Clock multiplication M-PSK

Hi all,

I would like to know how to regenerate the clock bit from the symbol
clock for multiple level PSK modulations ?

For QPSK modulation we need to recover a clock bit twice the symbol
clock.

I don't found any help on google...

Thanks.
Best regards.

patrick.melet@dmradiocom.fr wrote:
> Hi all,
>
> I would like to know how to regenerate the clock bit from the symbol
> clock for multiple level PSK modulations ?
>
> For QPSK modulation we need to recover a clock bit twice the symbol
> clock.
>
> I don't found any help on google...
>
> Thanks.
> Best regards.

If you have the symbol clock, you will need to send log2(M) bits out of
the demodulator in every symbol period. Depending on how the receiver
of these bits works, you could use a high rate free running clock to
essentially burst them out. Each time you get a new symbol, wait for
the next rising edge of the high rate clock. Shift out the first bit
then, wait for the next rising edge, then shift out the second bit,
etc. Also shift out rising and falling clock edges. Tell the guy
grabbing the bits to sample them on the falling edge of the gated clock
that you provide. 

John

"john" <johns@xetron.com> writes:

> patrick.melet@dmradiocom.fr wrote:
>> Hi all,
>>
>> I would like to know how to regenerate the clock bit from the symbol
>> clock for multiple level PSK modulations ?
>>
>> For QPSK modulation we need to recover a clock bit twice the symbol
>> clock.
>>
>> I don't found any help on google...
>>
>> Thanks.
>> Best regards.
>
> If you have the symbol clock, you will need to send log2(M) bits out of
> the demodulator in every symbol period. Depending on how the receiver
> of these bits works, you could use a high rate free running clock to
> essentially burst them out. Each time you get a new symbol, wait for
> the next rising edge of the high rate clock. Shift out the first bit
> then, wait for the next rising edge, then shift out the second bit,
> etc. Also shift out rising and falling clock edges. Tell the guy
> grabbing the bits to sample them on the falling edge of the gated clock
> that you provide. 

Couldn't one also use a frequency synthesizer to lock a bit clock at a
frequency of M times the symbol clock, where M = 2^k, k bits per
symbol?
-- 
%  Randy Yates                  % "Ticket to the moon, flight leaves here today 
%% Fuquay-Varina, NC            %  from Satellite 2"
%%% 919-577-9882                % 'Ticket To The Moon' 
%%%% <yates@ieee.org>           % *Time*, Electric Light Orchestra
http://home.earthlink.net/~yatescr

patrick.melet@dmradiocom.fr wrote:

> Hi all,
> 
> I would like to know how to regenerate the clock bit from the symbol
> clock for multiple level PSK modulations ?
> 
> For QPSK modulation we need to recover a clock bit twice the symbol
> clock.
> 
> I don't found any help on google...
> 
> Thanks.
> Best regards.
> 
I got 1500 hits on Altavista searching for +synchronize +QAM -- some of 
them even looked promising.

With the bit of work that I've done on cell phone stuff, the protocols 
either use a format that's easy to synchronize (such as MSK) or they 
provide pilot data sequences that make it easy to synchronize the 
carrier and symbol clocks.  Have you looked at your particular protocol 
to see if this is being done?

-- 

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

Posting from Google?  See http://cfaj.freeshell.org/google/

<patrick.melet@dmradiocom.fr> wrote in message 
news:1142260490.146538.116770@i39g2000cwa.googlegroups.com...
> Hi all,
>
> I would like to know how to regenerate the clock bit from the symbol
> clock for multiple level PSK modulations ?
>
> For QPSK modulation we need to recover a clock bit twice the symbol
> clock.
>
> I don't found any help on google...
>
If it's only QPSK I would insist that it's up to the analogue blokes to 
provide you with a clock at the symbol rate and at the bit rate because:
a) They can do it without using any of your precious DSP resources.
b) You can blame them for any poor performance later ;)

Best of luck - Mike