Nonbinary LDPC-Coded Modulation for Rate-Adaptive Optical Fiber Communication Without Bandwidth Expansion

A rate-adaptive nonbinary low-density parity-check-coded modulation scheme is proposed to enable fiber-optic transmission at variable bit rates by adjusting the spectral efficiency (SE) of transmission while keeping the occupied bandwidth fixed. To achieve a given SE within a fixed bandwidth, both the underlying signal constellation size and the forward error correction code rate are adjusted. Using the scarce resource of bandwidth more effectively, the proposed scheme is expected to find applications in both current fixed-grid networks and in future networks that might adopt flexible grid approach.