So maybe the PLL is not a good solution between it will have an unknown amount of initial phase offsets by the time it locks. Since the relative phase between different carriers is the essential information sought after, maybe the better way is to construct very narrowband filters. Now very narrowband can mean a lot of taps, hence a lot of resources consumed. Here is where I don't know the limitation of resources. If I want to set up a filter of say 4 Hz bandwidth for a signal at 1MHz, and if you have a lot of these signals at different frequencies, what would be the best way to extract these? Maybe the way to go is to have the LO at 1MHz, so the many signals being looked at are +/- many hundreds of kHz. How many taps would it require to extract a signal at say 300 kHz with the 4Hz bandwidth? Can the USRP do 200 taps for each of the 30 carriers (I am just asking without exact calculation here)?
Thanks, LD From: Marcus D. Leech [mailto:mle...@ripnet.com] Sent: Wednesday, May 08, 2013 3:39 PM To: LD Zhang Cc: discuss-gnuradio@gnu.org Subject: Re: [Discuss-gnuradio] How many multiple/simultaneous PLLs can I have running on USRP2? I guess there may be an issue that since different PLLs will lock up at different time, so there are unknown amount of initial phase offsets for each PLLs. Would love to know if there are any ways around that. LD Well, presumably, you'd be using a PFB filterbank or something to create the multiple streams, and then use PLL demodulators to extract bits from those. The PFB filterbank should have uniform group delay across all streams, as far as I know. -- Marcus Leech Principal Investigator Shirleys Bay Radio Astronomy Consortium http://www.sbrac.org
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