On May 13, 3:12 pm, Vladimir Vassilevsky <antispam_bo...@hotmail.com> wrote:> Not quite :-) Imagine an OFDM symbol as a member of the class of n-FSK > sequences designed for demodulation in the frequency domain... > > VLVFine, I suppose one can apply PPM-type coding, except that it's in the frequency domain :-). Julius
CE-OFDM
Started by ●May 12, 2007
Reply by ●May 13, 20072007-05-13
Reply by ●May 13, 20072007-05-13
julius wrote:>>Not quite :-) Imagine an OFDM symbol as a member of the class of n-FSK >>sequences designed for demodulation in the frequency domain... >> > Fine, I suppose one can apply PPM-type coding, except > that it's in the frequency domain :-).The engineer's approach will be take the standard OFDM and clip it so the envelope will have to be a constant :-) VLV
Reply by ●May 14, 20072007-05-14
On May 13, 10:12 pm, Vladimir Vassilevsky <antispam_bo...@hotmail.com> wrote:> julius wrote: > >>Not quite :-) Imagine an OFDM symbol as a member of the class of n-FSK > >>sequences designed for demodulation in the frequency domain... > > > Fine, I suppose one can apply PPM-type coding, except > > that it's in the frequency domain :-). > > The engineer's approach will be take the standard OFDM and clip it so > the envelope will have to be a constant :-) > > VLVCE-OFDM is OFDM with a Phase Modulator on the output. Google finds some references. John
Reply by ●May 14, 20072007-05-14
>On May 13, 10:12 pm, Vladimir Vassilevsky <antispam_bo...@hotmail.com> >wrote: >> julius wrote: >> >>Not quite :-) Imagine an OFDM symbol as a member of the class ofn-FSK>> >>sequences designed for demodulation in the frequency domain... >> >> > Fine, I suppose one can apply PPM-type coding, except >> > that it's in the frequency domain :-). >> >> The engineer's approach will be take the standard OFDM and clip it so >> the envelope will have to be a constant :-) >> >> VLV > >CE-OFDM is OFDM with a Phase Modulator on the output. Google finds >some references. > >John > >here is a link http://zeidler.ucsd.edu/pubs/ http://zeidler.ucsd.edu/pubs/C126.pdf http://zeidler.ucsd.edu/pubs/C114.pdf Best regards, -dvo _____________________________________ Do you know a company who employs DSP engineers? Is it already listed at http://dsprelated.com/employers.php ?
Reply by ●May 14, 20072007-05-14
sampson164@gmail.com wrote:> > CE-OFDM is OFDM with a Phase Modulator on the output. Google finds > some references.OFDM riding on FM is ridiculous; it is a way to combine the disadvantages of both modulations. This is the low energy and spectral efficiency, nonlinear effects, a complex equalization in the time domain and a sensitivity to selective fading. Why anybody needs this? Vladimir Vassilevsky DSP and Mixed Signal Design Consultant http://www.abvolt.com
Reply by ●May 14, 20072007-05-14
On May 14, 8:53 am, Vladimir Vassilevsky <antispam_bo...@hotmail.com> wrote:> OFDM riding on FM is ridiculous; it is a way to combine the > disadvantages of both modulations. This is the low energy and spectral > efficiency, nonlinear effects, a complex equalization in the time domain > and a sensitivity to selective fading. Why anybody needs this? > > Vladimir Vassilevsky > > DSP and Mixed Signal Design Consultant > > http://www.abvolt.comThe thought of coming up with a synchronizer for this gives me shivers, and it's only Monday morning. To be fair, John Proakis knows heck of a lot about synchronization and he builds impressive systems for all sorts of challenging environments, so I am going to wait until he builds a receiver system for this. Julius
Reply by ●May 14, 20072007-05-14
julius wrote:> >>OFDM riding on FM is ridiculous; it is a way to combine the >>disadvantages of both modulations. This is the low energy and spectral >>efficiency, nonlinear effects, a complex equalization in the time domain >>and a sensitivity to selective fading. Why anybody needs this? >> > > The thought of coming up with a synchronizer for this gives me > shivers, and it's only Monday morning. >They don't synchronize the FM demodulator. The whole thing operates like the OFDM modem working via the analog FM channel.> To be fair, John Proakis knows heck of a lot about synchronization and > he builds impressive systems for all sorts of challenging > environments, > so I am going to wait until he builds a receiver system for this.Well, I'd say the synchronization is one of the weakest spots of the book of Proakis on the Digital Communication. Mostly he cites Viterbi, Van Trees and other classics; there is no treatment on the acquisition of the sync, only the performance when the sync is in lock already, no description of the algorithms, etc. Vladimir Vassilevsky DSP and Mixed Signal Design Consultant http://www.abvolt.com
