[wsfii-discuss] Interesting URL

Fri Dec 16 13:11:14 UTC 2005

As someone who worked as a telecommunications engineer on
microwave, coaxial, analog freqency division multiplex and
digital time division multiplex systems mainly for
telephony in the late seventies and early eighties, I must 
admit to finding the article quoted and this discussion 
very interesting. 

Having seen the introduction of the first working optical
fibre transmission system used for real live telephony between
Stevenage and ( Welwyn ? ) a few miles away circa 1977, and then seen
the continuing revolution in telecommunications resulting from 
improvements in fibre optical modulation techniques and fibre 
purity over the last 3 decades I suspect it very unlikely that 
many of our communication systems are yet optimal in terms of
carrying capacity or modulation techniques. At that time we
believed very wrongly that the maximum practical transmission carrying 
capacity of the local copper loop was 9.6Kbit/s. The very same
twisted pair cabling is now carrying up to 8MBit/s ADSL
broadband. 

That said, we need to treat claims of large breakthroughs
in carrying capacity prior to publication of peer-reviewable
details with some caution. There is a danger that someone
will make such a claim with a view to artificially raising
the stock of a small company, and will succeed in bribing
or duping, or constructing a "respectable" academic reviewer
or other person with the ability supposedly to confirm the 
technical advantages claimed. Follow the money and buyer beware of
shares in hyped technology stocks ! Where the investors in
a claimed new technique are few, private and sufficiently within
the knowledge loop to be able to evaluate the risk and patents are
pending, breakthroughs which still represent trade
secrets can be ethically developed for the benefit of
all when the relevant patents are published and open review becomes
possible. 

The reason a claimed improvement in modulation technique
could affect copper circuits as much as wireless ones is 
because similar modulation schemes, are used on both, and
similar noise and crosstalk issues affect both, and
similar electronics are used to drive signal 
carriers into and out of both 
of these systems. Optical fibre system are thought to
be driven far less optimally in comparison to their
theoretical limits so I will be far less surprised to
see continued exponential improvements in practical and
achieved microwave and optical carrier capacity than I 
would be with twisted pair copper and radio frequencies below 500MHz
or so, where Shannon's law appears to leave less scope for
improvement in throughput than in the microwave or
the optical spectrum. 

One technique which has proved massively successful in multiplying
the capacity of particular radio frequency bands has been achieved
by replicating finite shared capacity by using many smaller geographical 
area cells, and using
lower power so that signals do not cross over much beyond
cell boundaries. This technique which has enabled
mobile telephony to become something very cheaply available to 
everyone, rather than just the tiny and rich minority which 
had access to wireless phones 40 years ago. 

Richard.

On Fri, Dec 16, 2005 at 04:08:16AM -0800, Charles core Stevenson wrote:
> Hi Karel,
> 
> On 12/16/05, Karel Kulhavy <clock at twibright.com> wrote:
> > Knowledge of the Shannon's law saves time reading these articles.
> 
> Looking at their FAQ (and yet still completely ignorant of these issues):
> 
>    	
> 
> DEFINITIONS - xMaxTM, xG Flash SignalingTM
> Questions:
> 
> 1.  Is the name xG meant to imply a comparison with 3G wireless technology?
> 2.  What is xMax?
> 3.  What is xG Flash Signaling?
> 4.  What is Index-NTM?
> 5.  What is VaribandTM?
> 6.  What is S/Nr?
> 7.  What is Shannon's Law?
> 8.  What is BER?
> 9.  What is RF?
> 10.  What is Modulation?
> 11.  What is the status of product development?
> 12.  I understand xMax can be used for both wired and wireless
> applications. Why would wired applications be an attractive market?
> 13.  What government approval is required to operate xMax?
> 14.  For broadband wireless applications, how far can xMax transmissions reach?
> 15.  What steps have been taken to protect xMax?
> 16.  What problem does xMax solve for wireless applications?
> 17.  What applications can xMax be used for?
> 18.  What testing and validation has been done on xMax?
> 19.  What is the error correction scheme used in FSK, QAM, AFSK, PSK
> or other modulation schemes?
> 20.  What is the BER (bit-error-rate) of xMax for different values of S/Nr?
> 21.  Does xMax require more transmitter power than other technologies?
> 