Re: Recording XM signals...an issue
- From: NewGuy <newguy@xxxxxxxxxxx>
- Date: Thu, 01 Dec 2005 23:30:22 GMT
People, thanks for the re-education. I am so energized I might make
love to my wife tonight!!!!!!!!!!!!!!!
H
On Tue, 29 Nov 2005 01:47:47 -0000, dplatt@xxxxxxxxxxxx (Dave Platt)
wrote:
>In article <8l9no15p3alngp6rlcatd1sjahlb1ti7gd@xxxxxxx>,
>NewGuy <newguy@xxxxxxxxxxx> wrote:
>
>>Wow! Well, I asked for it. I use to work in the spread spectrum world
>>and my hope was that technology would eventually render all this
>>bandwidth angst to the junk yard. True spread spectrum, like the
>>miliary use with very expensive...and in the past...GaAs based
>>processors, renders bandwidth an obsolete concern....in so far as
>>specrual allocations and bandwidth has the same narrow definition as
>>in the past.
>>
>>With SS, you actually spread the signal over such a large bandwidth
>>that any signal looks like noise...non-detectible noise against all
>>other signals cluttering any given bandwidth allocation....with enough
>>spectrum, signal reception, multipath, power, and signal fidelity and
>>noise in the traditional S/N become of historical interest. Sadly, the
>>technology in cheap silicon still looks deficient and too expensive.
>>However, it won't be long.
>
>T'ain't quite so simple, I'm afraid. You can't get something for
>nothing.
>
>Spread-spectrum comes at a price... it does raise the noise level (as
>seen by other users of that part of the spectrum) throughout whatever
>transmission bandwidth it uses. Although the increase in noise level
>created by one SS transmitter may be small and difficult to detect,
>put enough of 'em together in one area and you've got a large amount
>of added noise energy to deal with. This added noise can degrade both
>SS and non-SS uses of the frequencies in question.
>
>The amateur radio community has been dealing with the results of this
>for some time. I've been told that in many urban areas, it's no
>longer possible to do weak-signal work in the 2.4 GHz ham bands, due
>to the presence of many thousands of low-powered 802.11b/802.11g
>direct-sequence spread spectrum radios.
>
>> WiMax is suppose to be this technology, but I am not sure. As I look
>>at the way WiMax is being implemented, I suspect they are not using
>>true spread specturm.
>
>My understanding is that WiMax uses OFDM (orthogonal frequency
>division multiplexing), a system with large numbers of closely-spaced
>carriers. It's similar to 802.11g in that respect.
>
>There's some new UWB (ultra-wide-band) work being done, which shows
>promise for very high bandwidths over very short distances (ideal for
>in-home video and that sort of thing). One UWB group is proposing or
>using OFDM, while another is using high-speed-impulse modulations
>which I suspect are closer to the "true spread spectrum" stuff you
>worked on in the military.
.
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