Hi, I heard that there is a technique of detecting weak QPSK signal of very low SNR (e.g., -20dB) by multiply with 4 times the reference phase signals. May I know if any one knows the name of that technique? Thanks. Regards,
Detection of weak QPSK signal, e.g., SNR=-20dB
Started by ●January 16, 2014
Reply by ●January 17, 20142014-01-17
On Thu, 16 Jan 2014 18:03:06 -0800 (PST), yweesoon@gmail.com wrote:>Hi, >I heard that there is a technique of detecting weak QPSK signal of very low SNR (e.g., -20dB) by multiply with 4 times the reference phase signals. >May I know if any one knows the name of that technique? > >Thanks. >Regards,Sometimes relevant terms are "fourth-order nonlinearity" or "high-order spectra analysis". I've not known the technique to be called by a common name, assuming we're thinking of the same thing. Eric Jacobsen Anchor Hill Communications http://www.anchorhill.com
Reply by ●January 17, 20142014-01-17
On Thursday, January 16, 2014 9:03:06 PM UTC-5, ywee...@gmail.com wrote:> Hi, > > I heard that there is a technique of detecting weak QPSK signal of very low SNR (e.g., -20dB) by multiply with 4 times the reference phase signals. > > May I know if any one knows the name of that technique? > > > > Thanks. > > Regards,Maybe you are thinking of raising the signal itself to the fourth power to collapse the modulation into a carrier stick. That works but not at -20 dB SNR.
Reply by ●January 17, 20142014-01-17
On Friday, January 17, 2014 2:22:37 PM UTC-5, John wrote:> On Thursday, January 16, 2014 9:03:06 PM UTC-5, ywee...@gmail.com wrote: > > > Hi, > > > > > > I heard that there is a technique of detecting weak QPSK signal of very low SNR (e.g., -20dB) by multiply with 4 times the reference phase signals. > > > > > > May I know if any one knows the name of that technique? > > > > > > > > > > > > Thanks. > > > > > > Regards, > > > > Maybe you are thinking of raising the signal itself to the fourth power to collapse the modulation into a carrier stick. That works but not at -20 dB SNR.It's not clear to me whether the OP is considering detecting the presence of a QPSK signal at a known {fc, R} or if the OP is considering actually demodulating and/or detecting the bits.
Reply by ●January 17, 20142014-01-17
On Fri, 17 Jan 2014 12:59:15 -0800 (PST), julius <juliusk@gmail.com> wrote:>On Friday, January 17, 2014 2:22:37 PM UTC-5, John wrote: >> On Thursday, January 16, 2014 9:03:06 PM UTC-5, ywee...@gmail.com wrote: >> >> > Hi, >> >> > >> >> > I heard that there is a technique of detecting weak QPSK signal of very low SNR (e.g., -20dB) by multiply with 4 times the reference phase signals. >> >> > >> >> > May I know if any one knows the name of that technique? >> >> > >> >> > >> >> > >> >> > Thanks. >> >> > >> >> > Regards, >> >> >> >> Maybe you are thinking of raising the signal itself to the fourth power to collapse the modulation into a carrier stick. That works but not at -20 dB SNR. > >It's not clear to me whether the OP is considering detecting the presence of a QPSK signal at a known {fc, R} or if the OP is considering actually demodulating and/or detecting the bits.I think that's too low of an SNR to get any information, so I think just signal power detection is the only hope. Processing gain via the FFT length can go a long ways for this. Eric Jacobsen Anchor Hill Communications http://www.anchorhill.com
Reply by ●January 17, 20142014-01-17
