Wireless Access

Hello,

We are currently looking at beginning to use the AP-300 series.

I have a question regarding the AP-32x and AP-33x

Ignoring the extra smart rate supprt of the 33x vs 32x I'd like to ask a question about the radio and antennas within the AP.

I note the following:

The AP-335 has 12X omni-directional downtilt dual band and 4X4:4 for MU-MIMO, 4X4:4 for SU-MIMO

The AP-325 has 8X omni downtilt and 4X4:3 for MU-MIMO, 4X4:4 for SU-MIMO.

Can anyone please explain to me why the AP-335 needs an extra 4 antennas over the 325 to supply the extra spatial stream for 4x4:4 multi user MIMO? In short I'm asking why it has 12 antennas. 

Also, on the AP-334 and AP-324 we can only attach 4 x dual dand external antennas (meaning it has 8). So ignoring the smart rate features why is the price of the AP-334 the same as the 335 when it can support less antennas (335 has 12). Also, can it still do 4x4:4 with only 8 antennas? 

Thanks

Alexander

Anyone?

Alexander,

The set of 4 additional antennas on the AP-335 is used to provide "antenna polarization diversity" for the 5GHz radio. On that radio, we basically connected two antennas to each radio chain (so 2 sets of four altogether). One antenna is vertically polarized (which is typical/default), the other is horizontally polarized. We use an RF switch to allow us to dynamically select the best antenna for each transmit and receive packet (software controlled).

There is no impact on MIMO support, but this allows us to potentially gain the equivalent of up to a couple of dB by optimizing the coupling between the antennas on the AP and client device.

Note that the gain and coverage patterns of the vertical and horizontal antenna elements are (roughly) the same.

The tricky part obviously is determing which set of four antenna elements to use (VVVV to HHHH) for each packet to get the best performance. We continue to improve and tweak the algorithm for that.

When using external antennas, this dynamic behavior is obviously lost, and both radios use a fixed set of 4 antenna elements each (or rather a total of 4 dual-band elements). There is no reduction in the 4x4:4 MIMO capabilities.

While this is an interesting and performance enhancing feature of the 335, the true value of the 330 Series access points (over the 320 and 310 series for example) is in the high platform performance and Smart Rate interface.

Onno,

Are any white papers or other information available about the use of 12 instead 8 antennas for 4X4:4? Being dynamically able to select between these four additional antennas and their oppositely polarized counterparts is fascinating.  Would love to read more about that.

Thank you,

ScottD

No whitepaper I'm afraid.

Note that when the feature is enabled, the "magic" happens under the hood, and there's no access to any control.

In reality, while this feature adds value (SNR improvement of up to a couple of dB), it is not earth-shattering by any means.

Shame, I would love to read about it.

You're probably right that it won't make the evening news programs, but it's still very intriguing. The whole MIMO and beamforming thing is. I'm an old analog radio freak and all this signal processing stuff, and digital modulation, just blows me away.

Cheers,

-ScottD