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A novel low-complexity coherent receiver solution is presented to improve spectral efficiency in wavelength-division multiplexing (WDM) systems. It is based on the receiver-side partial-response equalization and maximum-likelihood sequence detection (MLSD) in prefiltered WDM systems. The partial-response equalization shapes the channel into an intermediate state with a known partial response which is finally recovered by MLSD without the need of channel estimation. In this scheme, the severe intersymbol interference induced by the prefiltering can be shared between the partial-response equalization and MLSD. Therefore, a tradeoff can be made between complexity and performance. The feasibility of receiver-side partial-response shaping relaxes the efforts and requirements on the transmitter-side prefiltering, which permits the mature …