Why Line of Sight (LOS) is so important

Do I need a line of sight between my 2 locations?

When designing an outdoor wireless network one of the first questions to ask is what is between point A (antenna 1) and point B (antenna 2). The path between two antennas is referred to as the Line of Sight. Continue reading to find out why the point-to-point wireless line of sight is so important.

There are three main categories of Line of Sight, the first being full Line of Sight (LOS) where no obstacles reside between the two antennas, the next is called Near Line of Sight (nLOS) which includes partial obstructions such as treetops between the two antennas, and lastly Non-Line of Sight (NLOS) where full obstructions exist between the two antennas. By determining the specific Line of Sight conditions in the Wi-Fi network area you can then determine the correct type of wireless system to install.

The Fresnel Zone referenced in the diagram below is an electromagnetic phenomenon, where light waves or radio signals get diffracted or bent from solid objects near their path. The radio waves reflecting off the objects may arrive out of phase with the signals that traveled directly to the receiving antenna thus reducing the power of the received signal.

For indoor wireless network installations, it is important to consider obstacles such as walls, ceilings, and furniture that will affect Line of Sight as these all play a role in wireless signal reception. In wireless transmissions, reflections (when wireless signals “bounce” off objects) and multipath (when wireless signals travel in multiple paths arriving at the receiver at different times) are as important as signal strength in determining the success of an installation. A signal will also exhibit peaks and nulls in its amplitude and alteration of its polarization (vertical or horizontal) when propagating through walls, ceilings, and reflecting off metallic objects. A Clear Line of Sight is also an important factor for inside WiFi network installations.

Path Loss is another area of concern when dealing with Line of Sight. For instance, although 2.4 GHz signals pass rather well through walls, they have a hard time passing through trees and leaves. This is due to the difference in water content in each. Walls are very dry and trees contain high levels of moisture. Radio waves in the 2.4 GHz band absorb water very easily. 900 MHz is a better frequency when faced with nLOS or NLOS conditions due to trees as it is not absorbed like 2.4 GHz.

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