From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-lb0-x229.google.com (mail-lb0-x229.google.com [IPv6:2a00:1450:4010:c04::229]) (using TLSv1 with cipher RC4-SHA (128/128 bits)) (Client CN "smtp.gmail.com", Issuer "Google Internet Authority G2" (verified OK)) by huchra.bufferbloat.net (Postfix) with ESMTPS id AC66021F5E1 for ; Sat, 23 Aug 2014 16:49:29 -0700 (PDT) Received: by mail-lb0-f169.google.com with SMTP id s7so10868181lbd.0 for ; Sat, 23 Aug 2014 16:49:27 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20120113; h=subject:mime-version:content-type:from:in-reply-to:date:cc :content-transfer-encoding:message-id:references:to; bh=jLL0hONnjK44pq3R0EQejOjudhUSCHd+gPwWGrxeFV0=; b=04AoMX2xaANlTrOJZsR31+CBnfYx0X9ufLRo1URL/0RzAEIf9ig5u6OyUsS2UhsXw/ c5QMHblWieziQapI+1ePw2au0S9Ga+/aVtbKj0qsJlkTuejhdQjdb1hEqYTGKsA4/dZ0 HqstbK1XIuGowpEYIgOgyrFzPqwZiKBsTVSmgRjUN02qDWPLAVxrezP6unSPVu8ScUyi reL6I9bQUwqLxS8XTl6TwPwQECt4L4t/0+CEr4RDDFTnKX3Kj+b/YlZvDbUpp6hAkKpE cRVj7XkSUeJR0Qkto4sIVkNm1IuzGSW5gqfVe/DbraijMpppef/CX7BV8ZQJlC7YaCqq FOog== X-Received: by 10.112.138.102 with SMTP id qp6mr11640788lbb.60.1408837767239; Sat, 23 Aug 2014 16:49:27 -0700 (PDT) Received: from bass.home.chromatix.fi (178-55-89-211.bb.dnainternet.fi. [178.55.89.211]) by mx.google.com with ESMTPSA id o8sm1193328laf.44.2014.08.23.16.49.25 for (version=TLSv1 cipher=ECDHE-RSA-RC4-SHA bits=128/128); Sat, 23 Aug 2014 16:49:26 -0700 (PDT) Mime-Version: 1.0 (Apple Message framework v1085) Content-Type: text/plain; charset=windows-1252 From: Jonathan Morton In-Reply-To: <20140823234055.GA8622@sesse.net> Date: Sun, 24 Aug 2014 02:49:23 +0300 Content-Transfer-Encoding: quoted-printable Message-Id: <41D2E5CF-E01F-4001-9902-D4B3980F4F0B@gmail.com> References: <91696A3A-EF44-4A1A-8070-D3AF25D0D9AC@netapp.com> <64CD1035-2E14-4CA6-8E90-C892BAD48EC6@netapp.com> <4C1661D0-32C6-48E7-BAE6-60C98D7B2D69@ifi.uio.no> <8651E326-171F-472F-9456-920A9E43367D@gmail.com> <20140823234055.GA8622@sesse.net> To: "Steinar H. Gunderson" X-Mailer: Apple Mail (2.1085) Cc: bloat@lists.bufferbloat.net Subject: Re: [Bloat] sigcomm wifi X-BeenThere: bloat@lists.bufferbloat.net X-Mailman-Version: 2.1.13 Precedence: list List-Id: General list for discussing Bufferbloat List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Sat, 23 Aug 2014 23:49:30 -0000 On 24 Aug, 2014, at 2:40 am, Steinar H. Gunderson wrote: > On Sun, Aug 24, 2014 at 02:29:50AM +0300, Jonathan Morton wrote: >> Multi-target MIMO allows an AP to transmit to several clients >> simultaneously, without requiring the client to support MIMO = themselves. >> This requires the AP's antennas and radios to be dynamically = reconfigured >> for beamforming - giving each client a clear version of its own = signal and >> a null for the other signals - which is a tricky procedure. APs that = do >> implement this well are highly valuable in congested situations. >=20 > FWIW; I don't think you're right about the nulls. Beamforming has some = gain, > and there are some =93darker spots=94, but they're not what the = algorithm is > aiming for (it aims to maximize the signal at the client, not to = minimize it > at all other clients), and it's not -inf dB, more like -10 dB. That's true of plain beamforming, whose goal is to increase SNR to a = particular client. That's been around since 802.11g days. But that's = not what I'm talking about here. I'm talking specifically about 802.11ac multi-target MIMO, which *does* = attempt to null out the other clients to which it is simultaneously = transmitting, purely so that it *can* transmit to them simultaneously. = But that's only two or three other clients to form nulls for, not the = hundred others who are not involved in that particular timeslot. - Jonathan Morton