"Spread spectrum is much more hype than real benefit.
      ...  Direct Sequence spreading helps you hide in the
      noise.  Both are useful for military applications, but
      have limited ligitimate civilian use."


Two civilain uses:

GPS and IS-95/CDMA 'PCS' (as employed by Verizon and, I believe, also
Sprint as pioneered by Qualcomm) -

Not to mention a variety of 'unlicenssed' apps (point to point T1 links)
in the ISM bands at 900 MHz and 2.4 GHz.

CDMA removes most of the nightamre that is known in the 'discrete
frequncy' world of telecom (all your flavors of TDMA like GSM,
IS-136) as 'system-channel planning'.

Instead of juggling just the same 416 channels (in a classical
cellular system) you get to also select different spreading
Walsh 'codes' from site to site ... that along with suitable
'offsets' in the stepping from sites with the same 'code'.

Jim


----- Original Message -----
From: "Douglas Butler" <dbutler@IMETRIX.COM>
To: <PICLIST@MITVMA.MIT.EDU>
Sent: Friday, April 12, 2002 1:07 PM
Subject: Re: [OT]:Spread Spectrum Efficiency for Continuous signals


> Spread spectrum is much more hype than real benefit.  Frequency hopping
> is good to prevent eavesdropping.  Direct Sequence spreading helps you
> hide in the noise.  Both are useful for military applications, but have
> limited ligitimate civilian use.
>
> If you had four channels of space with a varying number of users,
> sometimes more than four, who couldn't agree on who should use what
> space when, then spread spectrum helps to arbitrate the use of bandwith.
>  When too many users occupy the band everybody's signal to noise ratio
> degrades, and everybody suffers equally.
>
> I can stay on this soapbox for longer than anybody wants to read...
>
> Sherpa Doug
>
> > -----Original Message-----
> > From: Brandon Irwin [mailto:BrandonI@LEAKED.INFO]
> > Sent: Friday, April 12, 2002 1:30 PM
> > To: PICLIST@MITVMA.MIT.EDU
> > Subject: [OT]:Spread Spectrum Efficiency for Continuous signals
> >
> >
> >       I've been reading about spread spectrum and I don't see
> > how spread
> > spectrum techniques could be used for continuous transmissions.
> >
> >       Everyone seems to want to convert everything to spread spectrum
> > because of its greater efficiency. I don't see how it could
> > be any more
> > efficient when used on continuous transmissions such as a TV
> > video signal.
> > The following assumes that they would keep the signal in the
> > analog form.
> > If you have four available channels with four TV stations and
> > you implement
> > the freq hopping method, then all four channels will always
> > be full because
> > the TV stations would never have a pause to allow a fifth channel to
> > transmit. If you where to use a method similar to TDMA, then
> > you would see
> > little gaps in the picture.
> > It seems to me that the only way the "more efficient" spread spectrum
> > methods could be used would be to convert the signal to a
> > digital form so
> > it could be buffered on the TV side while the transmission ceased for
> > whatever amount of time.
> >
> >       Is there something I'm missing? Maybe the whole concept?
> >
> >
> >
> >
> > -Brandon Irwin
> >
> >
> >
> >
> >
> >
> > -------------------------------------
> > This message was written using the Dvorak keyboard layout.
> >
> > --
> > http://www.piclist.com hint: PICList Posts must start with ONE topic:
> > [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads
> >
> >
> >
>
> --
> http://www.piclist.com hint: PICList Posts must start with ONE topic:
> [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads
>
>

--
http://www.piclist.com hint: PICList Posts must start with ONE topic:
[PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads