Simulation results based on an UltraWideBand (UWB) system employing a gain-switched laser are presented. 156 Mb/s data stream modulates the position of short electrical pulses, which are then used to gain-switch the laser. The output optical pulses are then transmitted over fiber to a Remote Antenna Unit (RAU), where the signal is detected and undergoes spectral shaping (according to UWB requirements). The resulting Pulse Position Modulated (PPM) electrical impulses are then converted to an amplitude-modulated signal and down-converted. Bit Error Rate measurements are carried out on a back-to-back system and a transmission link (over different lengths of fiber)