Page 176 - DCAP311_DCAP607_WIRELESS_NETWORKS

Wireless Networks

Notes An omnidirectional antenna(Figure 11.2) transmits radio waves in all directions. Its gain is equal
to one, also called unity gain. For cellular phones unity gain antennas are good to use in cities
where there are tall buildings or in the mountains because they allow the signal to travel up and
over the buildings or mountains. Omnidirectional antennas are also good for indoor wireless
networks.

Figure 11.3: Directional Antenna

Source: http://k-12.pisd.edu/currinst/network/11_806A_4-2_SG.pdf
A directional antenna(Figure 11.3) concentrates its power in a certain direction and therefore has
higher gain. A directional antenna is good for point to point connections.

Task If you were using a cellular phone in a remote rural location, far from the nearest
base station, what type of antenna would you want to use?

Self-Assessment

State whether the following statements are true or false:
1. A WAN is formed by linking LANs together. True
2. A VAN is created by Bluetooth technology to wirelessly link personal devices together for
interoperability. False

3. Packet radio WAN users connect to their computers a packet radio modem with an
omnidirectional antenna. True
4. A directional antenna transmits radio waves in all directions. False
5. An antenna can decrease the power of the radio signal so that it can travel farther. False

11.2 Wireless WAN Systems

Most wireless WANs are cellular based, but some make use of space. Take a closer look at both
of these.

11.2.1 Cellular WANs

The convergence of telephony and computer networking means that cellular telephone networks,
designed for voice transmission, will be used more and more for data transmission. Cellular
phones currently transmit at about 14.4 Kbps but the technology, and speed is improving rapidly.
The original cellular telephone system was analog (called Analog Mobile Phone Service, AMPS)
because it was designed to carry data from an analog source: people,s voices. Telephone
companies have invested billions of dollars to create an infrastructure for carrying voice

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