Topic: Broadcasting the Blockchain - page 2. (Read 10518 times)

From your link:


I understand how it works.  What you don't seem to understand is that there is a reason it has been discontinued.  It's probably not a technical reason.

XR is not bullshitware.  I've seen it put into practice by hams.

http://www.qsl.net/kb9mwr/projects/wireless/modify.html

While these guys aren't to keen on it for their purposes, it does work somewhat.  Basicly the timing of transmissions are slowed down, to permit better low-signal copy.  A similar trick can be used with 100baseTX ethernet to extend the cable range limit between two bridge devices.  Your datarate is affected as well, which they admit.  Hams do something similar with very slow computer controlled morse code.

http://www.martellotowergroup.com/The_Martello_Tower_Group/QRSS.html

That chipset is pretty old.  Atheros was acquired by Qualcomm since then.  If it's supported in recent chipsets, Qualcomm is being quiet about it.

http://www.dd-wrt.com/phpBB2/viewtopic.php?t=73941


This project is getting interesting, for a whole host of reasons.

Within official specs, yes.  However there is an extended range mode that is supported by some chipsets.

http://www.qsl.net/kb9mwr/projects/wireless/atheros_XR_whitepaper.pdf

I have no idea how common such support is for cell phones, but with a receive sensitivity of -107 db the loss of data rate might actually make this thing workable.

Mostly because the "world record" link they cite is not 2.4ghz and uses carefully-aligned directional antennas on both ends and "high sensitivity" receivers.  Putting that in a cubesat and broadcasting to consumer grade hardware, without an antenna or tracking, stretches credulity a bit.

The closest precedent I've found is the CanX-2 satellite, which was 3u and broadcast in the S band at 256 kbps, though likely to a directional receiver.

http://www.utias-sfl.net/nanosatellites/CanX2/system.html

One of the other issues they have mentioned is that the 802.11 spec requires a minimum speed of 1 mbit.  So there is still a gap between what is clearly possible and what they claim to want to do.

That's just the thing, if you have to get a dd-wrt and a directional antenna to receive it, why not just use DRM and shortwave receivers?  Again, datacasting is what DRM was designed for, and it uses a much more "efficient" schema in addition to the much narrower bandwidth (power) requirement.  Sure, it's data rate is slower, but like you said, that's physics.


That's actually not true.  The license free ISM bands are only license free for terrestrial & incidental emitters, and every nation sets a pretty low transmission power limit.  The ISM license free argument, for a low earth orbit sat, fails on both counts.  They might get away with it, if they can get the sat up there and say "opps, sorry", but they won't get away with it if teh FCC gets wind of it.

Hmm, I was going off of memory, but upon checking it seems that 2.45 Ghz isn't the resonate frequency of hydrogen.  Apparently that's actually 1.42 Ghz, or more precisely 1,420,405,751.786 hertz.  And checking oxygen it's 5.85 Ghz.  So apparently I was wrong about 2.45 Ghz having a high attenuation point.  I just got called out, and failed to perform.  Well done, Death.

According to this page, 2.45 is a "good average" between those two, with the goal of permitting the radio signal some degree of penetration into the food, which (according to them) wouldn't be possible with a precise resonate frequency because the signal would dump all it's energy into the first couple of millimeters of the surface.

http://www.schoolphysics.co.uk/age16-19/Wave%20properties/Wave%20properties/text/Microwave_ovens/index.html

In my defense, there does exist a "magical attenuation window" in the microwave spectrum, it's just not at 2.45 Ghz.  So my complaints about high attenution in teh wifi spectrum are without merit.

I think using standard wifi gear (like an off the shelf usb dongle or a cellphone) is likely a pipe dream.  They were never really designed that kind of purpose.  Still there is merit in using the wifi frequency (and possibly channel structure) as it would drop the cost of mass producing customized receivers.  The chips that power wifi radios are dirt cheap because they are produced by the billions each year.    Hell you might get away with using a high gain antenna and a custom firmware flashed on a certain routers (think dd-wrt but for space based signal).

The other advantage is that there is no license required.  5 Ghz might be a better choice though, I wonder if there is any data on comparisons between 2.4 Ghz and 5.0 Ghz over this type of link.

Come on now, you can't be serious.  Yes water and hydrocarbons do attenuate all signals (to a different degree), but physics is physics and there isn't a magical attenuation window right at 2.4 Ghz.  

