What is PD-MRC?

PD-MRC (which consists of)

• Polarisation
• Diversity
• MRC (maximal ratio combining)

So that's the word broken down into its abbreviations.

What is Polarisation?

When a signal is sent from an antenna is it sent in one of two ways. Horizontally, so like a side winder snake in a desert on a horizontal plane left to right. The other way is a like a swimmer doing the butterfly stroke up and down.

A client devices antenna (iPhone, Ipad, laptop etc.) will also be either horizontally or vertically polarised.

Depending on the orientation of the device so whether it is sitting on a desk or in the hands of the user, you will naturally have a better position or orientation of the device to receive a stronger signal. In a nutshell that is polarisation.

Diversity

Diversity is the ability to diversify, so adapting and changing between the different polarisations of the signal depending on the orientation on the signal when received.

MRC (maximal ratio combining)

MRC is actually a 802.11n feature and all manufacturers who are using 802.11n utilise this feature. It stems from a standard called antenna diversity, I won't go into that now but effectively it means it has multiple antennas to listen and choose the antenna that receives the best signal.

If you had an access point that had 3 antennas that were programmed to be receiving signals. With standard antenna diversity is would pick which antenna heard the signal best and use it. With MRC it actually listens on all 3 of those antennas, and will utilise them all to combine the best of those signals into one.

PD-MRC

As I mentioned earlier PD-MRC is actually a Ruckus patented term and takes the terms above to another level. So not only does it change the polarisation of the signal to match the devices polarity. It does this for all the antennas that it has independently, so taking the best bits for each signal and combining them to become the ultimate signal.

Summary

Access points can't control a devices orientation. So it makes sense to ensure your access point listens on all orientations.

A signal changes its polarisation depending on how it bounces around an environment. Using PD-MRC on a packet by packet basis it will listen on each antenna using both polarisations and decipher the best signal by combining all the signals to become the penultimate signal.