Reply by Ali A Nasir August 21, 20092009-08-21
>Randy Yates <yates@ieee.org> writes: >> [...] >> However, note that this introduces a 2 * pi / M phase ambiguity, since >> if >> >> phi = m * 2 * pi / M, >> >> then >> >> M * phi = m * 2 * pi >> == 0. > >Let me rewrite this: > >if > > phi = m * 2 * pi / M + theta, > >then > > M * phi = m * 2 * pi + M * theta > == M * theta. >-- >Randy Yates % "Bird, on the wing, >Digital Signal Labs % goes floating by >mailto://yates@ieee.org % but there's a teardrop in his
eye..."
>http://www.digitalsignallabs.com % 'One Summer Dream', *Face The Music*,
ELO
>
Thanks a lot Randy for such detailed and good explanation. I am clear now.
Reply by Randy Yates August 20, 20092009-08-20
Randy Yates <yates@ieee.org> writes:
> [...] > However, note that this introduces a 2 * pi / M phase ambiguity, since > if > > phi = m * 2 * pi / M, > > then > > M * phi = m * 2 * pi > == 0.
Let me rewrite this: if phi = m * 2 * pi / M + theta, then M * phi = m * 2 * pi + M * theta == M * theta. -- Randy Yates % "Bird, on the wing, Digital Signal Labs % goes floating by mailto://yates@ieee.org % but there's a teardrop in his eye..." http://www.digitalsignallabs.com % 'One Summer Dream', *Face The Music*, ELO
Reply by Randy Yates August 20, 20092009-08-20
"Ali A Nasir" <aliarshad46@hotmail.com> writes:

>>> I have the information about the constellation that I am using but > not >>>allowed to use any training or preamble ( since its blind recovery ). >>Let >>>us say I am using pi/4 QPSK >>> >> >>pi/4 QPSK constellation is the same as 8PSK. Possible to use blind >>phase/frequency offset estimator based on 8-th power. >> >>Or you need only the removal of phase ambiguity? >> >> > > > I need the removal of small carrier frequency offset in addition to > constant phase offset. Can you please explain the offset estimator based on > 8th power ?
Ali, If you have an M-ary PSK signal, the possible phases are r[n] = exp(i * m[n] * 2 * pi / M + phi), m[n] \in {0, 1, ..., M-1}, where phi is some unknown phase. Thus (r[n])^M = exp(i * m[n] * 2 * pi + M * phi) = exp(i * M * phi) This is the basis of the Mth-power technique for carrier recovery. However, note that this introduces a 2 * pi / M phase ambiguity, since if phi = m * 2 * pi / M, then M * phi = m * 2 * pi == 0.
> Any paper or book reference ? Will that be blind estimator ?
Yes, it's a blind estimator in that it doesn't require any special source symbol sequence. -- Randy Yates % "Midnight, on the water... Digital Signal Labs % I saw... the ocean's daughter." mailto://yates@ieee.org % 'Can't Get It Out Of My Head' http://www.digitalsignallabs.com % *El Dorado*, Electric Light Orchestra
Reply by Alexander Petrov August 20, 20092009-08-20
> I need the removal of small carrier frequency offset in addition to >constant phase offset. Can you please explain the offset estimator based
on
>8th power ? Any paper or book reference ? Will that be blind estimator ? > >Regards, >Ali >
Look at these simulink models: http://electronix.ru/forum/index.php?showtopic=23652
Reply by Ali A Nasir August 20, 20092009-08-20
> > >Alexander Petrov wrote: > >> pi/4 QPSK constellation is the same as 8PSK. Possible to use blind >> phase/frequency offset estimator based on 8-th power. > >You would be better off by considering the two subsequent symbols and >the 4th power. > > >Vladimir Vassilevsky >DSP and Mixed Signal Design Consultant >http://www.abvolt.com >
Thanks Vladimir for your response. Can you please give me some reference so that I could better understand how to implement the blind phase and frequcency offset estimation considering two subsequent symbols and fourth power ? Regards Regards, Ali
Reply by Ali A Nasir August 20, 20092009-08-20
>> I have the information about the constellation that I am using but
not
>>allowed to use any training or preamble ( since its blind recovery ). >Let >>us say I am using pi/4 QPSK >> > >pi/4 QPSK constellation is the same as 8PSK. Possible to use blind >phase/frequency offset estimator based on 8-th power. > >Or you need only the removal of phase ambiguity? > >
I need the removal of small carrier frequency offset in addition to constant phase offset. Can you please explain the offset estimator based on 8th power ? Any paper or book reference ? Will that be blind estimator ? Regards, Ali
Reply by Vladimir Vassilevsky August 18, 20092009-08-18

