We present a multi-user multiple-input multipleoutput(MIMO) cognitive radio system consisting of a secondaryreceiver that deploys spatial multiplexing to decode signals frommultiple secondary transmitters, under the presence of primarytransmissions. The secondary receiver carries out minimummean-squared error detection to decode the secondary datastreams, while it performs spectrum sensing at the remainingsignal to capture the potential presence of primary activity.Assuming Rayleigh fading as well as the realistic cases of channelfading time variation and channel estimation errors, we presentnovel closed-form expressions for important system measures,namely, the detection and false-alarm probabilities as well asthe transmission power of the secondary nodes. The enclosednumerical results verify the accuracy of the presented analysis.
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