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IQ Receiver Processing

Started by Ali A Nasir August 9, 2009
   Can anyone please tell me one thing that in communication receiver,
after performing matched filtering and timing recovery seperately for I and
Q data, whether equalization works separately on I and Q data or we first
get the complex signal (combining I and Q) and perform equalization on
complex signal (or what is preferable) ?

   I am sorry for if this question is silly but its my first question so I
will be happy if anyone guides me!

Thanks
Ali



"Ali A Nasir" <aliarshad46@hotmail.com> writes:

> Can anyone please tell me one thing that in communication receiver, > after performing matched filtering and timing recovery seperately for I and > Q data, whether equalization works separately on I and Q data or we first > get the complex signal (combining I and Q) and perform equalization on > complex signal (or what is preferable) ?
Normally you would do all of the above in the complex domain. For one, any differential errors in timing frequency or phase would completely throw off the rest of the processing. Also, for equalization, you lose information if you only process an I or a Q at a time. -- Randy Yates % "How's life on earth? Digital Signal Labs % ... What is it worth?" mailto://yates@ieee.org % 'Mission (A World Record)', http://www.digitalsignallabs.com % *A New World Record*, ELO
>Normally you would do all of the above in the complex domain. For one, >any differential errors in timing frequency or phase would completely >throw off the rest of the processing. Also, for equalization, you >lose information if you only process an I or a Q at a time. >-- >Randy Yates % "How's life on earth? >Digital Signal Labs % ... What is it worth?" >mailto://yates@ieee.org % 'Mission (A World Record)', >http://www.digitalsignallabs.com % *A New World Record*, ELO
First of all, thanks a lot for your reply but how the timing recovery could be performed on complex samples ( matched filtered output processing the complex received data ) ?
On Aug 10, 3:03&#2013266080;am, "Ali A Nasir" <aliarsha...@hotmail.com> wrote:
> >Normally you would do all of the above in the complex domain. For one, > >any differential errors in timing frequency or phase would completely > >throw off the rest of the processing. Also, for equalization, you > >lose information if you only process an I or a Q at a time. > >-- > >Randy Yates &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080;% "How's life on earth? > >Digital Signal Labs &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080;% &#2013266080;... What is it worth?" > >mailto://ya...@ieee.org &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080;% 'Mission (A World Record)', > >http://www.digitalsignallabs.com% *A New World Record*, ELO > > &#2013266080; &#2013266080;First of all, thanks a lot for your reply but how the timing recovery > could be performed on complex samples ( matched filtered output processing > the complex received data ) ?
Basic questions regarding timing recovery has been asked countless times on this forum. Please use google groups to search through the archives. Many textbooks are already published on this subject. Personally I like Mengali/d'Andrea and Moeneclaey/Meyr/Fechtel. Julius
"Ali A Nasir" <aliarshad46@hotmail.com> writes:

>>Normally you would do all of the above in the complex domain. For one, >>any differential errors in timing frequency or phase would completely >>throw off the rest of the processing. Also, for equalization, you >>lose information if you only process an I or a Q at a time. >>-- >>Randy Yates % "How's life on earth? >>Digital Signal Labs % ... What is it worth?" >>mailto://yates@ieee.org % 'Mission (A World Record)', >>http://www.digitalsignallabs.com % *A New World Record*, ELO > > > First of all, thanks a lot for your reply but how the timing recovery > could be performed on complex samples ( matched filtered output processing > the complex received data ) ?
Timing recovery is a very wide, complicated subject. Can you be more specific? Take a look in any of the digital comm texts for ideas on how to do it. --Randy @BOOK{proakiscomm, title = "{Digital Communications}", author = "John~G.~Proakis", publisher = "McGraw-Hill", edition = "fourth", year = "2001"} @BOOK{couch, title = "{Digital and Analog Communication Systems}", author = "{Leon~W.~Couch}", publisher = "Prentice Hall", edition = "fifth", year = "1993"} @BOOK{sklar, title = "{Digital Communications}", author = "{Bernard~Sklar}", publisher = "Prentice Hall P T R", edition = "second", year = "2001"} @BOOK{leeandmesserschmitt3, title = "{Digital Communication}", author = "{John R. Barry and Edwared A. Lee and David G. Messerschmitt}", publisher = "Springer", edition = "third", year = "2004"} -- Randy Yates % "The dreamer, the unwoken fool - Digital Signal Labs % in dreams, no pain will kiss the brow..." mailto://yates@ieee.org % http://www.digitalsignallabs.com % 'Eldorado Overture', *Eldorado*, ELO
>"Ali A Nasir" <aliarshad46@hotmail.com> writes: > >>>Normally you would do all of the above in the complex domain. For one, >>>any differential errors in timing frequency or phase would completely >>>throw off the rest of the processing. Also, for equalization, you >>>lose information if you only process an I or a Q at a time. >>>-- >>>Randy Yates % "How's life on earth? >>>Digital Signal Labs % ... What is it worth?" >>>mailto://yates@ieee.org % 'Mission (A World Record)', >>>http://www.digitalsignallabs.com % *A New World Record*, ELO >> >> >> First of all, thanks a lot for your reply but how the timing
recovery
>> could be performed on complex samples ( matched filtered output
processing
>> the complex received data ) ? > >Timing recovery is a very wide, complicated subject. Can you be more >specific? Take a look in any of the digital comm texts for ideas on >how to do it. > >--Randy > >@BOOK{proakiscomm, > title = "{Digital Communications}", > author = "John~G.~Proakis", > publisher = "McGraw-Hill", > edition = "fourth", > year = "2001"} >@BOOK{couch, > title = "{Digital and Analog Communication Systems}", > author = "{Leon~W.~Couch}", > publisher = "Prentice Hall", > edition = "fifth", > year = "1993"} >@BOOK{sklar, > title = "{Digital Communications}", > author = "{Bernard~Sklar}", > publisher = "Prentice Hall P T R", > edition = "second", > year = "2001"} >@BOOK{leeandmesserschmitt3, > title = "{Digital Communication}", > author = "{John R. Barry and Edwared A. Lee and David G.
Messerschmitt}",
> publisher = "Springer", > edition = "third", > year = "2004"} > >-- >Randy Yates % "The dreamer, the unwoken fool - >Digital Signal Labs % in dreams, no pain will kiss the
brow..."
>mailto://yates@ieee.org % >http://www.digitalsignallabs.com % 'Eldorado Overture', *Eldorado*, ELO >
I do not know about the second and the fourth one but the first(Proakis) and the third(sklar) books are horrible. They just make the subject more complicated. When I read those two, I thought to forget about synchronization topic (both phase and timing). Then I asked many ques here and I am somehow into that now. I would personally stick to the books Julius has suggested. It is painful topic but at the same time interesting. Chintan
 Thanks Chintan, Julius and Randy for advising some good books. I have
them, let me make my question more clear as I have not found any block
diagram demonstrating my concern. 

