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Does Weather Effect Wireless? The 5 Misconceptions - Part 1

  
  
  
  

After a decade of designing, selling, and installing outdoor wireless backhaul systems I consistently come across five reoccurring questions that all clients ask and their misconceptions. Each week I'll present one of the five questions and answer them in plain English and put the misconceptions rest.

Question 1: Does the weather (like rain) effect wireless?

Well the answer is Yes & No!
Technically "Yes" - different forms of weather do have effects on various frequencies. Reality "No" - if the right frequency and antenna system is properly engineered, designed, and installed a wireless backhaul system can provide 99.999% reliability.

The obvious one is wind. Wind in itself doesn't effect the RF signal but it does put an external force (wind loading) on the antenna system that can cause it to move or come out of alignment. This is pretty easy to understand. The clear answer is to properly install antenna systems to withstand local wind patterns. Most antenna systems are designed to withstand wind gusts up to 110mph (varies by manufacture).

The main question arises with precipitation (e.g. fog, rain, and snow). All wireless signals that travel from one antenna system to another experiences some form of "Path Loss". Properly designed systems use the correct antennas, frequencies, and transmit power ("Tx") to overcome the Path Loss to get the desired Receive Signal Level ("RSL" measured in dBm). Radios are designed to operate with a certain level of "Fade Margin" that allows the system to operate at a predictable reliability (for most systems 20 to 25dB of Fade Margin is recommended). This means if a system has an RSL of -50dBm and it has a receiver threshold of -72dBm, you'll have 22dB of Fade Margin or the amount of dB signal strength a system can loose before you will experience errors or loss of connectivity.

wireless snow towerMoisture such as fog, rain, and snow (depending on its water content) adds attenuation to the signal's path. The amount of moisture is critical to understand here. Fog, although dense, has very low moisture when it comes to its effect on RF signal. With snow it all depends on its density. Snow typically has less moisture content than actual rain. Rain depends on the amount of rainfall (measured in mm/h) and the size of the raindrops. Heavier the raindrops and the higher velocity of rainfall the higher the attenuation. Typical rainfall produces roughly 5.5dB. Again it depends on the amount of rain coming down and the frequency being used.

Also, the amount of attenuation rain can cause depends on the frequency being used. The lower the frequency the less attenuation. The high the frequency the higher the attenuation. To design a outdoor wireless bridge system correctly rain modeling is used (along with other Path Loss factors) for calculating the RSL needed to provide adequate Fade Margin necessary for any given system.

So, if a system is designed and installed properly, a wireless backhaul system can still produce 99.999% (<5min predictable yearly outage) reliability. Note: amazingly good since most telco's only guarantee 99.9% reliability on their fiber infrastructure).


Comments

The wifi connection in our campus malfunctions (nobody far can connect but people close up can) from sunset to sunrise. At that time there is very dense fog. Does that imply that the fog is behind this??
Posted @ Saturday, December 10, 2011 9:57 PM by Tyko Brian
I don't think fog has anything to do with it (unless there is an install issue with weather proofing the connections). This sounds more like an issue with incorrect installation, wrong antennas, etc. It may also be what we call Man in the Middle effect. Meaning that during high usage times the closest users are very active and when you have a user(s) farther away the handshack of the AP and the clients take too long. Basically casuing drops.
Posted @ Thursday, December 15, 2011 9:16 AM by Joe
If wind does not affect radio signals, ie Bluetooth. Why is it that when I ride my bicycle, it loses connection? It has happened with different bluetooth devices and different phones. Even if the phone is in a shirt pocket. The only time it stays connected is if I hold the phone up like I am making a phone call
Posted @ Wednesday, September 12, 2012 7:39 PM by T. Davis
BlueTooth operates with low range 2.4GHz. Wind doesn't effect the wireless connectivity, but what might be happening is many headsets operate in TDD (meaning talk / listen relationship). As sound is received by the microphones in the headset it mutes the incomming speaker. Another possibility is that each headset is different in the dB level sensitivity.  
 
 
 
For instance: your post got me thinking so i got on my bike and tested thsi theory out. I used my iPhone (which was in my pouch on my bike) and tried three different headsets I own. My Blue Ant (with wind cancellation) worked well (poeple on the other line didn't even know I was riding. My Sound ID did well too. Cheaper Moto did have some issues.  
 
 
 
May be more of the fact that wind is hitting the microphone of the headset rather than the BlueTooth itself. Other issue may be interference where you are riding?
Posted @ Thursday, September 13, 2012 11:05 AM by Joe Wargo
right now i have a fixed wireless provider and i experience some packet loss when it rains. this affect the quallity of my calls. I have an AR 80 bridgewave 80 Ghz. can you tell me why this is happening. also some times i run it at a Gig and get problems alot of problems loss of connectivity ect.. but when i run it at 100mbps it works fine. except today it rained. can you please tell me how you would fix this thank you so much
Posted @ Thursday, October 11, 2012 12:21 PM by mohamed elbruki
There can be several issues that can cause loss. First i would check the antenna alignment (most common cause). In the case of the BridgeWave you want to make sure you are getting expected RSL and check the Qual Voltage. Needs to be around 2.9 to 3.3 vDC to perform forward error correction.  
 
 
 
Make sure you have a proper path calculation to verify the perfromance on the system based on your path length and geographic area. 
 
 
 
Make sure it is also properly mounted / installed. It has to be on a mast that is extremely rigged (no movement and is 100% plumb). 
 
 
 
Other potential issue could nbe with your fiber connections.  
 
 
 
Feel free to contact me and i can talk to you further. (I'll send you an email with my contact).
Posted @ Thursday, October 11, 2012 12:35 PM by Joe Wargo
We face the problem of interference during night but during day the value improves.What may be the remedy
Posted @ Saturday, November 10, 2012 11:14 PM by Rajesh
Night and day don't have any real effect when it comes to interference unless someone else is operating another wireless source during certain times. This is very rare thought since most RF sources are always on. 
 
What frequency are you using? Is it a point to point bridge or something else?  
 
What have you done to determine it is interference? The best way is to use a spectrum analyzer. Turn off you radios and put the analyzer on the same antenna and feed you are using. You can do this on both ends of a link. I would take a reading during the day and one at night to compare.  
 
Other possible issues if it's a drop in performance can be in the cabling and/or connectors due to moisture with temp change or connections.
Posted @ Monday, November 26, 2012 2:21 PM by Joe Wargo
I designed a wireless water level indicator and motor controller using RF module (315).but there is a problem in rainy season ,RF (TX) is transmitting properly but receiver is unable to receive the proper signal.By going through the above mentioned details somewhere i can understand what is happening here but system behaves randomly i.e; some time it is working perfectly and some times not why so...?  
please reply as soon as possible
Posted @ Friday, August 02, 2013 7:40 AM by bhavesh sharma
I'm not sure about he RF Module you are using or where and how it's deployed. Water will cause attenuation on the RF signal. The key is to design and deploy the RF system so that your gain is greater than the fade.  
 
Each frequency calculates into the free space path loss based on al the variables. For example 2.4GHz penetrates better than 5.8GHz. Questions that need to be address are what is the installed environment, type of antennas, frequency, and so on. What is the environment? Distance? Line of Sight? Modulation?  
 
The other thing to look at is potential interference if you are using unlicensed frequencies.  
 
If you have issues just during a rain then I would assume you have too much free space path loss going on. Meaning not enough gain and that's why the rain attenuation is knocking you below the radios receive threshold.
Posted @ Friday, August 02, 2013 10:06 AM by Joe Wargo
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