Joint Demapping and Decoding for DQPSK Optical Coherent Receivers
  We present a low-complexity joint demapper-decoder scheme for coherent optical receivers with DQPSK modulation. The new technique reduces to 0.7dB the gap between QPSK and DQPSK in 100Gb/s coherent optical systems. 
Mario A. Castrillon, Damian A. Morero, and Mario R. Hueda
cs.IT math.IT