> -----Original Message----- > From: [EMAIL PROTECTED] [mailto:discuss- > > 2007/2/27, Eric Blossom <[EMAIL PROTECTED]>: > > On Tue, Feb 27, 2007 at 05:07:31PM -0500, Tom Rondeau wrote: > > > > -----Original Message----- > > > > From: [EMAIL PROTECTED] > [mailto:discuss- > > > > [EMAIL PROTECTED] 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.
I was under the same opinion, which was why d_flip was in correlate_access_code originally, but that screwed some stuff up down the chain. I think whatever new solution we use should be general for non-differential MPSK and not just BPSK. > To make things a bit clearer: correlate_access_code is in reality a > preamble detector, or am I missing something? The access code, which is not only used to identify the start of a MAC frame, but it can also identify the network being used. Tom _______________________________________________ Discuss-gnuradio mailing list [email protected] http://lists.gnu.org/mailman/listinfo/discuss-gnuradio
