FPGA Central

Hi!

I have implemented blind equalization technique like CMA (Constan
Modulus Algorithm) and Dispersion Minimization algorithm but they ar
working only for real channel taps.

Can anyone tell me that if the channel taps are complex i.e. channe
is introducing phase offset, then how we can implement blind phase offse
recovery ? I would be grateful if someone could hint me about some goo
research paper on this issue. What I have searched works in Decisio
directed mode but is there any technique which do recover the phase offse
blindly ?

Regards

On Aug 13, 7:48*am, "Ali A Nasir" <aliarsha...@hotmail.com> wrote:
> Hi!
>
> * * *I have implemented blind equalization technique like CMA (Constant
> Modulus Algorithm) and Dispersion Minimization algorithm but they are
> working only for real channel taps.
>
> * * *Can anyone tell me that if the channel taps are complex i.e. channel
> is introducing phase offset, then how we can implement blind phase offset
> recovery ? I would be grateful if someone could hint me about some good
> research paper on this issue. What I have searched works in Decision
> directed mode but is there any technique which do recover the phase offset
> blindly ?
>
> Regards

If by "blind" you have no prior information of how the signal
or data should be, then this is impossible. For example, a
QPSK constellation rotated by pi/2, or pi, or 3pi/2, all look
the same.

In most practical systems you'll have a preamble to
solve this ambiguity.

Does that make sense or did I misunderstand your question?
Julius

>On Aug 13, 7:48=A0am, "Ali A Nasir" <aliarsha...@hotmail.com> wrote:
>> Hi!
>>
>> =A0 =A0 =A0I have implemented blind equalization technique like CM
(Cons=
>tant
>> Modulus Algorithm) and Dispersion Minimization algorithm but they are
>> working only for real channel taps.
>>
>> =A0 =A0 =A0Can anyone tell me that if the channel taps are complex i.e
c=
>hannel
>> is introducing phase offset, then how we can implement blind phas
offset
>> recovery ? I would be grateful if someone could hint me about som
good
>> research paper on this issue. What I have searched works in Decision
>> directed mode but is there any technique which do recover the phas
offse=
>t
>> blindly ?
>>
>> Regards
>
>If by "blind" you have no prior information of how the signal
>or data should be, then this is impossible. For example, a
>QPSK constellation rotated by pi/2, or pi, or 3pi/2, all look
>the same.
>
>In most practical systems you'll have a preamble to
>solve this ambiguity.
>
>Does that make sense or did I misunderstand your question?
>Julius
>

I have the information about the constellation that I am using but no
allowed to use any training or preamble ( since its blind recovery ). Le
us say I am using pi/4 QPSK

On Aug 13, 10:14*am, "Ali A Nasir" <aliarsha...@hotmail.com> wrote:
> >On Aug 13, 7:48=A0am, "Ali A Nasir" <aliarsha...@hotmail.com> wrote:
> >> Hi!
>
> >> =A0 =A0 =A0I have implemented blind equalization technique like CMA
> (Cons=
> >tant
> >> Modulus Algorithm) and Dispersion Minimization algorithm but they are
> >> working only for real channel taps.
>
> >> =A0 =A0 =A0Can anyone tell me that if the channel taps are complex i.e.
> c=
> >hannel
> >> is introducing phase offset, then how we can implement blind phase
> offset
> >> recovery ? I would be grateful if someone could hint me about some
> good
> >> research paper on this issue. What I have searched works in Decision
> >> directed mode but is there any technique which do recover the phase
> offse=
> >t
> >> blindly ?
>
> >> Regards
>
> >If by "blind" you have no prior information of how the signal
> >or data should be, then this is impossible. *For example, a
> >QPSK constellation rotated by pi/2, or pi, or 3pi/2, all look
> >the same.
>
> >In most practical systems you'll have a preamble to
> >solve this ambiguity.
>
> >Does that make sense or did I misunderstand your question?
> >Julius
>
> * *I have the information about the constellation that I am using butnot
> allowed to use any training or preamble ( since its blind recovery ). Let
> us say I am using pi/4 QPSK

Then you are out of luck, unless the data is differentially encoded or
something. You'll have to send some sort of sync word to solve the
ambiguity.

