A novel scheme for photonic envelope detection and fiber transmission of 24 GHz impulse radio ultra-wideband (IRUWB) signal is proposed based on phase modulator (PM). In the system, an optics assisted envelope detection unit (OAEDU) is used for filtering one of the first sidebands at the output of PM, then this narrow band optical signal transfers over single-mode fiber (SMF), and the envelope of 24 GHz IR-UWB signal is obtained after photodetection (PD) and low pass filter (LPF). The numerical simulation results show that the combination of PM and OAEDU can alleviate the fiber chromatic dispersion (CD) effectively. The proposed system may provide a simple and cost-effective solution for IR-UWB receiver.