Recently, the single-carrier transmission with frequency domain equalisation has attracted much attention for reasons of being able to obtain an excellent performance even in strong frequency selective channels. In the paper, the authors evaluate the performance of direct sequence - ultra wideband (DS-UWB) with frequency domain channel estimation (FDCE) and equalisation (FDE) in the UWB multipath channel and compare it to that of conventional DS-UWB with time domain channel estimation (TDCE) and RAKE receiver. The authors purpose is to compare the performances of both schemes under fair conditions. In particular, we focus on the computational complexity of frequency domain process (FDP) that uses FDCE and FDE and compare it to that of time domain process (TDP) that uses TDCE and RAKE receiver. The authors simulation results show that when Eb/N0 is high, DS-UWB with FDP has significantly less computational complexity and achieves a better performance than DS-UWB with TDP; conversely when Eb/N0 is low, DS-UWB with TDP has significantly more computational complexity and achieves a better performance than DS-UWB with FDP.