SNR penalty due to Linear Interpolation

On Mar 19, 5:18&#4294967295;am, "steveu" <ste...@coppice.org> wrote:
> >On Mar 18, 5:19=A0pm, "cpshah99" <cpsha...@rediffmail.com> wrote:
>
> >> Hi Jerry
>
> >> I think what I have done is correct. I am resampling the carrier
> modulate=
> >d
> >> signal. So this carrier phase and timing impairements.
>
> >> And the good thing is that at RX, using adaptive linear iterpolator,
> it
> >> locks to the value of velocity but at higher SNR.
>
> >> I am thinking I need to do detail study of this topic.
>
> >> Thanks
>
> >> Chintan
>
> >If you use a loop filter, the bandwidth of this filter has to be
> >sufficiently
> >high to handle the Doppler. &#4294967295;And that means that the filter admits
> >more
> >noise. &#4294967295;This is covered in Myer/Moeneclaey/Fechtel, page 97 ....
>
> I've never tried this, but it should be possible to keep the bandwidth of
> the loop filter narrow. Radar systems use Kalman and related techniques to
> track the ebb and flow of target doppler, as the target manoeuvres. It
> should be possible to use such an approach to make the loop adjust in a
> focused manner, rather than just widening the loop, and letting it move
> around in a rather unfocused manner. Of course, if your target tracking
> algorithm gets fooled by tricky manoeuvres, you might regret trying this.
> Watch out for targets doing inverted half loops, and reversing their
> Doppler shift in a few seconds. :-\
>
> Regards,
> Steve

Bingo, this is the key insight.  However, the OP said that he is not
doing _Doppler_ tracking explicitly, but rather rely on the symbol and
phase trackers to be able to follow the Doppler.

I was hoping that the OP himself will eventually realize this ....

Hi

The doppler correction I have simulated, that does track the velocity
variation.

Just imagine a case where both TX and RX are rock steady and suddenly the
wave hits the TX or RX with gr8 force and this will cause movement for some
time.

And this adaptive loop will track it.

But as u said before, it is has something to do with loop bandwidth.

BTW, I checked abt Myer book online on amazon and it has got 5*
rating.....read ur review as well....but this book is not for
bigginers....

I will read this book and get clear idea of this timing problem. I guess I
need to study very hard and simulate all these.

Thanks a lot again.

Chintan

On Mar 19, 9:47&#4294967295;am, "cpshah99" <cpsha...@rediffmail.com> wrote:
> Hi
>
> The doppler correction I have simulated, that does track the velocity
> variation.

Yes, but how is the correction done at the receiver?
You have asked many questions here, which is good,
but now I am confused as to which system is which.
I thought that you synchronize only by doing symbol
delay estimation instead of explicitly using the Doppler
information.

>
> Just imagine a case where both TX and RX are rock steady and suddenly the
> wave hits the TX or RX with gr8 force and this will cause movement for some
> time.
>
> And this adaptive loop will track it.
>
> But as u said before, it is has something to do with loop bandwidth.
>
> BTW, I checked abt Myer book online on amazon and it has got 5*
> rating.....read ur review as well....but this book is not for
> bigginers....

Yes, but this problem is also not for beginners, unfortunately ....

>
> I will read this book and get clear idea of this timing problem. I guess I
> need to study very hard and simulate all these.
>
> Thanks a lot again.

Good luck,
Julius

>I thought that you synchronize only by doing symbol
>delay estimation instead of explicitly using the Doppler
>information.

Yes, u r correct as always...

>Yes, but this problem is also not for beginners, unfortunately ....
>
>>

yeah...

>
>Good luck,
>Julius
>

Thanks for this......I badly need some good luck

Chintan