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Re: [Discuss-gnuradio] QPSK with direct-sequence spread spectrum


From: Tuan (Johnny) Ta
Subject: Re: [Discuss-gnuradio] QPSK with direct-sequence spread spectrum
Date: Wed, 2 Nov 2011 12:26:01 -0400

I second Peter. As long as you make sure in your gray-coded QPSK constellation, 0 is mapped to +1 and 1 is mapped to -1 then XOR is equivalent to multiplication. 

On Mon, Oct 31, 2011 at 1:59 PM, Peter Massam <address@hidden> wrote:

In general you're right, but it depends on the details.  Its usually quite
straightforward, but a common mistake is to use the wrong bit-to-symbol
mapping.  0 -> +1 and 1 -> -1 means that an XOR applied to bits is
equivalent to multiplication applied to symbols.


Nowlan, Sean wrote:
>
> Hi all,
>
> I'm wondering if spreading a bitstream (XOR-ing each bit with
> SPREAD_FACTOR bits of sequence) before QPSK modulation is equivalent to
> operating on the modulated stream, i.e., multiplying the complex output
> with -1's and 1's from the sequence. So far I can't get the math to work
> out. Any suggestions?
>
> Thanks,
> Sean
>
> _______________________________________________
> Discuss-gnuradio mailing list
> address@hidden
> https://lists.gnu.org/mailman/listinfo/discuss-gnuradio
>
>

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