What You Need to Know about Line of Sight

August 25, 2016 at 8:00 AM


When designing a wireless network, one of the most significant factors to consider is Line of Sight (LOS) - the path between two antennas. Obstructions in the LOS path can wreak havoc on a Wi-Fi signal so determining what, if anything, is between the antennas is crucial to your network working properly. Here, we’ll examine the main concepts you need to know in order to clear the path for Line of Sight and make sure your wireless network is a success.

 

The first step in navigating Line of Sight is to determine the LOS conditions. Once the conditions are defined, the correct type of wireless system can be chosen for the network area. There are three main Line of Sight conditions:

 

1.       Full Line of Sight (LOS) – no obstacles between the two antennas

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

3.       Non Line of Sight (NLOS) – full obstructions between the two antennas, such as an entire tree  

 

Outdoor networks may encounter the largest obstacles, but Line of Sight is also important for indoor wireless networks. Obstacles like walls, ceilings and furniture have to be considered because they will also affect the wireless signal reception.                                                                                                                         

In addition to obstructions, there are three other factors to consider that can affect Line of Sight:

 

1.       Multipath and Reflections

2.       Fresnel Zone

3.       Path Loss

 

In wireless transmissions, multipath and reflections are as important as signal strength because they too can degrade the performance of the network. Multipath is when wireless signals travel in multiple paths and arrive at the receiver at different times. Reflections occur when wireless signals "bounce" off of objects. When signals are transmitted through walls and ceilings and are reflected off of metallic objects, they will also have peaks and nulls in amplitude and changes in polarization (vertical or horizontal).

 

Fresnel Zone is an electromagnetic phenomenon where light waves or radio signals get diffracted or bent by solid objects near their path. The reflected waves/signals become out-of-sync with those that traveled directly to the receiving antenna, this delay reduces the power of the received signal.

 

Path Loss is another area of concern when determining Line of Sight. Some radio frequencies travel well through certain objects while other frequencies are not able to pass through, resulting in path loss. For example, 2.4 GHz radio waves easily pass through walls but experience path loss when going through trees and leaves. This is because walls are very dry, trees contain high levels of moisture and 2.4 GHz radio waves are easily absorbed into water. On the other hand, 900 MHz radio waves are not as easily absorbed by water. In cases like this, when trees cause nLOS or NLOS conditions, 900 MHz is a better frequency to use than 2.4 GHz to avoid path loss.

 

There are many factors to consider when designing a wireless network, but with proper site evaluation and planning you can correctly navigate Line of Sight obstacles to achieve peak performance.

 

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