Constellation Shaping for Bandwidth-Efficient Turbo-Coded Modulation With Iterative Receiver

This paper introduces a new technique for combining constellation shaping and bit-interleaved turbo-coded modulation (BITCM) over additive white Gaussian noise channel. The proposed scheme consists of serial concatenation of a binary turbo code, short-length binary shaping code, and mapping function using Gray labeling. The corresponding receiver is made up of four blocks (demapper, shaping decoder, and two constituent RSC decoders) exchanging extrinsic information in order to optimize error performance. A BITCM scheme employing 16-PAM constellation to achieve a rate of 3 bits/dim is considered as an example. It is shown that, by careful selection of the shaping code parameters, shaping gains almost equal to 0.8 dB can be obtained at a little cost in terms of system complexity.