ePMP 1000 and MCS 1

I have a pretty basic ePMP setup with 1 AP and 2 SM’s less than a mile from AP. I’ve ran spectrum analysis on each device and It’s pretty clean. I even changed from 40Mhz channels to 20Mhz just to make sure I was not hitting anything even close to me. eDetect tool and logs report no problems. My problem may not be a problem but both SM’s seem to want to modulate at 50% MCS 1 and 50% MCS 15. I’ve noticed that when there is no real throughput usage then the radios will modulate at MCS 1 and when I start a download or something then I will see the packet usage on MCS 15 kick up. Is this normal? I’m getting fantastic throughput and overall am very impressed. However, when I was running 2.1 firmware I don’t ever remember seeing this -only when I added the second SM and updated firmware to 2.3. Anyone have any ideas?

Hi Nathan, 

Yes, this is normal. The ePMP devices exchange control/management messages on MCS1. So if you don't have user traffic on the link, the wireless driver will be transmitting control messages on MCS1. Once user traffic starts, the rate adapt algorithm kicks in and uses the best modulation for the given RF environment. It sounds like you have a pretty clean spectrum, hence MCS15. Please note that, even in the presence of user traffic, control/management messages will still go on MCS1. 

Hope that explains what you are seeing.