pi/4 DQPSK with DSSS-CDMA

Discussion in 'VHDL' started by Patrick, Jun 14, 2004.

  1. Patrick

    Patrick Guest

    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...
    Patrick, Jun 14, 2004
    #1
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  2. Patrick

    Wallclimber Guest

    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


    (Patrick) wrote in message news:<>...
    > 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...
    Wallclimber, Jun 14, 2004
    #2
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  3. 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" <> wrote in message
    news:...
    > 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
    >
    >
    > (Patrick) wrote in message

    news:<>...
    > > 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...
    Chris Stratford, Jun 15, 2004
    #3
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