WIRELESS COMMUNICATIONS AND NETWORKS

WIRELESS COMMUNICATIONS

AND NETWORKS

Guglielmo Marconi invented the wireless telegraph in 1896.1 In 1901, he sent telegraphic

signals across the Atlantic Ocean from Cornwall to St. John's Newfoundland;

a distance of about 3200 km. His invention allowed two parties to communicate by

sending each other alphanumeric characters encoded in an analog signal. Over the

last century, advances in wireless technologies have led to the radio, the television,

the mobile telephone, and communications satellites. All types of information can

now be sent to almost every corner of the world. Recently, a great deal of attention

has been focused on satellite communications, wireless networking, and cellular

technology.

Communications satellites were first launched in the 1960s. Those first satellites

could only handle 240 voice circuits. Today, satellites carry about one-third of

the voice traffic and all of the television signals between countries [EVAN98].

Modern satellites typically introduce a quarter-second propagation delay to the

signals they handle. Newer satellites in lower orbits, with less inherent signal delay,

have been deployed to provide data services such as Internet access.

Wireless networking is allowing businesses to develop WANs, MANs, and

LANs without a cable plant.The IEEE has developed 802.11 as a standard for wireless

LANs. The Bluetooth industry consortium is also working to provide a seamless

wireless networking technology.

The cellular or mobile telephone is the modern equivalent of Marconi's wireless

telegraph, offering two-party, two-way communication. The first-generation

wireless phones used analog technology. These devices were heavy and coverage

was patchy, but they successfully demonstrated the inherent convenience of

mobile communications. The current generation of wireless devices is built using

digital technology. Digital networks carry much more traffic and provide better

reception and security than analog networks. In addition, digital technology has

made possible value-added services such as caller identification. Newer wireless

devices connect to the Internet using frequency ranges that support higher information

rates.

The impact of wireless communications has been and will continue to be profound.

Very few inventions have been able to "shrink" the world in such a manner.

The standards that define how wireless communication devices interact are quickly

converging and soon will allow the creation of a global wireless network that will

deliver a wide variety of services.

Figure 1.1 highlights some of the key milestones in the development of wireless

communications.2 Wireless technologies have gradually migrated to higher frequencies.

As will be seen in later chapters, higher frequencies enable the support of

greater data rates and throughput.