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From: McNab on 3 Oct 2006 08:36
Hi!

I'm working on a simulation of blind QAM demodulation in Matlab. So far i
have implemented AGC, Carrier Phase tracking loop and a CMA equalizer -
but i have not yet implemented symbol timing recovery.

I have seen numerous references to Band-Edge Timiing Recovery (BETR), wich
seem to do the trick quite well. I just can't seem to find a lot of
information on how it works! I have read "Passband Timing Recovery in an
All-Digital Modem Receiver" by Godard but haven't been able to make it
work. Is there any other descriptions of BETR out there?

Thanks,

McNab




From: Steve Underwood on 3 Oct 2006 08:58
McNab wrote:
> Hi!
>
> I'm working on a simulation of blind QAM demodulation in Matlab. So far i
> have implemented AGC, Carrier Phase tracking loop and a CMA equalizer -
> but i have not yet implemented symbol timing recovery.
>
> I have seen numerous references to Band-Edge Timiing Recovery (BETR), wich
> seem to do the trick quite well. I just can't seem to find a lot of
> information on how it works! I have read "Passband Timing Recovery in an
> All-Digital Modem Receiver" by Godard but haven't been able to make it
> work. Is there any other descriptions of BETR out there?
>
> Thanks,
>
> McNab

There isn't a lot in this which is blind equalisation related, because
many timing detectors are the first step in the data recovery chain
whether the demodulation is blind or trained. Its really a matter of
excess bandwidth.

If you have lots of excess bandwidth, things like Gardner work. You only
need to consider thing like band-edge when the excess bandwidth is
somewhat limited, as Gardner falls apart.

If the carrier is X, and the symbol rate is Y, the band will be X-Y/2 to
X+Y/2, ignoring the excess bandwidth. Consider what happens if you
filter tightly around those two band edge frequencies, and slide the
baud phase around.

Steve
From: Vladimir Vassilevsky on 3 Oct 2006 10:11


McNab wrote:

> Hi!
>
> I'm working on a simulation of blind QAM demodulation in Matlab. So far i
> have implemented AGC, Carrier Phase tracking loop and a CMA equalizer -
> but i have not yet implemented symbol timing recovery.

The key point is the "eyes" of the QAM should be open at least for the
small amount at the very beginning. Otherwise the training and locking
will take a lot of time or even may never be successful.

All of the parameters should be jointly estimated. The equalizer, the
carrier PLL and the symbol timing recovery PLL should be done in the way
that they don't interact with each other.



> I have seen numerous references to Band-Edge Timiing Recovery (BETR), wich
> seem to do the trick quite well. I just can't seem to find a lot of
> information on how it works! I have read "Passband Timing Recovery in an
> All-Digital Modem Receiver" by Godard but haven't been able to make it
> work. Is there any other descriptions of BETR out there?
>
> Thanks,
>
> McNab


Vladimir Vassilevsky

DSP and Mixed Signal Design Consultant

http://www.abvolt.com
From: McNab on 3 Oct 2006 14:41
>There isn't a lot in this which is blind equalisation related, because
>many timing detectors are the first step in the data recovery chain
>whether the demodulation is blind or trained. Its really a matter of
>excess bandwidth.
>
>If you have lots of excess bandwidth, things like Gardner work. You only

>need to consider thing like band-edge when the excess bandwidth is
>somewhat limited, as Gardner falls apart.
>
>If the carrier is X, and the symbol rate is Y, the band will be X-Y/2 to

>X+Y/2, ignoring the excess bandwidth. Consider what happens if you
>filter tightly around those two band edge frequencies, and slide the
>baud phase around.


Unfortunately I am not guarenteed lots of excess bandwidth, so I guess
Gardner is not the solution for me. If you have any references to
information on BETR, it would be greatly appreciated.

Thanks,

McNab


From: Steve Underwood on 3 Oct 2006 21:45
McNab wrote:
>> There isn't a lot in this which is blind equalisation related, because
>> many timing detectors are the first step in the data recovery chain
>> whether the demodulation is blind or trained. Its really a matter of
>> excess bandwidth.
>>
>> If you have lots of excess bandwidth, things like Gardner work. You only
>
>> need to consider thing like band-edge when the excess bandwidth is
>> somewhat limited, as Gardner falls apart.
>>
>> If the carrier is X, and the symbol rate is Y, the band will be X-Y/2 to
>
>> X+Y/2, ignoring the excess bandwidth. Consider what happens if you
>> filter tightly around those two band edge frequencies, and slide the
>> baud phase around.
>
>
> Unfortunately I am not guarenteed lots of excess bandwidth, so I guess
> Gardner is not the solution for me. If you have any references to
> information on BETR, it would be greatly appreciated.

I thought I provided the clue. Don't you expect to do any work on this?

Steve
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