From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-oi0-x234.google.com (mail-oi0-x234.google.com [IPv6:2607:f8b0:4003:c06::234]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by lists.bufferbloat.net (Postfix) with ESMTPS id 9ABED3B25E; Mon, 27 Jun 2016 13:39:54 -0400 (EDT) Received: by mail-oi0-x234.google.com with SMTP id s66so210291511oif.1; Mon, 27 Jun 2016 10:39:54 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20120113; h=mime-version:in-reply-to:references:from:date:message-id:subject:to :cc:content-transfer-encoding; bh=Mn/YOXcEE8ojPlm25CTA0YlqE2Jv3i/IFeVpc59f4N0=; b=Z0YtEub1CGl0fG/2cZad2qMw3OYjwEGebEVl78tJZ+4e20lAG800adVFeLSZ3QGuA+ 0tVwA8G76qeGepm/bZUVUPjo0ig0T4nfLJ/q5T/9M1k33KQGt2mC+z1iFnKssttlf7RZ IAYA3u5vWc0fPiGViBSnQcTAelznxtF3RoZPT96CNaQjOF2c1usGeIkcaoSqgN6BEXiZ Th24+2qv6409eKRZtKA+qTySCW3Ec1ckvHVxTEpD/2H72f4TXgp9SLspPfP11ZhOFhlw THic7auM2ev2Czr9SsmWQrIkFgd8xo2ApS9sIU4tmWfGcYnWxTw3LuCzwLN0RfQW8fY0 Z8CQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20130820; h=x-gm-message-state:mime-version:in-reply-to:references:from:date :message-id:subject:to:cc:content-transfer-encoding; bh=Mn/YOXcEE8ojPlm25CTA0YlqE2Jv3i/IFeVpc59f4N0=; b=Y8mMHUFdE6/uIfeOvkBLNoQe107HcyTz1w7KEiBPeXWquxcwGRSk6iEt6nsIJslSmA a9PycB2sH7sXNHjYDS7EO3OV9g0MzkSd0bGC7N2b9rNvjuS2JkdCbGvMDRzzEOox2kvO oOvCd6LMp+/u5P4ReHhUqH4Cpm/P+JYrQyxXCWvRJ+tyW+u+PdUmVScBtyO/+1UlziUu LLpfLVflyUB/439/I2hRWTBj3sHBTM7KFKiJHzXF86r5PqFD8eYnqMXSa3OyTAAZgM8H RSVFrwddVN5XO+QMyxUV+6ZCL3jWnMzLzb8p7ELm3wf6p842nKwbh6wDF4A0XuPXxWaE gmTA== X-Gm-Message-State: ALyK8tJuw8yOOPQkR8RyXgl/sof4xBcrBhF86lOIa8WhbdP/Hr/IgCfDTsBv/EUOq+p3E2VL7WM7VVmhwdfrRQ== X-Received: by 10.202.197.79 with SMTP id v76mr1441466oif.193.1467049193901; Mon, 27 Jun 2016 10:39:53 -0700 (PDT) MIME-Version: 1.0 Received: by 10.202.54.85 with HTTP; Mon, 27 Jun 2016 10:39:34 -0700 (PDT) In-Reply-To: <69058459-83F9-4FFB-871A-B83A2194DB4F@gmx.de> References: <1466803464.927322699@mobile.rackspace.com> <2D664EFF-A25C-46FA-A8F9-46CD7B8C2ECE@gmx.de> <69058459-83F9-4FFB-871A-B83A2194DB4F@gmx.de> From: Jason Abele Date: Mon, 27 Jun 2016 10:39:34 -0700 Message-ID: To: moeller0 Cc: David Lang , make-wifi-fast@lists.bufferbloat.net, Bob McMahon , "cerowrt-devel@lists.bufferbloat.net" Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable 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 17:39:54 -0000 On Mon, Jun 27, 2016 at 2:43 AM, moeller0 wrote: > Hi David, > >> On Jun 27, 2016, at 09:44 , David Lang wrote: >> >> On Mon, 27 Jun 2016, Sebastian Moeller wrote: >> >>>> On a wireless network, with 'normal' omnidirctional antennas, the sign= al drops off with the square of the distance. So if you want to service cli= ents from 1 ft to 100 ft away, your signal strength varies by 1000 (4 order= s 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) >>>> >>>> The receiver first normalized the strongest part of the signal to a co= nstant value, and then digitizes the result, (usually with a 12-14 bit AD c= onverter). 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 p= rocessing isn't able to receive multiple stations at the same time. >>> >>> But, I you add 10 Bits to your AD converter you basically solved th= is. Now, most likely this also needs to be of higher quality and of low int= ernal 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 conv= erter. On the bright side, mass-producing that might lower the price for ni= ce oscilloscopes... >> >> well, TI only manufactures AD converters up to 16 bit at these speeds, s= o 24 bit converters are hardly something to just buy. They do make 24 and 3= 2 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 simulta= neously, so we would need something like a down-mixer and an ADC system wit= h around 2GHz bandwidth (due to Nyquist), I believe multiplexing multiple s= lower ADC=E2=80=99s as done in better oscilloscopes might work, but that wi= ll not help reduce the price not solve the bit resolution question. > The reason you can not just add bits to the ADC is the thermal noise floor: https://en.wikipedia.org/wiki/Johnson%E2%80%93Nyquist_noise#Noise_po= wer_in_decibels If you assume a maximum transmit power of ~20dBm (100mW) and a 160MHz channel bandwidth (with a consequent thermal noise floor of -92 dBm), the total possible dynamic range is ~112dB, if you receiver and transmitter a coupled with no loss. At ~6dB/bit in the ADC, anything beyond 19bits is just quantizing noise and wasting power (which is heat, which raises your local thermal noise floor, etc). If your channel bandwidth is 1GHz, the effective noise floor rises by another ~2bits, so ~17bits of dynamic range max, before accounting for path loss and distortion. Speaking of distortion, look at the intermod (IP3) or harmonic distortion figures for those wideband ADC sometime, if the signals of interest are of widely varying amplitudes in narrower bandwidths, the performance limit will usually be distortion from the strongest signal, not the thermal noise floor. This usually limits dynamic range to less than 10 effective bits. Also transmitters are usually only required to suppress their adjacent channel noise to around -50dB below the transmit power, so a little over 8bits of dynamic range before the ADC is quantizing an interferer rather than the signal of interest. I am surprised that 802.11 still uses the same spreading code for all stations. I am no expert on cellular CDMA deployments, but I think they have been using different spreading codes for each station to increase capacity and improve the ability to mathematically remove the interference of other physically close stations for decades. As complex as the 802.11 MAC is becoming, I do not understand why an approach like MU-MIMO was chosen over negotiating a separate spreading code per station. My best guess is that it keeps the complexity (and therefore power) at the AP rather than in the (increasingly mobile, power-constrained) station. Hopefully the rise of mesh / peer-to-peer networks in mobile stations will apply the right engineering pressure to re-think the idea of keeping all complexity in the AP. Cheers, Jason