O-QPSK Demodulation
in [DSP]
|
Prev: OFDM Simulink problem, SOS!
Next: TI 320C6713
From: A.D. on 18 Dec 2005 11:57 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
From: Vladimir Vassilevsky on 18 Dec 2005 16:04 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
From: Tim Wescott on 18 Dec 2005 18:02 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
From: A.D. on 19 Dec 2005 03:43 "Vladimir Vassilevsky" <antispam_bogus(a)hotmail.com> ha scritto nel messaggio news:i9kpf.39953$tV6.22464(a)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
From: A.D. on 19 Dec 2005 03:46
"Tim Wescott" <tim(a)seemywebsite.com> ha scritto nel messaggio news:bMydnWHsbLEEdzjeRVn-uA(a)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 |