I am saying this because in theory, ppl assume that sin(2*pi*fc*t + Pshi) where Pshi = 1(for 0) and -1 (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/
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