Lecture 8:Fresnel Zone of Wireless Communication

Wireless Networks
Lecture 8: Fresnel zone of Wireless Communication.

Visual LOS:
If you stand on top of some tall building, you can see for a very great distance. You may even be able to see for many miles on a very clear day. If you can physically see something, it is said to be in your visual line of sight (visual LOS). This LOS is actually the transmission path of the light waves from the object you are viewing (transmitter) to your eyes (receiver).

RF LOS:
RF LOS is more sensitive than visible LOS to interference near the path between the transmitter and the receiver. You might say that more space is needed for the RF waves to be seen by each end of the connection. This extra space can actually be calculated and has a name: the Fresnel zone.

The Fresnel Zone:
The Fresnel zones (pronounced frah-nell), named after the French physicist Augustin-Jean Fresnel, are a theoretically infinite number of ellipsoidal areas around the LOS in an RF link. Many WLAN administrators refer to the Fresnel zone when it is more proper to refer to the first Fresnel zone, according to the science of physics. While it may be the intention of most WLAN administrators to reference the first Fresnel zone when they speak of only the Fresnel zone, it is important that you understand the difference. The first Fresnel zone is the zone with the greatest impact on a WLAN link in most scenarios. The Fresnel zones have been referenced as an ellipsoid-shaped area, an American football-shaped area. The following figure shows the intention of this analogy.