| Author |
Message |
A.D.
Guest
|
 Posted:
Sun Dec 18, 2005 5:15 pm Post subject:
O-QPSK Demodulation |
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Hi all,
I have to demodulate an O-QPSK signal. As usual in this kind of
modulation, symbols (chips) have an half-sine shape, and the Q channel
has a 90 degree (half simbol) offset with respect to the I channel.
The first thing I have to do (and perhaps the most difficult) is
removing the frequency offset from the received I and Q signals. I
cannot use a simple Costas loop since it doesn't work with O-QPSK
signals!
Are there dedicated loops for O-QPSK signals? Or it exists some simple
and effective way to demodultate such a signal?
Thank you in advance for any advice!
Antonio |
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Vladimir Vassilevsky
Guest
|
| Posted:
Mon Dec 19, 2005 1:15 am Post subject:
Re: O-QPSK Demodulation |
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A.D. wrote:
| Quote: | Hi all,
I have to demodulate an O-QPSK signal. As usual in this kind of
modulation, symbols (chips) have an half-sine shape, and the Q channel
has a 90 degree (half simbol) offset with respect to the I channel.
The first thing I have to do (and perhaps the most difficult) is
removing the frequency offset from the received I and Q signals. I
cannot use a simple Costas loop since it doesn't work with O-QPSK
signals!
Are there dedicated loops for O-QPSK signals? Or it exists some simple
and effective way to demodultate such a signal?
|
The demodulation of OQPSK is not much different from the demodulation of
the QPSK. Think of OPSK as of two BPSK signals shifted by 1/2 bit. All
you have to do is to jointly demodulate those two signals. Symbol sync
and carrier sync is not any different.
Vladimir Vassilevsky
DSP and Mixed Signal Design Consultant
http://www.abvolt.com |
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Tim Wescott
Guest
|
| Posted:
Mon Dec 19, 2005 1:15 am Post subject:
Re: O-QPSK Demodulation |
|
|
A.D. wrote:
| Quote: | Hi all,
I have to demodulate an O-QPSK signal. As usual in this kind of
modulation, symbols (chips) have an half-sine shape, and the Q channel
has a 90 degree (half simbol) offset with respect to the I channel.
The first thing I have to do (and perhaps the most difficult) is
removing the frequency offset from the received I and Q signals. I
cannot use a simple Costas loop since it doesn't work with O-QPSK
signals!
Are there dedicated loops for O-QPSK signals? Or it exists some simple
and effective way to demodultate such a signal?
Thank you in advance for any advice!
Antonio
O-QPSK with half-sine shaping also goes by the name 'MSK'. I built an |
MSK radio modem for my Master's thesis, which I have recently posted on
the web: http://www.wescottdesign.com/articles/MSK/mskTop.html. Chapter
3 should give a pretty good tutorial for how to do this, and Appendix B
is a pretty good example of just how execrable code can be while still
functioning as intended.
--
Tim Wescott
Wescott Design Services
http://www.wescottdesign.com |
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A.D.
Guest
|
| Posted:
Mon Dec 19, 2005 9:15 am Post subject:
Re: O-QPSK Demodulation |
|
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"Vladimir Vassilevsky" <antispam_bogus@hotmail.com> ha scritto nel messaggio
news:i9kpf.39953$tV6.22464@newssvr27.news.prodigy.net...
| Quote: |
The demodulation of OQPSK is not much different from the demodulation of
the QPSK. Think of OPSK as of two BPSK signals shifted by 1/2 bit. All you
have to do is to jointly demodulate those two signals. Symbol sync and
carrier sync is not any different.
|
Thank you Vladimir, I will try it.
Regards,
Antonio |
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A.D.
Guest
|
| Posted:
Mon Dec 19, 2005 9:15 am Post subject:
Re: O-QPSK Demodulation |
|
|
"Tim Wescott" <tim@seemywebsite.com> ha scritto nel messaggio
news:bMydnWHsbLEEdzjeRVn-uA@web-ster.com...
| Quote: |
O-QPSK with half-sine shaping also goes by the name 'MSK'. I built an MSK
radio modem for my Master's thesis, which I have recently posted on the
web: http://www.wescottdesign.com/articles/MSK/mskTop.html. Chapter 3
should give a pretty good tutorial for how to do this, and Appendix B is a
pretty good example of just how execrable code can be while still
functioning as intended.
|
Great! I will carefully read it.
Thank you very much,
Antonio |
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Guest
|
| Posted:
Tue Dec 20, 2005 1:16 am Post subject:
Re: O-QPSK Demodulation |
|
|
A.D. wrote:
| Quote: | Hi all,
I have to demodulate an O-QPSK signal. As usual in this kind of
modulation, symbols (chips) have an half-sine shape, and the Q channel
has a 90 degree (half simbol) offset with respect to the I channel.
The first thing I have to do (and perhaps the most difficult) is
removing the frequency offset from the received I and Q signals. I
cannot use a simple Costas loop since it doesn't work with O-QPSK
signals!
Are there dedicated loops for O-QPSK signals? Or it exists some simple
and effective way to demodultate such a signal?
Thank you in advance for any advice!
Antonio
|
how big do you expect the offset to be?, I believe differential chip
detection
can handle some offset but it will cost you a little over 3dB in
sensitivity
-Lasse |
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A.D.
Guest
|
| Posted:
Tue Dec 20, 2005 9:16 am Post subject:
Re: O-QPSK Demodulation |
|
|
<langwadt@ieee.org> ha scritto nel messaggio
news:1135022040.250858.304390@g43g2000cwa.googlegroups.com...
| Quote: |
how big do you expect the offset to be?, I believe differential chip
detection can handle some offset but it will cost you a little over
3dB in sensitivity
|
I'm trying to demodulate ZigBee signals, so I have a chip rate of 1Mcps on I
and Q channel and a maximum extimated offset of about 500KHz (wrost case).
But data are not differentially encoded, so I think that is not possible to
use a differential detection...
Regards,
Antonio |
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