The effect of the UWB interference on the GSM-900 and DCS-1800 downlink is studied for different UWB power densities. For relatively high UWB power density (-60 dBm/MHz), the effect of the UWB signals is very high when the distance between the UWB transmitter and the GSM-900 or DCS-1800 receiver is less than 1 m. For low UWB power density (-91 dBm/MHz), the effect of the UWB signals is very small if the distance between the UWB transmitter and the GSM-900 or DCS-1800 receiver is 1 m or higher. It is found that the spectrum mask proposed by the FCC for indoor application (-53 dBm/MHz in the DCS-1800 band and -41 dBm/MHz in the GSM-900 band) is too high to be tolerated by the two mobile system
