Re: [Discuss-gnuradio] Question about carrier syncronization fordemodulating QPSK/BPSK signal.

[Eric Blossom]

On Sat, Jun 03, 2006 at 02:49:16PM +0800, 2 1 wrote:
> Thanks for your working.
> 
> I wonder if 1.28Msymbol/s (2.56Mbps for qpsk) is possible to be archieved
> through costas loop.
> I'm worry about the 32Mbyte/s of USB 2.0 interface may not be enough.
> I've read the code from
> http://aphex.media.mit.edu/wiki/tiki-index.php?page=BPSK (using costas loop)
> and found that 8 samples are used to build a sinusoid wave at the baseband
> level. Consindering complex sampling (4 bytes for one samle), the
> maximum symbol rate is only 1M. If filter with over sampling is employed,
> the data rate may be much lower.
> 
> Right now, I'm thinking about using pilot seqence for doing carrier sync and
> symbol sync together. I hope it works, but more experiments are needed.

The QPSK code works fine at 2 or more samples/baud.
2 Mbaud (4 Mbit/sec) should be doable, modulo CPU consumption.
[We haven't measured the performance, or tried to do anything to make
it run faster.  Lots of room for improvement.]

We're currently using a Costas loop to track the carrier followed by a
complex M&M symbol timing block.  Seems to work fine.  We do whiten
the transmitted signal to ensure lots of transitions.

I'm giving a talk at USENIX today, and will get the rest of the QPSK
code checked in by Monday.

Eric