Hello People I have been scratching my head on this doppler problem: Because of the doppler effect, the received signal will either be expanded or compressed on time axis. Now, the expansion or compression is sampling rate conversion. So, I tried to use 'resample' function of matlab. The actual length of the signal is 30720 and sampling freq is 48000Hz. Now, when I use y=resample(x,10010,10000) i can find the peak i.e. start of my data by correlating the signal with training sequence. But when I use y=resample(x,10007,10000) i can't find the peak. So is there any better way to 1. model this exapnsion or compression or 2. to find peak when the received is corrupted by severe doppler. Help in this regard will be highly appreciated. Chintan
signal detection in doppler
Started by ●May 19, 2008
Reply by ●May 20, 20082008-05-20
On May 19, 8:28�am, "cpshah99" <cpsha...@rediffmail.com> wrote:> Hello People > > I have been scratching my head on this doppler problem: > > Because of the doppler effect, the received signal will either be expanded > or compressed on time axis. > > Now, the expansion or compression is sampling rate conversion. So, I tried > to use 'resample' function of matlab. The actual length of the signal is > 30720 and sampling freq is 48000Hz. > > Now, when I use y=resample(x,10010,10000) i can find the peak i.e. start > of my data by correlating the signal with training sequence. > > But when I use y=resample(x,10007,10000) i can't find the peak. > > So is there any better way to > 1. model this exapnsion or compression > or 2. to find peak when the received is corrupted by severe doppler. > > Help in this regard will be highly appreciated. > > ChintanAnswer to (1) is to write a Farrow interpolator, that way you can get almost arbitrary doppler rate.
Reply by ●May 21, 20082008-05-21
>On May 19, 8:28=A0am, "cpshah99" <cpsha...@rediffmail.com> wrote: >> Hello People >> >> I have been scratching my head on this doppler problem: >> >> Because of the doppler effect, the received signal will either beexpanded=> >> or compressed on time axis. >> >> Now, the expansion or compression is sampling rate conversion. So, Itried=> >> to use 'resample' function of matlab. The actual length of the signalis>> 30720 and sampling freq is 48000Hz. >> >> Now, when I use y=3Dresample(x,10010,10000) i can find the peak i.e.start=> >> of my data by correlating the signal with training sequence. >> >> But when I use y=3Dresample(x,10007,10000) i can't find the peak. >> >> So is there any better way to >> 1. model this exapnsion or compression >> or 2. to find peak when the received is corrupted by severe doppler. >> >> Help in this regard will be highly appreciated. >> >> Chintan > >Answer to (1) is to write a Farrow interpolator, that way you can get >almost arbitrary doppler rate. >%%%%%%% Hi Julius Thank you very much. I will write the function as u have said. Thanks again. Chintan
Reply by ●May 21, 20082008-05-21
On May 21, 3:04 am, "cpshah99" <cpsha...@rediffmail.com> wrote:> >On May 19, 8:28=A0am, "cpshah99" <cpsha...