Julius

On 8/13/2009 8:05 AM, julius wrote:
> On Aug 13, 10:14 am, "Ali A Nasir"<aliarsha...@hotmail.com> wrote:
>>> On Aug 13, 7:48=A0am, "Ali A Nasir"<aliarsha...@hotmail.com> wrote:
>>>> Hi!
>>>> =A0 =A0 =A0I have implemented blind equalization technique like CMA
>> (Cons=
>>> tant
>>>> Modulus Algorithm) and Dispersion Minimization algorithm but they are
>>>> working only for real channel taps.
>>>> =A0 =A0 =A0Can anyone tell me that if the channel taps are complex i.e.
>> c=
>>> hannel
>>>> is introducing phase offset, then how we can implement blind phase
>> offset
>>>> recovery ? I would be grateful if someone could hint me about some
>> good
>>>> research paper on this issue. What I have searched works in Decision
>>>> directed mode but is there any technique which do recover the phase
>> offse=
>>> t
>>>> blindly ?
>>>> Regards
>>> If by "blind" you have no prior information of how the signal
>>> or data should be, then this is impossible. For example, a
>>> QPSK constellation rotated by pi/2, or pi, or 3pi/2, all look
>>> the same.
>>> In most practical systems you'll have a preamble to
>>> solve this ambiguity.
>>> Does that make sense or did I misunderstand your question?
>>> Julius
>> 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
>
> Then you are out of luck, unless the data is differentially encoded or
> something. You'll have to send some sort of sync word to solve the
> ambiguity.
>
> Julius

If FEC is used sometimes you can use a FEC lock indicator to resolve the
phase ambiguity. It adds a little time to the acquisition process, but
it can often do the job.


--
Eric Jacobsen
Minister of Algorithms
Abineau Communications
http://www.abineau.com

julius wrote:

> On Aug 13, 7:48 am, "Ali A Nasir" <aliarsha...@hotmail.com> wrote:
>
>>Hi!
>>
>> I have implemented blind equalization technique like CMA (Constant
>>Modulus Algorithm) and Dispersion Minimization algorithm but they are
>>working only for real channel taps.
>>
>> Can anyone tell me that if the channel taps are complex i.e. channel
>>is introducing phase offset, then how we can implement blind phase offset
>>recovery ? I would be grateful if someone could hint me about some good
>>research paper on this issue. What I have searched works in Decision
>>directed mode but is there any technique which do recover the phase offset
>>blindly ?

This is quite possible if the eye diagram has at least a slight opening.

> If by "blind" you have no prior information of how the signal
> or data should be, then this is impossible. For example, a
> QPSK constellation rotated by pi/2, or pi, or 3pi/2, all look
> the same.

You don't have to worry about N * Pi/2 ambiguity if your goal is just to
equalize the phase offset. It could be equalized to the nearest multiple
of Pi/2.

> In most practical systems you'll have a preamble to
> solve this ambiguity.

Data recovery is a different problem.


Vladimir Vassilevsky
DSP and Mixed Signal Design Consultant
http://www.abvolt.com

>Hi!
>
> I have implemented blind equalization technique like CMA (Constant
>Modulus Algorithm) and Dispersion Minimization algorithm but they are
>working only for real channel taps.
>
> Can anyone tell me that if the channel taps are complex i.e
channel
>is introducing phase offset, then how we can implement blind phas
offset
>recovery ? I would be grateful if someone could hint me about some good
>research paper on this issue. What I have searched works in Decision
>directed mode but is there any technique which do recover the phas
offset
>blindly ?
>
>Regards
>

I have recently tried adaptive DFE with carrier phase recovery (provide
symbol synch is achieved) on real-time signals. It worked for me but I ha
to play with step size of NLMS and loop constant for phase correction. Thi
is explained in Proakis Comms. page 700.

