Quote from: nirom on March 26, 2014, 04:51:26 AM

Quote from: MoonShadow on February 03, 2014, 04:47:43 PM

Quote from: benjamindees on February 03, 2014, 06:59:43 AM

Looks like someone is going to attempt this:

https://www.outernet.is/

Quote

By leveraging datacasting technology over a low-cost satellite constellation, Outernet is able to bypass censorship, ensure privacy, and offer a universally-accessible information service at no cost to global citizens. It's the modern version of shortwave radio, or BitTorrent from space.

Unfortunately, I can see some very real technical and legal issues with trying to do this as described.

First off, Wifi is possible in only two bands. Since the higher N band is very new, and many smartphones still don't support it, I'm going to assume that the older B,G band is what they plan to use. But there was a technical reason that this band was chosen at the time of development; namely that the B,G band was license free worldwide. But why was that, since such license free technologies didn't really exist before Wifi itself? Because the B,G band is the resonate frequency of hydrogen. Thus, energy transmitted in this band is heavily attenuated by any water or hydrocarbons found in it's path, and was considered useless for distance communications. This is still true, and has much to do with why Wifi is so poor at clear range. It's also why this band is shared by every retail microwave that I know of, since food is pretty much all hydrocarbons and water. While there wouldn't likely be much risk of hydrocarbons in the line of sight from low earth orbit, there would be much water. On average, the Earth's atmosphere has enough water from space to sea level to equate to a 32 foot deep dive under the ocean's surface. The amount of power that would be required to push through this and be receivable by common wifi hardware on the Earth's surface would be rediculous.

Second, there are also sound techincal reasons as to why wifi multicasting is not commonly used. Mostly because wifi is a time-sharing technology that (generally) permits more than one unrelated connection to coexist on the same channel. This is permitted because normal mode wifi requires that the hotspot 'listen' to it's own channel several times per second for other broadcasters trying to share the channel space. This doesn't always work well, but it does work more often than most people realize. However, a hotspot in space couldn't coordinate timesharing of all the hotspots in it's radio shadow even if it were possible for it to hear them. In this case, the sat based signal would effectively 'jam' the chosen channel across the whole of it's radio shadow, and also be a violation of international communications treaties as a result.

Third, the licesne free broadcasting nature of the B,G band is limited to 'terrestrial' transmitters, and therefore doesn't apply to satillites at all. A new treaty would be required to even permit such a license, since every country has max transmitter powers in the B,G band that would be WAY what a sat would require.

While using the new N band would reduce the power requirements considerablely, the other two issues would still apply. Perhaps a lower frequency license free band would work with modified FM band recievers, but I can't see a way around the international communications treaties regarding this. Perhaps a broadcast stream that can switch around frequencies in the higher frequency shortwave bands would work, but the sat would have to be able to respond to the reflectivity of the ionosphere and changes in the critical frequency. Most Shortwave broadcasters have to stay the critical frequency so that their Earth bound transmitters can reflect their signal off of the F layer of the ionosphere, but what about a broadcaster in teh shortwave bands that deliberately stays above the critical frequency so that his signal is not reflected back into space? Regardless, the data throughput woudl be low due to a narrow usable bandwidth and a particularly 'noisey' radio environment in those bands.

Wow, where to begin. First of all, B, G and N are protocols in the 802.11 family, There are two bands of frequency used by wifi 2.4 Ghz and 5.8Ghz, the latter being 802.11n only. Wifi technology relies on having two-way communication, it is not a broadcast type of comm. Satellite are sending a lot of power on microwave bands (6Ghz to 10Ghz) but your cellphone won't ever be able to rech the satellite. Second, the signal coming down is picked up by a dish, which is essentially focusing the RF energy. Your cellphone work because it is pushing it's signal to nearby towers, not a sat in space.

I suggest reading up on material from the American Radio Relay League, which has amazing content out there that explains all radiofrequency communications.

Enjoy

nirom

I wrote a rather lengthly response to this, but it got destroyed by a database error. In short, you're misreading my posts & I have long ago gone to their forum to correct their misconceptions about what is feasible. They are now considering using Digital Radio Mondiale as their protocol, and I was thanked personally for that suggestion.