### Abstract

We study communication over atmospheric turbulence channels based on LDPC-coded, multidimensional OAM signal constellations. Multidimensional signal constellation is obtained as the Cartesian product of one-dimensional signal constellation X={(i-1)d, i=1, 2, ⋯, M} (where d is the Euclidean distance between neighboring signal constellation points and M is the number of amplitude levels) as X^{N}={(x_{1}, x_{2}, ⋯, x_{N})|x^{i} is from X, for every i}. This scheme represents an energy efficient alternative, since log_{2}(M ^{N}) bits/symbol can be transmitted. We describe two possible implementations of N-dimensional OAM modulator and demodulator: (1) volume holograms based, and (2) multimode fibers (MMFs) based. We evaluate the performance of this scheme by determining conditional symbol probability density functions (PDFs) from numerical propagation data. Two cases of practical interest are studied: (i) when conditional PDFs are known on the receiver side, and (ii) when conditional PDFs are not known and Gaussian approximation is used instead. We show that in case (ii) an early error floor occurs because of inaccurate PDF assumption, which is caused by OAM crosstalk introduced by the atmospheric turbulence. We also show that the OAM modulation is more sensitive to atmospheric turbulence as the number of dimensions increases. Finally, we evaluate the BER performance for different amplitude levels and different number of OAM dimensions.

Original language | English (US) |
---|---|

Title of host publication | Free-Space and Atmospheric Laser Communications XI |

DOIs | |

State | Published - Oct 17 2011 |

Event | Free-Space and Atmospheric Laser Communications XI - San Diego, CA, United States Duration: Aug 24 2011 → Aug 25 2011 |

### Publication series

Name | Proceedings of SPIE - The International Society for Optical Engineering |
---|---|

Volume | 8162 |

ISSN (Print) | 0277-786X |

### Other

Other | Free-Space and Atmospheric Laser Communications XI |
---|---|

Country | United States |

City | San Diego, CA |

Period | 8/24/11 → 8/25/11 |

### Fingerprint

### Keywords

- Atmospheric turbulence
- Coded modulation
- Forward error correction
- Free-space optical (FSO) communication
- Low-density parity-check (LDPC) codes
- Modulation
- Multiplexing
- Orbital angular momentum (OAM)

### ASJC Scopus subject areas

- Electronic, Optical and Magnetic Materials
- Condensed Matter Physics
- Computer Science Applications
- Applied Mathematics
- Electrical and Electronic Engineering

### Cite this

*Free-Space and Atmospheric Laser Communications XI*[81620G] (Proceedings of SPIE - The International Society for Optical Engineering; Vol. 8162). https://doi.org/10.1117/12.894263