<langwadt@ieee.org> ha scritto nel messaggio
news:1135022040.250858.304390@g43g2000cwa.googlegroups.com...
>
> 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
Reply by ●December 19, 20052005-12-19
A.D. wrote:
> 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
Reply by A.D.●December 19, 20052005-12-19
"Tim Wescott" <tim@seemywebsite.com> ha scritto nel messaggio
news:bMydnWHsbLEEdzjeRVn-uA@web-ster.com...
>
> 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
Reply by A.D.●December 19, 20052005-12-19
"Vladimir Vassilevsky" <antispam_bogus@hotmail.com> ha scritto nel messaggio
news:i9kpf.39953$tV6.22464@newssvr27.news.prodigy.net...
>
> 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
Reply by Tim Wescott●December 18, 20052005-12-18
A.D. wrote:
> 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
Reply by Vladimir Vassilevsky●December 18, 20052005-12-18
A.D. wrote:
> 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
Reply by A.D.●December 18, 20052005-12-18
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