Non-uniform Signaling Based LDPC Coded Modulation for High-Speed Optical Transport Networks

Orbital Angular Momentum Multiplexed Free-Space Optical Communication Systems Based on Coded Modulation

“…In the transmitter, a 1550 nm CW light is generated as the optical carrier, and passes to an optical I/Q modulator. The PRBS signals are coded by Huffman procedure to the symbol sequences with alphabet sizes of 5 and 9 respectively [30]; or uniformly mapped to symbol sequences with alphabet sizes of 4 and 8, respectively. Then the GF(5), GF(3 2 ) based nonbinary LDPC encoding is used, followed by mapping procedures from the coded sequences to 5-QAM and 9-QAM signals, respectively.…”

“…Huffman coding and optimal constellation design techniques are applied to generate the quadrature amplitude modulation (QAM) formats, i.e., 5/9-QAM formats. Meanwhile, the GF(5) based LDPC coding is implemented for 5-QAM symbol sequences, and GF(32) based LDPC coding is implemented for 9-QAM symbol sequences [30,31]. Unlike the classical OAM multiplexed FSO links, where all spatial mode channels are centrally aligned, binary FEC coding is used for error correction.…”

High-speed Orbital Angular Momentum Multiplexed Free-space Optical communication systems

“…Our experimental setup is depicted in Figure . At the transmitter side, the CW light with the wavelength centered at 1550 nm is sent to an I/Q modulator. The binary data sequences are nonuniformly mapped to symbols labeled by 0-4 for 5-QAM, and 0-8 for 9-QAM by Huffman coding [26,30]; or uniformly mapped to symbols labeled by 0-3 for QPSK, and 0-7 for 8-QAM. Then the GF(5), GF(3 2 ) based LDPC encoding are applied to 5-QAM and 9-QAM sequences, respectively; while conventional GF(2) based LDPC encoding to QPSK (or 4-QAM) and 8-QAM.…”

“…The mode crosstalk is first mitigated in optical domain by spatial offset, and then relieved in digital domain by coded modulation. The 5-quadrature amplitude modulation (5-QAM) and 9-QAM are used here based on Huffman coding and nonbinary LDPC coding [26][27][28]. Compared to the traditional systems, where the OAM beams are central aligned, and data are modulated with rectangular M-QAM formats, e.g., QPSK and 8-QAM, the proposed two-stage crosstalk mitigation method can largely improve the system performance.…”

Optical Communications and Networking

“…In order to close the gap, constellation shaping was introduced to optical communications. Constellation shaping, including PS [25,[35][36][37], geometric shaping (GS) [26,[38][39][40][41], and hybrid probabilistic-geometric shaping (HPGS) [42][43][44][45], is used to mimic a Gaussian distribution with limited constellation points. Although target at approaching Gaussian distribution, PS and GS have completely different generation and detection implementations.…”