Reply by ●May 14, 20072007-05-14
Vladimir Vassilevsky wrote:> > > julius wrote: > >> >>> OFDM riding on FM is ridiculous; it is a way to combine the >>> disadvantages of both modulations. This is the low energy and spectral >>> efficiency, nonlinear effects, a complex equalization in the time domain >>> and a sensitivity to selective fading. Why anybody needs this? >>> >> >> The thought of coming up with a synchronizer for this gives me >> shivers, and it's only Monday morning. >> > > They don't synchronize the FM demodulator. The whole thing operates like > the OFDM modem working via the analog FM channel. > >> To be fair, John Proakis knows heck of a lot about synchronization and >> he builds impressive systems for all sorts of challenging >> environments, >> so I am going to wait until he builds a receiver system for this. > > Well, I'd say the synchronization is one of the weakest spots of the > book of Proakis on the Digital Communication. Mostly he cites Viterbi, > Van Trees and other classics; there is no treatment on the acquisition > of the sync, only the performance when the sync is in lock already, no > description of the algorithms, etc.I'd say that Proakis book simply skips the whole subject of synchronisation, with a few words and a little hand waving. A very poor show from a smart guy. Steve
Reply by ●May 14, 20072007-05-14
On May 14, 9:53 am, Vladimir Vassilevsky <antispam_bo...@hotmail.com> wrote:> sampson...@gmail.com wrote: > > > CE-OFDM is OFDM with a Phase Modulator on the output. Google finds > > some references. > > OFDM riding on FM is ridiculous; it is a way to combine the > disadvantages of both modulations. This is the low energy and spectral > efficiency, nonlinear effects, a complex equalization in the time domain > and a sensitivity to selective fading. Why anybody needs this? > > Vladimir Vassilevsky > > DSP and Mixed Signal Design Consultant > > http://www.abvolt.comI believe that CE-OFDM was originally proposed as a way to modify OFDM such that an efficient nonlinear transmitter could be used, hopefully preserving the benefits of OFDM in a multipath channel. The nonlinear transmitter will distort the OFDM waveform but not the CE-OFDM one. I think the conclusion is that with a more complicated equalizer, CE- OFDM can do well compared to OFDM. A wider channel must also be required for CE-OFDM because of the frequency spreading in the modulator. The phase modulation also introduces a threshold effect in the receiver that isn't an issue for OFDM. John John
Reply by ●May 14, 20072007-05-14
Dear Group, Apologies in advance for the coming shameless plugs, but how can I resist? Many of the issues discussed in this discussion have been addressed in my PhD thesis: http://76.222.14.118/cv.pdf CE-OFDM is a fun idea since it is an easy way to get a wideband constant envelope signal with easy equalization. The equalization hinges on the cyclic prefix, which guarantees the theorem of circular convolution. This way, linear equalization may be performed with FFTs. Synchronization and channel estimation are performed just as they are in OFDM. The shameless plugging continues: http://76.222.14.118/pres/o/o18.pdf That presentations shows some pictures of our hardware prototype. Regards, Steve Thompson http://76.222.14.118/work/ PS: Why the cryptic IP address above? Because I just moved, and my server moved with me. As the DNS servers remap elsteve.com to my new IP address, the 76.222.14.118 must be used. After that, the above links should be equivalent to http://elsteve.com/cv.pdf, http://elsteve/pres/o/o18.pdf, and http://elsteve.com/work/ respectively.
