Re: [Discuss-gnuradio] Spread Spectrum question in gnuradio

[John Andrews]

Ok.

The block diagram in most of the textbook says the modulated signal is multiplied with the PN sequence. 

1. If I decide to do the same then my setup will look like this

     byte -> bytes_to_chunks -> chunks_to_symbols(BPSK) -> rrc_filter(X samples per bit)  -> DSSS

I am confused about the DSSS part. I am using a 63-bit PN sequence and spreading the BPSK symbols with this sequence means I have to pass each of the BPSK symbol through an interpolation filter with PN sequence as the taps(like in the barker example). Am I right? If this is not how it is done then can someone please suggest me a way. 

Thanks,

John

On Thu, Apr 29, 2010 at 8:11 AM, Martin DvH <address@hidden> wrote:

On Wed, 2010-04-28 at 11:23 -0700, Johnathan Corgan wrote:
> On Tue, Apr 27, 2010 at 21:19, John Andrews <address@hidden> wrote:
>
> > If I want to transmit a signal which is DSSS spread using BPSK. Is it
> > correct for me to first digitally spread the incoming data bits and then
> > apply BPSK before sending it to the USRP or should I first convert the
> > signal to BPSK and then multiply the output of the BPSK modulator with the
> > PN sequence although I don't know how to do it.
>
> Technically, these are equivalent.  However, it is easier and uses
> less CPU to XOR your data sequence with your PN code, then send it to
> the modulator.

I think there is a difference, if you use a root raised cosine filter,
set for your datarate and roll-off factor.

I think the correct version should then be:
BPSKmod -> RRCfilter -> DSSS

Martin
>
> Johnathan

>
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