# (no subject)

**URL:** <https://www.ruby-forum.com/t/no-subject/234534>\
**Category:** GNU Radio\
**Created:** [March 12, 2015, 7:37am UTC](https://www.ruby-forum.com/t/no-subject/234534 "2015-03-12T07:37:40Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![addis\_a](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/c4cdca/32.png) [@addis\_a](https://www.ruby-forum.com/u/addis_a)\
**Post date:** [March 12, 2015, 7:37am UTC](https://www.ruby-forum.com/t/no-subject/234534/1 "2015-03-12T07:37:40Z")

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sir, can we achieve 16 qam demodulation constellation without using  
costas  
loop? if possible please send me the flow graph. thank you

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**Author:** ![Vishwanatha\_H\_G](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/v/f19dbf/32.png) [@Vishwanatha\_H\_G](https://www.ruby-forum.com/u/Vishwanatha_H_G)\
**Post date:** [March 12, 2015, 9:43am UTC](https://www.ruby-forum.com/t/no-subject/234534/2 "2015-03-12T09:43:18Z")

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Hi Vishwanatha,

Demodulation of phase-depending modulations requires some kind of  
synchronization.

There’s more approaches than costas loops to phase synchronization;  
however, they’re usually very specific to a channel/signal model and  
can’t be universally applied, or very inefficient, or very complicated  
to explain. So the important question here is: Why do you need something  
else than a phase error feedback loop? You can of course just estimate  
your phase offset once using a set of known symbols (e.g. a preamble),  
and use that for as long as you think your channel and transceiver are  
coherent, but I think you’ve already considered that, since you ask how  
to get rid of the loop, and recognized that it’s a good idea to  
continuously account for changing phase.

Greetings,  
Marcus

PS: There’s not only sirs on this list, also ladies, and we’re not very  
formal on here, so a quick “hello” would totally be sufficient 🙂