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Proceedings Paper

Adaptive software-defined coded modulation for ultra-high-speed optical transport
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Paper Abstract

In optically-routed networks, different wavelength channels carrying the traffic to different destinations can have quite different optical signal-to-noise ratios (OSNRs) and signal is differently impacted by various channel impairments. Regardless of the data destination, an optical transport system (OTS) must provide the target bit-error rate (BER) performance. To provide target BER regardless of the data destination we adjust the forward error correction (FEC) strength. Depending on the information obtained from the monitoring channels, we select the appropriate code rate matching to the OSNR range that current channel OSNR falls into. To avoid frame synchronization issues, we keep the codeword length fixed independent of the FEC code being employed. The common denominator is the employment of quasi-cyclic (QC-) LDPC codes in FEC. For high-speed implementation, low-complexity LDPC decoding algorithms are needed, and some of them will be described in this invited paper. Instead of conventional QAM based modulation schemes, we employ the signal constellations obtained by optimum signal constellation design (OSCD) algorithm. To improve the spectral efficiency, we perform the simultaneous rate adaptation and signal constellation size selection so that the product of number of bits per symbol × code rate is closest to the channel capacity. Further, we describe the advantages of using 4D signaling instead of polarization-division multiplexed (PDM) QAM, by using the 4D MAP detection, combined with LDPC coding, in a turbo equalization fashion. Finally, to solve the problems related to the limited bandwidth of information infrastructure, high energy consumption, and heterogeneity of optical networks, we describe an adaptive energy-efficient hybrid coded-modulation scheme, which in addition to amplitude, phase, and polarization state employs the spatial modes as additional basis functions for multidimensional coded-modulation.

Paper Details

Date Published: 11 October 2013
PDF: 12 pages
Proc. SPIE 8915, Photonics North 2013, 89150E (11 October 2013); doi: 10.1117/12.2036191
Show Author Affiliations
Ivan B. Djordjevic, The Univ. of Arizona (United States)
Yequn Zhang, The Univ. of Arizona (United States)

Published in SPIE Proceedings Vol. 8915:
Photonics North 2013
Pavel Cheben; Jens Schmid; Caroline Boudoux; Lawrence R. Chen; André Delâge; Siegfried Janz; Raman Kashyap; David J. Lockwood; Hans-Peter Loock; Zetian Mi, Editor(s)

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