Complex signal processing in Spread Spectrum

Dear All,
I have a question about processing of complex signal in demodulating
spread spectrum signals. I have a signal that is spread using a PN
sequence. This received signal is at baseband and is complex i.e. The
received samples are in complex format at baseband. I want to multiply this
received signal at baseband the PN sequence so as to strip the modulated
signal of the PN sequence. How can I do this on a complex baseband signal?
If it wasn't a complex signal a simple multiplication would suffice but,
what about complex? Any thoughts?

Thanks,
John

On Jun 18, 10:26&#4294967295;am, "johnlovestohate" <murtuzaali...@gmail.com>
wrote:
> Dear All,
> I have a question about processing of complex signal in demodulating
> spread spectrum signals. I have a signal that is spread using a PN
> sequence. This received signal is at baseband and is complex i.e. The
> received samples are in complex format at baseband. I want to multiply this
> received signal at baseband the PN sequence so as to strip the modulated
> signal of the PN sequence. How can I do this on a complex baseband signal?
> If it wasn't a complex signal a simple multiplication would suffice but,
> what about complex? Any thoughts?
>
> Thanks,
> John

Is your spreading sequence real-valued or complex-valued?  If it's
real-valued,
then simply do complex multiplies.  If your spreading sequence is
complex-
valued, then you need to do complex correlation, which is convolution
with
a time-reversed, complex-conjugated version of the original
sequence.

Hope this helps,
Julius

On Jun 18, 11:52&#4294967295;am, julius <juli...@gmail.com> wrote:
> On Jun 18, 10:26&#4294967295;am, "johnlovestohate" <murtuzaali...@gmail.com>
> wrote:
>
> > Dear All,
> > I have a question about processing of complex signal in demodulating
> > spread spectrum signals. I have a signal that is spread using a PN
> > sequence. This received signal is at baseband and is complex i.e. The
> > received samples are in complex format at baseband. I want to multiply this
> > received signal at baseband the PN sequence so as to strip the modulated
> > signal of the PN sequence. How can I do this on a complex baseband signal?
> > If it wasn't a complex signal a simple multiplication would suffice but,
> > what about complex? Any thoughts?
>
> > Thanks,
> > John
>
> Is your spreading sequence real-valued or complex-valued? &#4294967295;If it's
> real-valued,
> then simply do complex multiplies. &#4294967295;If your spreading sequence is
> complex-
> valued, then you need to do complex correlation, which is convolution
> with
> a time-reversed, complex-conjugated version of the original
> sequence.
>
> Hope this helps,
> Julius

Think of it as a convolution (aka FIR filter) of your spread data with
the time-reversed, conjugated spreading sequence. If the spreading
sequence is real, then just do real multiplies on both I and Q of your
data. If it's complex, then you need full complex multiplies. This can
be done quite efficiently with FFTs.

John