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...