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Re: [Discuss-gnuradio] Question about carrier syncronization fordemodula
Re: [Discuss-gnuradio] Question about carrier syncronization fordemodulating QPSK/BPSK signal.
Sat, 3 Jun 2006 14:49:16 +0800
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.
2006/6/2, Matt Ettus <address@hidden>:
Eric Blossom wrote:
>On Thu, Jun 01, 2006 at 08:54:28AM -0400, Tom Rondeau wrote:
>> Set the
>>alpha value somewhere around 0.005 - 0.05 to get started (and play with it
>>from there). The beta value should be about an order of magnitude smaller
>>(it's been set to
0.25*alpha^2; I'm not sure where that comes from, though).
>>The next two arguments are the max and min frequency deviation in terms of
>>scaled frequency, so 0.05 and -0.05 work well. The final value of the
>>reference phase can just be set to 0. This block's been around for a bit of
>>time and used in BPSK.
beta = alpha^2/4 gives a critically damped loop.
>>>From here, you'll need to worry about symbol synchronization. We build a
>>complex modified Mueller and Muller clock recovery circuit for this called
>>gr_clock_recovery_mm_cc (this file existed already, but we modified it
>>some). Set mu=0.05, omega is approximately the samples per baud,
>>gain_mu=0.05, gain_omega=0.25*mu^2, and omega_rel_limit=0.5. These values
>>will get you started.
Same way of setting beta here.
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