Noise figure paradox
 

Hi Jim,

"Jim Lux" wrote in message
...
Actually, state of the art is probably Low Density Parity Check (LDPC)
codes, as far as approaching the limit.

I hadn't heard of them; thanks for the link. Can you comment on how they
compare to Reed-Solomon codes?

I have just enough background in error-correcting codes to spout off the right
keywords in nearly-coherent Usenet posts and wait for people to point out my
errors. :-)

---Joel

Noise figure paradox
 

Dear Jim:

I am obliged to you for the title correction. My memory might not be
what it was. Thanks also for the abstract.
While the paper (again from memory and poked by the abstract) is written
in terms of SSB/DSB, a main issue is that of vector addition of copies of a
signal with noise and interference not being coherent. One ends up with a
system that is resistive to noise and interference up to a point where it
stops working.
73, Mac N8TT
--
J. McLaughlin; Michigan, USA
Home:
"Jim Lux" wrote in message
...
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
 

Dear Joel - KE7CDV:

Sounds as if Jim has you pointed to a source. When you are in the library,
do find the follow-up comments. They are a big window, as I recall, into
the mind-set of the time. 73, Mac N8TT

--
J. McLaughlin; Michigan, USA
Home:
"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

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
 

On Mar 26, 9:35*am, "Joel Koltner"
wrote:
Hi Jim,

"Jim Lux" wrote in message

...

Actually, state of the art is probably Low Density Parity Check (LDPC)
codes, as far as approaching the limit.

I hadn't heard of them; thanks for the link. *Can you comment on how they
compare to Reed-Solomon codes?

I have just enough background in error-correcting codes to spout off the right
keywords in nearly-coherent Usenet posts and wait for people to point out my
errors. :-)


Much longer block length than typical R-S. Also, the way the check
bits are generated is different. Each check bit isn't formed by
combining ALL the source bits, just some of them (obviously a
different "some" for each of the check bits), hence the name Low
Density. Both are usually roughly rate 1/2.