WiFi Strength Signal

[borey_chum]

Can you explain why minimum recommended signal test for best use is -65 dbm? what if it goes to -72 dbm?

[robert_lowe_722]

what was the difference in signal? Devices can have different antenna inside therefore it is quite normal to get different signal reading from different devices in the same place. For example a laptop will generally report a signal up to 10dB stronger than a smartphone in the same location. Different antenna = different RSSI.

[it_registration]

Robert nailed it, but to explain differently.  Think of your Android phone like you do your car radios.  Some car radios receive radio stations better than others in the same exact location.  That because of the car radio (receiver) quality & antenna quality as well as placement.  As an example, one car will drop a radio station while driving through a tunnel while another will continue to play the radio station just fine driving through that same tunnel.

[seanmuir]

When designing a network you always have to design to the client, but you should not however be desiging to the worst client, especially if your trying to get that client to achieve -65dBm.

Note: Some clients are a lot worse than others and in certain cases can be in excess of 10dB when it comes to a signal delta.

One thing you should note is that Ruckus has Interference filters which will reduce your noise floor by about 12dB - think typical noise environment in a shopping mall where NF is around -85dBm, with Ruckus this could be lowered to around -97dBm, giving you more SNR room to play with.

One thing that has not been mentioned yet is how channel size increases noise floor and how that may affect your design.

Without Interference Filter and only 3dB noise figure at reciever:

20MHz = -97.99dBm
40MHz = -94.98dBm
80MHz = -91.97dBm
160MHz = -88.96dBm

With Interference Filter and only 3dB noise figure at reciever:

20MHz = -109.99dBm
40MHz = -106.98dBm
80MHz = -103.97dBm
160MHz = -100.96dBm

As you can see from the above if you dont have an intereference filter you may need a higher RX power value to obtain decent SNR /bitrate / throughput.

Note: The above only represents a clean environment though so lets look at a noisy one.

Without Interference Filter and only 15dB noise figure at reciever:

20MHz = -85.99dBm
40MHz = -82.98dBm
80MHz = -79.97dBm
160MHz = -76.96dBm

With Interference Filter and only 15dB noise figure at reciever:

20MHz = --97.99dBm
40MHz = -94.98dBm
80MHz = -91.97dBm
160MHz = -88.96dBm

Obvioulsy the 40, 80 and 160MHz channels are aimed at 5GHz, but as you can see it may impact your design if you are aiming at obiquitous coverage across both bands and then you still have the log value delta between 2.4GHz and 5GHz.

Personally I think this is how -65dBm came about, as 20dB SNR is considered to be a good value and if you were to look at the first of the 2 values above showing the 15dB noise figure, the NF at 20MHz is -85dBm... I'll let you do the remaining math 🙂