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					There are two types of media commonly used for wireless LAN, ie: radio waves and
infrared optical signals.
A. Media Radio
Radio waves have been used extensively for various applications (such as TVs, mobile
phones, DLS). The advantage is that radio waves can propagate through the object such
as walls and doors.

· Path loss
All radio receiver designed to operate at SNR (ratio of signal power to noise power) that
have been determined. Costs to be incurred in developing the wireless LAN interface is
mostly on the radio that could guarantee a high SNR. Factors that affect the SNR is the
receiver noise which is a function of ambient temperature and the bandwidth of the
received signal. Signal power is also a function of the distance between transmitter and
receiver. All of these factors form a radio channel path loss for wireless LAN systems.

· The adjacent Channel Interference
Because it uses the principle of transmitting radio waves, then to the transmitter that has
the same frequency and are in an adjacent building or space can experience interference
from one another. For Ad hoc systems, adjacent channel can be set up with different
frequencies as an insulator, while for the system infrastructure can be applied to three cell
repeater that each adjacent cell (3 cells) have a different frequency patterns of repetition.

· Multipath
Radio signals, as well as the optical signal is affected by multipath, ie, when the incident
in which a receiver receives multiple signals originating from the same transmitter, each
of the signal followed by a different path between the receiver and transmitter. This is
known as multipath dispersion which can cause intersymbol interference (ISI).

2. Infrared Media
· Infrared has a much higher frequency than radio waves, ie above 1014 Hz. Infrared is
used commonly expressed in wavelength (usually in nanometers) rather than in
frequency. Infrared is commonly used which has a wavelength of 800 nm and 1300nm.
The advantage of using infrared than radio waves are not that tough regulation is required
in its use. To reduce the effect of noise on the infrared signal, a bandpass filter is used.

· Infrared Device
For wireless LAN applications, the operational mode is used to modulate the output
intensity of infrared emitters using a modulated signal electrically. Variation of the
intensity of the infrared signal received by the detector is then converted to an equivalent
electrical signal. Mode of operation is known as Intensity Modulation with Direct
Detection (IMDD).

· Topology
Infrared link can be used as one of two modes: point to point and diffuse. In point to
point mode, the emitter is directed directly at the detector (photodiode). This operating
mode provides a good wireless link between two parts of equipment, such as to enable
the portable computer to download the file to another computer.
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posted:6/27/2012
language:English
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