Boffins teach Wi-Fi routers to dance to the same tune Research presented to this week's IEEE International Conference on Network Protocols suggests a fairly simple enhancement to Wi-Fi could help deal with the chronic congestion caused by its popularity. It would be nice if twenty different base stations in twenty different apartments could coordinate their transmissions, but …
"Kuzmanovic's paper explains that since FM has good propagation characteristics, there's a very good chance all of the base stations in a neigbourhood will lock on to the same station."
I don't know if this is as certain as claimed. Suppose the building in question is pretty big, yet plenty of hotspots clash. However, it's also within the reach of not one but many different FM stations each coming from different angles. There's a distinct chance different parts of the building will lock onto different stations due to the differing signal strengths. Also, suppose some of these stations have no (or worse, spotty) RDS.
Just pointing out this is more common than you think. I'm of a mind one should never tout a new technology until it's run the gauntlet of real-world testing under worst-case conditions that can be specified along with the results. I mean, I know plenty of radio station (particularly those low on the dial) whose reception quality differed considerably just by rotating the receiver around the vertical. And that's not even starting with fiddling with antennae.
Let's wait for some real-world tests before scrapping it...
In my apartment, I can often see over 20 WiFi networks, and FM reception is patchy (best near windows). I'm guessing this has something to do with the reinforced concrete construction of the building. This solution seems least likely to work where it is needed the most, but let's see the test results.
(I'm going to ask the building management to remove the reinforcing bars to improve the FM reception ;-)
The FM band should be scanned for the strongest signals. The scan should be repeated several times over a few minutes to smooth any transient signal changes. The lowest frequency one with the best weighted average should then be used.
That will avoid different routers locking onto marginal signals. There would still be a possibility of two routers selecting different stations eg where there are several stations on the same transmitter at the same nominal power.
Instead of messing about looking for a random radio station which not everyone agrees on (their method of just picking the lowest frequency with a good signal guarantees that different receivers in different positions will pick different stations) and then looking at arbitrary structure that happens to be present, why not just use the actual clock signals? Most countries have them, or can at least see the signals from neighbouring countries, and the technology is already extremely widespread in regular clocks.
You'll also find that time signals have inconsistent strength. For example, most radio devices are sharp enough to only try to pick up the NIST radio time signal WWVB at night because the signal doesn't propagate as far during the day. Also, WWVB is stationed in Colorado. Meaning cities like New York are a real stretch, even at night. Plus the signal has trouble with walls. So anyone seriously needing to use WWVB on the east coast usually have to dedicate hardware to the task: outdoors and facing west.
"So anyone seriously needing to use WWVB on the east coast usually have to dedicate hardware to the task: outdoors and facing west."
My several cheap and cheerful radio clocks work fine in Nova Scotia.
The obvious variable (explaining your "usually") is the ambient LF noise level at the receiver location.
If you live in "cities like New York", then you'll be surrounded by hundreds of switching power supplies and other RF noise sources, and the noise level at LF will be simply atrocious.
If you live on several acres of RF quiet suburban bliss, then the weak signal is reliably above the noise floor.
Actually very few countries have clock signals. While most of them are based on amplitude modulated LW, some are based on alternative techniques, these include the French TDF, the Rusian RBU. Of the amplitude modulated only MSF, JJY60 and WWVB share a frequency of 60kHz the 77.5kHz of DCF77 is also shared with BSF. This is important because the cheap receivers all used pre-tuned ferrite rod antennas, so even if you equip your WiFi hotspot with both 60kHz and 77.5kHz antennas it will be useless in northern Japan where you need a 40kHz antenna for JJY40. It will also be useless in China which you need a 68.5kHz antenna for BPC. The Russian RBU uses frequency modulation of the pulse which will require another completely different circuit for, and the French TDF uses phase modulate of the TDF radio station signal to encode the bits, which would also require a completely different circuit design.
There are no LW radio stations in South America, Africa, or Australia. There are SW radio time signals but these require much more expensive circuits to receive. Further complicating matters is the fact that many of these time signals are not broadcast 24/7 either.
I think people in Europe and North America tend to forget how fortunate they are to have reliable LW time signals.
@jabuzz
Fair points, but mostly not insurmountable. My watch happily picks up signals in the UK (60kHz), Germany (77.5kHz), USA (60kHz) and Japan (40 and 60kHz). And of course those are just the signal sources, it generally manages to pick up a signal practically anywhere in western Europe and that's just based on places I've actually travelled. If a small, fairly cheap, low power watch can manage that, it surely can't be beyond the wit of man to do so in kit like routers. Or of course there's always the possibility of simply making kit slightly more localised - everything stays the same except the antenna and decoder. Phones already need significantly more variation than that to operate in different countries. Although admittedly that doesn't help places with no time signal at all.
In any case, I'm still struggling to see how anything could be worse than "search for a random radio station and hope it's the same one someone else picked". My car routinely finds different stations than I can in my house, and getting in a friend's car will inevitably result in a different selection again. The idea that routers would reliably be able to all fix on the same signal is utterly ridiculous. Clock signals may not be a perfect solution, but they'd be a hell of a lot better than relying on blind luck.
If another time source is required, because your router can't get NTP where you live (huh!!??!!), then GPS provides a convenient source.
The real downside is cost, on the order of $10.
Good GPS chipsets are amazingly sensitive. I've got one in my basement, permanently locked on and happily blinking its LED at a synchronized to UTC 1 pps.
"an FM baseband receiver that's either lying unused in a device, or could be cheaply added to it."
Oh yes? Here's a device without an FM receiver. Now how do you propose to cheaply add one? Soldering iron, piece of twin-flex & a cheap tranny? Or is "add" an abbreviation for "throw it away & buy a new one"?
If your router is connected to the Internet, then it can execute a NTP inquiry. The End.
More?
Self-organizing TDMA exists already. One example, Marine AIS. Self-organization is robust. No need for absolute external references. The End again.
The assumption that a batch of routers in a given location would agree on a given reference station belies a deep ignorance of, for example, the impact of multipath.
The router is a repeater and depends on another Internet connection to reach the Internet itself, but to lock onto signals properly, it needs the Internet connection to synchronize itself with all the other routers. Hello, Catch-22.
As for self-organizing, that depends on the different device manufacturers actually cooperating with each other, and you underestimate the corner-cutting of cut-rate device manufacturers who will be willing to lie and cheat to get any kind of certification they need and then just dump whatever they've got on the open market.
AC: "The router is a repeater and depends on another Internet connection to reach the Internet itself, but to lock onto signals properly, it needs the Internet connection to synchronize itself with all the other routers. Hello, Catch-22."
I don't think that you understand how NTP works.
"...the Internet itself."
I don't think that you understand the Internet either.
We seem to agree that the whole concept is daft.
I don't think you understand how a WiFi repeater works. A repeater can't reach the Internet on its own, it needs to hook with with an access point. The catch it, under this scheme, you need an Internet connection to make an NTP request to synchronize yourself with all the other access points so as to be able to see them without clashing. See where the Catch-22 kicks in now? Or would you like some Spike Milligan instead? It'd be like trying to open the box with the crowbar you will find inside.
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