On Thu, Apr 5, 2012 at 8:02 PM, senthil murugan <amrita.sent...@gmail.com>wrote:
> I am saying this because in theory, ppl assume that sin(2*pi*fc*t + Pshi) > where Pshi = pi(for 0) and 0 (for 1). Where as in Gnu Radio, we have > root-raised cosine impulses and freq.xlating it is more like amplitude > modulation --> so, no possibility of having waveform > > > On Thu, Apr 5, 2012 at 7:53 PM, senthil murugan > <amrita.sent...@gmail.com>wrote: > >> Hi Tom, >> >> Yes, I am seeing sinusoids with low freq BPSK envelope --> But, Not clean >> shift of 180deg as shown in figures of standard text books. Am i rite?? >> >> Also I didn't get good idea of sps in root-raised cosine. I learnt that >> taps of filter = 11*sps --> smoothing freq domain. When googling mail list, >> i learnt that tx_original bw = 128e6 / interp / sps and hence i thought >> that for each symb, two samples (out of root-coisned wave from for each >> sym) and everything went fine. >> >> After seeing baseband waveform, I lost all my understanding. My >> questions;' >> >> 1. For vector source and psk mod, there is no option of sample rate. What >> is the input symbol rate to psk mod and output sample rate of psk mod >> block? For each symbol, I am getting 23 samples (for sps : 2 ). If that is >> the case, how come equation of tx_original bw valid? >> >> 2. As you said, I upsampled baseband signal before multiplying with >> signal source (for freq xlation simulation). Still I am not attaining clean >> shift of 180deg ? If you are able to attain that in GRC simulation, could >> you send that for me? >> >> Thanks >> Senthil >> >> Thanks >> Senthil >> >> On Thu, Apr 5, 2012 at 7:15 PM, Tom Rondeau <t...@trondeau.com> wrote: >> >>> On Thu, Apr 5, 2012 at 9:33 AM, senthil murugan >>> <amrita.sent...@gmail.com> wrote: >>> > Hi all, >>> > >>> > I have some doubt on the time domain view of bpsk signal generated in >>> > Gnuradio and usrp. I used psk mod block in GRC (sps =2) and created >>> bpsk >>> > (baseband )waveform with vector source producing 0,1,1 continuously. >>> > >>> > When I plotted the output of psk mod block using scope sink, I seen >>> waveform >>> > of constant 1 for some samples (for 0) , inverted root-raised cosine >>> > waveform (for 1) and another inverted root-raised cosine waveform (for >>> 1). >>> > This is repeated continuously and i understand that it because of >>> transmit >>> > pulse shaping. >>> > >>> > Now, the question is when I give this signal to USRP for transmission, >>> how >>> > the time-domain view of that waveform look like? Will it look like >>> sinusoid >>> > signal with 180deg phase shift as we all seen in stand. communication >>> text >>> > books? I guess it will not the case. I tried multiplying the baseband >>> > waveform with signal source (complex) -- mathematical equivalent of >>> what >>> > happening in usrp -- and seen waveform. No smooth shift of 180deg. >>> > >>> > If anyone having usrp and digital oscilloscope, could you please send >>> me the >>> > pic of time domain view of output of usrp? >>> > >>> > Thanks >>> > Senthil >>> >>> If you want to see this in simulation, make sure that you are >>> upsampling your signal before doing the frequency conversion so your >>> sample rate can support the new frequency range you are interested in >>> seeing. >>> >>> The answer is yes, the resulting waveform will be a sinusoid at the >>> carrier frequency with a lower frequency BPSK envelope. If you are >>> doing this over the air, remember that if the oscillators in your >>> transmitter and receiver are not locked together, there will be a >>> frequency offset between them. >>> >>> Tom >>> >> >> >> >> -- >> http://amritasenthil.wordpress.com/ >> >> >> >> -- >> http://amritasenthil.wordpress.com/ >> > > > > -- > http://amritasenthil.wordpress.com/ > -- http://amritasenthil.wordpress.com/
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