A REVIEW OF CONSTELLATION SHAPING AND BICM-ID OF LDPC CODES FOR DVB-S2 SYSTEMS

Abstract — Here an energy-efficient approach is presented for constellation shaping of a bit-interleaved low-density parity-check (LDPC) coded amplitude phase-shift keying (APSK) system. APSK is a modulation consisting of several concentric rings of signals, with each ring containing signals that are separated by a constant phase offset. APSK offers an attractive combination of spectral and energy efficiency, and is well suited for the nonlinear channels. A subset of the interleaved bits output by a binary LDPC encoder is passed through a nonlinear shaping encoder. An iterative decoder shares information among the LDPC decoder, APSK de-mapper, and shaping decoder. Information rates are computed for a discrete set of APSK ring radii and shaping bit probabilities, and here the additive white Gaussian noise (AWGN) channel is considered. In this paper, an adaptive equalizer is added in the iterative decoding path and its purpose is to reduce inter symbol interference to allow recovery of the transmit symbol. An adaptive equalizer one that automatically adapts to time-varying properties of the communication channel. The combination of shaping, use of LDPC codes, iterative decoding and with adaptive equalizer we can achieve a gain in excess of 1.18 dB in AWGN compared with a system that does not use shaping, uses an un optimized code from the DVB-S2 standard, and does not iterate between decoder and demodulator