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Open Spectrum: Toward Ubiquitous Connectivity
obiwan2u writes "ACM's Queue magazine has a moderately dense article describing how new intelligent radios may free up under-utilized spectrum bandwidth, possibly providing solutions to the
last mile bottleneck."
I believe that today under 20% of homes get TV via over the air broadcasts. And the number is dropping. The rest get satellite or cable.
It's clear that if we opened up all that broadcast spectrum to unlicenced use, it could easily generate enough revenue to provide free satellite or cable for those few homes still with an antenna.
And just think of the huge value from getting all that spectrum for new technology, largely unlicenced uses.
Of course, the National Association of Broadcasters is one of the most powerful forces in the country. They think of that spectrum as "their property" even though they are blocking much more productive use. Same with the military.
So it won't happen, but we can dream.
I live in a similar situation. I live in rural southern Indiana and it would cost thousands of dollars to get a cable to my house. Everything except the phone and electric lines is wireless.
I do have wireless broadband. Its from a local company (Ohio Valley Wireless cable). The service is called Speedex and it uses a Hybrid 3.5GHz microwave link. Its $50 a month for service that usually averages to about 95KB/s downstream and 16KB/s upstream. Its got a 30-35 mile radius from the tower, so the coverage is pretty darn good. To my knowledge, its been down only once in the year I've had it, and that was for 45 minutes. AT&T botched up their T lines.
-phish
I always thought that was weird. Modems are so slow because they have to use the crappy phone lines, but ADSL is fast because it uses the same crappy phone lines? Ok
:-D
ADSL doesn't use just any phone lines. I think that less than half of the houses in the US are wired with high enough quality lines to support DSL. Also, the drop-off of bandwidth as a function of distance from the phone company's substation is pretty rapid. If you live in even a fairly spread-out suburb, chances are you can get crap DSL at best, let alone semi-rural or full-blown rural areas. Oh, and when I say "phone lines" I don't just mean the twisted pair running into your wall (although the physical wire quality is part of it), I'm talking about the various switching hardware upstream, too. Do you think that Podunkville doesn't have DSL available yet just because the phone companies are jerks? No, it's because it's an expensive investment for them to upgrade their "lines" to provide DSL.
So, no, ADSL doesn't use "the same crappy phone lines"... it uses different, not-as-crappy phone lines.
Also I put "broadband" in quotes because it's not entirely a very well defined term. (Yes, I know that there have been a few things attempting to define the term in various places... even a lawsuit over the use of the term, but it's not settled yet.) You can call pretty much anything from 128k up "broadband", but its really not in the same ballpark as 512k or 1M (or possible higher, with various new technologies like 802.16 MAN).
Besides, all that said, I consider your ADSL (via phone lines) slow because I have a cable modem.
:Wq
Not an editor command: Wq
The open spectrum concept raises its ugly head again. I suppose I shouldn't be surprised; it combines the sexiest of terms (Moore's Law! Metcalfe's Law! SDR! UWB! Spread Spectrum! Mesh Networks! Open Source!) in one neat package, tied with a bow. If only they could work in the magnetic bracelet that cures arthritis, it would be a marketer's dream.
There are other reasons for spectrum allocation besides the "technology limitations" cited in the ACM article. Two of the most significant are:
1. The spectrum is used for many different services, with differing Quality of Service (QoS) requirements. Some of these, like the Instrument Landing Systems at airports, emergency services, GPS, etc. I'd like to have dedicated spectrum available solely to them 24x7; the idea that a trapped fireman's call on his handheld 2-way radio is not heard because of interference from a nearby mesh network providing video packets of a football game (or, if you like, the trapped fireman's call on his limited-range Open Spectrum radio is not heard because the burning building's network is already down) is not very appealing.
Other services, like industrial heating (and even microwave ovens) do not even use the RF spectrum for communication at all; if not limited in spectrum these large transmitted power services can render people incommunicado over large physical areas. Open Spectrum advocates will claim that this last problem will be overcome by the processing gain of the Open Spectrum radio itself; I merely note that increasing processing gain is increasingly expensive, and getting 60 dB of processing gain is a severe pain at wideband bit rates, while it is a trivial exercise for a tuned circuit if the spectrum is allocated properly.
2. The spectrum has different physical properties that make certain frequencies (and frequency bands) more suitable for certain services. Services that require ionospheric refraction need to operate below 30 MHz; systems using satellite-earth links must operate above 30 MHz. Systems requiring a lot of antenna gain, such as space probes and terrestrial point-to-point links, need to be a high frequency (multiple GHz), where high gain can be achieved in a small physical size by the use of parabolic antennas. Systems requiring worldwide underwater coverage must be below 100 Hz. There are atmospheric attenuation peaks at 24 and 60 GHz (and others higher) caused by oxygen absorption that make these frequencies useless for any trans-atmospheric links, but ideal for short-range unlicensed systems (that's why there are ISM unlicensed bands there). Rain (a.k.a. hydrometeors) becomes a significant attenuator above 5-20 GHz, depending on the rate at which it falls; this affects systems in tropical regions more than those in more temperate areas (see a graph of atmospheric attenuation). The hydrogen line (1420.40575 MHz), used by astronomers, is a fixed frequency. Etc.--this is just a partial list. All frequencies are not created equal.
However, if you'd like to stick to technical problems, consider the multiple access problem for these systems.
The success of 802.11b is often cited as an example for the Open Spectrum initiative--an unlicensed band being used productively. However, 11b has now become the 800-lb. gorilla in the 2.4 GHz ISM band; other services attempting to use that band must coexist with it, but it doesn't have to coexist with them. Any interference it causes to these new services must be borne by them; as a result, we have created a de facto allocated band.