hitting your points almost in reverse order
3) a) Variable rates: arguably a huge engineering design mistake for
multiple reasons (though understandably done this way.)
We know how to send data faster now than we did 5 years ago, which was faster
than we knew how to do 5 years before that, etc. We also will know how to send
data faster 5 years from now.
Unless you plan to ignore all future improvements, you cannot stick with just a
single data rate (and if you do, I'm sure that a competitor of yours who doesn't
ignore future improvements will eat your lunch in a couple of years)
This completely ignores the fact that some modulation schemes require a better
signal to noise ratio than others, so unless you want to either give up
distance, or give up speed, you cannot pick the "one and true" rate to use.
This is why wifi defaults to slowing down when it has trouble getting through.
if the problem is noise, this is the right thing to do, when the problem is
hidden transmitters, it's exactly the wrong thing to do) At the time it was
designed it was extremely expensive, so deployments were expected to be few, so
the biggest problem expected was noise
b) Aggregation: Artifact of media access latency that makes the
transport network incredibly difficult for things like TCP. Possibly
another eng. design flaw.
it's not that simple. It's not the latency, it's the per-transmission overhead
that's the difference. This is the same reason why wired networks sometimes use
jumbo frames, the per-transmission overhead is the same, so by packing more data
into a single transmission, you get more efficient use of the media, so faster
effective speeds.
2) Hidden transmitters. Does it really matter? Superposition applies
hidden or not so will fixing the "receiver confusion" get rid of this issue?
If transmitters aren't hidden from each other, they can wait until the airwaves
are quiet and then transmit. This works very well in practice. But eventually,
any successful network is going to grow until it exceeds the size at which all
stations can hear each other.
1) Drastic variation in signal strength. Reality of physics? Seems yes.
Solvable by math? I suspect so but could be wrong. Solvable by
engineering now? Not sure. In ten years? Not sure.
Improvements in 10 years, yes. solutions, no.
you are constrained by physics. you can only detect the signal that arrives at
your antennas. If you have two transmitters next to each other transmitting at
the same time, they are going to interfere with each other in ways that nothing
is going to be able to solve.
But similarly to the way that mu-mimo is able to use multiple antennas sending
different signals to create useful interference patterns so that multiple
stations that are 'far enough' apart can each receive a useable signal. Further
improvements in signal processing and Analog to Digital converters could make it
so that stations that are far enough apart in angle, but close enough in power
could be deciphered at the same time. I'd give good odds that data rates below
the signal station peak will be required to make this practical.
But the problem of being able to hear a whisper from across the room at the same
time that someone is yelling in your ear is such a problem that I don't believe
that it is ever going to be 'solved' as a general case. The noise and distortion
of the strong signal can be larger than the weak signal. And the strength of a
bounce of the strong signal can be larger than the weak signal.
getting to the point where several signals of similar strength could be handled
at the same time would be a big help.
I ask myself a question, "What happened in 2000 that wi-fi became viable
such that atheros and others were able to form new companies? Did a
mathematician discover some new math or did a physicist find a better way
to explain energy as a means for moving information?"
Mo, what happened was Moore's law came to help. It took equipment that was
selling at ~$1000/station and cut it's price to $100/station (and today better
equipment is available at <$10/station).
I remember putting a $750 deposit down (the purchase price of the card) at a
conference to borrow a 802.11b (1-11Mb/sec) pcmcia card for my laptop. At around
the same time, I spent ~$500 to equip a small office with a proprietary AP and
two 1Mb pcmcia cards (and considered it a bargin). Today you can buy USB 802.11n
dongles for <$10 and for ~$100 you can get a 802.11ac device that (under the
right conditions) can top 1Gb/sec.
The APs were several thousand dollars each. Today a $200-300 AP is near the high
end of the consumer devices, and you can get them for ~50 if you push (or ~$25
if you are willing to buy used)
It didn't take higher speeds (AC, N, or even G) to make wifi popular, it just
required that the equipment come down enough in price.
David Lang
On Sun, 26 Jun 2016, Bob McMahon wrote:
I appreciate and agree with what you posted, including that a wired network
without guides is not the same as a guide-less mobile network. I do think
the thought experiment can help set some goal posts and, where the
goalposts don't make sense, some can be thrown out. Also, there may be new
ones as well per mobility vs tertiary demands.
