The problem of decision fusion for cooperative spectrum sensing in cognitive radio networks is studied when noisy fading channels are present between the cognitive radios (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 cognitive radio 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 fusion center. The aim is to optimize the detection performance in terms of the achievable secondary throughput in the cognitive radio network. Toward this end, for each of the transmission schemes considered, first a weighted energy-detector is obtained. Then the detection threshold at the CR nodes as well as at the FC, the sensing weights and the sensing time are optimized to maximize the secondary throughput.