On Thu, 13 Nov 1997, Henri Kluytmans wrote:
> Isn't the amount of energy required for transmission of more concern
> than using the available bandwidth to it's limit.
Good point, in some situations one could imagine. But not all. Most
signals would not even be intended for reception outside a particular
solar system. Power limited? Who knows. Noise may even be quintillions
of simultanious transmissions from the same area, or just those that
happen to be pointed in this direction.
> Also by directing a focused beam you can prevent your
> "enemies" from detecting anything. (No need for stealth.)
Good point. But if we are lucky enough to be in the way of such a
signal, it's still likely to look like noise.
Spread spectrum is useful for several reasons besides stealth, including
reducing transmitted power requirements in some situations (PCS phones).
And the arguments re: data compression also tend to point to an advanced
transmission looking mostly like noise. Compression saves power.
> Furthermore a signal totally indistinguishable from random noise, so
> without any redundancy, will not be able to correct any errors
> created by damage to the signal, and should therefore not be
> practical.
Er, I don't buy this. First: who said "totally indistinguishable from
noise"? We are far from being able to looking at the radiation from a
single star and exahustively analyzing its signal possibilitys. We
probably look at 1% of it at best, from a bandwidth standpoint alone.
Also, error correction and/or redundancy could be in a form not
understandable unless you know the demodulation technique and/or codes.
- PW
PS: OK, now I'm bored of the subject. I'll shut up now.