You got a point on the power of the sat but water is going to look the same to a radio wave at 2.4Ghz as it does at 2.3 Ghz (and 2.5Ghz and 2.2 Ghz).  Now at 12 Ghz it would be a different story.  That is the major disadvantage of Ku sat communication band.  Much higher power (no interference with earth bound microwave transmitters) but in areas with a a lot of rainfall it is inferior to C band because water is almost opaque to a 12 Ghz radio wave.  So areas with a lot of rainfall generally use the lower end of C band instead (~4 Ghz).

I am not sure if it would have enough power, that is a good point, but the frequency is fine.  If you have a cite showing 2.4 Ghz attenuates far worse than 2.2 Ghz or 2.5 Ghz I would love to read it.  BTW I agree with you that the project is likely too ambitious for the power and size constraints.  To use consumer wifi band would probably require more power and more powerful transmitters.  Still I like the idea in general as a way to blanket the earth with the blockchain.

The best way to make the datacasting idea work with consumer class wifi devices, would be to choose the wifi channel that is the most "distant" from the frequency that microwave ovens use and set it to a quarter channel multicast mode.  Even still, the sat wouldn't be able to broadcast continuously and hit the -90 decibel signal point, it would have to broadcast in scheduled bursts.  That might be okay, but even at -90 decibels, I don't think a cell phone would be able to hear it.  A consumer grade hotspot with a marginally directional antenna pointed up might be able to receive the signal reliablely on a clear night (no clouds in the path, no sunlight induced ionosphere 'crashes' to raise the static background level) but if the guy wanting to receive these datacasts has to buy or build dedicated gear to receive it, then what good is trying to do it using wifi standards and channels?  Datacasting is one of the design goals for DRM shortwave broadcasting.

I'm not convinced that a 10 cube mini sat has the power to push a receivable DRM signal on a continuous basis anyway.  Again, an on-off transmit schedule might be best, particularly with the low earth orbit sats that circle the globe several times per day.  They are usually only 'visable' to any particular receiver for about a half an hour, so perhaps a 10 minute burst of data followed by 50 minutes of rest/solar charging might still work.  Of course, all these kinds of compromises reduce the actual amount of data that can be broadcast.  Eventually we end up back with a normal shortwave broadcasting operation on planet Earth that can transmit continuously from a grid and reflect their signal off the ionosphere.

There are many ways to solve the transaction propogation problem, the datacasting proposal in this thread is to solve the bulk blockchain distribution problem.

That is a full sized sat with much higher power levels.


And this is a full sized sat runing on much higher power levels.  And neither of them use the B/G wifi band, which as I have alrady noted, is heavily attenutated by water and hydrocarbons in a way that the rest of the S band is not, and is the primary reason that said band is unlicesned to start with.

The best comparison that we might have for a setup that would work woudl be a ham radio sat.  Here's one to compare...

http://www.amsat.org/amsat-new/satellites/sat_summary/ao51.php
http://en.wikipedia.org/wiki/AO-51

This one uses several transmitters, but keep in mind that not only is this device using much narrower bandwidths, it's not attempting to transmit continuously.  So putting out a 38 Kbps data signal at 300+ watts RMS for an average of a minute or two per hour is within the power requirements of a mini sat that has a 30 watt solar panel.

They won't.  However if they have even slow, weak internet access they can use that as the uplink and avoid the cost and frustration of trying to download the blockchain over that limited high cost link because it is being beamed out to blanket the entire earth.

The first sat internet worked on a similar fashion.  The sats were downlink only.  Your dish could only receive not send.  So your uplink was by modem and your downlink was by sat.  Another example is stock quotes.  They were at one time broadcast services for pro traders because the full feed exceeded what was available in internet connectivity (think dialup).  You could receive quote stream as a broadcast and use your slow limited internet connection just for trades.

Yeah antiquated by todays standards for the 1st world but still viable for bitcoin, because the bandwidth requirements are very asymmetric.  It is GB and GB to download (possibly GB a week in the future) but tx are very small so the uplink requirements are minimal.  You probably could do it by SMS to internet gateway if you had to.

Why is the response dubious.  Remember this isn't a two way system.  It is more like broadcast sat TV but for information.

2.4 Ghz is fine for sat downlink (remember one direction only).

For example one sat radio system runs on L brand which is 1 to 2 Ghz.
http://en.wikipedia.org/wiki/WorldSpace

In the US Sirius XM radio operates at 2.3 Ghz.
http://en.wikipedia.org/wiki/S_band

while kewl.  u are in receive only mode.

so if u make a payment, how they gonna get it with no internet?

