Systems and methods for data transport, comprising encoding one or more streams of input data with one or more low density parity check (LDPC) encoders, corresponding to one or more polarization/spatial mode branches. One or more encoded data streams are mapped to symbols, wherein the mapper is configured to assign bits of the symbols to a signal constellation and to associate the bits of the symbols with signal constellation points. A signal constellation is formulated which minimizes a mean-square error of the signal constellation representing the source. The optimum signal constellation size is adjusted to improve transmission quality by adjusting the signal constellation an optical signal to noise ratio (OSNR), wherein the signal constellation is selected using a look-up table (LUT); and the symbols are modulated in accordance with the output of the mapper onto a transmission medium.