Less then 5% of all buildings in the US have a direct connection to the very high speed (2.5-10 Gbps) fiber optic backbone, yet more than 75% of businesses are within 1 mile of the fiber backbone.
Most of these businesses are running some high speed data network within their building, such as fast Ethernet (100 Mbps), or Gigabit Ethernet (1.0 Gbps).
Yet, their Internet access is only provided by much lower bandwidth technologies available though the existing copper wire infrastructure (T-1 (1.5 Mbps), cable modem (5 Mbps shared) DSL (6 Mbps one way) ), etc.
The last mile problem is to connect the high bandwidth from the fiber optic backbone to all of the businesses with high bandwidth networks.
A high-bandwidth cost-effective solution to the last mile problem is to use free-space laser communication (also known as or optical wireless) in a mesh architecture to get the high bandwidth quickly to the customers.
To overcome the security in a network two conditions are necessary:
(1) Intercept enough of the signal to reconstruct data packets and
(2) Be able to decode that information .
Preventing Interception of the Signal Directional transmission: Narrow divergence of the FSO transmit path (shown in red) as compared to a typical Radio Frequency (RF) path (shown in blue). The tightly collimated FSO beam ensures that the signal energy is focused on the receiving unit, making interception of the beam extremely difficult.
Another view of the narrow beam divergence inherent in FSO transmission. (For clarity only one transit beam is shown.)
Fog : The major challenge to FSO communications is fog. The primary way to counter fog when deploying FSO is through a network design that shortens FSO link distances and adds network redundancies. FSO installations in foggy cities such as San Francisco have successfully achieved carrier-class reliability.
Absorption : Absorption occurs when suspended water molecules in the terrestrial atmosphere extinguish photons. This causes a decrease in the power density (attenuation) of the FSO beam and directly affects the availability of a system.
Scattering : Scattering is caused when the wavelength collides with the scatterer. The physical size of the scatterer determines the type of scattering. When the scatterer is smaller than the wavelength, this is known as Rayleigh scattering. When the scatterer is of comparable size to the wavelength, this is known as Mie scattering.
Physical obstructions : Flying birds can temporarily block a single beam, but this tends to cause only short interruptions, and transmissions are easily and automatically resumed.
Building sway/seismic activity : The movement of buildings can upset receiver and transmitter alignment.
Safety : To those unfamiliar with FSO, safety is often a concern because the technology uses lasers for transmission.
Scintillation : Heated air rising from the earth or man-made devices such as heating ducts creates temperature variations among different air pockets. This can cause fluctuations in signal amplitude which leads to image fluctuations at the FSO receiver end.
Disaster management as was exhibited during the Sept 11 attacks.
Merill Lynch & Co. has set up FSO system from its Vesey Street office towers across the Hudson River to an alternate site in New Jersey.
TeraBeam, a major producer of FSO equipment, successfully deployed FSO at the Sydney Summer Olympic Games.
A network of FSO devices is fast coming up in Seattle which is touted as the Capital of Fog. Manufacturers believe that if an FSO system can successfully work in Seattle then it can do so in any part of the world.