Bad MCS rates

How can I have such good SNRs and such awful MCS rates?


you're getting intermittent interference.  

the noise floor is the point where the channel is consumed 100% of the time at that power level.  

so in the city, with who knows how many devices talking in the background constantly, your equipment may hear that continuous noise at let's say, -80.  your RSSI is -60 giving you an SNR of 20db.  but you can have an interferer producing noise at -70 intermittently. your epmp will try and talk at mcs12, but if the intermittent interferer is causing too many dropped packets, the gear will downshift MCS states to get a reliable transmission.   giving you a max modulation of MCS 9 or MCS 2.  

this is a serious oversimplification of what may be happening, but if you run a spectrum analyzer you'll probably see some noise in the band, moving to a new channel or increasing your RSSI will resolve the issue. 

another possible situtaion is co-band noise, a very load signal on a near channel to this AP.  an EPMP2000 is designed to deal with that.   the smart antenna can aid in cleaning our uplink noise problems as well. 

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Shouldn't the SNR reflect that interference?

eDetect shows no interferers, which is crazy.

I've tried a number of different channels.

I agree it behaves like interference, but ePMP doesn't report noise very accurately.  Maybe a limitation of WIFI based chipsets?

eDetect will only show interferers of the same channel width on the same center channel.  It won't show anything else, including noise on adjacent but overlapping channels.

The only way to get an accurate noise picture unfortunately is to run the spectrum analyzer on each radio.

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@JLLC wrote:

eDetect shows no interferers, which is crazy.

eDetect doesn't show interferers, unless they just so happen to be on the exact same channel and width as you are.  So yeah, eDetect is currently not capable of showing an interferer 95% of the time that there is an interferer.

@Jacob Turner wrote:

The only way to get an accurate noise picture unfortunately is to run the spectrum analyzer on each radio.

 So if that's at a place where you can't get to via the Ethernet port (so at the customer's side, or at PTP clent side) you basically have to drive to each customer's/client's location and run a Spectrum Analyzer from each location. Currently no way to do that remotely.

Won't the radios show low MCS and Quality when they are inactive ?   Upon reading this logged into one of our AP's and there were several great RSSI/SNR but setting at like  MCS 5/3 and as soon as I logged into the radio and ran a link test (which came back great) the display jumped up to 15/14 and within a few seconds of the link test ending they dropped back down to 4/9 or something.