Optical Synchronization of Multiple Time-of-Flight Cameras Implementing TDMA

Time-of-Flight (ToF) cameras are a promising alternative to current 3-D imaging systems. A setup of multiple ToF cameras is used to overcome their comparatively lower resolution, increase the field of view, and to reduce occlusion. However, the simultaneous operation introduces the possibility of interference resulting in erroneous depth measurements. One option to mitigate interference is the consecutive arrangement of multiple cameras in time slots, such that each camera illuminates the scene exclusively, a procedure known as time division multiple access (TDMA). Instead of requiring a master synchronizing device, an approach is presented requiring no additional hardware or infrastructure to utilize TDMA by adding a synchronization software procedure to the camera's firmware. It effectively enables a camera to sense the acquisition process of other cameras and rapidly synchronize its acquisition times to operate without interference. During the experimental verification with three ToF cameras no interference occurred. The cameras each acquired 29 depth images per second while synchronizing themselves every 10 s. The proposed synchronization procedure implements an interference-free TDMA operation and overcomes traditional hard-wired synchronization setups, offering an easy setup and a methodology to upgrade existing systems without hardware modifications.