Re: VHT 160Mhz and nss related config.

[Ben Greear <greearb@candelatech.com>]

On 02/10/2017 08:37 PM, Adrian Chadd wrote:
> On 10 February 2017 at 20:22, Sebastian Gottschall
> <s.gottschall@dd-wrt.com> wrote:
>> i really can't believe this. if this is true the  160 mhz mode would not
>> make any sense.
>> the maximum tx / rx rate for 4x4 vht80 and 2x2 vht160 is identical. so
>> vht160 would not increase performance in any way
>
> Well, if it can also do 2x2 MU-MIMO at 160MHz then it can be a
> perfectly fine STA to a 4x4 160MHz MU-MIMO chip that can actually
> transmit 2x2 rates to different MU-MIMO peers.
>
> That's the outstanding question I have - is it like, 2x2 MU only, or
> is it say, 2 concurrently different spatial stream 2x2 MU? Ie, can you
> have 2 peers, different VHT spatial groups (or 4 peers, 1 spatial
> group each) all going at the same time?
>
> I'm .. not even sure how you're supposed to cleanly negotiate that you
> can do 4NSS in VHT80 but 2NSS in VHT160 to a peer... that only makes
> sense if you're doing lots of 1NSS and 2NSS MU-MIMO peers..

I think using the max-rx-rate logic might could imply this, but I am not sure
many drivers fill this out properly.

Looks like a mess waiting to happen to me.

Even if you can do 1x1 160Mhz MU-MIMO to two stations, and I am not certain you
can since in 80Mhz you can only do a 1x1 and a 2x2 (not two 2x2).

So, from what I know currently, 80+80 is not that useful on the 9984 NIC...

Thanks,
Ben

>
>
> -adrian
>
>>
>> Am 10.02.2017 um 23:58 schrieb Ben Greear:
>>>
>>> So, it appears that the ath10k QCA9984 4x4 160Mhz chip can do 4x4 MIMO at
>>> VHT80, but
>>> it can do only 2x2 MIMO at VHT160/80+80.
>>>
>>> When configuring a peer, we need to tell the firmware the number of
>>> spatial streams
>>> of the peer at VHT160 and at VHT80 and lower.  They are not the same
>>> value.
>>>
>>> I cannot think of any standard way to get this information based on VHT
>>> capabilities
>>> and such.  Currently, one could just assume VHT160 NSS is 1/2 of the VHT80
>>> NSS,
>>> but that is unlikely to be true for all vendors.
>>>
>>> Any ideas?
>>>
>>> Thanks,
>>> Ben
>>>
>>
>>
>> --
>> Mit freundlichen Grüssen / Regards
>>
>> Sebastian Gottschall / CTO
>>
>> NewMedia-NET GmbH - DD-WRT
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>> http://www.dd-wrt.com
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>>
>>
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>


-- 
Ben Greear <greearb@candelatech.com>
Candela Technologies Inc  http://www.candelatech.com


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