On Friday, January 17, 2014 7:03:53 PM UTC-5, Eric Jacobsen wrote:> On Fri, 17 Jan 2014 12:59:15 -0800 (PST), julius <juliusk@gmail.com> > > wrote: > > > > >On Friday, January 17, 2014 2:22:37 PM UTC-5, John wrote: > > >> On Thursday, January 16, 2014 9:03:06 PM UTC-5, ywee...@gmail.com wrote: > > >> > > >> > Hi, > > >> > > >> > > > >> > > >> > I heard that there is a technique of detecting weak QPSK signal of very low SNR (e.g., -20dB) by multiply with 4 times the reference phase signals. > > >> > > >> > > > >> > > >> > May I know if any one knows the name of that technique? > > >> > > >> > > > >> > > >> > > > >> > > >> > > > >> > > >> > Thanks. > > >> > > >> > > > >> > > >> > Regards, > > >> > > >> > > >> > > >> Maybe you are thinking of raising the signal itself to the fourth power to collapse the modulation into a carrier stick. That works but not at -20 dB SNR. > > > > > >It's not clear to me whether the OP is considering detecting the presence of a QPSK signal at a known {fc, R} or if the OP is considering actually demodulating and/or detecting the bits. > > > > I think that's too low of an SNR to get any information, so I think > > just signal power detection is the only hope. Processing gain via > > the FFT length can go a long ways for this. > > > > > > > > > > Eric Jacobsen > > Anchor Hill Communications > > http://www.anchorhill.comYes, the tools of the trade for this are giant FFTs and frame-synchronous integrators, assuming there is structure there. Even with that I still think -20 dB SNR is difficult because the signal is unlikely to hold still long enough for the required integration. John
Reply by ●January 17, 20142014-01-17
On Friday, January 17, 2014 8:50:11 PM UTC-5, John wrote:> On Friday, January 17, 2014 7:03:53 PM UTC-5, Eric Jacobsen wrote: > > > On Fri, 17 Jan 2014 12:59:15 -0800 (PST), julius <juliusk@gmail.com> > > > > > > wrote: > > > > > > > > > > > > >On Friday, January 17, 2014 2:22:37 PM UTC-5, John wrote: > > > > > > >> On Thursday, January 16, 2014 9:03:06 PM UTC-5, ywee...@gmail.com wrote: > > > > > > >> > > > > > > >> > Hi, > > > > > > >> > > > > > > >> > > > > > > > >> > > > > > > >> > I heard that there is a technique of detecting weak QPSK signal of very low SNR (e.g., -20dB) by multiply with 4 times the reference phase signals. > > > > > > >> > > > > > > >> > > > > > > > >> > > > > > > >> > May I know if any one knows the name of that technique? > > > > > > >> > > > > > > >> > > > > > > > >> > > > > > > >> > > > > > > > >> > > > > > > >> > > > > > > > >> > > > > > > >> > Thanks. > > > > > > >> > > > > > > >> > > > > > > > >> > > > > > > >> > Regards, > > > > > > >> > > > > > > >> > > > > > > >> > > > > > > >> Maybe you are thinking of raising the signal itself to the fourth power to collapse the modulation into a carrier stick. That works but not at -20 dB SNR. > > > > > > > > > > > > > >It's not clear to me whether the OP is considering detecting the presence of a QPSK signal at a known {fc, R} or if the OP is considering actually demodulating and/or detecting the bits. > > > > > > > > > > > > I think that's too low of an SNR to get any information, so I think > > > > > > just signal power detection is the only hope. Processing gain via > > > > > > the FFT length can go a long ways for this. > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > Eric Jacobsen > > > > > > Anchor Hill Communications > > > > > > http://www.anchorhill.com > > > > Yes, the tools of the trade for this are giant FFTs and frame-synchronous integrators, assuming there is structure there. Even with that I still think -20 dB SNR is difficult because the signal is unlikely to hold still long enough for the required integration. > > > > JohnAt the same time, it depends on the definition of "SNR".
