Page 54 - DCAP311_DCAP607_WIRELESS_NETWORKS

Wireless Networks

Notes
Figure 3.1: Both Diffused and Directed Light Signals Offer a Basis for Wireless Networks

Ceiling

Diffused
Light Signals

A B C

Directed A B
Light Signals

Source: http://etutorials.org/Networking/wn/Chapter+3.+Radio+Frequency+and+Light+Signal+Fundamentals+The+In
visible+Medium/Understanding+Light+Signals/
As with RF signals, the amplitude of light also decreases as distance between the sending and
receiving stations increase. The range of an infrared light system can vary from a few feet with
PDA applications to 1 mile with direct infrared systems. This is significantly less range than with
RF systems.
As compared to RF signals, light signals have the characteristics defined in Table 3-2.

Table 3 2: Comparing the Pros and Cons of Light Signals

Light Signal Pros Light Signal Cons
Extremely high throughput, Variable, unreliable performance in the presence of
up to the Gbps range significant smog, fog, rain, snow, and other airborne
particulate matter
High inherent security Relatively short-range (1 mile) capability
because of narrow laser
beam
License-free operation Requirement for line-of-sight operation, free from
obstructions such as buildings, trees, and telephone poles
Extremely low potential for Issues dealing with alignment because of building swaying
RF interference from external
systems

Source: http://etutorials.org/Networking/wn/Chapter+3.+Radio+Frequency+and+Light+Signal+Fundamentals+The+In
visible+Medium/Understanding+Light+Signals/
These characteristics make the use of light signals most effective for specialized applications
where extremely high performance is necessary. For example, a company can install an infrared
communications link between two nearby buildings in order to facilitate high-speed server
backups over a wireless network.

Light signal propagation is not free from difficulties. Impairments, such as interference and
obstructions, limit the performance of the wireless network that uses light signals.
Light signals are free from RF sources of interference such as cordless phones, and microwave
ovens. In fact, the FCC doesn’t regulate light signals because of extremely limited potential
interference among systems. Light signals have such a high frequency that their emissions are
well outside the spectrum of RF systems, which means that the FCC doesn’t regulate light signals.

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