Institute of Electrical & Electronic Engineers
An energy-efficient approach is presented for shaping a bit-interleaved Low-Density Parity-Check (LDPC) coded Amplitude Phase-Shift Keying (APSK) system. A subset of the interleaved bits output by a binary LDPC encoder are passed through a nonlinear shaping encoder whose output is more likely to be a zero than a one. The "Shaping" bits are used to select from among a plurality of sub-constellations, while the unshaped bits are used to select the symbol within the sub-constellation. Because the shaping bits are biased, symbols from lower-energy sub-constellations are selected more frequently than those from higher-energy sub-constellations. An iterative decoder shares information among the LDPC decoder, APSK de-mapper, and shaping decoder.