Chintan

>On 8/13/2009 8:05 AM, julius wrote:
>> On Aug 13, 10:14 am, "Ali A Nasir"<aliarsha...@hotmail.com> wrote:
>>>> On Aug 13, 7:48=A0am, "Ali A Nasir"<aliarsha...@hotmail.com> wrote:
>>>>> Hi!
>>>>> =A0 =A0 =A0I have implemented blind equalization technique like CMA
>>> (Cons=
>>>> tant
>>>>> Modulus Algorithm) and Dispersion Minimization algorithm but the
are
>>>>> working only for real channel taps.
>>>>> =A0 =A0 =A0Can anyone tell me that if the channel taps are comple
i.e.
>>> c=
>>>> hannel
>>>>> is introducing phase offset, then how we can implement blind phase
>>> offset
>>>>> recovery ? I would be grateful if someone could hint me about some
>>> good
>>>>> research paper on this issue. What I have searched works i
Decision
>>>>> directed mode but is there any technique which do recover the phase
>>> offse=
>>>> t
>>>>> blindly ?
>>>>> Regards
>>>> If by "blind" you have no prior information of how the signal
>>>> or data should be, then this is impossible. For example, a
>>>> QPSK constellation rotated by pi/2, or pi, or 3pi/2, all look
>>>> the same.
>>>> In most practical systems you'll have a preamble to
>>>> solve this ambiguity.
>>>> Does that make sense or did I misunderstand your question?
>>>> Julius
>>> I have the information about the constellation that I am using bu
not
>>> allowed to use any training or preamble ( since its blind recovery )
Let
>>> us say I am using pi/4 QPSK
>>
>> Then you are out of luck, unless the data is differentially encoded or
>> something. You'll have to send some sort of sync word to solve the
>> ambiguity.
>>
>> Julius
>
>If FEC is used sometimes you can use a FEC lock indicator to resolve th

>phase ambiguity. It adds a little time to the acquisition process, bu

>it can often do the job.
>
>
>--
>Eric Jacobsen
>Minister of Algorithms
>Abineau Communications
>http://www.abineau.com
>


@ Eric

Thanks for your guidance, Could you please explain some thing abou
FEC lock indicator. Is it Frequency Error Correction sort of thing used i
Frequency Locked Loops ?

>
>
>julius wrote:
>
>> On Aug 13, 7:48 am, "Ali A Nasir" <aliarsha...@hotmail.com> wrote:
>>
>>>Hi!
>>>
>>> I have implemented blind equalization technique like CM
(Constant
>>>Modulus Algorithm) and Dispersion Minimization algorithm but they are
>>>working only for real channel taps.
>>>
>>> Can anyone tell me that if the channel taps are complex i.e
channel
>>>is introducing phase offset, then how we can implement blind phas
offset
>>>recovery ? I would be grateful if someone could hint me about som
good
>>>research paper on this issue. What I have searched works in Decision
>>>directed mode but is there any technique which do recover the phas
offset
>>>blindly ?
>
>This is quite possible if the eye diagram has at least a slight opening.
>
>> If by "blind" you have no prior information of how the signal
>> or data should be, then this is impossible. For example, a
>> QPSK constellation rotated by pi/2, or pi, or 3pi/2, all look
>> the same.
>
>You don't have to worry about N * Pi/2 ambiguity if your goal is just t

>equalize the phase offset. It could be equalized to the nearest multipl

>of Pi/2.
>
>> In most practical systems you'll have a preamble to
>> solve this ambiguity.
>
>Data recovery is a different problem.
>
>
>Vladimir Vassilevsky
>DSP and Mixed Signal Design Consultant
>http://www.abvolt.com
>
>

@ Vladimir

Thanks for your reply. The blind equalization algorithm (Dispersio
Minimization) about which I talked before remove the ISI ( opens the ey
even for maximum ISI ) but in case of channel phase offsets, th
constellation is rotated in accordance with the phase offset. But tha
phase offset results in wrong decision at slicer during decoding. So m
question is what could be done to mitigate that phase offset ( say afte
the ISI is removed ) ? Can I find the channel phase offset blindly and th
rotate my equalized constellation accordingly to get accurate detection ?

