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Summary form only given. We adopt a general Gaussian function shifted in time by 0.5 ns and truncated at ±0.25 ns and its derivatives for a UWB waveform and its shaping, and employ a TH-SS (time hopping spread spectrum) technique. Three types of typical data modulation schemes - PPM, BPSK and BPAM - are used. It is important to choose an appropriate modulation scheme that has a smooth spectrum reducing the spectral lines to result in maximum power efficiency because of possible limits on the UWB transmit power emission level for wireless network applications. The adopted UWB systems are designed to consume extremely low AC power. We describe some UWB features which attract many battery operated mobile applications such as WPANs. The UWB signal can be seen as random noise to the IEEE 802.11 WLAN signal, whose bandwidth is 22 MHz. The bandwidth of the WLAN interference signal is only a small fraction of the UWB signal bandwidth, which means that the UWB system has robust noise performance. The transmitted average power of the UWB signal is extremely low. Therefore, the WLAN and WPAN systems can coexist in the same 2.4 GHz ISM band.