Constellation symbol OAM encoding for an atmospheric turbulence-resistant optical transmission method based on trellis-coded modulation

The discovery of the vortex beam carrying orbital angular momentum (OAM) has made it a popular research object for enhancing the transmission capacity in free-space optical communication. However, the atmospheric turbulence effect in space has become a negative factor affecting the transmission quality of the vortex beam. Therefore, this paper proposes an anti-turbulence method of vortex beam OAM coding based on the trellis-coded modulation technique. Instead of traditional OAM coding of the bit stream, the source information is first modulated into constellation symbols after error correction coding, and then OAM coding is performed based on the constellation symbols and detected using a convolutional neural network. The experimental results confirm that the scheme proposed in this paper has a better bit error rate (BER) performance compared with the traditional scheme under different turbulence intensities, as well as more stable turbulence suppression at different transmission distances, and the BER performance shows a more significant improvement after increasing the number of samples, which provides a reference for studying the anti-turbulence effect of vortex beams based on coding techniques.