Nonlinear frequency-division multiplexing (NFDM) is a communication scheme in which users' signals are multiplexed in the nonlinear Fourier domain. The contributions of this paper are twofold. First, the achievable information rates (AIRs) of NFDM based on an integrable model of the optical fiber are summarized. For this ideal model, it is shown that the AIR of the NFDM is greater than the AIR of the wavelength-division multiplexing (WDM) for a given bandwidth and signal power, in a

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... ve system with five users and one symbol per user. The improvement results from nonlinear signal multiplexing. Second, the impact of some of the main perturbations on NFDM are investigated, including the fiber loss, polarization effects and the third-order dispersion. For a realistic non-ideal model, it is shown that the WDM AIR with joint dual-polarization back-propagation and third-order dispersion compensation is approximately equal to the NFDM AIR with two independent single-polarization demodulations and without third-order dispersion compensation. Using a joint dualpolarization receiver and perturbations compensation is expected to increase the NFDM AIR.