0 A.S. Madhukumar, Zhenzhen Ye and S. Majhi 2007 WSEAS Transactions on Communications 6 2 318-324 02/2007 Ultra-Wideband (UWB) radio technology is one promising solution for short-range indoor wireless communication applications. UWB systems spread the transmitted signal power over an extremely large frequency band, and the power spectral density of the signal is very low. Due to the wide bandwidth of the transmitted signal, UWB signal energy will spread over the frequency bands allocated to other radio systems. In order to evaluate the effects of UWB system to narrowband systems (such as IEEE802.11a wireless LAN) in its overlay band, it is important to understand and quantify the power spectral density (PSD) of UWB signal. In this paper, a detailed analysis on the PSD of direct sequence coded UWB (DS-UWB) signal is presented. The theoretical and simulation results reveal that the interfering DS-UWB power can be reduced in the victim narrowband systems by regulating chip rate, pulse shape and width and scrambling codes in the frequencies of UWB system.