Application of Shaping Technique With Turbo Coset Codes

This paper presents a method for the combined turbo code and quadratic-amplitude modulation using coset coding. It also presents a fixed-rate shaping algorithm offering lower complexity as compared to all relevant methods reported in the literature. A symbol-based turbo code acting on symbols of size 4 is used to select a coset along each 1D subconstellation (using the partition Z/4Z). The proposed coset coding method satisfies the conditions for the separability of shaping and coding, and, consequently, can be easily integrated with the shaping algorithm. Numerical results are presented for an additive white Gaussian noise channel. The proposed coding-shaping algorithm offers the best performance reported in the literature, enjoys very low complexity, can be easily scaled to accommodate different bit rates and spectral efficiencies, and does not suffer from an early error floor, as observed in many other related works.