@rediffmail.com> wrote: > >> Hello People > > >> I have been scratching my head on this doppler problem: > > >> Because of the doppler effect, the received signal will either be > expanded= > > >> or compressed on time axis. > > >> Now, the expansion or compression is sampling rate conversion. So, I > tried= > > >> to use 'resample' function of matlab. The actual length of the signal > is > >> 30720 and sampling freq is 48000Hz. > > >> Now, when I use y=3Dresample(x,10010,10000) i can find the peak i.e. > start= > > >> of my data by correlating the signal with training sequence. > > >> But when I use y=3Dresample(x,10007,10000) i can't find the peak. > > >> So is there any better way to > >> 1. model this exapnsion or compression > >> or 2. to find peak when the received is corrupted by severe doppler. > > >> Help in this regard will be highly appreciated. > > >> Chintan > > >Answer to (1) is to write a Farrow interpolator, that way you can get > >almost arbitrary doppler rate. > > %%%%%%% > > Hi Julius > > Thank you very much. I will write the function as u have said. > > Thanks again. > > ChintanAnother solution is to use resample in stages to get the target ratio, e.g. P/Q = (P1/Q1)*(P2/Q2) where P1,Q1,P2,Q2 are legal. John
Reply by ●May 22, 20082008-05-22
On May 19, 9:28 am, "cpshah99" <cpsha...@rediffmail.com> wrote:> Hello People > > I have been scratching my head on this doppler problem: > > Because of the doppler effect, the received signal will either be expanded > or compressed on time axis. > > Now, the expansion or compression is sampling rate conversion. So, I tried > to use 'resample' function of matlab. The actual length of the signal is > 30720 and sampling freq is 48000Hz. > > Now, when I use y=resample(x,10010,10000) i can find the peak i.e. start > of my data by correlating the signal with training sequence. > > But when I use y=resample(x,10007,10000) i can't find the peak. > > So is there any better way to > 1. model this exapnsion or compression > or 2. to find peak when the received is corrupted by severe doppler. > > Help in this regard will be highly appreciated. > > ChintanJust clarify - a doppler shift isn't modeled by a frequency shift. It is really a time dilation. For pure sinusoids it then appears as a frequency shift. If you signal doesn't have a lot of bandwidth wrt the center frequency then you can approximate the doppler shift by a frequency shift. Cheers, David
Reply by ●May 23, 20082008-05-23
>On May 19, 9:28 am, "cpshah99" <cpsha...@rediffmail.com> wrote: >> Hello People >> >> I have been scratching my head on this doppler problem: >> >> Because of the doppler effect, the received signal will either beexpanded>> or compressed on time axis. >> >> Now, the expansion or compression is sampling rate conversion. So, Itried>> to use 'resample' function of matlab. The actual length of the signalis>> 30720 and sampling freq is 48000Hz. >> >> Now, when I use y=resample(x,10010,10000) i can find the peak i.e.start>> of my data by correlating the signal with training sequence. >> >> But when I use y=resample(x,10007,10000) i can't find the peak. >> >> So is there any better way to >> 1. model this exapnsion or compression >> or 2. to find peak when the received is corrupted by severe doppler. >> >> Help in this regard will be highly appreciated. >> >> Chintan > >Just clarify - a doppler shift isn't modeled by a frequency shift. It >is really a time dilation. For pure sinusoids it then appears as a >frequency shift. If you signal doesn't have a lot of bandwidth wrt the >center frequency then you can approximate the doppler shift by a >frequency shift. > >Cheers, >David >%%%%% Hi David My center freq is 12KHz and BW is 4 KHz. I understand as u said, the doppler effect is time dilation, but should I just shift the center freq or sampling freq to approximate the doppler shift because if I shift carrier freq then it will just add phase shift but it will not expand or compress the signal. Also I am reading Multirate Digital Signal Processing by Crochiere and Rabiner to implement Farrow Interpolator, suggested by Julius. Thanks you again. Chintan.
