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In this paper, an infrared intervehicle ranging and vehicle-to-roadside communication systems are studied. A direct-sequence spread-spectrum (DS-SS) technology is employed to obtain the robustness against multiuser interference and ambient light noise. We compare the correlation properties for various optical spreading codes such as an optical orthogonal code (OOC), a prime code, an extended prime code, and a modified m-sequence. The performance of the infrared DS-SS ranging and communication system is evaluated by computer simulation over a channel in consideration of multipath dispersion, multiuser interference, and a background light noise. The infrared DS-SS intervehicle ranging system using an OOC has lower ranging error rate (RER) than ranging systems using a prime code, an extended prime code, and modified m-sequences even if there is the interference from other users and lightwave dispersion. In the infrared DS-SS vehicle-to-roadside communication system, L-ary pulse position modulation (L-PPM) is used as a modulation scheme due to high average power efficiency. It is shown that the proposed system achieves smaller BER performance as the modulation order L increases and the proposed system with a (361,6,1,1) OOC has a smaller BER than that with a (181,6,1,1) OOC.