Ada,
>As I looked up from the documents, it was said that the signal after the usrp source at the receiver, is baseband signal, whose central >frequency is around 0 Hz, and already take off the carrier frequency. But in the demodulation, there are still freq_recov and time_recov block. >Are they at the symbol level? Yes and there is always a freq-difference between Tx and Rx LO due to this there will always be some freq-offset http://gnuradio.org/redmine/projects/gnuradio/wiki/FAQ#Why-is-there-always-a-frequency-offset-when-transmitting-from-one-USRP-to-another >I'm quite confused with how the benchmark, actually the demodulation in generic_mod_demod.py works. When does the carrier frequency is >taken off? In USRP. Timing recovery for compensating timing-offset, Freq-Recovery for freq-offset. http://gnuradio.org/doc/doxygen/classdigital__pfb__clock__sync__ccf.html http://gnuradio.org/doc/doxygen/classdigital__fll__band__edge__cc.html -Adeel
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