I ask myself a question, "What happened in 2000 that wi-fi became viable
such that atheros and others were able to form new companies? Did a
mathematician discover some new math or did a physicist find a better way
to explain energy as a means for moving information?" Superposition
certainly applied 50+ years ago and I suspect most physicists understood it
equally well back then.
Hence, wi-fi isn't a triumph of math nor physics but rather an advancement
in engineering, aka the realization of those fields into products useful to
humans. I suspect the future of wi-fi is more of the same - hence the
desire to set some engineering goal posts.
So to your points (and in the thought experiment context:)
1) Drastic variation in signal strength. Reality of physics? Seems yes.
Solvable by math? I suspect so but could be wrong. Solvable by
engineering now? Not sure. In ten years? Not sure.
2) Hidden transmitters. Does it really matter? Superposition applies
hidden or not so will fixing the "receiver confusion" get rid of this issue?
3) a) Variable rates: arguably a huge engineering design mistake for
multiple reasons (though understandably done this way.)
b) Aggregation: Artifact of media access latency that makes the
transport network incredibly difficult for things like TCP. Possibly
another eng. design flaw.
Trying to learn from experts so thanks again for including me in these
discussions.
Bob
On Sun, Jun 26, 2016 at 5:00 PM, David Lang <da...@lang.hm> wrote:
I don't think anyone is trying to do simultanious receive of different
stations. That is an incredibly difficult thing to do right.
MU-MIMO is aimed at haivng the AP transmit to multiple stations at the
same time. For the typical browser/streaming use, this traffic is FAR
larger than the traffic from the stations to the AP. As such, it is worth
focusing on optimizing this direction.
While an ideal network may resemble a wired network without guides, I
don't think it's a good idea to think about wifi networks that way.
The reality is that no matter how good you get, a wireless network is
going to have lots of things that are just not going to happen with wired
networks.
1. drastic variations in signal strength.
On a wired network with a shared buss, the signal strength from all
stations on the network is going to be very close to the same (a difference
of 2x would be extreme)
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)
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.
2. 'hidden transmitters'
On modern wired networks, every link has exactly two stations on it, and
both can transmit at the same time.
On wireless networks, it's drastically different. You have an unknown
number of stations (which can come and go without notice).
Not every station can hear every other station. This means that they
can't avoid colliding with each other. In theory you can work around this
by having some central system coordinate all the clients (either by them
being told when to transmit, or by being given a schedule and having very
precise clocks). But in practice the central system doesn't know when the
clients have something to say and so in practice this doesn't work as well
(except for special cases like voice where there is a constant amount of
data to transmit)
3. variable transmit rates and aggregation
Depending on how strong the signal is between two stations, you have
different limits to how fast you can transmit data. There are many
different standard modulations that you can use, but if you use one that's
too fast for the signal conditions, the receiver isn't going to be able to
decode it. If you use one that's too slow, you increase the probability
that another station will step on your signal, scrambling it as far as the
receiver is concerned. We now have stations on the network that can vary in
speed by 100x, and are nearing 1000x (1Mb/sec to 1Gb/sec)
Because there is so much variation in transmit rates, and older stations
will not be able to understand the newest rates, each transmission starts
off with some data being transmitted at the slowest available rate, telling
any stations that are listening that there is data being transmitted for X
amount of time, even if they can't tell what's going on as the data is
being transmitted.
The combination of this header being transmitted inefficiently, and the
fact that stations are waiting for a clear window to transmit, means that
when you do get a chance to transmit, you should send more than one packet
at a time. This is something Linux is currently not doing well, qdiscs tend
to round-robin packets without regard to where they are headed. The current
work being done here with the queues is improving both throughput and
latency by fixing this problem.
You really need to think differently when dealing with wireless network.
The early wifi drivers tried to make them look just like a wired network,
and we have found that we just needed too much other stuff to be successful
whith that mindset.
The Analog/Radio side of things really is important, and can't just be
abstracted away.
David Lang
On Sun, 26 Jun 2016, Bob McMahon wrote:
Is there a specific goal in mind? This seems an AP tx centric proposal,
though I may not be fully understanding it. I'm also curious as why not
scale in spatial domain vs the frequency domain, i.e. AP and STAs can also
scale using MiMO. Why not just do that? So many phones today are 1x1,
some
2x2 and few 3x3. Yet APs are moving to 4x4 and I think the standard
supports 8x8. (I'm not sure the marginal transistor count increase per
each approach.) On the AP tx side, MuMIMO is also there which I think is
similar to the DAC proposal.