>>Hi!
>>
>> I have implemented blind equalization technique like CMA (Constant
>>Modulus Algorithm) and Dispersion Minimization algorithm but they are
>>working only for real channel taps.
>>
>> Can anyone tell me that if the channel taps are complex i.e.
>channel
>>is introducing phase offset, then how we can implement blind phase
>offset
>>recovery ? I would be grateful if someone could hint me about some good
>>research paper on this issue. What I have searched works in Decision
>>directed mode but is there any technique which do recover the phase
>offset
>>blindly ?
>>
>>Regards
>>
>
>I have recently tried adaptive DFE with carrier phase recovery (provided
>symbol synch is achieved) on real-time signals. It worked for me but
had
>to play with step size of NLMS and loop constant for phase correction
This
>is explained in Proakis Comms. page 700.
>
>Chintan
>

@ Chintan,

Thanks for your guidance. Yup, symbol synchronization is achieved i
my case. Have you implemented DFE in a system which was initially traine
with some training preamble and then you used DFE to adapt the equalize
coefficients in decision directed mode ? Actually I have to equalize i
blind environment ( with no training ). The situation is that after IS
removal and equalization for the channel amplitude, the resultant
constellation is rotated in accordance with the channel phase offset. Bu
that phase offset results in wrong decision at slicer during decoding. S
my question is what could be done to mitigate that phase offset ? Can
find the channel phase offset blindly and then rotate my equalize
constellation accordingly to get accurate detection ?

On 13 Aug, 13:48, "Ali A Nasir" <aliarsha...@hotmail.com> wrote:
> Hi!
>
> * * *I have implemented blind equalization technique like CMA (Constant
> Modulus Algorithm) and Dispersion Minimization algorithm but they are
> working only for real channel taps.
>
> * * *Can anyone tell me that if the channel taps are complex

There might be a terminology question here, but what do
you mean by 'complex channel taps'? In common DSP terminology,
'tap' refers to coefficients in a FIR filter. If the channel
is indeed modeled as a FIR filter, then the coefficients of
that FIR filter should be real-valued.

So just out of curiosity: Do you really suggest that certain
channels have complex-valued responses?

Rune

>On 13 Aug, 13:48, "Ali A Nasir" <aliarsha...@hotmail.com> wrote:
>> Hi!
>>
>> =A0 =A0 =A0I have implemented blind equalization technique like CM
(Cons=
>tant
>> Modulus Algorithm) and Dispersion Minimization algorithm but they are
>> working only for real channel taps.
>>
>> =A0 =A0 =A0Can anyone tell me that if the channel taps are complex
>
>There might be a terminology question here, but what do
>you mean by 'complex channel taps'? In common DSP terminology,
>'tap' refers to coefficients in a FIR filter. If the channel
>is indeed modeled as a FIR filter, then the coefficients of
>that FIR filter should be real-valued.
>
>So just out of curiosity: Do you really suggest that certain
>channels have complex-valued responses?
>

As far as I know, real- world channels are complex valued. I have no
encountered any channel that is real.

