This paper studies the effects of channel estimation in ultra wideband (UWB) systems using a multiband-OFDM (MB-OFDM) approach. The system used consists of a three-band OFDM transmitter, each band having 128 equally spaced subcarriers, which carry both the information data and the pilot signals. The channel estimation is based on the principle of pilot-symbol aided channel estimation (PACE), and it has been implemented using comb-type and block-type pilot subcarrier arrangements. The algorithms used here are based on the least squares (LS) and the linear minimum mean-square error (LMMSE) approaches supported by linear and cubic interpolation, and an IFFT-based time channel estimation, which uses a zero-padding interpolation approach with and without Wiener filtering. In frequency domain algorithms, phase compensation is also taken into account. Bit error rate (BER) versus signal-to-noise ratio Eb/N0results show that the frequency based methods generally perform better than the corresponding time based ones. Furthermore, the performances of LS and LMMSE methods are quite similar, leading us to suggest the use of LS estimator for uncoded MB-OFDM systems. Phase compensation is required in comb-type pilot sub-carrier arrangement when a low number of pilot sub-carriers is used

This paper evaluates the level of interference caused by different ultra-wideband (UWB) signals to other various radio systems, as well as the performance degradation of UWB systems in the presence of narrowband interference and pulsed jamming. The in-band interference caused by a selection of UWB signals is calculated at GSM900, UMTS/wideband code-division multiple-access (WCDMA), and Global Position System (GPS) frequency bands as a function of the UWB pulsewidth. Several short-pulse waveforms, based on the Gaussian pulse, can be used to generate UWB transmission. The two UWB system concepts studied here are time hopping and direct sequence spread spectrum. Baseband binary pulse amplitude modulation is used as the data modulation scheme. Proper selection of pulse waveform and pulsewidth allows one to avoid some rejected frequency bands up to a certain limit. However, the pulse shape is also intertwined with the data rate demands. If short-pulses are used in UWB communication the high-pass filtered waveforms are preferred according to the results. The use of long pulses, however, favors the generic Gaussian waveform instead. An UWB system suffers most from narrowband systems if the narrowband interference and the nominal center frequency of the UWB signal overlap. This is proved by bit-error rate simulations in an additive white Gaussian noise (AWGN) channel with interference at global system for mobile communication (GSM) and UMTS/WCDMA frequencies.