Ultra Wideband (UWB) system is overlapped with various wireless systems, such as WLAN, WiMax and UMTS, which limits the use of UWB. Cognitive Radio (CR) enables UWB systems to efficiently use the overlapped spectrum without causing interference to other wireless systems. In this paper, we focuses on the low-complexity joint optimization algorithm design with respect to transmit power allocation and spectrum sensing time (SST) for maximizing the spectrum efficiency of the Orthogonal Frequency

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... ision Multiplexing based CR-UWB system. The SST optimization algorithm minimizes the spectrum sensing time in order to maximize the time length of applying the power allocation algorithm for data transmission. The proposed group power allocation algorithm adaptively assigns the transmit power to the subcarrier groups according to the effective signal-to-noise ratio (SNR) of each subcarrier group based on greedy algorithm. The proposed joint optimization algorithm can maximize the CR-UWB systems spectrum efficiency at a extremely low primary user SNR regime with low complexity.