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#26 2016-Dec-12 17:20:07

loho2027
Member
Registered: 2016-Aug-16
Posts: 42

Re: 802.11 Reference Design- making AP send multiple SSIDs

Hi,

I have basically implemented the access point to support multiple SSIDs. It works for my newer devices (laptops, mobile phones). However, for two of my older laptops they do not connect properly to the Internet. They connect to the access points initially, but soon after they disconnect automatically.

On an access point without multiple SSIDs, those older laptops connect successfully to the Internet.

Could you suggest what could be wrong with my implementation?

Regards,
loho2027

Last edited by loho2027 (2016-Dec-12 17:24:41)

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#27 2016-Dec-13 08:41:53

chunter
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From: Mango Communications
Registered: 2006-Aug-24
Posts: 1064

Re: 802.11 Reference Design- making AP send multiple SSIDs

It's really hard to say. One debugging step would be to use Wireshark on a device with monitor mode support to oversee the communication between the AP and devices that do work in the multiple-BSS setup. Compare that to a similar capture with devices that don't work. You might be able to see why the devices that fail refuse to communicate.

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#28 2017-Jan-26 18:03:47

loho2027
Member
Registered: 2016-Aug-16
Posts: 42

Re: 802.11 Reference Design- making AP send multiple SSIDs

For the devices that don't work, it (the client) sends a Deauthentication packet with Reason Code 1 (Unspecified failure). What could be a reason why that is happening? Is there a way to check (the client is a windows 7 machine)?

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#29 2017-Jan-30 13:20:10

chunter
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From: Mango Communications
Registered: 2006-Aug-24
Posts: 1064

Re: 802.11 Reference Design- making AP send multiple SSIDs

Since you don't have access to the internal workings of the commercial STA, it's hard to tell why it is throwing an "Unspecified failure. It might be worth trying to capture an association exchange between the client that is failing with a commercial AP and comparing it with the association to your modified multi-BSS AP. That might point out some non-standard behavior that some clients are willing to overlook and this Windows 7 client is not.

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#30 2017-Feb-05 20:52:10

loho2027
Member
Registered: 2016-Aug-16
Posts: 42

Re: 802.11 Reference Design- making AP send multiple SSIDs

I've fixed the issue, it's due to a bug I had. Thanks for that.

Another question I have is, if I could implement sending multiple BSSIDs from one AP, how difficult would it be to assign traffic priorities (like Quality of Service) to each BSSID? Say, for example, I give 1/4 of the bandwidth to one BSSID while giving 3/4 bandwidth to the other BSSID.

Also, are there many uses to have an AP send multiple BSSIDs (virtualisation)? Maybe it facilitates monetisation by different service providers?

Regards,
loho2027

Last edited by loho2027 (2017-Feb-05 22:16:47)

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#31 2017-Feb-06 08:04:14

chunter
Administrator
From: Mango Communications
Registered: 2006-Aug-24
Posts: 1064

Re: 802.11 Reference Design- making AP send multiple SSIDs

On the downlink side of things, you could alter the round-robin tx queue polling to poll the higher-priority queues more often than lower priority. There isn't too much you can do on the uplink side of things, short of intentionally failing to ACK some receptions to cause the STA to increase its contention window and back off the medium for a higher priority STA. It's also worth looking at the EDCA for some inspiration and how it handles traffic priority. Note: we do not implement the EDCA behavior in the reference design.

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#32 2017-Feb-13 17:11:50

loho2027
Member
Registered: 2016-Aug-16
Posts: 42

Re: 802.11 Reference Design- making AP send multiple SSIDs

Hi,

I'd like to know if it's possible to determine the SINR of clients, rather than just the RSSI? Can that be determined from the channel estimate information provided, for 802.11 Reference Design?

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#33 2017-Feb-14 09:04:34

murphpo
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From: Mango Communications
Registered: 2006-Jul-03
Posts: 4615

Re: 802.11 Reference Design- making AP send multiple SSIDs

The RSSI signal from the MAX2829 provides an estimate of total received power. The Rx PHY does not implement any method for estimating interference power separate from signal power. In theory you could derive this from the EVM after the equalizer (i.e. high EVM at high power -> high interference likely). The current Rx PHY doesn't estimate EVM - you would need to add this to the Rx PHY model. You could only derive EVM from the channel estimates if you know what the actual channel coefficients are.

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#34 2017-Mar-27 18:44:07

loho2027
Member
Registered: 2016-Aug-16
Posts: 42

Re: 802.11 Reference Design- making AP send multiple SSIDs

So are you saying that the only information WARP receives is the RSSI? As I recall each message in 802.11 Reference Design also contains a 'channel estimate' as well. I'm not sure what the difference between channel estimate and channel coefficients are. Aren't they the same thing?

Regards,
loho2027

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#35 2017-Mar-28 08:01:31

murphpo
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From: Mango Communications
Registered: 2006-Jul-03
Posts: 4615

Re: 802.11 Reference Design- making AP send multiple SSIDs

The 802.11 Rx PHY calculates channel estimates from the preamble's long training symbols. One complex coefficient is calculated per subcarrier. These channel estimates are used by the equalizer and are stored in the Rx packet buffer. The C code copies the estimates from the packet buffer to the log along with the other Rx packet details (Rx RSSI, AGC gain selections, Rx timestamp, etc).

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#36 2017-Mar-29 21:07:26

loho2027
Member
Registered: 2016-Aug-16
Posts: 42

Re: 802.11 Reference Design- making AP send multiple SSIDs

To get the complex coefficient per subcarrier, and subsequently EVM, would I need to modify the code at the FPGA level?

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#37 2017-Mar-30 07:46:39

murphpo
Administrator
From: Mango Communications
Registered: 2006-Jul-03
Posts: 4615

Re: 802.11 Reference Design- making AP send multiple SSIDs

I think we're talking about different things. The Rx PHY saves the channel estimates (1 per subcarrier) to the Rx packet buffer. It does not save the equalized data symbols.

The Rx PHY computes an FFT of each received OFDM symbol. The FFT outputs one complex value per subcarrier per OFDM symbol.

For channel training OFDM symbols these complex values are the channel estimates, the Rx PHY's best guess at the actual (unknowable, random) channel coefficient for that subcarrier. The Rx PHY saves these channel estimates to the Rx packet buffer so they can be logged by wlan_exp. The equalizer block uses the same channel estimates.

For data OFDM symbols the FFT output is a complex value Y, the product of the transmitted data symbol (X) and the random channel coefficient (H). The Rx equalizer estimates X by dividing Y by H_est. The result is X_est, the Rx PHY's best guess at the transmitted symbol. EVM is the distance between X (the actual transmitted symbol) and X_est (the Rx equalizer's estimate of X). The Rx PHY does not save the X_est values - these values are consumed by the demod/decode logic to recover the transmitted data bytes.

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