Xref: utzoo rec.ham-radio:4148 sci.electronics:2401
Path: utzoo!mnetor!uunet!lll-winken!lll-lcc!ames!ll-xn!mit-eddie!bbn!uwmcsd1!dogie!uwvax!umn-d-ub!umn-cs!hyper!guest
From: guest@hyper.UUCP (guest)
Newsgroups: rec.ham-radio,sci.electronics
Subject: Spread Spectrum
Message-ID: <1474@hyper.UUCP>
Date: 1 Mar 88 17:06:12 GMT
Organization: Network Systems Corp., Mpls. MN
Lines: 38
Keywords: detection-unlikely


I think I can demonstrate the whole concept of spread spectrum
stealthiness with the following simple BASIC program:

Input "Value to be sent";V
Input "Number of bands used";B
Vx=V/B
R=0
 For J=1 to B
  R=R+Vx+(1-RND(0)*2)
 Next J
Print "Value received =";R
Print "Signal power in each band =";Vx
End

As you can see, the signal V has its energy distributed at B points with
strength Vx.  Vx is superimposed on the pre-existing random noise (here
confined to a range of + and - 1) at each point J in B.

As long as Vx is not too far below +and- 1, and there are sufficient bands,
the random noise tends to cancel, leaving the original signal R, which
is correlated here by simple addition.

There is no need, however, to have the bands evenly spaced. In fact the
spacing of the bands should be a changing function. Any other stealth
xmitter would, in all probability, be using a different band spacing
function at any given time. Thus there is no interference because there
is no correlation.  Correlation is the key to reception, interference and
detection.

So if the signal (in its discrete components) looks like noise, tastes like
noise and feels like noise (to an uninformed receiver) then it must be
noise. You can claim you have detected it, but I think not.


John Logajan            umn-cs!hyper!ns!logajan
Network Systems Corp
7600 Boone Ave
Brooklyn Park, MN  55428