In this paper, a general architecture of impulse based UWB (Ultra-Wide Band) system is analyzed and the performance of Time- Hopping Pulse Shape Modulation (TH-PSM) is assessed in AWGN (Additive White Gaussian Noise) as well as in standard IEEE 802.15.3a indoor multipath channel. UWB pulses based on B-splines are used for the analysis, which not only preserve orthogonality but also utilize the available spectrum efficiently respecting the FCC mask as well. Afterwards, the measurements that form the basis for IEEE standard channel model are discussed. Rake receiver is used for the evaluation of bit error rate. The performance of all rake (A-rake), selective rake (S-rake) and partial rake (P-rake) is evaluated using maximum ratio combining (MRC) assuming perfect knowledge of the channel state. Finally, based on simulation results, conclusions are drawn about the system performance.