Reply by ●May 23, 20082008-05-23
On May 23, 3:54 pm, "cpshah99" <cpsha...@rediffmail.com> wrote:> Also I am reading Multirate Digital Signal Processing by Crochiere and > Rabiner to implement Farrow Interpolator, suggested by Julius.:For an alternative perspective, see also F.J. Harris's article: http://www.signumconcepts.com/download/paper018.pdf -- Oli
Reply by ●May 24, 20082008-05-24
On May 23, 10:54 am, "cpshah99" <cpsha...@rediffmail.com> wrote:> >On May 19, 9:28 am, "cpshah99" <cpsha...@rediffmail.com> wrote: > >> Hello People > > >> I have been scratching my head on this doppler problem: > > >> Because of the doppler effect, the received signal will either be > expanded > >> or compressed on time axis. > > >> Now, the expansion or compression is sampling rate conversion. So, I > tried > >> to use 'resample' function of matlab. The actual length of the signal > is > >> 30720 and sampling freq is 48000Hz. > > >> Now, when I use y=resample(x,10010,10000) i can find the peak i.e. > start > >> of my data by correlating the signal with training sequence. > > >> But when I use y=resample(x,10007,10000) i can't find the peak. > > >> So is there any better way to > >> 1. model this exapnsion or compression > >> or 2. to find peak when the received is corrupted by severe doppler. > > >> Help in this regard will be highly appreciated. > > >> Chintan > > >Just clarify - a doppler shift isn't modeled by a frequency shift. It > >is really a time dilation. For pure sinusoids it then appears as a > >frequency shift. If you signal doesn't have a lot of bandwidth wrt the > >center frequency then you can approximate the doppler shift by a > >frequency shift. > > >Cheers, > >David > > %%%%% > > Hi David > > My center freq is 12KHz and BW is 4 KHz. > > I understand as u said, the doppler effect is time dilation, but should I > just shift the center freq or sampling freq to approximate the doppler > shift because if I shift carrier freq then it will just add phase shift but > it will not expand or compress the signal. > > Also I am reading Multirate Digital Signal Processing by Crochiere and > Rabiner to implement Farrow Interpolator, suggested by Julius. > > Thanks you again. > > Chintan.What type of system is this? Sonar? What is the speed of propagation in your medium? What is the format of your signal? Is it a LFM or HFM pulse? For these types of signals in sonar they use banks of matched filters, which are constructed by time dilating the analytic formula for the pulse. For more detail you can see Neilson's "Sonar Signal Processing". For Farrow information I found Harris's book quite good. I also posted some matlab code on this group to do derive the Farrow spline coefficients - it doesn't do the online resampling. Cheers, David
Reply by ●May 25, 20082008-05-25
>On May 23, 10:54 am, "cpshah99" <cpsha...@rediffmail.com> wrote: >> >On May 19, 9:28 am, "cpshah99" <cpsha...@rediffmail.com> wrote: >> >> Hello People >> >> >> I have been scratching my head on this doppler problem: >> >> >> Because of the doppler effect, the received signal will either be >> expanded >> >> or compressed on time axis. >> >> >> Now, the expansion or compression is sampling rate conversion. So,I>> tried >> >> to use 'resample' function of matlab. The actual length of thesignal>> is >> >> 30720 and sampling freq is 48000Hz. >> >> >> Now, when I use y=resample(x,10010,10000) i can find the peak i.e. >> start >> >> of my data by correlating the signal with training sequence. >> >> >> But when I use y=resample(x,10007,10000) i can't find the peak. >> >> >> So is there any better way to >> >> 1. model this exapnsion or compression >> >> or 2. to find peak when the received is corrupted by severedoppler.>> >> >> Help in this regard will be highly appreciated. >> >> >> Chintan >> >> >Just clarify - a doppler shift isn't modeled by a frequency shift. It >> >is really a time dilation. For pure sinusoids it then appears as a >> >frequency shift. If you signal doesn't have a lot of bandwidth wrtthe>> >center frequency then you can approximate the doppler shift by a >> >frequency shift. >> >> >Cheers, >> >David >> >> %%%%% >> >> Hi David >> >> My center freq is 12KHz and BW is 4 KHz. >> >> I understand as u said, the doppler effect is time dilation, but shouldI>> just shift the center freq or sampling freq to approximate the doppler >> shift because if I shift carrier freq then it will just add phase shiftbut>> it will not expand or compress the signal. >> >> Also I am reading Multirate Digital Signal Processing by