The reliable detection of unused spectrum while meeting a required probability of detecting primary user activity is a key functionality of cognitive radio systems. In cooperative spectrum sensing, the detection results of multiple cognitive radios are combined to a global result with high reliability. In order to transmit the local decisions a signaling channel is required. It can be realized by ultra-wideband underlay communications in arallel to primary user activity. Due to strict limitations on the transmission power for ultra-wideband communications, it is crucial to carefully allocate power levels to minimize channel errors, which could corrupt the transmission of local decisions. In this paper, an approach for the allocation of transmission power levels for the signaling channel is proposed, which aims to maximize the global probability of detecting spectrum holes while detecting primary user activity with a given reliability. Numerical results based on real spectrum measurements show the feasibility and illustrate the performance of the approach.
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