Sun Aug 8 10:35:36 CEST 2010
LFSR beacon detection
Actually, this might be interesting to use together with the krikit
idea. Or how to make a variant of GPS using LFSR audio-beacons.
Problem: we have plenty of bandwidth (say 3 - 10 kHz) but not dynamic
range (environment noise, and "noisyness" of the transmitter). We
want to transmit a low bitrate signal.
Solution: using spread-spectrum techiques we can trade bandwidth for
A PSK baseband signal after heterodyne filtering by the carrier wave
is a complex phase signal. It might have some small residual
modulation that is easy to track, so let's ignore it.
The basic idea is to use the LFSR to perform a local prediction for
the I and Q signals separately, keeping the operation itself linear.
(I.e. if more than one bit of information is available, it can be
We integrate the output of this predictor to yield a slow-varying
information carrier. A Schmitt trigger on the output of the
integrator should be enough.