Four-dimensional modulation formats with coherent detection for spectrally efficient fiber-optic communication systems
Final Report Abstract
Throughout this project, multidimensional modulation formats for optical communication systems were investigated. The four degrees of freedom of the optical electromagnetic field (real and imaginary part in two orthogonal polarizations) enable us to construct power-efficient signal constellation in the 4-D space. Various optimized 4-D modulation formats were considered and studied by numerical simulation and transmission experiments. These formats together with standard 2-D modulation formats enable a high degree of flexibility for future elastic transceivers. Moreover, 4-D TCM and TTCM are analyzed and evaluated in conjunction with FEC codes. The project can be divided into two parts: In the first phase of the project, the task of finding the optimal placement of the signal points in the 4-D space was considered. It was discussed that a signal constellation with up to 1.51 dB coding gain can be constructed by selecting its points from the densest lattice D4. An elaborate study of some interesting 4-D modulation formats was presented, showing their potential performance advantages over their 2-D counterparts. In addition, three DSP algorithms for specific 4-D modulation formats were developed: 1- A joint-polarization CPE algorithm for PS-QPSK format was investigated. It was shown by numerical simulation that the tolerance to laser phase noise can be doubled by coupling the phase noise information between the two polarization components. Also, the tolerance to nonlinear distortions was examined in a NWDM transmission experiment, where it was noticed that the algorithm does not suffer in the presence of nonlinear impairments and shows comparable results to a decision-feedback equalizer. 2- A novel CPE algorithm for 6PolSK-QPSK signal was described. 3- An adaptive equalizer algorithm for 6PolSK-QPSK modulation format was proposed. In addition, a special way to initialize the filter coefficients which guarantees a fast convergence of the equalizer was suggested. The proposed algorithm has been found to perform well in both numerical simulations and transmission experiments. Optimized 4-D modulation formats were found to be an interesting complement for standard modulation formats (i.e. PDM-MPSK and PDM-MQAM) for future bandwidth variable transceivers (BVT). These formats support fractional SEs and hence enable a smooth transition of the bit rate and reach based on the actual network demand. Another attractive feature is their potential coding gain over conventional formats. The coding gain is more apparent at high SNR regime and vanishes as the SNR degraded; this is due to the increase number of nearest neighbors for multi-D modulation formats. Therefore, optimized 4-D modulation formats, especially those with large number of nearest neighbors, are more practical for latency constrained systems or low complexity systems where no FEC or only a simple FEC code is employed. The second part of this project deals with the coded modulations, which have been considered as an interesting approach to provide moderate coding gain while keeping the complexity reasonable. To this end, 4-D TCM schemes based on PDM-MQAM were implemented and evaluated by numerical simulation and transmission experiment. A multi-rate optical transceiver was realized by a single encoder/decoder structure. In addition, Resilience against cycle-slip events was enabled by the rotational invariant feature of the 4-D TCM scheme. Moreover, TTCM scheme was experimentally evaluated and its superior performance over TCM was validated. Furthermore, the performance of 4-D TCM and TTCM was compared with standard PDM-MQAM formats combined with the SD-FEC codes. It was shown that 4-D TCM concatenated with a low complexity HD-FEC could be an interesting candidate for complexity-performance tradeoff with SD-FEC.
Publications
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“Experimental Investigation of 126-Gb/s 6PolSK-QPSK signals,” Opt. Express, vol. 20, no. 26, pp. B232–B237, Dec 2012
J. K. Fischer, S. Alreesh, R. Elschner, F. Frey, C. Meuer, L. Molle, C. Schmidt-Langhorst, T. Tanimura, and C. Schubert
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“Joint-Polarization Carrier Phase Estimation for PS-QPSK Signals,” IEEE Photon. Technol. Lett., vol. 24, no. 15, pp. 1282– 1284, Aug 2012
S. Alreesh, J. K. Fischer, M. Nölle, and C. Schubert
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“Blind adaptive equalization for 6PolSK-QPSK signals,” in Proc. 39th Eur. Conf. Opt. Commun. (ECOC), London, United Kingdom, 2013, p. Mo.4.D.3.
S. Alreesh, J. K. Fischer, P. W. Berenguer, and C. Schubert
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“Nonlinear transmission of 6PolSK-QPSK signals using coded modulation and digital back propagation,” in Proc. Opt. Fiber Commun. Conf. (OFC), Anaheim, CA, 2013, p. OTu3B.3.
T. Tanimura, S. Alreesh, J. K. Fischer, C. Schmidt-Langhorst, F. Frey, C. Meuer, R. Elschner, L. Molle, and C. Schubert
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“Bandwidth-Variable Transceivers based on Four-Dimensional Modulation Formats,” J. Lightw. Technol., vol. 32, pp. 2886–2895, Aug. 2014
J. K. Fischer, S. Alreesh, R. Elschner, F. Frey, M. Nölle, C. Schmidt-Langhorst, and C. Schubert
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“Transmission of 512SP-QAM Nyquist-WDM signals,” in Proc. 40th Eur. Conf. Opt. Commun. (ECOC), Sept. 2014, p. Tu.3.3.2
J. K. Fischer, C. Schmidt-Langhorst, S. Alreesh, R. Elschner, F. Frey, P. W. Berenguer, L. Molle, M. Nölle, and C. Schubert
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“Experimental investigation of a fourdimensional 256-ary lattice-based modulation format,” in Proc. Opt. Fiber Commun. Conf. (OFC), Los Angeles, CA, Mar. 2015, p. W4K.3.
T. A. Eriksson, S. Alreesh, C. Schmidt-Langhorst, F. Frey, P. W. Berenguer, C. Schubert, J. K. Fischer, P. A. Andrekson, M. Karlsson, and E. Agrell
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“Generation, Transmission, and Detection of 4-D Set- Partitioning QAM Signals,” J. Lightwave Technol., vol. 33, no. 7, pp. 1445–1451, Apr 2015
J. K. Fischer, C. Schmidt-Langhorst, S. Alreesh, R. Elschner, F. Frey, P. W. Berenguer, L. Molle, M. Nölle, and C. Schubert
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“Transmission of 2048SP-QAM Nyquist-WDM signals,” in Proc. 16. ITG-Fachtagung Photonische Netze, Leipzig, May 2015, pp. 88–91
S. Alreesh, C. Schmidt-Langhorst, R. Elschner, F. Frey, P. W. Berenguer, L. Molle, M. Noelle, C. Schubert, and J. K. Fischer
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“Transmission Performance of 4D 128SP-QAM With Forward Error Correction Coding,” IEEE Photon. Technol. Lett., vol. 27, no. 7, pp. 744–747, Apr. 2015
S. Alreesh, C. Schmidt-Langhorst, F. Frey, P. W. Berenguer, C. Schubert, and J. K. Fischer
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“Four-Dimensional Trellis Coded Modulation for Flexible Optical Transponders,” in Proc. 42th Eur. Conf. Opt. Commun. (ECOC), Düsseldorf, Germany, 2016, p. W.1.C.4.
S. Alreesh, C. Schmidt-Langhorst, R. Emmerich, P. W. Berenguer, C. Schubert, and J. K. Fischer
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“Four-Dimensional Trellis Coded Modulation for Flexible Optical Communications,” J. Lightw. Technol., vol. 35, no. 2, pp. 152-158, Jan. 2017
S. Alreesh, C. Schmidt-Langhorst, R. Emmerich, P. W. Berenguer, C. Schubert, and J. K. Fischer
