Barco ClickShare User Manual download pdf (Page 9)

Wi-Fi and Security Considerations for ClickShare

Page 9 of 14

The ClickShare AP does not support DFS as specified in the

IEEE802.h standard.

The 802.11h standard – commonly referred to as Dynamic

Frequency Selection (DFS) – was created to define a set of

procedures to detect and avoid interference with radar

systems operating in the 5GHz range (UNII channels – 52-64

& 100-140). The part of the specification that is most visible to

users is the ability of a DFS-capable AP to detect and move

away from a channel that interferes with radar systems. APs

that do not support DFS are not allowed to operate on the

channels where interference occurs, which limits the number of

channels available in the 5GHZ spectrum.

The various mechanisms that affect the propagation of radio

signals can be attributed to 5 main physical phenomena:

reflection, diffraction, refraction, scattering and absorption

(Hucaby, 2007; Durgin, et al, 1998; Sarkar, et al., 2003).

These basic mechanisms distort the propagating signal

(making the signal stronger or weaker), and they can also

create additional propagation paths beyond the direct line of

sight path between the radio transmitter and the receiver. This

results in multiple signals reaching the receiver with different

delays, causing shadowing and multi-path fading which affect

performance.

In general, these phenomena depend on the surrounding

environment and the frequency of the signal being used.

Determining the effect of each of these phenomena for a given

environment for a given frequency is a very complex task. As

IEEE802.n uses MIMO, which involves multiple frequencies, the

situation becomes even more complex.

Over the years, a number of mathematical radio propagation

models have been developed to accurately predict the

potential propagation of signals within an environment

(Durgin, et al, 1998; Iskander & Yun, 2002; Mikas, et al.,

2003; Garg, 2007). Basically, there are two approaches to

modeling radio networks – the Empirical (or Statistical)

method, and the Deterministic method:

• The empirical method is based on site survey and uses

measurements gathered from the actual environment

that is to be modeled.

• The deterministic method (also known as the Ray-

Optical or Ray-Tracing model) uses software based on

the theory of electromagnetic wave propagation.

DYNAMIC

FREQUENCY

SELECTION

SIGNAL

PROPAGATION IN

THE REAL WORLD

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Barco ClickShare User Manual Page 9

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