Another issue that I can see with using the small 10-cube type sats for broadcasting a wifi signal, even using the 5 Ghz N band, is that wifi channels are normally 20 Mhz wide, which is a particularly broadband signal to produce.  With wifi, this is a good thing, as your signal can cover the office without much interference and signals produced by nearby offices are strongly attenuated before they get into your office, and permits a high data rate.  However, all things being equal, a signal that is twice as broad requires twice the power to be recieved at the same distance under the same conditions.  The wifi standards permit quarter width band signals, but almost no one uses them because they don't help under normal hotspot ranges and conditions.  So, at a minimum, a wifi datacast would have to be 5 Mhz wide.  However, the DRM standard is a digital sound & data standard that uses the bandwidth of the old fashioned shortwave & AM channel standards; which is 9 Kilohertz wide in Europe and 10 Kiloherts wide in the rest of the world.  However, DRM also permits doubled or halved channel widths.  So if we compare the double DRM channel for data throughput versus the quarter width wifi for reduced power requirements and the wifi broadcast would still require roughly 250 times as much power to acheive the same signal quality on the ground versus a double wide DRM broadcast, using the same frequency, sat quality, etc.

And again, the common shortwave receiver is a far better receiver than the common wifi phone chip, so the DRM signal would be much more likely to be clearly received than the wifi signal even if the 10 cube sats could actually produce the 250 times power level.  I'd be surprised if those cube sats can produce a 50 watt RMS output on a continuous basis, and (off the top of my head) I'd say that a DRM transmission would require around 3Kilowatts to properly blanket a 600 mile circle footprint to a clear & receivable degree.  Even a half channel width DRM broadcast (4.5 Khtz wide, minimum) would require at least 1000 watts on an ongoing basis.  Keep in mind, DRM is the digital version of an AM talk radio broadcast.  A local AM broadcaster generally uses between 3 Kilowatts (at night, when the D layer doesn't attentuate the middle wave band) and 20 kilowatts just to cover a major metro area and the surrounding countryside, with a practical coverage radius of 100 to 150 miles.

I'm thinking that mini sats broadcasting a DRM channel in the 15 meter band works well.  Common shortwave receivers are much better at reception than a cell phone wifi chip anyway.

Well, it's either misinformed or deliberately false.  I've had my kids look at this site and another site (waterstep.org) to compare the tech claims of one charity asking for money compared to another, and we've largely come to the conclusion that this outer.in site is a scam designed to illicit donations from well intended.  As my son noted, the first clue is the "for free" claim.  That can never happen.  While it might be free to receive, there would still need be advertisments and such.  And it's not false that low earth orbit sats have used the S band, but that particular section of the S band is where the attenuation from water is greatest.

EDIT:  By "that particular" section of the S band, I mean the sliver of unlicensed bandwidth that B/G wifi occupies.  The S band is very wide, but only that portion is unlicensed, and because it's an ISM band (Insustrial, Scientific & Medical) that is used primarily for purposes besides communication.  There are other ISM bands, but none that are so wide as the one that B/G wifi (and Bluetooth, and several other short range techs) utilizes.  It's that wide because microwave ovens (in particular) use that band due to the fact that the high attenuation of radio waves by hydrogen is useful for heating with radio waves, and microwaves are so paowerful that they produce a lot of 'splatter'.  Until wifi came out, it was largely believed that  the band was useless for communications due to both the high attenuation and the likelyhood of interfereance from microwaves.  Wifi protocols are designed with the likelyhood of occasional interference in mind, however.  So is Bluetooth.  The rest of the S band experiences attentuation due to water in much the same way that radio does in general, in that the higher the frequency the greater the attenuation from water.  Both the US and Russia have massive ultra-low-frequency transmitters, with enormouse power ratings, in order to communicate with submerged submarines via morse code.  There are ham radio geeks called "lowfers" who try to communicate in this range as well, but it's hard to do anything when the wavelength of the signal is hundreds of kilometers long.  So while there are useful frequencies outside of the wifi band on the S band, they generally require more power for the same task than a lower frequency band such as the L band, and less than higher frequency bands such as the K band.  So most of the S band is particularly good for a low power downlink to consumer class receivers, just not within the B/G wifi band.

There are many ways to transmit data other than wifi.. perhaps we will find a suitable substitute...

You know more about it than I do, but perhaps this is relevant:



http://www.reddit.com/r/technology/comments/1wqgmh/outernet_wifi_for_the_world_from_outer_space/cf4nshr

Actually, now that I look, someone also asked this question on their forum.  The response seems dubious:

https://discuss.outernet.is/t/can-2-4ghz-even-penetrate-the-atmosphere-efficiently/34