From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mout.gmx.net (mout.gmx.net [212.227.15.15]) (using TLSv1.2 with cipher DHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by lists.bufferbloat.net (Postfix) with ESMTPS id 6BBE63B2B3; Mon, 27 Jun 2016 05:44:09 -0400 (EDT) Received: from [172.17.3.79] ([134.76.241.253]) by mail.gmx.com (mrgmx003) with ESMTPSA (Nemesis) id 0Lmqxo-1bpPql1AUu-00h36a; Mon, 27 Jun 2016 11:43:59 +0200 Content-Type: text/plain; charset=utf-8 Mime-Version: 1.0 (Mac OS X Mail 8.2 \(2104\)) From: moeller0 In-Reply-To: Date: Mon, 27 Jun 2016 11:43:55 +0200 Cc: Bob McMahon , make-wifi-fast@lists.bufferbloat.net, "cerowrt-devel@lists.bufferbloat.net" Content-Transfer-Encoding: quoted-printable Message-Id: <69058459-83F9-4FFB-871A-B83A2194DB4F@gmx.de> References: <1466803464.927322699@mobile.rackspace.com> <2D664EFF-A25C-46FA-A8F9-46CD7B8C2ECE@gmx.de> To: David Lang X-Mailer: Apple Mail (2.2104) X-Provags-ID: V03:K0:mMohHS50eHFyurDiX+Y3bUNybBQNHgeFxG4DLC5hHA8kysm/MSn wrGKE9I0bXtt5rgQ8Q+XWtnKQZekkS7DhYPh1+doJZqD+thtN+Pd8WlasFALtKKLB1X3aCg uyTsp32ASUXWCTXCG9bW1MvZ9kl33+z2lZFz0/ajMVyI5MnfKbYvoipceCNAaovUzZCCj7R FB4qCh9tLlaSl6l69gxrw== X-UI-Out-Filterresults: notjunk:1;V01:K0:x75kjxirktQ=:Zc+YFQGmpcFdrerwsW1phY 8GdcezVv7zMpdr16Ibssw4aMfHlX+nnziyswJqUWxfkDdBidrX37pQ6zw9WQG1+3MuvXWlFxC ncyc1KwSS3/GD988O7+9d1qfb2VNxPThyX/ucN0MZt6wx6NrA0Yq+quxozGDJ5VgKh2tZxAKa AimIaXw+9XXMGT+v/PQLcyawHwStfC7MP0eJHBq+U9qvzkR+Jn/YOoBxWUTLzLEG9rOiYdpAe td3RTLCpmFueCkl+lE//GMdv8K5CgXCprIswxjjUZlVulS+PIdwN4GhGx4Kfkp8has1Xb/YDg Lll9LOu9Rmm8k92l1LoOSGfnZNRwuKu6D/ySxT27dYgANe0d7f/G8tYf3UkUiLXPPHQWGTfd3 siPUG2M2sooKxvb53yB5pfdY9Q6MvL3cQeQHL8cyOm+BNduegPyCykmryRikD5y12G1TPB/zV ld/runDQrE80XXO6jyvcP/De9r4QEIVpEkuNFo62BT0FGtU8EAk1YWDpg7lv3Zal8bpDuZDgN 1RrClurhMC3WvXNT4K58p5KKNqMtwPGonoeFX++Uec5FbMzTF3a1JB0Lub34FhdWmzeicMYCp VkG9s5atA2AS16KG5Ig6k1I+iJDDM03i/JtF2oMcDBWpLR/EWaBYpQ/XRWykpWpxbM81we/we qOmCzbz+Y1vTyjQ8ltX3ySbvcSh98vehaO7NFTxvOQG29KNrfwGRFfckkNW/VeFh2qTRpG9oX gtpVxcALUzSGYPYf6EigmC/XYSJdYxXX9hoIfwmD4wUuYQYmPynSopX+Af9vwaLuW25p/Mp1Q PMs3Fyw Subject: Re: [Make-wifi-fast] [Cerowrt-devel] more well funded attempts showing market demandfor better wifi X-BeenThere: make-wifi-fast@lists.bufferbloat.net X-Mailman-Version: 2.1.20 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Mon, 27 Jun 2016 09:44:09 -0000 Hi David, > On Jun 27, 2016, at 09:44 , David Lang wrote: >=20 > On Mon, 27 Jun 2016, Sebastian Moeller wrote: >=20 >>> On a wireless network, with 'normal' omnidirctional antennas, the = signal drops off with the square of the distance. So if you want to = service clients from 1 ft to 100 ft away, your signal strength varies by = 1000 (4 orders of magnatude), this is before you include effects of = shielding, bounces, bad antenna alignment, etc (which can add several = more orders of magnatude of variation) >>>=20 >>> The receiver first normalized the strongest part of the signal to a = constant value, and then digitizes the result, (usually with a 12-14 bit = AD converter). Since 1000x is ~10 bits, the result of overlapping = tranmissions can be one signal at 14 bits, and another at <4 bits. This = is why digital processing isn't able to receive multiple stations at the = same time. >>=20 >> But, I you add 10 Bits to your AD converter you basically solved = this. Now, most likely this also needs to be of higher quality and of = low internal noise, so probably expensive... Add to this the wide-band = requirement of the sample the full band approach and we are looking at a = price ad converter. On the bright side, mass-producing that might lower = the price for nice oscilloscopes... >=20 > well, TI only manufactures AD converters up to 16 bit at these speeds, = so 24 bit converters are hardly something to just buy. They do make 24 = and 32 bit ADCs, but only ones that could be used for signals <5MHz wide = (and we are pushing to 160 MHz wide channels on wifi) But David=E2=80=99s idea was to sample the full 5GHz band = simultaneously, so we would need something like a down-mixer and an ADC = system with around 2GHz bandwidth (due to Nyquist), I believe = multiplexing multiple slower ADC=E2=80=99s as done in better = oscilloscopes might work, but that will not help reduce the price not = solve the bit resolution question. >=20 > also note my comment about walls/etc providing shielding that can add = a few more orders of magnatude on the signals. Well, yes, but in the end the normalizing amplifier really can = be considered a range adjustor that makes up for the ADC=E2=80=99s lack = of dynamik resolution. I would venture the guess not having to normalize = might allow speed up the =E2=80=9Cwifi pre-amble=E2=80=9D since one = amplifier less to stabilize=E2=80=A6 >=20 > And then when you start being able to detect signals at that level, = the first ones you are going to hit are bounces from your strongest = signal off of all sorts of things. But that is independent of whether you sample to whole 5GHz = range in one go or not? I would guess as long as the ADC/amplifier does = not go into saturation both should perform similarly. >=20 > You will also find that noise and distortion in the legitimate strong = signal is going to be at strengths close to the strength of the weak = signal you are trying to hear. But if that noise and distortion appear in the weak signals = frequency band we have issues already today? >=20 > As I said, I see things getting better, but it=E2=80=99s going to be a = very hard thing to do, and I'd expect to see reverse mu-mimo (similarly = strong signals from several directions) long before the ability to = detect wildly weaker signals. You are probably right. >=20 > I also expect that as the ability to more accurately digitize the = signal grows, we will first take advantage of it for higher speeds. Yes, but higher speed currently means mostly wider bands, and = the full 4-5GHz range is sort of the logical end-point ;). Best Regards Sebastian >=20 > David Lang