Chintan
>Rune
>

>>>Hi!
>>>
>>> I have implemented blind equalization technique like CM
(Constant
>>>Modulus Algorithm) and Dispersion Minimization algorithm but they are
>>>working only for real channel taps.
>>>
>>> Can anyone tell me that if the channel taps are complex i.e.
>>channel
>>>is introducing phase offset, then how we can implement blind phase
>>offset
>>>recovery ? I would be grateful if someone could hint me about som
good
>>>research paper on this issue. What I have searched works in Decision
>>>directed mode but is there any technique which do recover the phase
>>offset
>>>blindly ?
>>>
>>>Regards
>>>
>>
>>I have recently tried adaptive DFE with carrier phase recover
(provided
>>symbol synch is achieved) on real-time signals. It worked for me but I
>had
>>to play with step size of NLMS and loop constant for phase correction.
>This
>>is explained in Proakis Comms. page 700.
>>
>>Chintan
>>
>
>@ Chintan,
>
> Thanks for your guidance. Yup, symbol synchronization is achieved in
>my case. Have you implemented DFE in a system which was initiall
trained
>with some training preamble and then you used DFE to adapt the equalizer
>coefficients in decision directed mode ? Actually I have to equalize in
>blind environment ( with no training ). The situation is that after ISI
>removal and equalization for the channel amplitude, the resultant
>constellation is rotated in accordance with the channel phase offset
But
>that phase offset results in wrong decision at slicer during decoding
So
>my question is what could be done to mitigate that phase offset ? Can I
>find the channel phase offset blindly and then rotate my equalized
>constellation accordingly to get accurate detection ?
>
>


I had to use training of 511 to achieve initial convergence of th
equalizer. But I am not sure how to design a complete blind receiver.
personally think that these blind receivers work provided the channe
variations are constant during the packet.

Chintan

On Aug 14, 3:30*am, Rune Allnor <all...@tele.ntnu.no> wrote:
> On 13 Aug, 13:48, "Ali A Nasir" <aliarsha...@hotmail.com> wrote:
>
> > Hi!
>
> > * * *I have implemented blind equalization technique like CMA (Constant
> > Modulus Algorithm) and Dispersion Minimization algorithm but they are
> > working only for real channel taps.
>
> > * * *Can anyone tell me that if the channel taps are complex
>
> There might be a terminology question here, but what do
> you mean by 'complex channel taps'? In common DSP terminology,
> 'tap' refers to coefficients in a FIR filter. If the channel
> is indeed modeled as a FIR filter, then the coefficients of
> that FIR filter should be real-valued.
>
> So just out of curiosity: Do you really suggest that certain
> channels have complex-valued responses?
>
> Rune

They are probably referring to complex baseband representations.
The actual physical (passband) channel itself is then still real-
valued.

Julius

>On Aug 14, 3:30=A0am, Rune Allnor <all...@tele.ntnu.no> wrote:
>> On 13 Aug, 13:48, "Ali A Nasir" <aliarsha...@hotmail.com> wrote:

>>
>> Rune
>
>They are probably referring to complex baseband representations.
>The actual physical (passband) channel itself is then still real-
>valued.
>
>Julius
>

I am sorry for poor choice of words. I meant the same thing what Julius i
saying.

