Abstract—In this paper, a model is proposed to analyze the influence of timing imperfections on ultra-wide bandwidth (UWB) time-hopping spread-spectrum (TH-SS) signaling schemes, where N pulses are coherently added to increase the received signal-tonoise ratio (SNR). Based on this model, we derive asymptotical (valid for large N) expressions for the received signal after pulse summation and matched filtering. As an application example, we study the influence of timing jitter and frequency offsets on the maximum SNR, assuming a 2nd derivative Gaussian pulse shape. The analytical results we obtain are verified with numerical simulations.