Brad Ideas - Replacing the FCC with "don't be spectrum selfish." - Comments

Omnidirectional antennas

Brett Glass — Mon, 29 Jan 2007 18:01:59 -0800

Omnidirectional antennas (a misnomer, actually; they really should be called "antennas with 360 degree horizontal beamwidth) are not a menace. In fact, they are necessary to follow one of the precepts Brad advocates above: to use as little spectrum as possible and not hog it.

Many wireless ISPs use multiple sector antennas on multiple frequencies at their access points, unnecessarily congesting the spectrum. It is easy to demonstrate that the most efficient use of spectrum and the least interference in a point-to-multipoint system are achieved when each provider uses an omnidirectional antenna and a single channel, rather than multiple sectors and multiple channels.

Unfortunately, many of today's wireless ISPs use the multiple channel/multiple sector approach, with antenna gains and power levels that violate the FCC's Part 15 rules. Why? In part, because equipment vendors -- who get to sell them more equipment if they do this -- tell them to. Another reason is that no one is enforcing any requirement not to hog spectrum, so they just use it all. This approach backfires, however, when multiple providers must coexist -- especially on bands such as the 2.4 GHz ISM band. The 4 Color Theorem says that even if each WISP used a different channel on a directional channel pointed at each given area and the signal did not splatter into others, there STILL wouldn't be enough channels for interference to be avoided unless the number of available channels 4 times the number of WISPs serving the area. However, there's no "4 Color Theorem" for spectrum. So, if there are as many channels as there are WISPs (which can be achieved by using slightly narrower channels than standard Wi-Fi) you can have no interference between them.

Omnidirectional antennas

brad — Mon, 29 Jan 2007 15:14:39 -0800

Have their place, of course. For handheld devices, for example and today for most mobile devices. (It's not that hard to imagine, however, the availability of mass-produced directional self-aiming antenna systems for vehicles that are cheap enough to do away with omnis there.)

Fixed wireless should be directional, clearly. That is more work and a touch more expensive, but again it is the sort of thing that can come down in price. One can even make fairly simple mildly directional antennas without moving parts if you have multiple elements and can switch among them by electronic means. Expensive today -- but in quantity 100 million, almost everything is cheap.

Very small devices like bluetooth dongles and the like will continue to have omnidirectional elements, but at low powers and high bands, mostly.

Omnis can also make sense if you legitimately have a giant audience. If you have millions of people tuning in to a broadcast, using high-power, omni signals like a modern TV station is not selfish, in fact it's efficient. It is an interesting challenge to work out what the audience threshold is -- in this case we do have a scarce piece of bandwidth. To show you are not selfish in using it, you would just show that your audience is at some percentile of size.

omnis!!!

Alex Goldman — Mon, 29 Jan 2007 14:04:39 -0800

I think that some may have comments on most of your ideas, but surely everyone agrees that omnis can be a menace?? That's what I hear from the WISPs I talk to.

Interference

brad — Wed, 24 Jan 2007 15:11:54 -0800

Radio waves do not interfere in space. Two radio waves can pass through one another without effect. Interference only occurs when they both reach the same receiver on the same band with sufficient power for the unintended one to disrupt the intended one. The higher the frequency, the more bound the path of the waves can be. Low frequency waves like FM will spread everywhere, they should only be used when that is the goal — to go everywhere. High frequency waves can have directional transmitters and receivers that will only interfere when two transmitters are along the line the directional receiving antenna (or in particular dish) is aimed — or over a wider swath when the application demands less directionality in the antenna. And again, only if the unwanted transmission has enough power to interfere with the desired signals, since they should be using a noise tolerant system.

Low frequencies should be used only for rural applications, where you need to go long distances to mobile devices.

Alas, the news for hams is not good under my regime. Hams would have to stop using bands the way they do, and experiment with new technologies to be unselfish. But in fact that’s what being a ham is all about, after the initial learning phase. It’s not about using ancient technology, it’s no longer about code, and if you want to socialize with remote people, there are far better and less selfish ways to do that now.

Though on the other hand, there really is so much spectrum out there, if we opened it all up, that there should be enough for people to “play” and experiment and engage in activities that would be selfish if there were other people with a better use for the spectrum. But if there aren’t, then hams could feel free. No need for a licence, actually.

Comment on Radio/Interference

Earl Voss — Wed, 24 Jan 2007 10:17:15 -0800

Hi Brad,
Regarding Amateur (Ham) Radio, at least, there are regulations which stipulate which party must correct interference; these regs do follow common sense. In truth, most operators operate in a good faith manner.

I do agree with using the internet whenever possible; again, in Amateur Radio, this technology shift has been felt; many operators use packet-based communications, etc. via the internet.
Regarding interference "in the ether", we perceive the interference at the receiver, because that's how we hear it. There are occasions, however, when 2 distinct signals operating at the same frequency, but originating from different sources, can find themselves in the same space at the same time. It is for this reason that some transmitters (ususally FM) transmit at much higher power levels during the day than they do in the evening, because of ionospheric ceiling changes. I recall travelling back home from the NJ shore to my home in Northern NJ and there was a distance during which the FM signal 92.7 recieved by my car's FM radio kept switching between the South-Jersey based WOBM and the Long Island based WLIR, and that happened despite FCC transmission power regs.

for whatever it's worth :-)

Earl

Replacing the FCC with "don't be spectrum selfish."

brad — Mon, 22 Jan 2007 14:02:45 -0800

Radio technology has advanced greatly in the last several years, and will advance more. When the FCC opened up the small “useless” band where microwave ovens operate to unlicenced use, it generated the greatest period of innovation in the history of radio. As my friend David Reed often points out, radio waves don’t interfere with one another out in the ether. Interference only happens at a receiver, usually due to bad design. I’m going to steal several of David’s ideas here and agree with him that a powerful agency founded on the idea that we absolutely must prevent interference is a bad idea.

My overly simple summary of a replacement regime is just this, “Don’t be selfish.” More broadly, this means, “don’t use more spectrum than you need,” both at the transmitting and receiving end. I think we could replace the FCC with a court that adjudicates problems of alleged interference. This special court would decide which party was being more selfish, and tell them to mend their ways. Unlike past regimes, the part 15 lesson suggests that sometimes it is the receiver who is being more spectrum selfish.

Here are some examples of using more spectrum than you need:

Using radio when you could have readily used wires, particularly the internet. This includes mixed mode operations where you need radio at the endpoints, but could have used it just to reach wired nodes that did the long haul over wires.
Using any more power than you need to reliably reach your receiver. Endpoints should talk back if they can, over wires or radio, so you know how much power you need to reach them.
Using an omni antenna when you could have used a directional one.
Using the wrong band — for example using a band that bounces and goes long distance when you had only short-distance, line of sight needs.
Using old technology — for example not frequency hopping to share spectrum when you could have.
Not being dynamic — if two transmitters who can’t otherwise avoid interfering exist, they should figure out how one of them will fairly switch to a different frequency (if hopping isn’t enough.)

As noted, some of these rules apply to the receiver, not just the transmitter. If a receiver uses an omni antenna when they could be directional, they will lose a claim of interference unless the transmitter is also being very selfish. If a receiver isn’t smart enough to frequency hop, or tell its transmitter what band or power to use, it could lose.

Since some noise is expected not just from smart transmitters, but from the real world and its ancient devices (microwave ovens included) receivers should be expected to tolerate a little interference. If they’re hypersensitive to interference and don’t have a good reason for it, it’s their fault, not necessarily the source’s.