Hi Richard,

"Richard Clark" wrote in message
...
In other posts related to deep space
probe's abilities to recover data from beneath the noise floor, much
less cell phones to operate in a sea of congestion, I encountered the
economic objection that such methods cost too much - expense of
bandwidth.

I don't think anyone stated they cost "too much," just that there is a cost in
increased bandwidth, and bandwidth isn't free.

In general the spread spectrum processing gain is proportional to the
bandwidth increase over what the original data stream would require without
any spreading.

Well, not having seen anything more than yet another qualification -
how much is "too much?"

Definitely depends on "the market." You can bet the cell phone developers
have sophisticated models of possible radios and the channel and associate
with each piece a cost (e.g., bandwidth = $xx/Hz, improving close-in phase
noise of master oscillator = $xx/dBc, etc.), and then run a lot of simulations
to try to make the average cost of each bit as low as possible. Of course,
there are many variables that are impossible to ascertain precisely such as
how quickly uptake of new cell services (e.g., 3G data) will be in a given
area (as this drives how many towers you put there initially and how quickly
you roll out more), how fast fab yields will improve that lower your costs and
improve RF performance, etc.

Starting with BPSK and a S+N/N of roughly 10.5 dB, the bit error rate
is one bad bit in one million bits. This is probably the most
plug-ordinary form of data communication coming down the pike; so one
has to ask:
"is this good enough?"
If not, then "SNR of 60dB" is going to have to demand some really
astonishing expectations to push system designers to ante up the
additional 49.5 dB.

Why Richard, I'm starting to think you don't spend thousands of dollars per
meter on your speaker cables. :-) Hey, see this:
http://www.noiseaddicts.com/2008/11/...st-audiophile/ -
- $7,000/m speaker cables! Includes, "Spread Spectrum Technology!" :-)

That being said, back in the analog broadcast TV days (oh, wait, not all of
them are gone yet, but they will be soon), I believe that "studio quality"
NTSC is considered to be 50dB SNR (for the video), whereas people would start
to notice the noise if the received signal's SNR had dropped below 30ish dB,
and 10dB produces an effectively unwatchable pictures. This reinforces your
point that "good enough" is highly subjective depending on how the
"information" transmitted is actually used.

You make a good point that the Shannon limit gives a good quantitative measure
of how you go about trading off bandwidth for SNR (effectively power if your
noise if fixed by, e.g., atmospheric noise coming into an antenna). Shannong
doesn't give any hint as to how to achieve the limits specified, although I've
read that with fancy digital modulation techniques and "turbo"
error-correcting codes, one can come very close to the limit.

---Joel