Optimal power and bit allocation schemes for ultra wideband cognitive radio systems

An optimal power and bit allocation scheme for rate maximization in the ultra wideband (UWB) cognitive radio system is presented in this paper. The scheme generates a series of M-ary quadrature amplitude modulation (M-QAM) zones over each UWB subcarrier. Total transmit power is optimally distributed among the UWB subcarriers for the use of the M-QAM modulation with a maximum M on each subcarrier. This optimization is constrained by the probability of detection, probability of false alarm, bit error rate and the UWB transmit power spectral density mask. The performance of the scheme is analyzed over different UWB fading channels. The results show that the system data rate is significantly improved by using the proposed power and bit allocation scheme.