Hi Roee,
you forgot that there is a delay between sending and receiving, and that
the receiver LO is not at the same phase as the transmitter LO.
So in your receiver I(t) and Q(t), you don't mix with a cos(w0*t) and a
-sin(w0*t), but with cos(w0*t+tau) and a -sin(w0*t+tau), respectively,
with tau
Yes, the images came ok.
Using your original example of transmitting I(t)=cos(wm*t), Q(t)=sin(wm*t),
let’s take I(t)=cos(wm*t) and Q(t)=0:
sout(t) = cos(wm*t)*cos(wo*t) - 0*sin(wo*t) = 1/2 * [ cos(wm*t-wo*t) +
cos(wm*t+wo*t) ]
At the receiver (sorry if the derivation is too explicit):
I(t) = s
I'm referring to the receiver. It's essentially two receivers in parallel,
one mixing down with the local oscillator (cosine) and the other mixing
down with the same local oscillator, but phase shifted -90 degrees (sine).
This is how it generates two components for the input signal. Of course,
you
Thanks James,
What do you mean by “USRP will generate the in-phase and quadrature
components”? Are you referring to the USRP receiver or transmitter? I am
feeding the USRP transmitter with a real only signal s(t)=cos(w0*t), why does
the received signal has an imaginary component (i.e. Q(t) is n
Hi Roee,
The USRP is not expecting any particular type of data. The USRP is a direct
conversion transceiver that operates on I and Q samples, so in theory, you
should be able to generate/receive any type of signal. If you input a
cosine to the USRP, in will generate the in-phase and quadrature com
Hi James,
Thank you very much for your time and effort!
Your explanation of the USRP complex modulation/demodulation is equivalent to
what I originally described.
Since my experiments show that the receiver did not always received what was
transmitted, I thought there was something wrong with
Hello,
I am trying to understand how the USRP performs the
modulation/demodulation to/from higher frequencies.
Let's say I have a complex signal s(t). When I feed it to the USRP
block, my understanding is that the USRP performs something like
s(t)*exp(i*w*t), and transmit the real part of it
