Systems and methods of transmitting includes one or more low-density parity-check (LDPC) encoders configured to adaptively encode one or more streams of input data by adjusting error correction strength based upon channel conditions. One or more mappers are configured to map one or more encoded data streams to symbols by associating bits of the symbols to points of an optimum signal constellation design (OSCD) based on one or more encoded data streams, the OSCD being decomposed into two or more sub-constellations. A spectral multiplexer is configured to combine symbol streams for the one or more encoded data streams to provide a plurality of spectral band groups. A mode multiplexer is configured to combine spectral contents of the plurality of spectral band groups allocated to a plurality of spatial modes for transmission over a transmission medium.