From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-ed1-x52b.google.com (mail-ed1-x52b.google.com [IPv6:2a00:1450:4864:20::52b]) (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 056BF3B29E for ; Mon, 27 Aug 2018 03:06:15 -0400 (EDT) Received: by mail-ed1-x52b.google.com with SMTP id s10-v6so9668930edb.11 for ; Mon, 27 Aug 2018 00:06:14 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=broadcom.com; s=google; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=dLltkEIDn2iM0dAIh3X2Hx7nQNmThJTj7lIOLrU0ZMI=; b=BWZs6e/lujIKHr1ZCCAEoPJWYpY5ZRDeQJJVR8BhihSeehzUtCn6SLn/aetdCOK6+V B+xEf71LInkQhju6iCvdfuwZET+jrw7Tnuud3oJttn/JALcxC1XAb+KDUzafRE6NRANB dlJCuaCk9+OfdZZ1Fgz9Mo1eL2Q+0r6yqHzyo= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=dLltkEIDn2iM0dAIh3X2Hx7nQNmThJTj7lIOLrU0ZMI=; b=CJno5z0OlptWV/00EhDnzRdX1yThRONKBGL5MHb6UScNJXXdtBPAvZ8DkjhC42VTYA pME8x3Nxv6dCz+WzA+CjlKykwckohfh3qTeCPU1JHoqtpm/ZFS2KiB4YBlGhQlBi1qG+ njZpP1sV/v4yjWu4G1mV9jTlDOdYRZpcHLWxdp3dkf+vvkELltFRhe+mE1XKgPNo98v2 RzsuznfLFt32z7TtTZO+KoxzHWwv1i1pdGaJ5pP0qo+wwTyr4ePdNxSTeabPRKd+yBwS p7gSINUWOo+W8xdYfEdDpReDahXwmAQzzNIlYhKndv26V36g6bjavkBtg6gHA9kPB5Ax XJJg== X-Gm-Message-State: APzg51BWc0FTBlitd1rP8w5dIjKLHrJj3h7XEvfRtwpu5l36/df3aX78 wJlERpwaRVOLCf6KVYBIDY3URodi0Axs/gJ2LSfzHg== X-Google-Smtp-Source: ANB0VdZEA7CUHbQqkJAO8CVudAcTorl4VtYEZR8Y8u81HH2Z8jooB28uJhYun3p7Xb9/akbr87LvWmXlca39A6ha1aM= X-Received: by 2002:aa7:c699:: with SMTP id n25-v6mr14348768edq.302.1535353573748; Mon, 27 Aug 2018 00:06:13 -0700 (PDT) MIME-Version: 1.0 References: <1535286372.35121837@apps.rackspace.com> <2282D31E-CBEF-4B42-A6A6-4D6394EE0DF7@gmail.com> In-Reply-To: <2282D31E-CBEF-4B42-A6A6-4D6394EE0DF7@gmail.com> From: Bob McMahon Date: Mon, 27 Aug 2018 00:06:02 -0700 Message-ID: To: chromatix99@gmail.com Cc: dpreed@deepplum.com, bloat-announce@lists.bufferbloat.net, Make-Wifi-fast , cerowrt-devel@lists.bufferbloat.net, bloat Content-Type: multipart/alternative; boundary="0000000000005e5d470574655ca9" Subject: Re: [Bloat] [Make-wifi-fast] [Cerowrt-devel] closing up my make-wifi-fast lab X-BeenThere: bloat@lists.bufferbloat.net X-Mailman-Version: 2.1.20 Precedence: list List-Id: General list for discussing Bufferbloat List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Mon, 27 Aug 2018 07:06:15 -0000 --0000000000005e5d470574655ca9 Content-Type: text/plain; charset="UTF-8" hmm, "going back" to TDM, doesn't that lose the benefits and efficiencies per statistical multiplexing? How can a centralized device predict the many "end stations'" network demand in its time scheduling? Note: I think with 802.11ax this is happening to some extent per uplink OFDMA but that requires both time scheduling and transmit power setting so the AP receives the "simultaneous signals" with similar SINRs. This is supposed to help with LBT but not really completely solve it. Curious if eliminating LBT is possible per a distributed solution (with partial network awareness) vs having a centralized scheduler (with "full" network awareness)? Bob On Sun, Aug 26, 2018 at 11:26 PM Jonathan Morton wrote: > > On 27 Aug, 2018, at 9:00 am, Bob McMahon > wrote: > > > > Curious to how LBT can be solved at the PHY level and if the potential > solution sets preserve the end to end principle. > > The usual alternatives include TDM, usually coordinated by a master device > (eg. the AP); full-duplex operation via diplexers and/or orthogonal coding; > and simply firing off a packet and retrying with exponential backoff if an > acknowledgement is not heard. > > TDM and diplexing are already used by both DOCSIS and LTE. They are > proven technology. However, in DOCSIS the diplexing is greatly simplified > by the use of a copper channel rather than airwaves, and in LTE the > diplexer is fitted only at the tower, not in each client - so the tower can > transmit and receive simultaneously, but an individual client cannot, but > this is still useful because there are many clients per tower. Effective > diplexers for wireless are expensive. > > Orthogonal coding is already used by GPS and, in a rather esoteric form, > by MIMO-grade wifi. IMHO it works rather better in GPS than in wifi. In > GPS, it allows all of the satellites in the constellation to transmit on > the standard frequency simultaneously, while still being individually > distinguishable. The data rate is very low, however, since each > satellite's signal inherently has a negative SNR (because there's a dozen > others shouting over it) - that's why it takes a full minute for a receiver > to get a fix from cold, because it simply takes that long to download the > ephemeris from the first satellite whose signal is found. > > A future version of wifi could reasonably use TDM, I think, but not > diplexing. The way this would work is that the AP assigns each station > (including itself) a series of time windows in which to transmit as much as > they like, and broadcasts this schedule along with its beacon. Also > scheduled would be windows in which the AP listens for new stations, > including possibly other nearby APs with which it may mutually coordinate > time. A mesh network could thus be constructed entirely out of mutually > coordinating APs if necessary. > > The above paragraph is obviously a giant handwave... > > - Jonathan Morton > > --0000000000005e5d470574655ca9 Content-Type: text/html; charset="UTF-8" Content-Transfer-Encoding: quoted-printable
hmm, "going back" to TDM, doesn't that lose = the benefits and efficiencies per statistical multiplexing?=C2=A0 =C2=A0How= can a centralized device predict the many "end stations'" ne= twork demand in its time scheduling?