I'm far from a PHY & DSP expert, but I think the simultaneous AP receive
is
the most difficult issue per the power variations, aka SNR. Each of the
mobile device energies is affected per inverse square law (unless some
form
of wave guide is used.) Hence wi-fi use of time domain slots prior to
transmit (no longer simultaneous in time.) Particularly needed for
devices
that communicate with one another. Unfortunately, "collocated"
energy/information sources must honor this TDM even when not
communication
with one another per tragedy of the commons. (Agreed there is no such
thing as a collision so let's redefine it to mean that the receiver is
unable to receive per RF energy "confusion", still a tragedy of the
commons. I don't know what drives the limits to DSP decode that could
minimize or eliminate this tragedy.)
At the end of the day, would the ideal network would resemble a wired
ethernet (including ethernet switch fabric) without the waveguides (or
wires/fibers)? From that perspective, here are some thoughts to the goals
o) TX op/access to transmit driven to zero. (Collision avoidance isn't
nearly as good as instantaneous collision detect in this context, though
"collision" should replaced with "confusion")
o) RX confusion detection time propagated to stop offending TX(s) driven
to zero
o) Support of different encodings (e..g phy rates) pushes towards virtual
output queueing prior (queuing at the transmitter)
o) Power per bit xfered towards zero or driven per cost & energy density
of batteries. Note: Atomic batteries not allowed per humans being
involved.
o) Transistor count (chip cost) per bit moved driven by Moore's law and
those economics
o) Reduce "collision/confusion" domain (less STAs per AP) ideally to zero
Just some thoughts off the top of my head. Please do comment and correct.
Thanks in advance for the discussion.
Bob
On Fri, Jun 24, 2016 at 2:24 PM, <dpr...@reed.com> wrote:
Without custom silicon, doing what I was talking about would involve non
standard MAC power management, which would require all devices to agree.
David Lang's explanation was the essence of what I meant. the
transmission
from access point on multiple channels is just digital addition if the
DACs
have enough bits per sample. to make sure that the signals to the AP are
equalized, just transmit at a power that makes that approximately true...
which means a power amp with at most 30 dB of dynamic gain setting.
typical
dynamic path attenuation range (strongest to weakest ratio) among
stations
served by an AP is < 20 dB from my past experiments on well
operating-installtions, but 25 can be seen in reflection heavy
environments.-----Original Message-----
From: "David Lang" <da...@lang.hm>
Sent: Fri, Jun 24, 2016 at 1:19 am
To: "Bob McMahon" <bob.mcma...@broadcom.com>
Cc: "Bob McMahon" <bob.mcma...@broadcom.com>,
make-wifi-f...@lists.bufferbloat.net, "
cerowrt-devel@lists.bufferbloat.net"
<cerowrt-devel@lists.bufferbloat.net>
Subject: Re: [Make-wifi-fast] more well funded attempts showing market
demandfor better wifi
well, with the kickstarter, I think they are selling a bill of goods.
Just using the DFS channels and aggregating them as supported by N and AC
standards would do wonders (as long as others near you don't do the same)
David Lang
On Thu, 23 Jun 2016, Bob McMahon wrote:
Date: Thu, 23 Jun 2016 20:01:22 -0700
From: Bob McMahon
To: David Lang
Cc: dpr...@reed.com, make-wifi-f...@lists.bufferbloat.net,
"cerowrt-devel@lists.bufferbloat.net"
Subject: Re: [Make-wifi-fast] more well funded attempts showing market
demand
for better wifi
Thanks for the clarification. Though now I'm confused about how all
the
channels would be used simultaneously with an AP only solution (which is
my
understanding of the kickstarter campaign.)
Bob
On Thu, Jun 23, 2016 at 7:14 PM, David Lang wrote:
I think he is meaning when one unit is talking to one AP the signal
levels
across multiple channels will be similar. Which is probably fairly true.
David Lang
On Thu, 23 Jun 2016, Bob McMahon wrote:
Curious, where does the "in a LAN setup, the variability in [receive]
signal strength is likely small enough" assertion come? Any specific
power numbers here? We test with many combinations of "signal strength
variability" (e.g. deltas range from 0 dBm - 50 dBm) and per
different
channel conditions. This includes power variability within the
spatial
streams' MiMO transmission. It would be helpful to have some physics
combined with engineering to produce some pragmatic limits to this.
