Correlation doesn't always return real numbers, only if its the correlation of the same the PN sequence(including phase). The received signal could have a phase shift, complex numbers are needed.
On Mon, Jul 13, 2009 at 8:48 AM, Jordan J Riggs <[email protected]> wrote: > I'm not an expert on the matter, but I suspect that the XCVR2450 board > requires some sort of command to select the 5GHz band, which would need to > be implemented in the sounder's FPGA code. > At a chip rate of 32MHz, you have a resolution of 3e8/32e6 meters. The > length of the PN sequence determines the maximum unambiguous distance at > which multipaths can be detected. So with a degree-12 sequence, you have > (2^12 - 1)*3e8 meters to work with. With long sequences, however, you are > limited by the capabilities of the USRP. Depending on your DBoard, you have > ~20mW of output. Your antenna also makes a big difference. Especially if you > want to do any work outside, I would use something like a log-periodic > antenna. If you can get your hands on an amplifier, you can significantly > boost your range. > In my experience (with a sounder of my own design), averaging multiple IR's > appreciably reduces the noise. > > While I'm at it, can anyone explain why a complex correlation vector is > coming out of the sounder FPGA? Doesn't a mathematical correlation return > real values? > > Jordan > > On Fri, Jul 10, 2009 at 5:49 AM, Martin Braun > <[email protected]>wrote: > >> Hi, >> >> I was wondering if there's a way to use the channel sounder (gr-sounder) >> with the XCVR d'boards at 5 GHz. I gave it a try, but the channel >> impulse responses only popped up +-1s and zeros. Well, I wasn't >> expecting it to work since the XCVR is not mentioned in the README, but >> can it be tweaked? >> >> Plus, does anyone have any experience with the sounder they'd share? >> If so, there's a couple of things I'd be interested to know: >> >> - What's a sensible distance for getting useful results without any >> additional hardware? >> - Can I tune the amp/gain settings to increase my SNR without distorting >> the result? >> - Assume the channel's stationary. In that case, every IR vector >> should contain the same data (up to some phase shift, probably). I'm >> figuring I could further increase the SNR by averaging >> (phase-correctly) over several IRs, right? >> >> If anyone has any interesting stories on channel sounding with GR/USRP, >> I'd be grateful for any info. >> >> Cheers, >> MB >> >> -- >> Dipl.-Ing. Martin Braun Phone: +49-(0)721-608 3790 >> Institut fuer Nachrichtentechnik Fax: +49-(0)721-608 6071 >> Universitaet Karlsruhe (TH) http://www.int.uni-karlsruhe.de/ >> >> _______________________________________________ >> Discuss-gnuradio mailing list >> [email protected] >> http://lists.gnu.org/mailman/listinfo/discuss-gnuradio >> >> > > _______________________________________________ > Discuss-gnuradio mailing list > [email protected] > http://lists.gnu.org/mailman/listinfo/discuss-gnuradio > >
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