Cisco Cisco Aironet 1522 Lightweight Outdoor Mesh Access Point Guía De Diseño

Design recommendations for mesh links are as follows:

MAP deployment cannot exceed 35 feet in height above the street.

MAPs are deployed with antennas pointed down toward the ground.

Typical 5-GHz RAP-to-MAP distances are 1000 to 4000 feet.

 RAP locations are typically towers or tall buildings.

Typical 5-GHz MAP-to-MAP distances are 500 to 1000 feet.

MAP locations are typically short building tops or streetlights.

Typical 2.4-GHz MAP-to-client distances are 300 to 500 feet.

Client locations are typically laptops, CPEs, or professionally house-mounted antennas.

When you determine the suitability of a successful link, you must define how far the link is expected to 
transmit and at what radio data rate. Very close links, one kilometer or less, are fairly easy to achieve 
assuming there is clear line of sight (LOS)–a path with no obstructions.

Since mesh radio waves have very high frequency in the 5-GHz band, the radio wavelength is small; 
therefore, the radio waves do not travel as far as radio waves on lower frequencies, given the same 
amount of power. This higher frequency range makes the mesh ideal for unlicensed use because the radio 
waves do not travel far unless a high-gain antenna is used to tightly focus the radio waves in a given 
direction.

This high-gain antenna configuration is recommended only for connecting RAP to the MAP. To optimize 
mesh behavior, omnidirectional antennas are used because mesh links are limited to one mile (1.6 km). 
The curvature of the earth does not impact line-of-sight calculations because the curvature of the earth 
changes every six miles (9.6 km).

In addition to free space path loss and line of sight, weather can also degrade a mesh link. Rain, snow, 
fog, and any high humidity condition can slightly obstruct or affect line of sight, introducing a small loss 
(sometimes referred to as rain fade or fade margin), which has little effect on the mesh link. If you have 
established a stable mesh link, weather should not be a problem; however, if the link is poor to begin 
with, bad weather can degrade performance or cause loss of link.

Ideally, you need line of sight; a white-out snow storm does not allow line of sight. Also, while storms 
may make the rain or snow itself appear to be the problem, many times it might be additional conditions 
caused by the adverse weather. For example, perhaps the antenna is on a mast pipe and the storm is 
blowing the mast pipe or antenna structure and that movement is causing the link to come and go, or 
there might be a large build-up of ice or snow on the antenna.

A Fresnel zone is an imaginary ellipse around the visual line of sight between the transmitter and 
receiver. As radio signals travel through free space to their intended target, they could encounter an 
obstruction in the Fresnel area, degrading the signal. Best performance and range are attained when there 
is no obstruction of this Fresnel area. Fresnel zone, free space loss, antenna gain, cable loss, data rate, 
link distance, transmitter power, receiver sensitivity, and other variables play a role in determining how 
far your mesh link goes. Links can still occur as long as 60–70 percent of the Fresnel area is 
unobstructed, as illustrated in