Wireless media transmit information as electromagnetic signals through the air in much the same way as a battery-operated radio sends radio waves. Individual users, businesses, and organizations are rapidly embracing wireless technologies as workers become more mobile and wireless devices become more powerful. Wireless technologies include:
⚫ microwave systems
⚫ satellite systems
⚫ infrared technology
⚫ cellular technology Wi-Fi technology
⚫ Bluetooth technology
Microwave Systems
Microwave transmission involves the sending and receiving of information in the form of high-frequency radio signals. A microwave system transmits data through the atmosphere from one microwave station to another, or from a microwave station to a satellite and then back to earth to another micro- wave station, as shown in Figure 6-10. When data is sent between microwave stations, the stations must be positioned at relatively short line-of-sight intervals because radio signals cannot bend around mountains and other obstacles. Therefore, there must be no visible obstructions between the sending and receiving microwave stations. The terrain determines the distance between microwave stations; it is rarely more than 25 miles. Microwave stations are often placed on top of hills, mountains, or buildings to ensure unobstructed transmission routes.
Satellite Systems
A communications satellite is a solar-powered electronic device containing several small, specialized radios called transponders. A tran- sponder receives signals from a transmission station on the ground, called an earth station. Communications satellites are positioned thousands of miles above the earth. A satellite receives transmitted signals, amplifies them, and then retransmits them to the appropriate locations on earth. Satellites orbit the earth at the same speed as the earth's rotation, making them appear stationary when viewed from the ground. This is called a geosynchronous orbit One of the benefits of satellite systems is the small number of satellites needed to transmit data over long distances. In fact, a small number of satellites properly positioned can receive and transmit information to any location on earth.
Communications satellites are capable of transmitting billions of bits per second, making them ideal for transmitting very large amounts of data. Because of the time it takes to send and receive data across such long distances, satellites are more appropriate for one-way communications such as television and radio applications, rather than for interactive applications such as telephone conversations or computer conferencing. The expense involved in building a satellite, sending it into orbit, and maintaining it is very high. Because of this, companies often share satellite technology as they are unable to bear the full cost of operating their own system.
Several satellites now in orbit handle domestic and international data, video, and voice communications for owners and subscribers. For instance, banks use satellites to transmit thousands of customer transactions to other banks. Money can be trans- ferred from an account in New York to an account in London within seconds.
Infrared Technology
In recent years infrared technology has become increasingly popular for providing wireless communication links between computers and peripheral devices. Infrared technology transmits data as light waves instead of radio waves . Television remote control units use the same technology. One drawback to infrared technology is that objects placed between sending and receiving devices can interrupt transmissions because the light waves must follow a line-of-sight path.
Wireless keyboards, also called cordless keyboards, are a recent application of infrared technology. The battery-powered keyboards communicate with computers by transmitting data to a receiver connected to a port on the computer's system unit. A wireless mouse is another popular infrared device that works in the same way as a wireless keyboard, requiring less desktop space because there is no need for a cable.
Cellular Technology
People can communicate wirelessly to and from nearly any-where in the world using cellular technology. Cellular phones and devices work by maintaining contact with cellular antennae that resemble metal telephone poles positioned throughout a cellular calling area. Each area, called a cell, has its own
antenna encompassing an area approximately 10 to 12 square miles in diameter. As users move from cell to cell, the closest antenna picks up the signal and relays it to the appropriate destination.
Communications networks that support cellular communications also work well for handling business data. Using a portable computer with a cellular modem, a person can access both Internet resources and information stored on a company's intranet databases. This can be especially important for users in areas where communications facilities are crude or nonexistent. Wireless modems may be used with a variety of mobile devices, including notebook and handheld computers, personal digital assistants (PDAs), and cellular telephones. Using a device with a wireless modem requires the services of a wireless service provider (WSP) to provide wireless Internet access. The newest generation of cellular technology Wireless 4G.
Wi-Fi Technology
The most commonly used wireless technology today is Wi-Fi (wireless fidelity). Wi-Fi is a wireless local area network (WLAN) technology based on the 802.11 standards of the Institute of Electrical and Electronics Engineers (IEEE). The 802.11 standards are discussed later in this chapter. A Wi-Fi device, such as a PDA or a notebook computer with a Wi-Fi card, must be in close proximity (usually within 150 feet indoors or 300 feet outdoors) to a device called a wireless access point. The wireless access point is a hard- ware device that transmits a wireless network signal to Wi-Fi-enabled devices. A Wi-Fi hotspot is a location that has one or more wireless access points. Many restaurants, hotels, school campuses, and airports provide Wi-Fi hotspots for a fee or at no charge. Home networks can also take advantage of Wi-Fi by adding a wireless access point to a broadband mortem or router.