Chintan

On 8/13/2009 11:40 PM, Ali A Nasir wrote:
>> On 8/13/2009 8:05 AM, julius wrote:
>>> On Aug 13, 10:14 am, "Ali A Nasir"<aliarsha...@hotmail.com> wrote:
>>>>> On Aug 13, 7:48=A0am, "Ali A Nasir"<aliarsha...@hotmail.com> wrote:
>>>>>> Hi!
>>>>>> =A0 =A0 =A0I have implemented blind equalization technique like CMA
>>>> (Cons=
>>>>> tant
>>>>>> Modulus Algorithm) and Dispersion Minimization algorithm but they
> are
>>>>>> working only for real channel taps.
>>>>>> =A0 =A0 =A0Can anyone tell me that if the channel taps are complex
> i.e.
>>>> c=
>>>>> hannel
>>>>>> is introducing phase offset, then how we can implement blind phase
>>>> offset
>>>>>> recovery ? I would be grateful if someone could hint me about some
>>>> good
>>>>>> research paper on this issue. What I have searched works in
> Decision
>>>>>> directed mode but is there any technique which do recover the phase
>>>> offse=
>>>>> t
>>>>>> blindly ?
>>>>>> Regards
>>>>> If by "blind" you have no prior information of how the signal
>>>>> or data should be, then this is impossible. For example, a
>>>>> QPSK constellation rotated by pi/2, or pi, or 3pi/2, all look
>>>>> the same.
>>>>> In most practical systems you'll have a preamble to
>>>>> solve this ambiguity.
>>>>> Does that make sense or did I misunderstand your question?
>>>>> Julius
>>>> 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
>>> Then you are out of luck, unless the data is differentially encoded or
>>> something. You'll have to send some sort of sync word to solve the
>>> ambiguity.
>>>
>>> Julius
>> If FEC is used sometimes you can use a FEC lock indicator to resolve the
>
>> phase ambiguity. It adds a little time to the acquisition process, but
>
>> it can often do the job.
>>
>>
>> --
>> Eric Jacobsen
>> Minister of Algorithms
>> Abineau Communications
>> http://www.abineau.com
>>
>
>
> @ Eric
>
> Thanks for your guidance, Could you please explain some thing about
> FEC lock indicator. Is it Frequency Error Correction sort of thing used in
> Frequency Locked Loops ?

No. There are techniques to tell whether some FEC decoders are working
on valid data or not. This is sometimes done in Viterbi decoders by
observing the frequency of register renormalization. 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 Communications
http://www.abineau.com

On Aug 15, 10:35*am, Eric Jacobsen <eric.jacob...@ieee.org> wrote:
> On 8/13/2009 11:40 PM, Ali A Nasir wrote:
[snip]
> > * * * Thanks for your guidance, Could you please explain some thing about
> > FEC lock indicator. Is it Frequency Error Correction sort of thing usedin
> > Frequency Locked Loops ?
>
> No. * There are techniques to tell whether some FEC decoders are working
> on valid data or not. * This is sometimes done in Viterbi decoders by
> observing the frequency of register renormalization. * 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

On Aug 13, 10:01*am, Eric Jacobsen <eric.jacob...@ieee.org> wrote:
> If FEC is used sometimes you can use a FEC lock indicator to resolve the
> phase ambiguity. * It adds a little time to the acquisition process, but
> it can often do the job.

A brute force solution would be to run multiple decoders in parallel,
one for each ambiguous quadrature phase for instance. That method
would trade off higher computational cost for minimized acquisition
time.


IMHO. YMMV.
---
rhn A.T nicholson d.0.t C-o-M

>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 som
thi=
>ng about
>> > FEC lock indicator. Is it Frequency Error Correction sort of thin
used=
> in
>> > Frequency Locked Loops ?
>>
>> No. =A0 There are techniques to tell whether some FEC decoders ar
workin=
>g
>> on valid data or not. =A0 This is sometimes done in Viterbi decoder
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 acquire
a
>> valid data stream then the phase ambiguity of the constellation mus
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. S
you think that rotationally invariant trellis codes or reed solomon coding
can help in this regard ?

On Aug 16, 7:07*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 explainsome
> 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 ?

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

> 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 blin
phase/frequency offset estimator based on 8-th power.

Or you need only the removal of phase ambiguity?

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

>> I have the information about the constellation that I am using bu
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 t
constant phase offset. Can you please explain the offset estimator based o
8th power ? Any paper or book reference ? Will that be blind estimator ?

Regards,
Ali

>
>
>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 referenc
so that I could better understand how to implement the blind phase an
frequcency offset estimation considering two subsequent symbols and fourt
power ?

Regards

Regards,
Ali

> I need the removal of small carrier frequency offset in addition to
>constant phase offset. Can you please explain the offset estimator base
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