How Line of Sight (LoS) Can Affect Your Wireless Installation

September 18, 2014 at 10:00 AM

 

Though the term Line of Sight seems self explanatory, there’s actually more than meets the eye when it comes to LoS and installing a wireless network.

 

As you might already know, Line of Sight is the path between two antennas. One of the first questions you’ll want to ask yourself when designing an outdoor wireless network is what is between point A (antenna 1) and point B (antenna 2)?

 

These details are important since Line of Sight does not only apply to a straight line. Wireless signals being sent from point A to point B can and will, most likely, run into to some obstacles that will alter the path they take.

 

When light waves or radio signals get diffracted or bent due to solid objects near their path, it’s an electromagnetic phenomenon referred to as The Fresnel Zone (referenced in the diagram below). 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.

 

It is important to also note that the line of site broadens with wavelength, which means that for low frequency, high wavelength signals, you need to have a larger Fresnel radius free of obstructions.  

 

 

 

 

As you can see, there are three main categories of Line of Sight to use as guidelines:

1.       Full Line of Sight (LOS), where no obstacles reside between the two antennas.

2.       Near Line of Sight (nLOS) which includes partial obstructions, such as tree tops between the two antennas.

3.        Non Line of Sight (NLOS), where full obstructions exist between the two antennas.

 

By determining the specific line of sight conditions in the WiFi network area, you can then determine the correct type of wireless system to install.

 

For example, most WiFi systems typically run on the 2.4 GHz and 5.8 GHz frequencies. Both of these frequencies are very dependent on a clear line of sight to obtain good performance, so clear LoS is very important.

 

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