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The problem of decision fusion for cooperative spectrum sensing in cognitive radio (CR) networks is studied when fading channels are present between the CRs and the fusion center (FC). The CRs perform spectrum sensing using energy detection and transmit their binary decisions to the FC for a final decision on the absence or presence of the primary user activity. Considering the limited resources in CR networks, which makes it difficult to acquire the instantaneous channel-state information, noncoherent transmission schemes with on-off keying (OOK) and binary frequency-shift keying (BFSK) are employed to transmit the binary decisions to the FC. For each of the transmission schemes considered, energy- and decoding-based fusion rules are developed first. Then, the detection threshold at the CR nodes and at the FC, the combining weights (in the case of the energy-based fusion rule), and the sensing time are optimized to maximize the achievable secondary throughput of the CR network. Simulation results verify the theoretical analysis. It is also shown that the energy-based fusion rule outperforms the decoding-based fusion rule when the signal-to-noise ratios (SNRs) of the reporting channels are low, whereas the opposite is true for high SNRs. For the simpler energy-based fusion rule, BFSK achieves higher secondary throughput than OOK, at the expense of a larger transmission bandwidth.