Abstract: Structures of the extended quadratic time-hopping sequences, the general class ofquadratic time-hopping sequences and some of their special kinds were discussed. Their Hamming cross- correlation propertieswere compared. Based on the discussion and comparison, the error rate of the ultra-wide band (UWB) systems with these quadratic time-hopping sequences and pulse position modulation (PPM) were compared, and the numerical resultswere presented. It is shown that these quadratic time-hopping sequences have the same system performance, and the general class of quadratic time-hopping sequences have a larger family size.