An orbital angular momentum (OAM) based LDPC-coded modulation scheme suitable for use in FSO communication is proposed. We demonstrate that the proposed scheme can operate under strong atmospheric turbulence regime and enable 100 Gb/s optical transmission while employing 10 Gb/s components. Both binary and nonbinary LDPC-coded OAM modulations are studied. In addition to providing better BER performance, the nonbinary LDPC-coded modulation reduces overall decoder complexity and latency. The

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... nary LDPC-coded OAM modulation provides a net coding gain of 9.3 dB at the BER of 10 8 . The maximum-ratio combining scheme outperforms the corresponding equalgain combining scheme by almost 2.5 dB.