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We studied by simulation the nonlinear propagation of 222-Gb/s (27.75 GBaud) wavelength-division-multiplexing coherent nonreturn-to-zero polarization-multiplexed 16 quadrature amplitude modulation systems over long-haul links, considering both standard single-mode fiber (SSMF) and nonzero dispersion-shifted fiber. Many different dispersion maps, including precompensation, were explored to try and mitigate the impact of propagation impairments. Full electronic dispersion compensation without in-line dispersion-compensating units (DCUs) granted best performance with a system reach on SSMF fiber of ten spans with a span loss 23 dB. The presence of DCUs, as in lines designed for legacy 10-Gb/s intensity-modulated direct-detection systems, enhances nonlinear propagation penalties and the use of precompensation does not grant a significant advantage. A practical reach of 500-800 km can be estimated, when system margins are factored in .