 It is clearly mentioned in different books that timing recovery ( finding
the correct sampling point i.e. maximum SNR point ) is separately performed
on I and Q parts of the received signal. Now my question is that after
performing timing recovery, whether equalization is done separately on the
I and Q branches or we have to combine I&Q output of timing recovery block
and perform equalization on complex signal? 
>>@BOOK{proakiscomm, >> title = "{Digital Communications}", >> author = "John~G.~Proakis", >> publisher = "McGraw-Hill", >> edition = "fourth", >> year = "2001"} >>@BOOK{couch, >> title = "{Digital and Analog Communication Systems}", >> author = "{Leon~W.~Couch}", >> publisher = "Prentice Hall", >> edition = "fifth", >> year = "1993"} >>@BOOK{sklar, >> title = "{Digital Communications}", >> author = "{Bernard~Sklar}", >> publisher = "Prentice Hall P T R", >> edition = "second", >> year = "2001"} >>@BOOK{leeandmesserschmitt3, >> title = "{Digital Communication}", >> author = "{John R. Barry and Edwared A. Lee and David G. >Messerschmitt}", >> publisher = "Springer", >> edition = "third", >> year = "2004"} > >I do not know about the second and the fourth one but the first(Proakis) >and the third(sklar) books are horrible. They just make the subject more >complicated. When I read those two, I thought to forget about >synchronization topic (both phase and timing).
They don't make timing recovery complicated. They just gloss over it, and don't talk about most of the issues, or most of the interesting techniques.
>Then I asked many ques here and I am somehow into that now. I would >personally stick to the books Julius has suggested. It is painful topic >but at the same time interesting.
It doesn't have to be painful. Recovering timing blindly sounds like it will be painful. However, once you get to grips with the issues and the popular algorithms its not that bad. The problem is books that skirt around the topic, rather than facing it head on. The Proakis book is pretty thick. How many pages are devoted to timing recovery? Steve
> Thanks Chintan, Julius and Randy for advising some good books. I have >them, let me make my question more clear as I have not found any block >diagram demonstrating my concern. > > It is clearly mentioned in different books that timing recovery (
finding
>the correct sampling point i.e. maximum SNR point ) is separately
performed
>on I and Q parts of the received signal. Now my question is that after >performing timing recovery, whether equalization is done separately on
the
>I and Q branches or we have to combine I&Q output of timing recovery
block
>and perform equalization on complex signal? >
In my opinion it does not matter. I have seen people doing timing recovery separately on I and Q and then do equalization either separately or on combined complex signal. Hope this helps. Chintan
On Aug 10, 10:57&#2013266080;pm, "Ali A Nasir" <aliarsha...@hotmail.com> wrote:
> &#2013266080;Thanks Chintan, Julius and Randy for advising some good books. I have > them, let me make my question more clear as I have not found any block > diagram demonstrating my concern. > > &#2013266080;It is clearly mentioned in different books that timing recovery ( finding > the correct sampling point i.e. maximum SNR point ) is separately performed > on I and Q parts of the received signal. Now my question is that after > performing timing recovery, whether equalization is done separately on the > I and Q branches or we have to combine I&Q output of timing recovery block > and perform equalization on complex signal?
For passband-modulated signals you will have to do both timing and phase recovery. Phase offset makes the I and Q parts dependent on each other. Some timing recovery schemes are indifferent to phase offsets, and some are sensitive to it. Equalization should be done AFTER timing and phase synchronization, otherwise you screw up your equalization. If you have a frequency offset, for example, your phase offset will change linearly, and throw off your equalizer. You need to learn to do both equalization and synchronization. Maybe you should take smaller steps and learn them separately, and then figure out how to do both at the same time. Julius