Effect of MIMO on Legacy Clients Beamforming

[Mansoor1]

Hi All. 

I'm struggling with some Legacy devices on dedicated WLAN with 802.11g enabled only. AP we are using are Cisco AP1852e with Directional Antennae, we don't have any coverage issue in terms of RSSI, but instead more sort of Clients compatibility issue with Radio Card of Honey well Devices.

The radio cannot decode the multi-streaming from newer infrastructures and sees this as noise which leads to RF disconnects. The fix has been to set the infrastructure to some variant of a Legacy mode which inhibits multi-streaming and beam forming.
It can also cause the AP to shift to one antenna operation for that client.

Since we already have deployed AP1852 which best work on TxBF instead of legacy beamforming.

I have disabled all 802.11a on AP and also WLAN.

To resolve this I can think of two steps,
Step 1: Disable 802.11n on problematic WLAN and disable MIMO, as this deployment is mostly based on Line of sight with directional antenae.

Step 2: enable legecy Beamformaing per AP basis.

well appreciate your feedback.

[Scott Fella]

I think you are on the right direction, but do your test and make sure.  Talk to the vendor in regard to their device and ask if any other companies are using those devices in new wireless environments and get a call with that company.  The one thing I always look at also is your configuration, especially on the WLAN.  best thing to do is create a new test SSID and change it from WPA/WPA2 to open and don't change any other value.  Test to see if you still have issues.  Also, you mentioned patch antennas, are these patches used in high ceilings or something else?  You need to be careful in regard to TX power.  When using a patch with a gain, your signal will be focused to an area and coverage, or RSSI, will look good.  However, the client signal is omni and might not be 100mW for example, so the AP might not even hear the transmission from the client.  Look at the RSSI from a client in a specific spot and then look at the controller to see what the AP is seeing as far as RSSI and SNR.

[Leo Laohoo]

Talk to the vendor. See if they have recent software patches to update the firmware of the legacy NIC cards.