  Two signal multiplexing schemes for optical fiber communication are
considered: Wavelength-division multiplexing (WDM) and nonlinear
frequency-division multiplexing (NFDM), based on the nonlinear Fourier
transform (NFT). Achievable information rates (AIRs) of NFDM and WDM are
compared in a network scenario with an ideal lossless model of the optical
fiber in the defocusing regime. It is shown that the NFDM AIR is greater than
the WDM AIR subject to a bandwidth and average power constraint, in a
representative system with one symbol per user. The improvement results from
nonlinear signal multiplexing.
