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Re: [Discuss-gnuradio] Modulation scheme for DSSS

From: Henry Barton
Subject: Re: [Discuss-gnuradio] Modulation scheme for DSSS
Date: Tue, 8 Mar 2016 23:19:48 +0000

Thanks, Ed. I figured the PSK’s would work. Do you think the +1/-1 codes used in CDMA have anything to do with PSK? If I could somehow send them into a coil as voltages at a high rate, would it make an intelligible signal? I’m guessing it wouldn’t, which leads me to believe that the +1/-1 codes are just for demonstration purposes and in reality you just transmit your spreaded (repeated and XOR-ed bits) as ordinary PSK.

Sent from Windows Mail

From: Ed Criscuolo
Sent: ‎Tuesday‎, ‎March‎ ‎8‎, ‎2016 ‎6‎:‎11‎ ‎PM
To: Henry Barton

NASA successfully uses BPSK, QPSK and OQPSK (offset QPSK)
with CDMA DSSS on its TDRS satellites.  For historical reasons,
they don't use differential coding, but it makes the demod much

@(^.^)@  Ed

On 3/8/16 11:18 AM, Henry Barton wrote:
> As you know, I’ve written a baseband DSSS modulator and demodulator.
> I’ve got the waveform samples, but I know I need a modulation scheme to
> actually send it through the air. I’ve heard somewhere that OFDM can be
> used for CDMA DSSS, and also 4-qam/QPSK. Can anyone tell me what
> modulation schemes are appropriate for CDMA DSSS so multiple
> transmitters can coexist like they’re supposed to? Thanks.
> Sent from Windows Mail
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