From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from smtp73.iad3a.emailsrvr.com (smtp73.iad3a.emailsrvr.com [173.203.187.73]) (using TLSv1 with cipher ADH-AES256-SHA (256/256 bits)) (No client certificate requested) by lists.bufferbloat.net (Postfix) with ESMTPS id 254E03B2C6 for ; Thu, 23 Jun 2016 17:08:51 -0400 (EDT) Received: from smtp18.relay.iad3a.emailsrvr.com (localhost.localdomain [127.0.0.1]) by smtp18.relay.iad3a.emailsrvr.com (SMTP Server) with ESMTP id D7A4B28032A; Thu, 23 Jun 2016 17:08:50 -0400 (EDT) Received: from app26.wa-webapps.iad3a (relay-webapps.rsapps.net [172.27.255.140]) by smtp18.relay.iad3a.emailsrvr.com (SMTP Server) with ESMTP id C2D572802E0; Thu, 23 Jun 2016 17:08:50 -0400 (EDT) X-Sender-Id: dpreed@reed.com Received: from app26.wa-webapps.iad3a (relay-webapps.rsapps.net [172.27.255.140]) by 0.0.0.0:25 (trex/5.5.4); Thu, 23 Jun 2016 17:08:51 -0400 Received: from reed.com (localhost [127.0.0.1]) by app26.wa-webapps.iad3a (Postfix) with ESMTP id B25BAE12F5; Thu, 23 Jun 2016 17:08:50 -0400 (EDT) Received: by apps.rackspace.com (Authenticated sender: dpreed@reed.com, from: dpreed@reed.com) with HTTP; Thu, 23 Jun 2016 17:08:50 -0400 (EDT) Date: Thu, 23 Jun 2016 17:08:50 -0400 (EDT) From: dpreed@reed.com To: "David Lang" Cc: "Bob McMahon" , make-wifi-fast@lists.bufferbloat.net, "cerowrt-devel@lists.bufferbloat.net" MIME-Version: 1.0 Content-Type: text/plain;charset=UTF-8 Content-Transfer-Encoding: quoted-printable Importance: Normal X-Priority: 3 (Normal) X-Type: plain In-Reply-To: References: <1466714880.88621749@apps.rackspace.com> X-Auth-ID: dpreed@reed.com Message-ID: <1466716130.728219772@apps.rackspace.com> X-Mailer: webmail/12.5.1-RC Subject: Re: [Cerowrt-devel] [Make-wifi-fast] more well funded attempts showing market demand for better wifi X-BeenThere: cerowrt-devel@lists.bufferbloat.net X-Mailman-Version: 2.1.20 Precedence: list List-Id: Development issues regarding the cerowrt test router project List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Thu, 23 Jun 2016 21:08:51 -0000 =0A=0A=0A=0AOn Thursday, June 23, 2016 4:52pm, "David Lang" = said:=0A=0A> On Thu, 23 Jun 2016, dpreed@reed.com wrote:=0A> =0A>> The act= ual issues of transmitting on multiple channels at the same time are=0A>> q= uite minor if you do the work in the digital domain (pre-DAC). You just ne= ed=0A>> a higher sampling rate in the DAC and add the two signals together = (and use a=0A>> wideband filter that covers all the channels). No RF probl= em.=0A> =0A> that works if you are using channels that are close together, = and is how the=0A> current standard wide channels in N and AC work.=0A> =0A= > If you try to use channels that aren't adjacent, this is much harder to d= o.=0A>=0AThe whole 5 GHz U-NII band is not that wide. It's easy to find DA= Cs that run at 1 Gsps or better. On transmission you don't need to filter t= he bands where you put no energy in the middle (or not much).=0A =0A> Remem= ber that the current adjacent channel use goes up to 160MHz wide, going=0A>= wider than that starts getting hard.=0A> =0A>> Receiving multiple transmis= sions in different channels is pretty much the same=0A>> problem - just dig= itize (ADC) a wider bandwidth and separate in the digital=0A>> domain. the= only real issue on receive is equalization - if you receive two=0A>> diffe= rent signals at different receive signal strengths, the lower strength=0A>>= signal won't get as much dynamic range in its samples.=0A>>=0A>> But in a = LAN setup, the variability in signal strength is likely small enough=0A>> t= hat you can cover that with more ADC bits (or have the MAC protocol manage= =0A>> the station transmit power so that signals received at the AP are nea= rly the=0A>> same power.=0A>>=0A>> Equalization at transmit works very well= when there is a central AP (as in=0A>> cellular or normal WiFi systems).= =0A> =0A> define 'normal WiFi system'=0AOnes based on access points. In gen= eral, in typical WiFi deployments one prefers to make smaller cells so that= the signal level variation between "near" and "far" signals is modest, whi= ch makes equalization much easier or even optional. If there is a large var= iation of power received at the access point then CSMA is hard to achieve, = and the far stations have to run at slow rates, occupying more than their f= air share of airtime.=0A(a non-normal system would be a peer-to-peer mesh o= ver a wide enough area that you end up with "hidden terminal" issues all ov= er the place)=0A> =0A> It's getting very common for even moderate size hous= es to need more than one AP=0A> to cover the entire house.=0A> =0AAgree. No= question about that.