I have two complex signals (Input and output) of a channel I need to equalize. I can have 2 linear equalizers one for the real part and one for the imaginary and train them independently or I can use one complex equalizer and train it using the complex signal. My questions are which one is better? Is there any advantage of one on the other or they are equivalent ? Regards Tom

# Equalizer

Started by ●June 11, 2007

Reply by ●June 11, 20072007-06-11

Tom wrote:> I have two complex signals (Input and output) of a channel I need to > equalize. I can have 2 linear equalizers one for the real part and one for > the imaginary and train them independently^^^^^^^^^^^^^^^^^^^^^^ This is completely wrong.> or I can use one complex > equalizer and train it using the complex signal. My questions are which one > is better? Is there any advantage of one on the other or they are equivalentIf you are working with the real signal, you should use the real equalizer. If you are working with the complex signal, you use the complex equalizer. Which way is preferred depends on the application. Vladimir Vassilevsky DSP and Mixed Signal Design Consultant http://www.abvolt.com

Reply by ●June 11, 20072007-06-11

Why the first option can not work ? "Vladimir Vassilevsky" <antispam_bogus@hotmail.com> wrote in message news:8Aebi.25140$YL5.22280@newssvr29.news.prodigy.net...> > > Tom wrote: > >> I have two complex signals (Input and output) of a channel I need to >> equalize. I can have 2 linear equalizers one for the real part and one >> for the imaginary and train them independently > > ^^^^^^^^^^^^^^^^^^^^^^ > > This is completely wrong. > > >> or I can use one complex equalizer and train it using the complex signal. >> My questions are which one >> is better? Is there any advantage of one on the other or they are >> equivalent > > If you are working with the real signal, you should use the real > equalizer. If you are working with the complex signal, you use the complex > equalizer. Which way is preferred depends on the application. > > > Vladimir Vassilevsky > > DSP and Mixed Signal Design Consultant > > http://www.abvolt.com

Reply by ●June 11, 20072007-06-11

Becase the phase shift is different at the different frequencies. VLV Tom wrote:> Why the first option can not work ? > > "Vladimir Vassilevsky" <antispam_bogus@hotmail.com> wrote in message > news:8Aebi.25140$YL5.22280@newssvr29.news.prodigy.net... > >> >>Tom wrote: >> >> >>>I have two complex signals (Input and output) of a channel I need to >>>equalize. I can have 2 linear equalizers one for the real part and one >>>for the imaginary and train them independently >> >>^^^^^^^^^^^^^^^^^^^^^^ >> >>This is completely wrong. >> >> >> >>>or I can use one complex equalizer and train it using the complex signal. >>>My questions are which one >>>is better? Is there any advantage of one on the other or they are >>>equivalent >> >>If you are working with the real signal, you should use the real >>equalizer. If you are working with the complex signal, you use the complex >>equalizer. Which way is preferred depends on the application. >> >> >>Vladimir Vassilevsky >> >>DSP and Mixed Signal Design Consultant >> >>http://www.abvolt.com > > >

Reply by ●June 11, 20072007-06-11

What if I transform the real and imaginary to Amplitude and phase signals and use them to train 2 equalizers separately and then transform back the output of the equalizers to real and Imaginary signals. Will this work in theory ? regards Tom "Vladimir Vassilevsky" <antispam_bogus@hotmail.com> wrote in message news:mggbi.13524$2v1.1260@newssvr14.news.prodigy.net...> Becase the phase shift is different at the different frequencies. > > VLV > > > Tom wrote: >> Why the first option can not work ? >> >> "Vladimir Vassilevsky" <antispam_bogus@hotmail.com> wrote in message >> news:8Aebi.25140$YL5.22280@newssvr29.news.prodigy.net... >> >>> >>>Tom wrote: >>> >>> >>>>I have two complex signals (Input and output) of a channel I need to >>>>equalize. I can have 2 linear equalizers one for the real part and one >>>>for the imaginary and train them independently >>> >>>^^^^^^^^^^^^^^^^^^^^^^ >>> >>>This is completely wrong. >>> >>> >>> >>>>or I can use one complex equalizer and train it using the complex >>>>signal. My questions are which one >>>>is better? Is there any advantage of one on the other or they are >>>>equivalent >>> >>>If you are working with the real signal, you should use the real >>>equalizer. If you are working with the complex signal, you use the >>>complex equalizer. Which way is preferred depends on the application. >>> >>> >>>Vladimir Vassilevsky >>> >>>DSP and Mixed Signal Design Consultant >>> >>>http://www.abvolt.com >> >>

Reply by ●June 11, 20072007-06-11

"Tom" <tomdarel@yahoo.com> wrote in message news:466d725c$0$12085$c3e8da3@news.astraweb.com...> I have two complex signals (Input and output) of a channel I need to > equalize. I can have 2 linear equalizers one for the real part and one for > the imaginary and train them independently or I can use one complex > equalizer and train it using the complex signal. My questions are whichone> is better? Is there any advantage of one on the other or they areequivalent> ? > > Regards > > Tom > >Unless you have absolutlely zero carrier offset (which is impossible if either receiver or transmitter is moving) you can not adapt real and imaginary independently. I think you have to use a complexe equalizer. That said, there are ways to implement the complex multiply with only three real multiplies, but I don't think that is where you were heading. -Clark

