some use "invisible" light in the infrared (IR) spectrum.

Wireless Network Infrastructures

The wireless data industry is still working out the bugs in developing and building data transmission networks and agreeing on standards and protocols. While there are several competing visions, many experts believe that the growing market for wireless data will support many networks and protocols, such as the following:

• Global Systems for Mobile (GSM) Communication is a digital cellular or Personal Communications Services (PCS) standard used throughout the world and is the de facto standard in Europe. GSM is used in Asia (except Japan) and is being used as the PCS standard in the United States at 1900 MHz (GSM and PCS1900 are the same standard; PCS is a two-way, 1900 MHz digital offering now being rolled out across the United States). GSM is based on Time Division Multiple Access (TDMA) technology (a digital air interface technology used in cellular and personal communications services), and includes a data-only channel used for Short Message Service (SMS). GSM is also referred to as "2G" technology, or "second-generation." 2G cell phones have a clearer signal (audio converted to digital code) that can also be encrypted. Data-only services, such as Palm, are considered second generation.
• Cellular Digital Packet Data (CDPD) is a packet data protocol designed to work over the Advanced Mobile Phone System, or AMPS (the original cellular network) or as a protocol for TDMA. The AMPS standard is referred to as first generation, or 1G, and any AMPS-based networks are analog. Such networks can be used only for voice transmission and suffer from interference, which greatly varies the quality of the transmission. There is little to no security with 1G networks as anyone with a radio tuner can eavesdrop on calls.
• Code Division Multiple Access (CDMA) is a spread spectrum air interface technology used in some digital cellular, personal communications services, and other wireless networks. The idea of spread spectrums was developed during World War II in an effort to thwart the enemy's attempt to listen to or jam radio signals. CDMA was thought to be too complicated for use in wireless networks until the late 1990s when it was resurrected by Qualcomm.

Two types of spread spectrum are in use today: Frequency Hopping Spread Spectrum (FHSS), which uses rapidly alternating FM signals known in advance by the sender and receiver, and Direct Sequence Spread Spectrum (DSSS), which covers a wide range of frequencies transmitting simultaneously. DSSS requires high bandwidth, usually in the megahertz (MHz) range. As an interesting side note, 1940s actress Heddy Lamarr is co-holder of the patent (issued in 1942) for FHSS, which was originally invented as a concept for using radio waves to control torpedo navigation during World War II.

Bluetooth^TM: A Global Wireless Communications Specification

The term Bluetooth^TM refers to an open specification for a technology that enables short-range wireless voice and data communications anywhere in the world. The Bluetooth specification, referred to as [BTSIG99] after the Bluetooth Special Interest Group that created the Version 1 spec in 1999, explicitly defines a method for wireless transports to replace serial cables that would be used with modems, digital cameras, personal digital assistants (PDAs), keyboards, printers, external zip drives, scanners, mice, and many other peripherals.

Bluetooth wireless communication uses radio frequency technology to communicate through the air in basically the same way as broadcast radio or television. Because there is a limit to the usable bandwidth for radio frequency, it is highly regulated and licensed by government agencies. Frequencies in the 900 MHz and 2.4 GHz frequency range are unlicensed in the United States and throughout the world (though there are some rules in place for its use). Bluetooth wireless communication will operate in the 2.4 GHz frequency range. For additional information on the Bluetooth Open Specification, go to www.bluetooth.com. [Note: Bluetooth is a trademark of Telefonaktiebolaget L M Ericsson, Sweden.]