Hi, As we know, any non-linearity on matched filter output contians two spectral lines at +/- symbol rate. I am a little confused about how to use that for timing compensation. If it is used as a TED for a PLL, will not the loop filter reject this line? Secondly, coming to the time domain, is the top of this sinusoid refers to the ideal timing phase? Thanks.
Spectral line for timing recovery
Started by ●October 15, 2012
Reply by ●October 15, 20122012-10-15
>Hi, > As we know, any non-linearity on matched filter output contians two >spectral lines at +/- symbol rate. I am a little confused about how touse>that for timing compensation. If it is used as a TED for a PLL, will not >the loop filter reject this line? Secondly, coming to the time domain, is >the top of this sinusoid refers to the ideal timing phase? >Thanks.A classic way to use the band edge effect for symbol timing recovery may be found in: Dominique N. Godard, “Passband Timing Recovery in an All-Digital Modem Receiver,” IEEE Transactions on Communications, Vol. COM-26, No. 5, May 1978 Regards, Steve
Reply by ●October 15, 20122012-10-15
>>Hi, >> As we know, any non-linearity on matched filter output contians two >>spectral lines at +/- symbol rate. I am a little confused about how to >use >>that for timing compensation. If it is used as a TED for a PLL, will not >>the loop filter reject this line? Secondly, coming to the time domain,is>>the top of this sinusoid refers to the ideal timing phase? >>Thanks. > >A classic way to use the band edge effect for symbol timing recovery maybe>found in: > >Dominique N. Godard, “Passband Timing Recovery in an All-Digital Modem >Receiver,” IEEE Transactions on Communications, Vol. COM-26, No. 5, May >1978 > >Regards, >Steve >I remember Goddard takes the imaginary part of the conjugate product of the two bandpass filter outputs and uses that as an error signal for input to the loop filter. Can there be any feedforward implementation too?
Reply by ●October 15, 20122012-10-15
"commsignal" <58672@dsprelated> wrote in message news:OeOdnQre064gPOHNnZ2dnUVZ_smdnZ2d@giganews.com...> Hi, > As we know, any non-linearity on matched filter output contians two > spectral lines at +/- symbol rate."We" know?> I am a little confused about how to use that for timing compensationThe underlying concept is very simple: at the output of matched filter, energy is pulsating with the baud rate.> If it is used as a TED for a PLL, will not the loop filter reject this > line?No slightest clue, huh ?> Secondly, coming to the time domain, is > the top of this sinusoid refers to the ideal timing phase?Yes. Maximum of energy corresponds to symbol sampling instant. VLV
Reply by ●October 15, 20122012-10-15
"commsignal" <58672@dsprelated> wrote: in message news:8dedna_L_f1mMuHNnZ2dnUVZ_rqdnZ2d@giganews.com...> I remember Goddard takes the imaginary part of the conjugate product of > the > two bandpass filter outputs and uses that as an error signal for input to > the loop filter.That's minor technical details of implementation.> Can there be any feedforward implementation too?
Reply by ●October 15, 20122012-10-15
"steveu" <31473@dsprelated> wrote in message news:_fCdnYuccrR9NuHNnZ2dnUVZ_rOdnZ2d@giganews.com...> >Hi, >> As we know, any non-linearity on matched filter output contians two >>spectral lines at +/- symbol rate. I am a little confused about how to > use >>that for timing compensation. If it is used as a TED for a PLL, will not >>the loop filter reject this line? Secondly, coming to the time domain, is >>the top of this sinusoid refers to the ideal timing phase?> > A classic way to use the band edge effect for symbol timing recovery may > be > found in: > > Dominique N. Godard, “Passband Timing Recovery in an All-Digital Modem > Receiver,” IEEE Transactions on Communications, Vol. COM-26, No. 5, May > 1978There is a lot of smoke and mirrors although underlying concepts are very simple: taking the derivative of signal energy either in time or in frequency domain. I think OP was inquiring about time domain method. VLV
Reply by ●October 16, 20122012-10-16
>>>Hi, >>> As we know, any non-linearity on matched filter output contians two >>>spectral lines at +/- symbol rate. I am a little confused about how to >>use >>>that for timing compensation. If it is used as a TED for a PLL, willnot>>>the loop filter reject this line? Secondly, coming to the time domain, >is >>>the top of this sinusoid refers to the ideal timing phase? >>>Thanks. >> >>A classic way to use the band edge effect for symbol timing recovery may >be >>found in: >> >>Dominique N. Godard, “Passband Timing Recovery in an All-Digital Modem >>Receiver,” IEEE Transactions on Communications, Vol. COM-26, No. 5,May>>1978 >> >>Regards, >>Steve >> > > >I remember Goddard takes the imaginary part of the conjugate product ofthe>two bandpass filter outputs and uses that as an error signal for input to >the loop filter. Can there be any feedforward implementation too?What exactly do you mean by feedforward in this context? Are you looking for a technique which directly estimates the sampling phase error and just feeds that to a Farrow filter to retime the signal? Would that have any advantage over the loop approach? You'd need to heavily damp the timing error estimate to get good results in poor SNR conditions, so you might as well let a loop provide your damping. Regards, Steve