Reply by ●June 11, 20072007-06-11

Once you convert to magnitude and phase the operations are no longer linear, right? The phase at least is modulo 2 pi. The equalizer is just a filter. The filter can be applied in time or frequency domain. In the frequency domain an FFT would need to convert the time waveform to frequency domain, then multiply by the FFT of the equalizer filter, and do an inverse FFT to get back to time. But I don't see any way to convolve the data and the filter in magnitude/phase terms? -Clark "Tom" <tomdarel@yahoo.com> wrote in message news:466db4d4$0$10511$c3e8da3@news.astraweb.com...> What if I transform the real and imaginary to Amplitude and phase signals > and use them to train 2 equalizers separately and then transform back the > output of the equalizers to real and Imaginary signals. Will this work in > theory ? > > regards > > Tom > "Vladimir Vassilevsky" <antispam_bogus@hotmail.com> wrote in message > news:mggbi.13524$2v1.1260@newssvr14.news.prodigy.net... > > Becase the phase shift is different at the different frequencies. > > > > VLV > > > > > > Tom wrote: > >> Why the first option can not work ? > >> > >> "Vladimir Vassilevsky" <antispam_bogus@hotmail.com> wrote in message > >> news:8Aebi.25140$YL5.22280@newssvr29.news.prodigy.net... > >> > >>> > >>>Tom wrote: > >>> > >>> > >>>>I have two complex signals (Input and output) of a channel I need to > >>>>equalize. I can have 2 linear equalizers one for the real part and one > >>>>for the imaginary and train them independently > >>> > >>>^^^^^^^^^^^^^^^^^^^^^^ > >>> > >>>This is completely wrong. > >>> > >>> > >>> > >>>>or I can use one complex equalizer and train it using the complex > >>>>signal. My questions are which one > >>>>is better? Is there any advantage of one on the other or they are > >>>>equivalent > >>> > >>>If you are working with the real signal, you should use the real > >>>equalizer. If you are working with the complex signal, you use the > >>>complex equalizer. Which way is preferred depends on the application. > >>> > >>> > >>>Vladimir Vassilevsky > >>> > >>>DSP and Mixed Signal Design Consultant > >>> > >>>http://www.abvolt.com > >> > >> >

Reply by ●June 11, 20072007-06-11

My signal does not have a carrier, it is a baseband. do I still have to use a complex equalizer ? "cpope" <cepope@nc.rr.com> wrote in message news:466dcb50$0$17118$4c368faf@roadrunner.com...> > "Tom" <tomdarel@yahoo.com> wrote in message > news:466d725c$0$12085$c3e8da3@news.astraweb.com... >> I have two complex signals (Input and output) of a channel I need to >> equalize. I can have 2 linear equalizers one for the real part and one >> for >> the imaginary and train them independently or I can use one complex >> equalizer and train it using the complex signal. My questions are which > one >> is better? Is there any advantage of one on the other or they are > equivalent >> ? >> >> Regards >> >> Tom >> >> > > Unless you have absolutlely zero carrier offset (which is impossible if > either receiver or transmitter is moving) you can not adapt real and > imaginary independently. I think you have to use a complexe equalizer. > That > said, there are ways to implement the complex multiply with only three > real > multiplies, but I don't think that is where you were heading. > > -Clark > >

Reply by ●June 11, 20072007-06-11

On Jun 11, 6:58 pm, "John" <j...@excite.com> wrote:> My signal does not have a carrier, it is a baseband. do I still have to use > a complex equalizer ?"cpope" <cep...@nc.rr.com> wrote in message >Even though it's at baseband, in any practical system, your signal is probably going to be transmitted on a carrier at some point. Your receiver's LO is going to have some frequency error with respect to your transmitter's oscillator, which will cause a low-frequency complex sinusoidal modulation on your received symbols. Your equalizer can correct this if the error is small enough, but it needs both the real and imaginary components to do so (since the modulation caused by the frequency error is complex). Why are you so averse to implementing a complex equalizer anyway? The underlying structure is the same; you just need to allow all quantities to be complex and remember to put in complex conjugates at the right places, depending on the equalizer's type. Jason

Reply by ●June 12, 20072007-06-12

cincydsp@gmail.com wrote:> On Jun 11, 6:58 pm, "John" <j...@excite.com> wrote: >> My signal does not have a carrier, it is a baseband. do I still have to use >> a complex equalizer ?"cpope" <cep...@nc.rr.com> wrote in message >> > > Even though it's at baseband, in any practical system, your signal is > probably going to be transmitted on a carrier at some point. Your > receiver's LO is going to have some frequency error with respect to > your transmitter's oscillator, which will cause a low-frequency > complex sinusoidal modulation on your received symbols. Your equalizer > can correct this if the error is small enough, but it needs both the > real and imaginary components to do so (since the modulation caused by > the frequency error is complex). > > Why are you so averse to implementing a complex equalizer anyway? The > underlying structure is the same; you just need to allow all > quantities to be complex and remember to put in complex conjugates at > the right places, depending on the equalizer's type.I think he wants to know the difference between a complex filter (that obviously has real and imaginary parts) and two filters, one for the real part of the signal and another for the imaginary part. Do do I. Jerry -- Engineering is the art of making what you want from things you can get. ¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