Forums

Oversampling and receiver

Started by Awal March 3, 2009
Hi all,

I would like to know if the folling would be possible.

Lets say that my tx use a raised cosine filter to limit the bandwidth of
my transmitted signal. At the receiver I would oversample the received
signal by a factor of x and by using a Viterbi algorithm I would be able to
approximate every symbol affected by ISI caused by the memory of my raised
cosine filter. By doing this would it be possible to eliminate the need of
a clock recovery system if my transmitted data frame is preceded by a
header that I would correlate on in order to indicate when valid data can
be process by the viterbi 

On Mar 3, 2:05 pm, "Awal" <sacha.at...@lacime.etsmtl.ca> wrote:
> Hi all, > > I would like to know if the folling would be possible. > > Lets say that my tx use a raised cosine filter to limit the bandwidth of > my transmitted signal. At the receiver I would oversample the received > signal by a factor of x and by using a Viterbi algorithm I would be able to > approximate every symbol affected by ISI caused by the memory of my raised > cosine filter. By doing this would it be possible to eliminate the need of > a clock recovery system if my transmitted data frame is preceded by a > header that I would correlate on in order to indicate when valid data can > be process by the viterbi
If the timing mismatch is constant, then this should work. Does your channel have memory? You are considering a complicated (and expensive to implement) solution to what is possibly a simple problem.
>On Mar 3, 2:05 pm, "Awal" <sacha.at...@lacime.etsmtl.ca> wrote: >> Hi all, >> >> I would like to know if the folling would be possible. >> >> Lets say that my tx use a raised cosine filter to limit the bandwidth
of
>> my transmitted signal. At the receiver I would oversample the received >> signal by a factor of x and by using a Viterbi algorithm I would be
able to
>> approximate every symbol affected by ISI caused by the memory of my
raised
>> cosine filter. By doing this would it be possible to eliminate the need
of
>> a clock recovery system if my transmitted data frame is preceded by a >> header that I would correlate on in order to indicate when valid data
can
>> be process by the viterbi > >If the timing mismatch is constant, then this should work. Does >your channel have memory? You are considering a complicated >(and expensive to implement) solution to what is possibly a simple >problem. >
I would start with a simple channel model: only white noise and transmission delay. No multipath, channel memory etc.. I know it&rsquo;s a complicated solution, I'm just playing with idia at the moment. The complexity of my viterbi would be proportional to the raised cosine filter. thanks
Awal <sacha.atwal@lacime.etsmtl.ca> wrote:

>Lets say that my tx use a raised cosine filter to limit the bandwidth of >my transmitted signal. At the receiver I would oversample the received >signal by a factor of x and by using a Viterbi algorithm I would be able to >approximate every symbol affected by ISI caused by the memory of my raised >cosine filter. By doing this would it be possible to eliminate the need of >a clock recovery system if my transmitted data frame is preceded by a >header that I would correlate on in order to indicate when valid data can >be process by the viterbi
Yes, it is sometimes possible to derive all of your timing recovery from headers. Whether you can do this may not have anything to do with your raised cosine function or Viterbi equalizer. Good luck. Steve

Awal wrote:

> Hi all, > > I would like to know if the folling would be possible. > > Lets say that my tx use a raised cosine filter to limit the bandwidth of > my transmitted signal. At the receiver I would oversample the received > signal by a factor of x and by using a Viterbi algorithm I would be able to > approximate every symbol affected by ISI caused by the memory of my raised > cosine filter. By doing this would it be possible to eliminate the need of > a clock recovery system if my transmitted data frame is preceded by a > header that I would correlate on in order to indicate when valid data can > be process by the viterbi
This is possible but cumbersome and inefficient. Unless there are some special requirements, clock recovery is better solution. Vladimir Vassilevsky DSP and Mixed Signal Design Consultant http://www.abvolt.com
Looking up references to the IS-54 cellular system from the 90's might 
be helpful.

Awal wrote:
>> On Mar 3, 2:05 pm, "Awal" <sacha.at...@lacime.etsmtl.ca> wrote: >>> Hi all, >>> >>> I would like to know if the folling would be possible. >>> >>> Lets say that my tx use a raised cosine filter to limit the bandwidth > of >>> my transmitted signal. At the receiver I would oversample the received >>> signal by a factor of x and by using a Viterbi algorithm I would be > able to >>> approximate every symbol affected by ISI caused by the memory of my > raised >>> cosine filter. By doing this would it be possible to eliminate the need > of >>> a clock recovery system if my transmitted data frame is preceded by a >>> header that I would correlate on in order to indicate when valid data > can >>> be process by the viterbi >> If the timing mismatch is constant, then this should work. Does >> your channel have memory? You are considering a complicated >> (and expensive to implement) solution to what is possibly a simple >> problem. >> > > I would start with a simple channel model: only white noise and > transmission delay. No multipath, channel memory etc.. > > I know it&rsquo;s a complicated solution, I'm just playing with idia at the > moment. The complexity of my viterbi would be proportional to the raised > cosine filter. > > > thanks
> > >Awal wrote: > >> Hi all, >> >> I would like to know if the folling would be possible. >> >> Lets say that my tx use a raised cosine filter to limit the bandwidth
of
>> my transmitted signal. At the receiver I would oversample the received >> signal by a factor of x and by using a Viterbi algorithm I would be
able to
>> approximate every symbol affected by ISI caused by the memory of my
raised
>> cosine filter. By doing this would it be possible to eliminate the need
of
>> a clock recovery system if my transmitted data frame is preceded by a >> header that I would correlate on in order to indicate when valid data
can
>> be process by the viterbi > >This is possible but cumbersome and inefficient. Unless there are some >special requirements, clock recovery is better solution. > >Vladimir Vassilevsky >DSP and Mixed Signal Design Consultant >http://www.abvolt.com >
The reiceved signal as not cyclostationry. Which mean I cannot used Gardner algorithm or other algorithm that use non-linear tranformation to recover the clk.

Awal wrote:


> The reiceved signal as not cyclostationry. Which mean I cannot used > Gardner algorithm or other algorithm that use non-linear tranformation to > recover the clk.
What does the clock mean if the signal is not cyclostationary? Vladimir Vassilevsky DSP and Mixed Signal Design Consultant http://www.abvolt.com
> > >Awal wrote: > > >> The reiceved signal as not cyclostationry. Which mean I cannot used >> Gardner algorithm or other algorithm that use non-linear tranformation
to
>> recover the clk. > >What does the clock mean if the signal is not cyclostationary? > > >Vladimir Vassilevsky >DSP and Mixed Signal Design Consultant >http://www.abvolt.com >
At the receiver I oversample the signal and undo the tx transformation that render the signal non cyclostationary in parallele to viterbi decodign.
On Mar 3, 2:05&#2013266080;pm, "Awal" <sacha.at...@lacime.etsmtl.ca> wrote:
> Hi all, > > I would like to know if the folling would be possible. > > Lets say that my tx use a raised cosine filter to limit the bandwidth of > my transmitted signal. At the receiver I would oversample the received > signal by a factor of x and by using a Viterbi algorithm I would be able to > approximate every symbol affected by ISI caused by the memory of my raised > cosine filter.
Here symbol refers to the oversampled one at the receiver or the one at the transmitter side? By doing this would it be possible to eliminate the need of
> a clock recovery system if my transmitted data frame is preceded by a > header that I would correlate on in order to indicate when valid data can > be process by the viterbi
I am a little bit confused here. By using viterbi, one assumption is that you have estimated the channel, which means you already have the clock recovered. If you do not know the channel, how could you use viterbi?