Re: [Discuss-gnuradio] Spread Spectrum question in gnuradio
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 wrote: > On Wed, 2010-04-28 at 11:23 -0700, Johnathan Corgan wrote: > > On Tue, Apr 27, 2010 at 21:19, John Andrews 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 > > > > > > ___ > > Discuss-gnuradio mailing list > > Discuss-gnuradio@gnu.org > > http://lists.gnu.org/mailman/listinfo/discuss-gnuradio > > > > ___ Discuss-gnuradio mailing list Discuss-gnuradio@gnu.org http://lists.gnu.org/mailman/listinfo/discuss-gnuradio
Re: [Discuss-gnuradio] Spread Spectrum question in gnuradio
On Wed, 2010-04-28 at 11:23 -0700, Johnathan Corgan wrote: > On Tue, Apr 27, 2010 at 21:19, John Andrews 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 > > > ___ > Discuss-gnuradio mailing list > Discuss-gnuradio@gnu.org > http://lists.gnu.org/mailman/listinfo/discuss-gnuradio > ___ Discuss-gnuradio mailing list Discuss-gnuradio@gnu.org http://lists.gnu.org/mailman/listinfo/discuss-gnuradio
Re: [Discuss-gnuradio] Spread Spectrum question in gnuradio
On Tue, Apr 27, 2010 at 21:19, John Andrews 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. Johnathan ___ Discuss-gnuradio mailing list Discuss-gnuradio@gnu.org http://lists.gnu.org/mailman/listinfo/discuss-gnuradio
Re: [Discuss-gnuradio] Spread Spectrum question in gnuradio
this would be similar to 802.11b's PHY at 1Mbps, except it uses the barker sequence as opposed to the sequence you mention. It spreads a BPSK signal using the barker sequence. You can take a look at the BBN 802.11b code in CGRAN to see how they implement this: https://www.cgran.org/browser/projects/bbn_80211/branches/usrp2_version/gr-bbn/src/examples/bbn_80211b_pkt.py#L126 It modulates to BPSK, and then spreads it out via the interpolation filter. - George On Wed, Apr 28, 2010 at 12:19 AM, John Andrews wrote: > Hi, > 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. > > 1. If '1' is the data bit then convert it to '1010100111' (lets say this is > the PN sequence) and then input it into a BPSK modulator. > 2. If '1' is the data bit first input it into a BPSK modulator and then > mutiply the interpolated output with the PN sequence. > > Theoretically, these two methods will lead to the same result but I am not > sure how to do this in gnuradio. > > Any ideas? > > Thanks > John > > ___ > Discuss-gnuradio mailing list > Discuss-gnuradio@gnu.org > http://lists.gnu.org/mailman/listinfo/discuss-gnuradio > > ___ Discuss-gnuradio mailing list Discuss-gnuradio@gnu.org http://lists.gnu.org/mailman/listinfo/discuss-gnuradio
[Discuss-gnuradio] Spread Spectrum question in gnuradio
Hi, 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. 1. If '1' is the data bit then convert it to '1010100111' (lets say this is the PN sequence) and then input it into a BPSK modulator. 2. If '1' is the data bit first input it into a BPSK modulator and then mutiply the interpolated output with the PN sequence. Theoretically, these two methods will lead to the same result but I am not sure how to do this in gnuradio. Any ideas? Thanks John ___ Discuss-gnuradio mailing list Discuss-gnuradio@gnu.org http://lists.gnu.org/mailman/listinfo/discuss-gnuradio
