TY - GEN

T1 - On the LDPC-coded OAM modulation for communication over atmospheric turbulence channels

AU - Djordjevic, Ivan B.

AU - Anguita, Jaime

AU - Vasic, Bane

PY - 2011

Y1 - 2011

N2 - 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 XN={(x1, x2, ⋯, xN)|xi is from X, for every i}. This scheme represents an energy efficient alternative, since log2(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.

AB - 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 XN={(x1, x2, ⋯, xN)|xi is from X, for every i}. This scheme represents an energy efficient alternative, since log2(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.

KW - Atmospheric turbulence

KW - Coded modulation

KW - Forward error correction

KW - Free-space optical (FSO) communication

KW - Low-density parity-check (LDPC) codes

KW - Modulation

KW - Multiplexing

KW - Orbital angular momentum (OAM)

UR - http://www.scopus.com/inward/record.url?scp=80053960749&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=80053960749&partnerID=8YFLogxK

U2 - 10.1117/12.894263

DO - 10.1117/12.894263

M3 - Conference contribution

AN - SCOPUS:80053960749

SN - 9780819487728

T3 - Proceedings of SPIE - The International Society for Optical Engineering

BT - Free-Space and Atmospheric Laser Communications XI

T2 - Free-Space and Atmospheric Laser Communications XI

Y2 - 24 August 2011 through 25 August 2011

ER -