I'm writing a program to use QAM using a combination of Matlab and gnuradio (QAM demod hasn't been implemented in gnuradio). My Matlab code does all of the baseband signal processing, produces a complex vector of samples at the transmitter. It also takes a complex vector of samples to decode at the receiver. My question is how do I use my complex vector in Matlab as the input to the USRP? Similarly, how do I take the complex output samples of the USRP and put them in a Matlab vector?