Error-Correction Coded Orbital-Angular-Momentum Modulation for FSO Channels Affected by Turbulence

• Published in: Journal of lightwave technology Vol. 30; no. 17; pp. 2846 - 2852
• Main Authors: Djordjevic, I. B., Anguita, J. A., Vasic, B.
• Format: Journal Article
• Language: English
• Published: New York, NY IEEE 01.09.2012; Institute of Electrical and Electronics Engineers
• Subjects: Applied sciences; Atmospheric turbulence; Bit error rate; coded modulation; Coding, codes; Constellation diagram; Crosstalk; Exact sciences and technology; free-space optical communication; Information, signal and communications theory; low-density parity-check (LDPC) codes; modulation; Numerical models; Optical telecommunications; orbital angular momentum (OAM); Receivers; Signal and communications theory; Silicon; Telecommunications; Telecommunications and information theory; Wireless optical communications; Performance evaluation; modulation; Optical telecommunication; Crosstalk; Wireless telecommunication; Conditional probability; low-density parity-check (LDPC) codes; Electric power consumption; Probability density function; Pulse amplitude modulation; Parity check codes; Minimum energy; free-space optical communication; Free space optics; Multidimensional system; orbital angular momentum (OAM); Statistical method; Free space propagation; Atmospheric turbulence; Laser beam; coded modulation; One dimensional model; Angular momentum; Signal processing; Error correcting code; Error correction; Low-power electronics
• ISSN: 0733-8724; 1558-2213
• DOI: 10.1109/JLT.2012.2206560

The performance of LDPC-precoded, orbital-angular-momentum (OAM) modulation is studied over a 1-km free-space laser communication link subject to OAM modal crosstalk induced by atmospheric turbulence. The multidimensional signal constellation is designed as the Cartesian product of a one-dimensional non-negative pulse-amplitude modulation and a set of orthogonal OAM modes. We evaluate the performance of this modulation scheme by first determining conditional probability density functions (PDFs) of the modal crosstalk for each symbol, resulting from the propagation in weak turbulence using a numerical propagation model. It is observed that OAM modulation is more sensitive to atmospheric turbulence as the number of dimensions increases. However, this can be efficiently mitigated by an error-correction code. The coded OAM modulation scheme provides an energy-efficient alternative to single-mode transmission, since a larger rate can be obtained per given bandwidth.