Method and device for temporal synchronization of optical transmission of data in free space

A method for time synchronisation of optical transmission of data in free space from a transmitter to at least one receiver,

• wherein the transmitter is an imaging device with a plurality of pixels, which are controlled by image data (s(i, j, m)) of an image sequence (sn(i, j)) that represent images, and the data provided for transmission are divided into a data sequence (dn(i, j)) from a data packet comprising a number of data bits and each data bit is associated with at least one of the pixels, and wherein the data packets are each modulated onto the image data (s(i, j, m)) of at least one image of the image sequence (sn(i, j)) in pixel-based fashion in the form of an amplitude modulation,
• wherein the modulation of the image data (s(i, j, m)) is performed with a time difference,
• the image sequence (sn(i, j)) is formed from image pairs of successive images, and wherein the data sequence (dn(i, j)) is formed from pixel-based data packets (d(i, j, m)), of which each second data packet to be superposed (d(i, j, 2m+1)) corresponds to the preceding first pixel-based data packet to be superposed (d(i, j, 2m)) with reversed sign, and wherein each first pixel-based data packet to be superposed (d(i, j, 2m)) is superposed with each first image of an image pair and each second pixel-based data packet (d(i, j, 2m+1)) to be superposed is superposed with each second image of the image pair, and a difference image is generated in the receiver for recovery of the data sequence (dn(i, j)) from each image pair by subtraction of the second image of an image pair from the first image of the same image pair pixel by pixel,
• the receiver comprises a camera capable of recording video to be arranged at a distance from the imaging device, wherein the camera receives the image sequence (sn(i, j)) sent by the imaging device
• wherein the method includes making an unsynchronized image recording of the image sequence by the camera at a random recording start time, and
• performing a synchronisation after the image recording based on the unsynchronized image recording which is not synchronized in time.