From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from cassarossa.samfundet.no (cassarossa.samfundet.no [IPv6:2001:67c:29f4::29]) (using TLSv1 with cipher DHE-RSA-AES128-SHA (128/128 bits)) (Client did not present a certificate) by huchra.bufferbloat.net (Postfix) with ESMTPS id 6FA5221F5D9 for ; Sat, 23 Aug 2014 16:41:00 -0700 (PDT) Received: from pannekake.samfundet.no ([2001:67c:29f4::50] ident=unknown) by cassarossa.samfundet.no with esmtps (TLS1.2:DHE_RSA_AES_128_CBC_SHA1:128) (Exim 4.80) (envelope-from ) id 1XLKvY-0004cf-1z for bloat@lists.bufferbloat.net; Sun, 24 Aug 2014 01:40:56 +0200 Received: from sesse by pannekake.samfundet.no with local (Exim 4.80) (envelope-from ) id 1XLKvX-0003NA-M4 for bloat@lists.bufferbloat.net; Sun, 24 Aug 2014 01:40:55 +0200 Date: Sun, 24 Aug 2014 01:40:55 +0200 From: "Steinar H. Gunderson" To: bloat@lists.bufferbloat.net Message-ID: <20140823234055.GA8622@sesse.net> 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> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <8651E326-171F-472F-9456-920A9E43367D@gmail.com> X-Operating-System: Linux 3.16.0-rc5 on a x86_64 User-Agent: Mutt/1.5.21 (2010-09-15) 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 23:41:00 -0000 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. FWIW; I don't think you're right about the nulls. Beamforming has some gain, and there are some “darker spots”, 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. See in particular http://apenwarr.ca/log/?m=201408#01 and play around with the applet. /* Steinar */ -- Homepage: http://www.sesse.net/