We use average MCS in the 10 last seconds to calculate the link capacity value. So if some packets are going on MCS14 or MCS13 you will see capacity less then 100%. You can see detailed statistics under Monitor->Wireless.
OH - that's good info. We had asked this at the Training course Edmonton, but they didn't know. So, basically, it's a percentage of theoretical compared to IF the link was MCS15, right?
So - if the signal is lower because the distances are greater, and if a link is doing MCS11, then that's 108Mbit vs 270 Mbit, so it might say 40% link capacity - BUT that's not necessarily indicating a problem or an interference or corrupted packets, just indicating that it's 40% of theoretical under ideal conditions.
Link quality is based on current MCS and average ARQ retries. So if you have no retries on current MCS you will have 100% quality. Low quality indicating a problem usually caused by interference.
Link capacity is based on current MCS theoretical throughput compared to the theoretical throughput of the highest MCS (MCS15). So, nidnedd, your assumption is right. Low capacity is usually indicating low link budget.
>Does The MCS depend on operating condition such as distance between AP and SM, antenna alignment, transmit power?
That is absolutly true: MCS depends on distance between AP and SM, antenna alignment, transmit power, interference and etc