AV Design Reference Manual - InfoComm

Chapter 6: Networking
Wireless Transmission
All of the wireless communications use electromagnetic energy to transfer signals from the
source to the destination. Examples of electromagnetic radiation include radio waves, light
particles, and x-rays. National and international communications agencies use a subset of the
spectrum to create an RF allocation chart, which is used to display the allocated and available
frequencies for the purposes of radio wave communications in a given area. The chart, issued
by the Office of Spectrum Management (OSM) in the United States Department of
Commerce, spans the frequency range from 3 kilohertz (kHz) to 300 gigahertz (GHz).
Many devices and applications use RF, creating the possibility of interference in a given
location. To minimize disruption caused by simultaneous transmissions in the same RF band,
regulatory agencies allocate and control usage rights to specific radio band frequencies in
every geographic area within their jurisdiction. A narrowband license, for example, provides its
holder with the right to transmit over a limited frequency range in a specific geographic area.
In addition to licensed narrowband frequencies, there are also unlicensed frequency bands
where the right to transmit is freely available to anyone. An example is the 2.4 GHz industrial,
scientific, and medical (ISM) band, used by Bluetooth ® WPANs as well as several IEEE
WLANs.
NOTE:
Other devices (e.g., microwave ovens and cordless telephones) also operate in
this range, at various power levels. This type of frequency sharing in unlicensed
bands can cause disruptions in network communications if such devices operate in
close proximity to a wireless network.
Most wireless network devices exchange messages using RF signaling, although it is also
possible to use light beams (infrared). RF signaling can be narrowband or spread spectrum.
Narrowband RF is associated with fixed-base-to-fixed-base signaling, also referred to as
wireless PTP or wireless bridge. In such cases, the devices at both ends of the wireless link
cannot be moved (e.g., the connection between two buildings on opposite sides of a river).
RF-based WPANs and most WLANs use spread spectrum RF technologies in the unlicensed
ISM band. In contrast to narrowband RF, spread spectrum uses a large band of frequencies
for signaling. Two types of spread spectrum signaling are available, frequency hopping or
direct sequence.
Wireless Local Area Network (WLAN)
In general, WLANs provide a wire-free environment to LAN users within a given facility. A
properly designed and installed WLAN enables connection to a LAN from any location within
a predefined zone. They are intended to provide network connectivity, flexibility, and mobility
to the controllable set of users within a common physical area where network wiring is not
practical.
Although flexibility and mobility in today’s working environment is important, WLANs should
not be considered equivalent substitutes for a switched 10Base-T or 100Base-T network, as
their connectivity is limited to a shared environment and are highly dependent on their ability to
transmit and receive radio waves with minimal interference. As an example, a building
construction makeup can help or hinder the WLAN’s range and performance levels.
AVDRM, 1st edition 6-26 © 2006 BICSI ® /InfoComm International ®