Re: [Discuss-gnuradio] No BPSK modulator?

[Trond Danielsen]

2007/2/27, Eric Blossom <address@hidden>:
> On Tue, Feb 27, 2007 at 05:07:31PM -0500, Tom Rondeau wrote:
> > > -----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.
>
> You could use bit 2 of the output stream of
> gr_correlate_access_code_bb to encode the "I've seen the inverted
> pattern".  Then anybody who cared could look at it and take action if
> they wanted to, but it wouldn't interfere with any existing code.
>
> Eric

Thank you all for anwering. What I am really looking for is just BPSK,
so that should simplify things a bit. I intent to demodulate the BPSK
modulated message from GPS satellites, therefore the interest in
not-differential PSK modulation.

To make things a bit clearer: correlate_access_code is in reality a
preamble detector, or am I missing something?


--
Trond Danielsen