Note: I think with 802.11ax thi= s is happening to some extent per uplink OFDMA but that requires both time = scheduling and transmit power setting so the AP receives the "simultan= eous signals" with similar SINRs.=C2=A0 =C2=A0This is supposed to help= with LBT but not really completely solve it.

Curious if eliminating= LBT is possible per a distributed solution (with partial network awareness= ) vs having a centralized scheduler (with "full" network awarenes= s)?=C2=A0

Bob

O= n Sun, Aug 26, 2018 at 11:26 PM Jonathan Morton <chromatix99@gmail.com> wrote:
> On 27 Aug, 2018, at 9:00 am, Bob McMahon <bob.mcmahon@broadc= om.com> wrote:
>
> Curious to how LBT can be solved at the PHY level and if the potential= solution sets preserve the end to end principle.

The usual alternatives include TDM, usually coordinated by a master device = (eg. the AP); full-duplex operation via diplexers and/or orthogonal coding;= and simply firing off a packet and retrying with exponential backoff if an= acknowledgement is not heard.

TDM and diplexing are already used by both DOCSIS and LTE.=C2=A0 They are p= roven technology.=C2=A0 However, in DOCSIS the diplexing is greatly simplif= ied by the use of a copper channel rather than airwaves, and in LTE the dip= lexer is fitted only at the tower, not in each client - so the tower can tr= ansmit and receive simultaneously, but an individual client cannot, but thi= s is still useful because there are many clients per tower.=C2=A0 Effective= diplexers for wireless are expensive.

Orthogonal coding is already used by GPS and, in a rather esoteric form, by= MIMO-grade wifi.=C2=A0 IMHO it works rather better in GPS than in wifi.=C2= =A0 In GPS, it allows all of the satellites in the constellation to transmi= t on the standard frequency simultaneously, while still being individually = distinguishable.=C2=A0 The data rate is very low, however, since each satel= lite's signal inherently has a negative SNR (because there's a doze= n others shouting over it) - that's why it takes a full minute for a re= ceiver to get a fix from cold, because it simply takes that long to downloa= d the ephemeris from the first satellite whose signal is found.

A future version of wifi could reasonably use TDM, I think, but not diplexi= ng.=C2=A0 The way this would work is that the AP assigns each station (incl= uding itself) a series of time windows in which to transmit as much as they= like, and broadcasts this schedule along with its beacon.=C2=A0 Also sched= uled would be windows in which the AP listens for new stations, including p= ossibly other nearby APs with which it may mutually coordinate time.=C2=A0 = A mesh network could thus be constructed entirely out of mutually coordinat= ing APs if necessary.

The above paragraph is obviously a giant handwave...

=C2=A0- Jonathan Morton

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