Outdoor Wireless Networks

Outdoor wireless network experience the same factors such as reflections and multipath as indoor networks. For outdoor wireless installations clear line of sight is optimal. Trees and leaves are obstructions to 802.11 frequencies so they will partially or entirely block the signal if not cleared.

Before deploying any wireless network a site survey is recommended. The site survey typically entails installing an access point at each location where user groups are located and then monitoring the wireless signal strength by walking varying distances away from the access points using a laptop with site survey software. The result will show you where out may need more access points to provide sufficient coverage or where you may need to move an access point for optimal wireless connectivity.

Antenna Height

The correct installation height of an antenna depends on the factors outlined below.

1. Distance between the sites: The longer the link, the higher the antenna needs to be due to the earth’s curvature. (This relation is not proportional) See table 1.

2. The Fresnel Zone: This is an electromagnetic phenomenon, where light or radio signals get diffracted or bent from solid objects near their path. See table 1 showing the 60% of Fresnel Zone values (accepted clearing on path). Add this to the earth curvature height.

3. Objects in the path: At a frequency of 2.4 GHz, you need a clear line of sight (LOS). Tree tops will reflect or ground the signal. The theory is that the height of the tallest object in the path of the signal should be added to the Fresnel Zone and earth curvature clearance heights. In your case, you should have to check the height of the trees, hills, buildings or any object on the link path and add this to the measurement for the total of the tower height.

The above three conditions make up the Radio Line of Sight. See table 1