A CDMA Modulation Technique for Automotive Time-of-Flight LiDAR Systems

We present the application of optical code division multiple access (OCDMA) modulation based on optical orthogonal codes for automotive time-of-flight light detection and ranging (LiDAR) system sensors using avalanche photodiode (APD) detectors. The modulation opens the possibility to discriminate single laser transmissions. This allows the realization of additional features like enhancing the systems' interference robustness or accelerating their scanning rate. The requirements on automotive LiDAR OCDMA modulation differs from telecommunication's demands in several ways: The sensor must guarantee absolute laser safety; front facing devices must be able to provide reliable long range results up to a distance of 150 m and beyond; and the signal is transmitted through free space. After outlining the basic functionality of the sort of sensors in consideration, the properties of the optical orthogonal codes (OOC) modulation are compared with the state of the art theoretically. The influence of OOC parameters with respect to scanning LiDAR systems is examined. The modulation technique is then demonstrated experimentally with two examples: The detection and separation of coded and traditional signals is shown using a matched filter detection algorithm. In the same way, differently coded signals can be separated from each other. Impediments of the interference suppression quality are discussed. Finally, an overview of possible applications of the proposed technique in automotive LiDAR systems is given, which are enabled by the OCDMA modulation in the first place.