This thesis focuses on transmitted-reference ultra wideband (TR-UWB) systems coexistence with IEEE802.11a WLAN systems. TR-UWB systems can relax the difficult synchronization requirements and can provide a simple receiver architecture that gathers the energy from many resolvable multipath components. However, UWB TR systems are susceptible to interference which comes from other wireless systems. In this thesis, TR-UWB system performance is studied in the presence of strong IEEE 802.11a WLAN interference in both AWGN and IEEE channel model. In order to reduce both the effects of interference by and into UWB signals, we propose a new method in conjunction with a multi-carrier type transmission pulse using wavelet analysis and notch filtering. Using wavelet analysis, spectral density of the transmitted UWB signal around the interfering band is reduced by 60 dB lower than the peak. With the modified TR-UWB receiver, the TR-UWB system shows performance improvement in the presence of strong IEEE 8-2.11a interference in both AWGN and IEEE channel models. The proposed method can be used for the coexistence of different wireless systems with UWB system.