Also, mobile devices have a goal of reducing power in order to be
efficient
with their battery (vs a goal to balance power such that an AP can
receive simultaneously.) Power per bit usually trumps most other
design
goals. There market for battery powered wi-fi devices drives a
semi-conductor mfg's revenue so my information come with that bias.
Bob
On Thu, Jun 23, 2016 at 1:48 PM, wrote:
The actual issues of transmitting on multiple channels at the same
time
are quite minor if you do the work in the digital domain (pre-DAC).
You
just need a higher sampling rate in the DAC and add the two signals
together (and use a wideband filter that covers all the channels).
No RF
problem.
Receiving multiple transmissions in different channels is pretty much
the
same problem - just digitize (ADC) a wider bandwidth and separate in
the
digital domain. the only real issue on receive is equalization - if
you
receive two different signals at different receive signal strengths,
the
lower strength signal won't get as much dynamic range in its samples.
But in a LAN setup, the variability in signal strength is likely
small
enough that you can cover that with more ADC bits (or have the MAC
protocol
manage the station transmit power so that signals received at the AP
are
nearly the same power.
Equalization at transmit works very well when there is a central AP
(as
in
cellular or normal WiFi systems).
On Thursday, June 23, 2016 4:28pm, "Bob McMahon" >>>
bob.mcma...@broadcom.com>
said:
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An AP per room/area, reducing the tx power (beacon range) has been
my
approach and has scaled very well. It does require some wires to
each
AP
but I find that paying an electrician to run some quality wiring to
things
that are to remain stationary has been well worth the cost.
just my $0.02,
Bob
On Thu, Jun 23, 2016 at 1:10 PM, David Lang wrote:
Well, just using the 5GHz DFS channels in 80MHz or 160 MHz wide
chunks
would be a huge improvement, not many people are using them (yet),
and
the
wide channels let you get a lot of data out at once. If everything is
within a good range of the AP, this would work pretty well. If you
end
up
needing multiple APs, or you have many stations, I expect that you
will
be
better off with more APs at lower power, each using different
channels.
David Lang
On Thu, 23 Jun 2016, Bob McMahon wrote:
Date: Thu, 23 Jun 2016 12:55:19 -0700
From: Bob McMahon
To: Dave Taht
Cc: make-wifi-f...@lists.bufferbloat.net,
"cerowrt-devel@lists.bufferbloat.net"
Subject: Re: [Make-wifi-fast] more well funded attempts showing
market
demand
for better wifi
hmm, I'm skeptical. To use multiple carriers simultaneously is
difficult
per RF issues. Even if that is somehow resolved, to increase
throughput
usually requires some form of channel bonding, i.e. needed on both
sides,
and brings in issues with preserving frame ordering. If this is just
channel hopping, that needs coordination between both sides (and
isn't
simultaneous, possibly costing more than any potential gain.) An
AP
only
solution can use channel switch announcements (CSA) but there is a
cost to
those as well.
I guess don't see any break though here and the marketing on the
site
seems
to indicate something beyond physics, at least the physics that I
understand. Always willing to learn and be corrected if I'm
misunderstanding things.
Bob
On Wed, Jun 22, 2016 at 10:18 AM, Dave Taht
wrote:
On Wed, Jun 22, 2016 at 10:03 AM, Dave Taht
wrote:
https://www.kickstarter.com/projects/portalwifi/portal-turbocharged-wifi?ref=backerkit
"Portal is the first and only router specifically engineered to
cut
through and avoid congestion, delivering consistent,
high-performance
WiFi with greater coverage throughout your home.
Its proprietary spectrum turbocharger technology provides access
to
300% more of the radio airwaves than any other router, improving
performance by as much as 300x, and range and coverage by as
much as
2x in crowded settings, such as city homes and multi-unit
apartments"
It sounds like they are promising working DFS support.
It's not clear what chipset they are using (they are claiming
wave2)
-
but they are at least publicly claiming to be using openwrt. So I
threw in enough to order one for september, just so I could
comment
on
their kickstarter page. :)
I'd have loved to have got in earlier (early shipments are this
month
apparently), but those were sold out.
https://www.kickstarter.com/projects/portalwifi/portal-turbocharged-wifi/comments
--
Dave Täht
Let's go make home routers and wifi faster! With better
software!
http://blog.cerowrt.org
--
Dave Täht
Let's go make home routers and wifi faster! With better software!
http://blog.cerowrt.org
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