Noise figure paradox
 

On Wed, 25 Mar 2009 09:44:45 -0700, "Joel Koltner"
wrote:

As to sampling error via the net. Time was when 16x over-sampling for
RS-232 was the norm.

I've meet many RS-232 routines that don't do any over-sampling at all

Which is no more complex than setting 4 register bits - I wouldn't
call that a "routine," however.

-- I've
even written a few. :-)

Why more than one? Were the rest undersampling routines?

Fuzzy-232? That copyrighted form of communication is an information
network layer supporting Cecil's (r) "standing wave current" (c)
explanation with answers that appear first, tailor-fitted to the
strawman question that follows - otherwise known as the Sub-optimal
Conjugated Hypothesis Information Transform (SCHIT) routine found in
quantum babbelizers everywhere. Discarding random bytes improves the
intelligibility and will whiten teeth.

73's
Richard Clark, KB7QHC

Noise figure paradox
 

Dear Joel Koltner (no call sign):

I know of no site where the classic paper may be downloaded. The paper
had a significant influence on how people thought about modulation and
frequency allocation. "Shannon, Poison (I can not think how to spell his
name) and the Radio Amateur" is the title of the paper. A good library
should be able to get you a copy. The same issue had a paper on small,
loaded cavities, which became the norm for front end selectivity in VHF
communication receivers.

Regards, Mac N8TT

--
J. McLaughlin; Michigan, USA
Home:
"Joel Koltner" wrote in message
...
"Joel Koltner" wrote in message
...
Is that available publicly anywhere?

What I really meant here was, "Is that available *to download from the
Internet* publicly anywhere?"

Noise figure paradox
 

Thanks Mac, I'll take a look next time I'm near a university library. (I'm in
southern Oregon and there aren't any engineering schools down here...)

---Joel (KE7CDV)

Noise figure paradox
 

On Wed, 25 Mar 2009 14:45:33 -0700, "Joel Koltner"
wrote:

These were software RS-232 receivers, so you make use of whatever timers, edge
interrupts, etc. that you have sitting around to first the start bit, load up
a timer to then trigger in (what should be) the middle of the bit time for the
sample, etc. I've written pretty much the same routines a small handful of
times on different CPUs and in different languages.

Hi Joel,

Pretty deep in the basement, there. Sounds like the way Apple used to
run their floppy disc, read it, and write it with a minimum of parts
(and expense).

73's
Richard Clark, KB7QHC

Noise figure paradox
 

Joel Koltner wrote:
"Joel Koltner" wrote in message
...
Is that available publicly anywhere?

What I really meant here was, "Is that available *to download from the
Internet* publicly anywhere?"

Yes.

To get more than the abstract for free you have to be an IEEE member and
a member of MTTS or otherwise subscribed to the online system.

For the abstract start at:
http://ieeexplore.ieee.org/xpl/Recen...number=4547924

and for $29...
http://ieeexplore.ieee.org/guide/g_tools_apo.jsp

Happy trails!
- Galen, W8LNA

Noise figure paradox
 

Joel-- think you might be impressed with the collection in K.Fall's
(Oregon Institute of Technology) they run EE course's there! Jim NN7K

Joel Koltner wrote:
Thanks Mac, I'll take a look next time I'm near a university library. (I'm in
southern Oregon and there aren't any engineering schools down here...)

---Joel (KE7CDV)

Noise figure paradox
 

J. Mc Laughlin wrote:
Dear Joel Koltner (no call sign):

I know of no site where the classic paper may be downloaded. The paper
had a significant influence on how people thought about modulation and
frequency allocation. "Shannon, Poison (I can not think how to spell his
name) and the Radio Amateur" is the title of the paper.

Actually, the title is "Poisson, Shannon, and the Radio Amateur",
Proceedings of the IRE, Dec 1959, Vol 47, Issue 12, pages 2058-2068. The
abstract is:


Congested band operation as found in the amateur service presents an
interesting problem in analysis which can only be solved by statistical
methods. Consideration is given to the relative merits of two currently
popular modulation techniques, SSB and DSB. It is found that in spite of
the bandwidth economy of SSB this system can claim no over-all advantage
with respect to DSB for this service. It is further shown that there are
definite advantages to the use of very broadband techniques in the
amateur service. The results obtained from the analysis of the radio
amateur service are significant, for they challenge the intuitively
obvious and universally accepted thesis that congestion in the radio
frequency spectrum can only be relieved by the use of progressively
smaller transmission bandwidths obtained by appropriate coding and
modulation techniques. In order to study the general problem of spectrum
utilization, some basic results of information theory are required. Some
of the significant work of Shannon is reviewed with special emphasis on
his channel capacity formula. It is shown that this famous formula, in
spite of its deep philosophical significance, cannot be used
meaningfully in the analysis and design of practical, present day
communications systems. A more suitable channel capacity formula is
derived for the practical case. The analytical results thus obtained are
used to show that broadband techniques have definite merit for both
civil and military applications.

Phil Karn (KA9Q) had some comments:
http://www.ka9q.net/vmsk/shannon.html

Noise figure paradox
 

Joel Koltner wrote:
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.


For very low level signals spread spectrum doesn't necessarily buy you
much. If you use 10 times the BW, you have 10 times the noise, so your
received SNR is worse by a factor of 10dB. But you get 10dB of
processing gain when you despread, and your output SNR is the same as it
was before.

Of course, you consumed some electrical power on both ends to spread and
despread things. wideband amplifiers are less efficient than narrow band
ones, as well. Saturated amplifiers are more efficient than non
saturated amplifiers.

In general, the most efficient (considering power consumed on both ends)
transmission is a very narrow band signal, where the bandwidth is just
wide enough to contain the required data rate.

This drives you to things like BPSK, GMSK, and QPSK. Ideally, the
signal spectrum would be a nice fat rectangular pulse.

In the deep space probe business, watts count at every step of the way.


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.

Actually, state of the art is probably Low Density Parity Check (LDPC)
codes, as far as approaching the limit. They've become more practical
because digital logic is becoming a lot cheaper (in a nanowatts per bit
sense) to do the coding/decoding. They're also unencumbered by the
patents for turbo codes.

http://en.wikipedia.org/wiki/Low-den...ity-check_code

Noise figure paradox
 

The "Turbo" codes are achievable in silicon with moderate effort.

And the payment of a suitable fee to the folks who OWN the turbo codes
at France Telecom
http://www.francetelecom.com/en_EN/i...y/turbo_codes/
http://www.spectralicensing.com/licfaq.htm


Note also that turbo and LDPC are really suited to longer block lengths
(1000 bits and bigger). For small block lengths, codes like Hamming
might be better.

Reed-Solomon combined with Viterbi decoders of convolutional codes are
also popular.

Note that in deep space, at a bit rate of 8 bps, you might not want to
use a code with a 1000 bit codeblock..

A
work going back a dozen years or more can be found at:
http://sss-mag.com/G3RUH/index2.html
(consult the adjoining pages for fuller discussion)

73's
Richard Clark, KB7QHC

Noise figure paradox
 

"Jim-NN7K" . wrote in message
...
Joel-- think you might be impressed with the collection in K.Fall's
(Oregon Institute of Technology) they run EE course's there! Jim NN7K

Thanks, I'll have to make a trip over. Heck of a lot closer than Corvallis...