Reply by ●January 17, 20142014-01-17
Reply by ●January 18, 20142014-01-18
On Fri, 17 Jan 2014 18:46:43 -0800 (PST), julius <juliusk@gmail.com> wrote:>On Friday, January 17, 2014 8:50:11 PM UTC-5, John wrote: >> On Friday, January 17, 2014 7:03:53 PM UTC-5, Eric Jacobsen wrote: >>=20 >> > On Fri, 17 Jan 2014 12:59:15 -0800 (PST), julius <juliusk@gmail.com> >>=20 >> >=20 >>=20 >> > wrote: >>=20 >> >=20 >>=20 >> >=20 >>=20 >> >=20 >>=20 >> > >On Friday, January 17, 2014 2:22:37 PM UTC-5, John wrote: >>=20 >> >=20 >>=20 >> > >> On Thursday, January 16, 2014 9:03:06 PM UTC-5, ywee...@gmail.com wr= >ote: >>=20 >> >=20 >>=20 >> > >>=20 >>=20 >> >=20 >>=20 >> > >> > Hi, >>=20 >> >=20 >>=20 >> > >>=20 >>=20 >> >=20 >>=20 >> > >> >=20 >>=20 >> >=20 >>=20 >> > >>=20 >>=20 >> >=20 >>=20 >> > >> > I heard that there is a technique of detecting weak QPSK signal of= > very low SNR (e.g., -20dB) by multiply with 4 times the reference phase si= >gnals. >>=20 >> >=20 >>=20 >> > >>=20 >>=20 >> >=20 >>=20 >> > >> >=20 >>=20 >> >=20 >>=20 >> > >>=20 >>=20 >> >=20 >>=20 >> > >> > May I know if any one knows the name of that technique? >>=20 >> >=20 >>=20 >> > >>=20 >>=20 >> >=20 >>=20 >> > >> >=20 >>=20 >> >=20 >>=20 >> > >>=20 >>=20 >> >=20 >>=20 >> > >> >=20 >>=20 >> >=20 >>=20 >> > >>=20 >>=20 >> >=20 >>=20 >> > >> >=20 >>=20 >> >=20 >>=20 >> > >>=20 >>=20 >> >=20 >>=20 >> > >> > Thanks. >>=20 >> >=20 >>=20 >> > >>=20 >>=20 >> >=20 >>=20 >> > >> >=20 >>=20 >> >=20 >>=20 >> > >>=20 >>=20 >> >=20 >>=20 >> > >> > Regards, >>=20 >> >=20 >>=20 >> > >>=20 >>=20 >> >=20 >>=20 >> > >>=20 >>=20 >> >=20 >>=20 >> > >>=20 >>=20 >> >=20 >>=20 >> > >> Maybe you are thinking of raising the signal itself to the fourth po= >wer to collapse the modulation into a carrier stick. That works but not at = >-20 dB SNR. >>=20 >> >=20 >>=20 >> > > >>=20 >> >=20 >>=20 >> > >It's not clear to me whether the OP is considering detecting the prese= >nce of a QPSK signal at a known {fc, R} or if the OP is considering actuall= >y demodulating and/or detecting the bits.=20 >>=20 >> >=20 >>=20 >> >=20 >>=20 >> >=20 >>=20 >> > I think that's too low of an SNR to get any information, so I think >>=20 >> >=20 >>=20 >> > just signal power detection is the only hope. Processing gain via >>=20 >> >=20 >>=20 >> > the FFT length can go a long ways for this. >>=20 >> >=20 >>=20 >> >=20 >>=20 >> >=20 >>=20 >> >=20 >>=20 >> >=20 >>=20 >> >=20 >>=20 >> >=20 >>=20 >> >=20 >>=20 >> >=20 >>=20 >> > Eric Jacobsen >>=20 >> >=20 >>=20 >> > Anchor Hill Communications >>=20 >> >=20 >>=20 >> > http://www.anchorhill.com >>=20 >>=20 >>=20 >> Yes, the tools of the trade for this are giant FFTs and frame-synchronous= > integrators, assuming there is structure there. Even with that I still thi= >nk -20 dB SNR is difficult because the signal is unlikely to hold still lon= >g enough for the required integration. >>=20 >>=20 >>=20 >> John > >At the same time, it depends on the definition of "SNR".As always. ;) Eric Jacobsen Anchor Hill Communications http://www.anchorhill.com
Reply by ●January 21, 20142014-01-21
Hi all, Sorry for the late reply as I went overseas for a couple of days, and didn't check the forum during this period. May I know if any one know any good papers on this technique, and can share with me its title, thanks! To John, Yes. The purpose is to detect the QPSK signal (either before demodulation or after demodulation; both way are allowed). Yes, that guy told me that there is this approach by raising the signal itself to the fourth power and this collapse the modulation into a carrier stick, and it will work for -20 dB SNR. To Mark: Yes, I mean -20dB, and it is in-band SNR meaning that the SNR is -20dB in the bassband of the QPSK signal. To julius: I am considering detecting the weak QPSK signal with a band of frequency from 500MHz to 700MHz, and I do not know exactly what frequency it is using. I am consider detecting the presence of a QPSK signal at a known frequency band.
