From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from smtp105.iad3a.emailsrvr.com (smtp105.iad3a.emailsrvr.com [173.203.187.105]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (Client did not present a certificate) by huchra.bufferbloat.net (Postfix) with ESMTPS id 406CD21F4E4 for ; Thu, 18 Sep 2014 17:18:18 -0700 (PDT) Received: from localhost (localhost.localdomain [127.0.0.1]) by smtp30.relay.iad3a.emailsrvr.com (SMTP Server) with ESMTP id 4FCEE3803E2; Thu, 18 Sep 2014 20:18:17 -0400 (EDT) X-Virus-Scanned: OK Received: from app13.wa-webapps.iad3a (relay-webapps.rsapps.net [172.27.255.140]) by smtp30.relay.iad3a.emailsrvr.com (SMTP Server) with ESMTP id 24F57380437; Thu, 18 Sep 2014 20:18:17 -0400 (EDT) X-Sender-Id: MAILER-DAEMON Received: from app13.wa-webapps.iad3a (relay-webapps.rsapps.net [172.27.255.140]) by 0.0.0.0:25 (trex/5.2.10); Fri, 19 Sep 2014 00:18:17 GMT Received: from reed.com (localhost.localdomain [127.0.0.1]) by app13.wa-webapps.iad3a (Postfix) with ESMTP id 11DE238005D; Thu, 18 Sep 2014 20:18:17 -0400 (EDT) Received: by apps.rackspace.com (Authenticated sender: dpreed@reed.com, from: dpreed@reed.com) with HTTP; Thu, 18 Sep 2014 20:18:17 -0400 (EDT) Date: Thu, 18 Sep 2014 20:18:17 -0400 (EDT) From: dpreed@reed.com To: "David Lang" MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_20140918201817000000_81590" Importance: Normal X-Priority: 3 (Normal) X-Type: html In-Reply-To: References: Message-ID: <1411085897.071719971@apps.rackspace.com> X-Mailer: webmail7.0 Cc: "cerowrt-devel@lists.bufferbloat.net" Subject: Re: [Cerowrt-devel] =?utf-8?q?full_duplex_wifi=3F?= X-BeenThere: cerowrt-devel@lists.bufferbloat.net X-Mailman-Version: 2.1.13 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: Fri, 19 Sep 2014 00:18:47 -0000 ------=_20140918201817000000_81590 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable =0AThis is not completely crazy. A couple of grad students and I demonstra= ted this type of thing with USRP's in my lab at MIT. The problem you, David= Lang, refer to is basically the key thing to deal with, but the physics an= d information theory issues can be dealt with.=0A =0AThere's significant wo= rk in the RADAR (not radio) field that bears on the design of this. I am s= ure there is more of that that is currently classified.=0A =0AThere are a l= ot of practical design issues in the front-end and the waveform design to b= e able to do this sort of thing well - especially in the field rather than = the lab. Your receive antenna will receive echoes of your own transmissio= n that have to be separated from your signal and the source you are listeni= ng to.=0A =0ASince this is full-duplex, there are only two signals involved= and each knows its own signal's waveform pretty precisely - you can even a= ttenuate the antenna output to get a precise measure of your signal.=0A =0A= So I think in a few years this might be practical - but a protocol to explo= it this capability optimally would be complicated because of the need to co= mpensate for the propagation environment effects.=0A=0AOn Tuesday, Septembe= r 16, 2014 11:08pm, "David Lang" said:=0A=0A=0A=0A> On Tue,= 16 Sep 2014, David Lang wrote:=0A> =0A> > On Tue, 16 Sep 2014, Dave Taht w= rote:=0A> >=0A> >> It would be very nice to get some TXOPs back:=0A> >>=0A>= >> Is this crazy or not?=0A> >>=0A> >> http://web.stanford.edu/~skatti/pub= s/sigcomm13-fullduplex.pdf=0A> >=0A> > I start of _extremely_ skeptical of = the idea. While it would be a=0A> > revolutionary improvement if it can wor= k, there are some very basic points of=0A> > physics that make this very ha= rd to achieve.=0A> >=0A> > If they can do it, they double the capacity of e= xisting wireless systems,=0A> > which helps, but it's not really that much = (the multipath directed=0A> > beamforming helps more)=0A> >=0A> > I'll read= though the paper and comment more later.