In this paper, timing synchronization in high-rate ultra-wideband (UWB) block transmission systems is investigated. A new joint timing and channel estimation scheme is proposed for orthogonal frequency division multiplexing (OFDM) and single carrier block transmission with frequency domain equalization (SC-FDE) UWB systems. The scheme is based on a newly designed preamble for both coarse timing and the subsequent channel estimation. Despite of the presence of coarse timing error, the estimated channel impulse response (CIR) is simply the cyclic shifted version of the real CIR, thanks to the unique structure of the preamble. The coarse timing error (CTE) is then determined from the CIR estimation and used to fine tune the timing position and the frequency domain equalization coefficients. The proposed scheme saves preamble overhead by performing joint synchronization and channel estimation, and outperforms existing timing acquisition methods in the literature in dense multipath UWB channels. In addition, the impact of timing error on channel estimation and the performance of SC-FDE UWB systems are analyzed, and the bit-error-rate (BER) degradation with respect to a certain timing error is derived.