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SNR – Signal To Noise Ratio – What Is It?

September 13, 2015 by Rowell Dionicio Leave a Comment

Imagine being at a large, crowded concert. Everyone is screaming and singing along to the music. You turn to your significant other and say how awesome the concert is. Even though you’re right next to each other, you can barely hear one another.

Speaking above the concert noise floor.
You have to speak loud above the concert noise floor to be heard.

The people around you and the band playing is called the noise floor. That is what would be the ambient noise for the duration of the concert.

Download the free PDF: What Is SNR

You would have to speak above the noise floor for your partner to hear and understand what you’re saying. The difference between your voice and the noise floor is what SNR is.

It’s important to know that the receiving person not only HEAR you but also UNDERSTAND. This is comparable to saying a wireless radio has signal, but can’t demodulate a signal from an access point. The device radio must be able to demodulate in order to understand the bits.

Signal-To-Noise Ratio

SNR stands for Signal-to-Noise Ratio. SNR is a comparison of the signal to the background noise or otherwise known as noise floor. In fact, it’s not actually a ratio at all.

If the signal level is near the noise floor level then we witness data corruption. Not only is this bad for the sending and receiving radio, but also for surrounding radios (clients). The sender, such as an access point, will need to retransmit the frames back to the receiver because of data corruption. This is more known as retry rates.

A large retry rate decreases throughput. Everyone gets less airtime because of those retransmissions. Thus the wireless network appears slow, if not unusable. Frame retry rates as high as or above 15% should be looked into. And this could be a result of interference from neighboring access points, large number of clients, microwave ovens, bluetooth headsets, and other interferers.

Ideally, you want to aim for a higher SNR. I’d say 20 dB or greater is good SNR. Greater than 40 dB is even better!

Recommended minimum SNR for data is 18 dB and for voice over wifi it is 25 dB. As more interference is introduced, the SNR decreases because it raises the noise floor.

[Read more…] about SNR – Signal To Noise Ratio – What Is It?

Wifi Optimization Using Wifi Explorer

June 1, 2015 by Rowell Dionicio 2 Comments

Wireless requires occasional love and care. You can’t set and forget. The wireless spectrum can change so quickly and end users will be the first to experience poor service. In this post, I am going to use my home network as an example. Recently, we moved to the Bay Area. There were hardly any neighbors making my AP the sole wireless transmitter in the area.

As more families started moving in nearby I began to notice the degradation of my wireless network.

I booted up my laptop and opened Wifi Explorer, a useful OS X application use to scan, monitor, and troubleshoot wireless networks.

Upon opening the application it will display a list of wireless networks nearby, what channel they are utilizing, and what their signal strength is.

Wireless Networks
My wireless environment before making changes

My wifi network is D-NET and you can see other networks on the same channel on both 2.4 GHz and 5 GHz. I thought I’d be fine on 5 GHz because it is less utilized in home networks but I didn’t realize other networks were all on the same channel.

With Wifi Explorer I can quickly identify problematic channels and make the changes on my Open Mesh AP.

Wifi channel changes
Wifi channel utilization after changes.

I quickly got off the AP taking up channels 1 and 6 on 2.4 GHz and moved to channel 11 where the other SSIDs have a weaker signal. On the 5 GHz channel I avoided everyone else and went to channel 44 on the UNII-1 band.

Wifi Explorer can be purchased on the App store for $14.99. This is a tool I will keep for quick wireless troubleshooting. Highly recommended for anyone wanting to take wireless seriously. Adrian Granados is the author of Wifi Explorer and has other useful applications worth checking out.

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