Reply by ●October 16, 20122012-10-16
> >"steveu" <31473@dsprelated> wrote in message >news:_fCdnYuccrR9NuHNnZ2dnUVZ_rOdnZ2d@giganews.com... >> >Hi, >>> As we know, any non-linearity on matched filter output contians two >>>spectral lines at +/- symbol rate. I am a little confused about how to >> use >>>that for timing compensation. If it is used as a TED for a PLL, willnot>>>the loop filter reject this line? Secondly, coming to the time domain,is>>>the top of this sinusoid refers to the ideal timing phase? > >> >> A classic way to use the band edge effect for symbol timing recovery may>> be >> found in: >> >> Dominique N. Godard, “Passband Timing Recovery in an All-DigitalModem>> Receiver,” IEEE Transactions on Communications, Vol. COM-26, No. 5,May>> 1978 > >There is a lot of smoke and mirrors although underlying concepts are very>simple: taking the derivative of signal energy either in time or in >frequency domain. I think OP was inquiring about time domain method. > >VLV > > > >I guess differentiating that in frequency domain leads to a frequency matched filter, and the power difference between the two bandedge filters can be used as a frequency error detector. However, I am still confused about that twice symbol rate spectral line. Essentially it's a sinusoid in noise. How can that be used as a timing error detector?
Reply by ●October 16, 20122012-10-16
>>>>Hi, >>>> As we know, any non-linearity on matched filter output contians two >>>>spectral lines at +/- symbol rate. I am a little confused about how to >>>use >>>>that for timing compensation. If it is used as a TED for a PLL, will >not >>>>the loop filter reject this line? Secondly, coming to the time domain, >>is >>>>the top of this sinusoid refers to the ideal timing phase? >>>>Thanks. >>> >>>A classic way to use the band edge effect for symbol timing recoverymay>>be >>>found in: >>> >>>Dominique N. Godard, “Passband Timing Recovery in an All-DigitalModem>>>Receiver,” IEEE Transactions on Communications, Vol. COM-26, No. 5, >May >>>1978 >>> >>>Regards, >>>Steve >>> >> >> >>I remember Goddard takes the imaginary part of the conjugate product of >the >>two bandpass filter outputs and uses that as an error signal for inputto>>the loop filter. Can there be any feedforward implementation too? > >What exactly do you mean by feedforward in this context? Are you looking >for a technique which directly estimates the sampling phase error andjust>feeds that to a Farrow filter to retime the signal? Would that have any >advantage over the loop approach? You'd need to heavily damp the timing >error estimate to get good results in poor SNR conditions, so you mightas>well let a loop provide your damping. > >Regards, >Steve > >You are right. But the confusion still remains. How can that spectral line be used in the timing error detector of the loop?
Reply by ●October 16, 20122012-10-16
On Tuesday, October 16, 2012 1:40:03 AM UTC-4, commsignal wrote:> > > > >"steveu" <31473@dsprelated> wrote in message > > >news:_fCdnYuccrR9NuHNnZ2dnUVZ_rOdnZ2d@giganews.com... > > >> >Hi, > > >>> As we know, any non-linearity on matched filter output contians two > > >>>spectral lines at +/- symbol rate. I am a little confused about how to > > >> use > > >>>that for timing compensation. If it is used as a TED for a PLL, will > > not > > >>>the loop filter reject this line? Secondly, coming to the time domain, > > is > > >>>the top of this sinusoid refers to the ideal timing phase? > > > > > >> > > >> A classic way to use the band edge effect for symbol timing recovery may > > > > >> be > > >> found in: > > >> > > >> Dominique N. Godard, �Passband Timing Recovery in an All-Digital > > Modem > > >> Receiver,� IEEE Transactions on Communications, Vol. COM-26, No. 5, > > May > > >> 1978 > > > > > >There is a lot of smoke and mirrors although underlying concepts are very > > > > >simple: taking the derivative of signal energy either in time or in > > >frequency domain. I think OP was inquiring about time domain method. > > > > > >VLV > > > > > > > > > > > > > > > > I guess differentiating that in frequency domain leads to a frequency > > matched filter, and the power difference between the two bandedge filters > > can be used as a frequency error detector. However, I am still confused > > about that twice symbol rate spectral line. Essentially it's a sinusoid in > > noise. How can that be used as a timing error detector?Feed the nonlinearity result through a narrow bandpass filter, then interpolate the matched filter outputs at alternate zero crossings of the BPF output using a cubic interpolator. John
