Performance evaluation of orthogonal frequency-division multiplexing (OFDM) ultra-wideband (UWB) radio signals distribution over standard single-mode fiber (SSMF), using binary phase-shift keying symbol mapping, is numerically assessed. A directly-modulated laser (DML) is used to transmit simultaneously four OFDM-UWB sub-bands through SSMF. Some of the key system parameters that influence the transmission performance are identified and optimized through extensive simulations namely, the modulation-index, and the electrical and optical filters -3dB bandwidths. Bit-error ratios in each UWB sub-band lower than 10^(-12) have been achieved for a dispersion of 1700ps/nm, with a modulation-index of about 8.4%. Good system performance robustness to modulation-index, electrical and optical filter bandwidth variations is observed. The results presented in this work suggest the possibility of distributing several UWB sub-bands using DML in long-reach passive optical networks.