Crochiere and >> Rabiner to implement Farrow Interpolator, suggested by Julius. >> >> Thanks you again. >> >> Chintan. > >What type of system is this? Sonar? What is the speed of propagation >in your medium? What is the format of your signal? Is it a LFM or HFM >pulse? > >For these types of signals in sonar they use banks of matched filters, >which are constructed by time dilating the analytic formula for the >pulse. For more detail you can see Neilson's "Sonar Signal >Processing". > >For Farrow information I found Harris's book quite good. I also posted >some matlab code on this group to do derive the Farrow spline >coefficients - it doesn't do the online resampling. > >Cheers, >David >%%%%% Hi David This system is for underwater communications, where speed of acousticwave is 1500 m/s. And also I am not using LFM or HFM. My signal format is 500 symbols long PN sequence to find the start of that (not to do anything with DSSS) and after this PN 2000 data symbols. Can u please post that code here again, if you don't mind. Thanks, Chintan
Reply by ●May 25, 20082008-05-25
On May 25, 4:32 am, "cpshah99" <cpsha...@rediffmail.com> wrote:> >On May 23, 10:54 am, "cpshah99" <cpsha...@rediffmail.com> wrote: > >> >On May 19, 9:28 am, "cpshah99" <cpsha...@rediffmail.com> wrote: > >> >> Hello People > > >> >> I have been scratching my head on this doppler problem: > > >> >> Because of the doppler effect, the received signal will either be > >> expanded > >> >> or compressed on time axis. > > >> >> Now, the expansion or compression is sampling rate conversion. So, > I > >> tried > >> >> to use 'resample' function of matlab. The actual length of the > signal > >> is > >> >> 30720 and sampling freq is 48000Hz. > > >> >> Now, when I use y=resample(x,10010,10000) i can find the peak i.e. > >> start > >> >> of my data by correlating the signal with training sequence. > > >> >> But when I use y=resample(x,10007,10000) i can't find the peak. > > >> >> So is there any better way to > >> >> 1. model this exapnsion or compression > >> >> or 2. to find peak when the received is corrupted by severe > doppler. > > >> >> Help in this regard will be highly appreciated. > > >> >> Chintan > > >> >Just clarify - a doppler shift isn't modeled by a frequency shift. It > >> >is really a time dilation. For pure sinusoids it then appears as a > >> >frequency shift. If you signal doesn't have a lot of bandwidth wrt > the > >> >center frequency then you can approximate the doppler shift by a > >> >frequency shift. > > >> >Cheers, > >> >David > > >> %%%%% > > >> Hi David > > >> My center freq is 12KHz and BW is 4 KHz. > > >> I understand as u said, the doppler effect is time dilation, but should > I > >> just shift the center freq or sampling freq to approximate the doppler > >> shift because if I shift carrier freq then it will just add phase shift > but > >> it will not expand or compress the signal. > > >> Also I am reading Multirate Digital Signal Processing by Crochiere and > >> Rabiner to implement Farrow Interpolator, suggested by Julius. > > >> Thanks you again. > > >> Chintan. > > >What type of system is this? Sonar? What is the speed of propagation > >in your medium? What is the format of your signal? Is it a LFM or HFM > >pulse? > > >For these types of signals in sonar they use banks of matched filters, > >which are constructed by time dilating the analytic formula for the > >pulse. For more detail you can see Neilson's "Sonar Signal > >Processing". > > >For Farrow information I found Harris's book quite good. I also posted > >some matlab code on this group to do derive the Farrow spline > >coefficients - it doesn't do the online resampling. > > >Cheers, > >David > > %%%%% > > Hi David > > This system is for underwater communications, where speed of acousticwave > is 1500 m/s. And also I am not using LFM or HFM. My signal format is 500 > symbols long PN sequence to find the start of that (not to do anything with > DSSS) and after this PN 2000 data symbols. > > Can u please post that code here again, if you don't mind. > > Thanks, > > ChintanIt's on my other computer. I'll try to post it on Monday. Given you're dealing with probably +- 30 knots doppler (or more) and the band & bandwidth you should take into account the dilation, but normally the PN , LFM , HFM signals have fairly broad ambiguity functions so they still correlate over broad dopplers - you shouldn't need that many doppler replicas to find a peak. Normally the replicas are set at the -3dB points in the ambiguity function. Cheers, David