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pi/4 DQPSK with DSSS-CDMA

 
 
Patrick
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      06-14-2004
hello,

I have to implement an pi/4 DQPSK modulation with Direct Sequence
Spread Spectrum.

When I modulate the binary dats with pi/4 DQPSK, the output of the
modulator have 5 values : -1 -0.7 0 0.7 and 1...

Then I spread theses datas with a PN-code, but when the output of the
modulator have the value 0, the spread data will be 0 too : 0 *
pn_code = 0

And if I spread (first) the binary datas with the pn_code and then
modulate in DQPSK, the pn will be modified by the DQPSK modulation..
and the datas in the channel will not real pn_code because have been
modified by the DQPSK modulation

Do you have an idea how to implant the pi/4 DQPSK DSSS modem ?

Thanks...
 
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Wallclimber
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      06-14-2004
Hello Patrick,

this newsgroups talks about VHDL specific issues. Language features,
how to do certain constructs, optimizations etc.

Your question is about system implementation of certain signal
processing algorithm. I'm afraid this is totally out of the scope of
this newsgroup.

Tom


http://www.velocityreviews.com/forums/(E-Mail Removed) (Patrick) wrote in message news:<(E-Mail Removed) om>...
> hello,
>
> I have to implement an pi/4 DQPSK modulation with Direct Sequence
> Spread Spectrum.
>
> When I modulate the binary dats with pi/4 DQPSK, the output of the
> modulator have 5 values : -1 -0.7 0 0.7 and 1...
>
> Then I spread theses datas with a PN-code, but when the output of the
> modulator have the value 0, the spread data will be 0 too : 0 *
> pn_code = 0
>
> And if I spread (first) the binary datas with the pn_code and then
> modulate in DQPSK, the pn will be modified by the DQPSK modulation..
> and the datas in the channel will not real pn_code because have been
> modified by the DQPSK modulation
>
> Do you have an idea how to implant the pi/4 DQPSK DSSS modem ?
>
> Thanks...

 
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Chris Stratford
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Posts: n/a
 
      06-15-2004
You would have two channels, I & Q. The input binary stream is
differentially encoded by xor'ing between consecutive bits. Pairs of di-bits
[groups of two bits] are then mapped to constellation points -1,+1,+j and -j
with a selected encoding scheme 00, 01,10,11 [binary or grey coded, etc].

The symbols are then spread by multiplying by the PN spread code whereby
binary 0 = +1, binary 1 = -1 for instance.

The modulation is then shifted by pi/4 to the complex constellation points :
1/sqrt(2)+j/sqrt(2), e.g the two channels I & Q

Bits can represent anything...


"Wallclimber" <(E-Mail Removed)> wrote in message
news:(E-Mail Removed) om...
> Hello Patrick,
>
> this newsgroups talks about VHDL specific issues. Language features,
> how to do certain constructs, optimizations etc.
>
> Your question is about system implementation of certain signal
> processing algorithm. I'm afraid this is totally out of the scope of
> this newsgroup.
>
> Tom
>
>
> (E-Mail Removed) (Patrick) wrote in message

news:<(E-Mail Removed) om>...
> > hello,
> >
> > I have to implement an pi/4 DQPSK modulation with Direct Sequence
> > Spread Spectrum.
> >
> > When I modulate the binary dats with pi/4 DQPSK, the output of the
> > modulator have 5 values : -1 -0.7 0 0.7 and 1...
> >
> > Then I spread theses datas with a PN-code, but when the output of the
> > modulator have the value 0, the spread data will be 0 too : 0 *
> > pn_code = 0
> >
> > And if I spread (first) the binary datas with the pn_code and then
> > modulate in DQPSK, the pn will be modified by the DQPSK modulation..
> > and the datas in the channel will not real pn_code because have been
> > modified by the DQPSK modulation
> >
> > Do you have an idea how to implant the pi/4 DQPSK DSSS modem ?
> >
> > Thanks...



 
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