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The ultra wideband (UWB) interference to direct sequence spread spectrum (DSSS) receiver is analyzed. Two popular UWB modulation schemes, the time hopping pulse position modulation (TH-PPM) and time hopping pulse amplitude modulation (TH-PAM), are considered. The pulse repetition rate (PRR) of UWB signal and the frequency band of the DSSS play the primary roles in the BER performance of the DSSS receiver in the presence of UWB interference. The UWB signal parameters raising the interference to the DSSS receiver are discussed. The characteristics of an aggregation of multiple UWB signals are somehow different from that of a single UWB device, especially for the TH-PPM scheme, where discrete spectral lines maybe exist in the band of the DSSS receiver. The system parameters of TH-PPM such as the modulation index and maximum shift incurred by the time hopping code determine the amplitude of the discrete spectral lines. In the multiuser case of TH-PPM, sometimes one discrete spectral line leads to serious BER performance. It is observed from both theoretical analysis and computer simulations that the interference with the DSSS receiver from the UWB device is very little in common cases.