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* [RFC] VHT MU-MIMO correction
@ 2015-10-21  9:15 Johannes Berg
       [not found] ` <1445418906.4558.7.camel-cdvu00un1VgdHxzADdlk8Q@public.gmane.org>
  0 siblings, 1 reply; 3+ messages in thread
From: Johannes Berg @ 2015-10-21  9:15 UTC (permalink / raw)
  To: radiotap-S783fYmB3Ccdnm+yROfE0A

Hi,

As we're looking into MU-MIMO again, we found some issue with the way
the VHT radiotap field is defined. The issue is the following: the VHT
SIG-A field defines the NSTS (NSS) for each user, and it would be good
to have that shown. However, radiotap ties the validity of the MCS to
the existence of the NSS, which is incorrect.

Therefore, I suggest to make the following edit:

Change this language:

    If the NSS field for a user is zero, the user is not present and
    the MCS and coding (in the coding field) associated with that user
    are not valid. For SU PPDUs, only the first user will have a
    nonzero NSS field.

To read:

    If the NSS field for a user is zero, the user is not present and
    the MCS and coding (in the coding field) associated with that user
    are not valid. If the NSS field for a user is non-zero, but the MCS
    is not known (for example due to receiving only data for a single
    user), the MCS shall be set to 15.
    For SU PPDUs, only the first user will have a nonzero NSS field.


The coding should be known for all, since it's also part of VHT-SIG-A,
so I'm not suggesting to add validity flags for that. Does anyone think
that is necessary?

A wireshark patch won't really be necessary since it will already
display the MCS as "15 (invalid)" in this case, which seems reasonable
though it could be changed to just "not known" instead.

johannes

^ permalink raw reply	[flat|nested] 3+ messages in thread

* Re: [RFC] VHT MU-MIMO correction
       [not found] ` <1445418906.4558.7.camel-cdvu00un1VgdHxzADdlk8Q@public.gmane.org>
@ 2015-12-04 10:48   ` Johannes Berg
       [not found]     ` <1449226120.2574.0.camel-cdvu00un1VgdHxzADdlk8Q@public.gmane.org>
  0 siblings, 1 reply; 3+ messages in thread
From: Johannes Berg @ 2015-12-04 10:48 UTC (permalink / raw)
  To: radiotap-S783fYmB3Ccdnm+yROfE0A

I guess this has passed a three-week minimum review time - bump, I'll
make those changes unless I hear objections within ~a week?

johannes

On Wed, 2015-10-21 at 11:15 +0200, Johannes Berg wrote:
> Hi,
> 
> As we're looking into MU-MIMO again, we found some issue with the way
> the VHT radiotap field is defined. The issue is the following: the VHT
> SIG-A field defines the NSTS (NSS) for each user, and it would be good
> to have that shown. However, radiotap ties the validity of the MCS to
> the existence of the NSS, which is incorrect.
> 
> Therefore, I suggest to make the following edit:
> 
> Change this language:
> 
>     If the NSS field for a user is zero, the user is not present and
>     the MCS and coding (in the coding field) associated with that user
>     are not valid. For SU PPDUs, only the first user will have a
>     nonzero NSS field.
> 
> To read:
> 
>     If the NSS field for a user is zero, the user is not present and
>     the MCS and coding (in the coding field) associated with that user
>     are not valid. If the NSS field for a user is non-zero, but the MCS
>     is not known (for example due to receiving only data for a single
>     user), the MCS shall be set to 15.
>     For SU PPDUs, only the first user will have a nonzero NSS field.
> 
> 
> The coding should be known for all, since it's also part of VHT-SIG-A,
> so I'm not suggesting to add validity flags for that. Does anyone think
> that is necessary?
> 
> A wireshark patch won't really be necessary since it will already
> display the MCS as "15 (invalid)" in this case, which seems reasonable
> though it could be changed to just "not known" instead.
> 
> johannes
> 

^ permalink raw reply	[flat|nested] 3+ messages in thread

* Re: [RFC] VHT MU-MIMO correction
       [not found]     ` <1449226120.2574.0.camel-cdvu00un1VgdHxzADdlk8Q@public.gmane.org>
@ 2016-01-20 12:44       ` Johannes Berg
  0 siblings, 0 replies; 3+ messages in thread
From: Johannes Berg @ 2016-01-20 12:44 UTC (permalink / raw)
  To: radiotap-S783fYmB3Ccdnm+yROfE0A

On Fri, 2015-12-04 at 11:48 +0100, Johannes Berg wrote:
> I guess this has passed a three-week minimum review time - bump, I'll
> make those changes unless I hear objections within ~a week?
> 

Quite late, but I've made those changes now.

johannes

^ permalink raw reply	[flat|nested] 3+ messages in thread

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Thread overview: 3+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2015-10-21  9:15 [RFC] VHT MU-MIMO correction Johannes Berg
     [not found] ` <1445418906.4558.7.camel-cdvu00un1VgdHxzADdlk8Q@public.gmane.org>
2015-12-04 10:48   ` Johannes Berg
     [not found]     ` <1449226120.2574.0.camel-cdvu00un1VgdHxzADdlk8Q@public.gmane.org>
2016-01-20 12:44       ` Johannes Berg

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