Alexander Petrov wrote:

> pi/4 QPSK constellation is the same as 8PSK. Possible to use blind > phase/frequency offset estimator based on 8-th power.
You would be better off by considering the two subsequent symbols and the 4th power. Vladimir Vassilevsky DSP and Mixed Signal Design Consultant http://www.abvolt.com
Reply by Alexander Petrov August 18, 20092009-08-18
> I have the information about the constellation that I am using but not >allowed to use any training or preamble ( since its blind recovery ).
Let
>us say I am using pi/4 QPSK >
pi/4 QPSK constellation is the same as 8PSK. Possible to use blind phase/frequency offset estimator based on 8-th power. Or you need only the removal of phase ambiguity?
Reply by julius August 16, 20092009-08-16
On Aug 16, 7:07&#2013266080;am, "Ali A Nasir" <aliarsha...@hotmail.com> wrote:
> >On Aug 15, 10:35=A0am, Eric Jacobsen <eric.jacob...@ieee.org> wrote: > >> On 8/13/2009 11:40 PM, Ali A Nasir wrote: > >[snip] > >> > =A0 =A0 =A0 Thanks for your guidance, Could you please explain some > thi= > >ng about > >> > FEC lock indicator. Is it Frequency Error Correction sort of thing > used= > > in > >> > Frequency Locked Loops ? > > >> No. =A0 There are techniques to tell whether some FEC decoders are > workin= > >g > >> on valid data or not. =A0 This is sometimes done in Viterbi decoders > by > >> observing the frequency of register renormalization. =A0 Similarly a > >> Reed-Solomon decoder generates a syndrome which can be used to tell > >> whether the codeword was valid or not. > > >> The idea, then, is that if the FEC is indicating that it has acquired > a > >> valid data stream then the phase ambiguity of the constellation must > be > >> correct. > > >> -- > >> Eric Jacobsen > >> Minister of Algorithms > >> Abineau Communicationshttp://www.abineau.com > > >Another thing to consider is the use of rotationally-invariant > >trellis code. &#2013266080;But the OP said no preamble. &#2013266080;Can you use > >a code? > > >Julius > > &#2013266080; &#2013266080; Yup Julius, I can use encoding but no initial preamble or training. So > you think that rotationally invariant trellis codes or reed solomon coding > can help in this regard ?
It will have the same problem as with any convolutional code without proper start and ending points. You have to at least agree on which one is the first symbol, right? So maybe it's not as bad a problem. Julius
Reply by Ali A Nasir August 16, 20092009-08-16
>On Aug 15, 10:35=A0am, Eric Jacobsen <eric.jacob...@ieee.org> wrote: >> On 8/13/2009 11:40 PM, Ali A Nasir wrote: >[snip] >> > =A0 =A0 =A0 Thanks for your guidance, Could you please explain some
thi=
>ng about >> > FEC lock indicator. Is it Frequency Error Correction sort of thing
used=
> in >> > Frequency Locked Loops ? >> >> No. =A0 There are techniques to tell whether some FEC decoders are
workin=
>g >> on valid data or not. =A0 This is sometimes done in Viterbi decoders
by
>> observing the frequency of register renormalization. =A0 Similarly a >> Reed-Solomon decoder generates a syndrome which can be used to tell >> whether the codeword was valid or not. >> >> The idea, then, is that if the FEC is indicating that it has acquired
a
>> valid data stream then the phase ambiguity of the constellation must
be
>> correct. >> >> -- >> Eric Jacobsen >> Minister of Algorithms >> Abineau Communicationshttp://www.abineau.com > >Another thing to consider is the use of rotationally-invariant >trellis code. But the OP said no preamble. Can you use >a code? > >Julius >
Yup Julius, I can use encoding but no initial preamble or training. So you think that rotationally invariant trellis codes or reed solomon coding can help in this regard ?