=0A> =0A> Ok, they are working on = exacty the problem I described. They do a significant=0A> amount of the wor= k in digital, which is probably why they get an 87% improvement=0A> instead= of a 2x improvement. This also will eat a fair bit of the DSP processing= =0A> capacity.=0A> =0A> As they note, this only works with single antenna s= ystems. They list support for=0A> multi-antenna systems as future work, and= that's going to be quite a bit of work=0A> (not impossible, but very hard)= =0A> =0A> This will be a great thing for point-to-point infrastructure type= links, but=0A> isn't that useful for more 'normal' situations (let alone h= igh density=0A> environments)=0A> =0A> MIMO multi-destination can provide a= s much or more airtime saving when you=0A> actually have multiple places to= send the data=0A> =0A> think of it as the core frequency vs core count typ= e of tradeoff.=0A> =0A> David Lang=0A> =0A> >=0A> > warning, radio primer b= elow=0A> >=0A> > the strength of a radio signal drops off FAST ( distance^3= in the worst case,=0A> > but close to distance^2 if you have pretty good a= ntennas)=0A> >=0A> > you loose a lot of signal in the transition from the a= ntenna wire to the air=0A> > and from the air to the antenna wire.=0A> >=0A= > > The result of this is that your inbound signal is incredibly tiny compa= red to=0A> > your outbound signal.=0A> >=0A> > In practice, this is dealt w= ith by putting a very high power amplifier on the=0A> > inbound signal to m= ake it large enough for our electronics to deal with. to=0A> > do this effe= ctively for signals that vary wildly in strength, this amplifier=0A> > is v= ariable, and amplifies all the signals that it gets until the strongest=0A>= > one is at the limits of the amplifier's output.=0A> >=0A> > Because of t= his, a receiver without a good input filter can get into a=0A> > situation = where it cannot recive it's desired signal because some other=0A> > signal = somewhat near the signal it wants is strong enough to cause problems.=0A> >= =0A> > digital signal processing is no help here. If you digitize the signa= l (let's=0A> > talk 8 bits for the moment, although 12-14 bits is more comm= on in the real=0A> > world), and you have one signal that's 100 times as st= rong as the other=0A> > (which could be that one is 10 ft away and the othe= r 100 ft away), the near=0A> > signal is producing samples of 0-255, while = the far signal is producing=0A> > samples 0-2. there's not much you can do = to get good fidelity when your only=0A> > hvae 3 possible values for your d= ata.=0A> >=0A> > Real radios deal with this by having analog filters to cut= out the strong=0A> > signal so that they can amplify the weak signal more = before it hits the=0A> > digital section.=0A> >=0A> > But if we are trying = to transmit and receive at the same time, on the same=0A> > channel, then w= e are back to the problem of the transmit vs receive power.=0A> >=0A> > Tak= ing a sample radio, the Baofeng uv-5r handheld (because I happen to have=0A= > > it's stats handy)=0A> >=0A> > on transmit, it is producing 5w into a 50= ohm load, or ~15v (v=3Dsqrt(P*R)),=0A> > while it is setup to receive signa= ls of 0.2u volt.=0A> >=0A> > being able to cancel the transmitting signal p= erfectly enough to be able to=0A> > transmit and at the same time receive a= weak signal on a nearby frequency=0A> > with the same antenna is a HARD th= ing to do, and the tools to do so tend to=0A> > be very finicky (read tempe= rature sensitive)=0A> >=0A> > David Lang=0A> > ____________________________= ___________________=0A> > Cerowrt-devel mailing list=0A> > Cerowrt-devel@li= sts.bufferbloat.net=0A> > https://lists.bufferbloat.net/listinfo/cerowrt-de= vel=0A> >=0A> _______________________________________________=0A> Cerowrt-d= evel mailing list=0A> Cerowrt-devel@lists.bufferbloat.net=0A> https://lists= .bufferbloat.net/listinfo/cerowrt-devel=0A> ------=_20140918201817000000_81590 Content-Type: text/html; charset="UTF-8" Content-Transfer-Encoding: quoted-printable

