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RE: [Discuss-gnuradio] No BPSK modulator?

From: Tom Rondeau
Subject: RE: [Discuss-gnuradio] No BPSK modulator?
Date: Tue, 27 Feb 2007 17:07:31 -0500

> -----Original Message-----
> From: address@hidden [mailto:discuss-
> address@hidden On Behalf Of Trond Danielsen
> Sent: Tuesday, February 27, 2007 10:46 AM
> To: gnuradio mailing list
> Subject: [Discuss-gnuradio] No BPSK modulator?
> Hi,
> Is there a reason why there is no "ordinary" n-PSK modulator and
> demodulator available, only the differential one? If not, I'll modify
> the existing one and submit a patch.

It's not so much that there isn't a non-differential BPSK modulator, it's
that there is no demod for it. Basically, we have to be able to determine
the phase orientation of the incoming signal in some way to know what our
phase is. In BPSK, this is simple, and this was the original reason why
gr_correlate_access_code_bb had a d_flip variable in it, so that when the
phase inversion was detected, it would decode it properly.

However, this was never a good solution and ended up hurting us because
sometimes we'd trigger this flip with random data, which would screw up the
packets. This was the reason the SSH sessions would crash and why Johnathan
made the original fix in the whitener.

The solution to this is to use the correlator to detect the phase, but let
the next guy down the line understand what to do with it. We probably want
to send a control signal out to set the phase derotation and trigger the
access code found state at the same time, specifically, in the simple framer
state machine.


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