From mboxrd@z Thu Jan 1 00:00:00 1970 From: Johannes Berg Subject: Re: [RFC] VHT MU-MIMO correction Date: Fri, 04 Dec 2015 11:48:40 +0100 Message-ID: <1449226120.2574.0.camel@sipsolutions.net> References: <1445418906.4558.7.camel@sipsolutions.net> Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable Return-path: In-Reply-To: <1445418906.4558.7.camel-cdvu00un1VgdHxzADdlk8Q@public.gmane.org> Sender: radiotap-owner-sUITvd46vNxg9hUCZPvPmw@public.gmane.org To: radiotap-S783fYmB3Ccdnm+yROfE0A@public.gmane.org List-Id: radiotap@radiotap.org 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, >=20 > 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. >=20 > Therefore, I suggest to make the following edit: >=20 > Change this language: >=20 > =C2=A0=C2=A0=C2=A0=C2=A0If the NSS field for a user is zero, the user i= s not present and > =C2=A0=C2=A0=C2=A0=C2=A0the MCS and coding (in the coding field) associ= ated with that user > =C2=A0=C2=A0=C2=A0=C2=A0are not valid. For SU PPDUs, only the first use= r will have a > =C2=A0=C2=A0=C2=A0=C2=A0nonzero NSS field. >=20 > To read: >=20 > =C2=A0=C2=A0=C2=A0=C2=A0If the NSS field for a user is zero, the user i= s not present and > =C2=A0=C2=A0=C2=A0=C2=A0the MCS and coding (in the coding field) associ= ated with that user > =C2=A0=C2=A0=C2=A0=C2=A0are not valid. If the NSS field for a user is n= on-zero, but the MCS > =C2=A0=C2=A0=C2=A0=C2=A0is not known (for example due to receiving only= data for a single > =C2=A0=C2=A0=C2=A0=C2=A0user), the MCS shall be set to 15. > =C2=A0=C2=A0=C2=A0=C2=A0For SU PPDUs, only the first user will have a n= onzero NSS field. >=20 >=20 > 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? >=20 > 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. >=20 > johannes >=20