This is not completely cra= zy.  A couple of grad students and I demonstrated this type of thing w= ith USRP's in my lab at MIT. The problem you, David Lang, refer to is basic= ally the key thing to deal with, but the physics and information theory iss= ues can be dealt with.

=0A

 

=0A

There's significant work in the RADAR (not radio) field that bears on the = design of this.  I am sure there is more of that that is currently cla= ssified.

=0A

 

=0A

There are a l= ot of practical design issues in the front-end and the waveform design to b= e able to do this sort of thing well - especially in the field rather than = the lab.   Your receive antenna will receive echoes of your own transm= ission that have to be separated from your signal and the source you are li= stening to.

=0A

 

=0A

Since this= is full-duplex, there are only two signals involved and each knows its own= signal's waveform pretty precisely - you can even attenuate the antenna ou= tput to get a precise measure of your signal.

=0A

 =

=0A

So I think in a few years this might be practical -= but a protocol to exploit this capability optimally would be complicated b= ecause of the need to compensate for the propagation environment effects.=0A


On Tuesday, September 16, 2014 11:08pm, "David = Lang" <david@lang.hm> said:

=0A
=0A

> On Tue, 16 Sep 2014, David Lang wrote:>
> > On Tue, 16 Sep 2014, Dave Taht wrote:
> &g= t;
> >> It would be very nice to get some TXOPs back:
&g= t; >>
> >> Is this crazy or not?
> >>
> >> http://web.stanford.edu/~skatti/pubs/sigcomm13-fullduplex.p= df
> >
> > I start of _extremely_ skeptical of the id= ea. While it would be a
> > revolutionary improvement if it can = work, there are some very basic points of
> > physics that make = this very hard to achieve.
> >
> > If they can do it,= they double the capacity of existing wireless systems,
> > whic= h helps, but it's not really that much (the multipath directed
> &g= t; beamforming helps more)
> >
> > I'll read though t= he paper and comment more later.
>
> Ok, they are working = on exacty the problem I described. They do a significant
> amount o= f the work in digital, which is probably why they get an 87% improvement> instead of a 2x improvement. This also will eat a fair bit of the D= SP processing
> capacity.
>
> As they note, this o= nly works with single antenna systems. They list support for
> mult= i-antenna systems as future work, and that's going to be quite a bit of wor= k
> (not impossible, but very hard)
>
> This will = be a great thing for point-to-point infrastructure type links, but
>= ; isn't that useful for more 'normal' situations (let alone high density> environments)
>
> MIMO multi-destination can provi= de as much or more airtime saving when you
> actually have multiple= places to send the data
>
> think of it as the core frequ= ency vs core count type of tradeoff.
>
> David Lang
&= gt;
> >
> > warning, radio primer below
> &g= t;
> > the strength of a radio signal drops off FAST ( distance^= 3 in the worst case,
> > but close to distance^2 if you have pre= tty good antennas)
> >
> > you loose a lot of signal = in the transition from the antenna wire to the air
> > and from = the air to the antenna wire.
> >
> > The result of th= is is that your inbound signal is incredibly tiny compared to
> >= ; your outbound signal.
> >
> > In practice, this is = dealt with by putting a very high power amplifier on the
> > inb= ound signal to make it large enough for our electronics to deal with. to> > do this effectively for signals that vary wildly in strength, = this amplifier
> > is variable, and amplifies all the signals th= at it gets until the strongest
> > one is at the limits of the a= mplifier's output.
> >
> > Because of this, a receive= r without a good input filter can get into a
> > situation where= it cannot recive it's desired signal because some other
> > sig= nal somewhat near the signal it wants is strong enough to cause problems.> >
> > digital signal processing is no help here. If = you digitize the signal (let's
> > talk 8 bits for the moment, a= lthough 12-14 bits is more common in the real
> > world), and yo= u have one signal that's 100 times as strong as the other
> > (w= hich could be that one is 10 ft away and the other 100 ft away), the near> > signal is producing samples of 0-255, while the far signal is= producing
> > samples 0-2. there's not much you can do to get g= ood fidelity when your only
> > hvae 3 possible values for your = data.
> >
> > Real radios deal with this by having an= alog filters to cut out the strong
> > signal so that they can a= mplify the weak signal more before it hits the
> > digital secti= on.
> >
> > But if we are trying to transmit and rece= ive at the same time, on the same
> > channel, then we are back = to the problem of the transmit vs receive power.
> >
> &= gt; Taking a sample radio, the Baofeng uv-5r handheld (because I happen to = have
> > it's stats handy)
> >
> > on tran= smit, it is producing 5w into a 50ohm load, or ~15v (v=3Dsqrt(P*R)),
&= gt; > while it is setup to receive signals of 0.2u volt.
> ><= br />> > being able to cancel the transmitting signal perfectly enoug= h to be able to
> > transmit and at the same time receive a weak= signal on a nearby frequency
> > with the same antenna is a HAR= D thing to do, and the tools to do so tend to
> > be very finick= y (read temperature sensitive)
> >
> > David Lang
> > _______________________________________________
> > = Cerowrt-devel mailing list
> > Cerowrt-devel@lists.bufferbloat.n= et
> > https://lists.bufferbloat.net/listinfo/cerowrt-devel
> >
> _______________________________________________
&= gt; Cerowrt-devel mailing list
> Cerowrt-devel@lists.bufferbloat.ne= t
> https://lists.bufferbloat.net/listinfo/cerowrt-devel
> =

=0A
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