The application of the precoding technique to turbo codes is investigated, resulting in a new class of turbo-like codes named precoded turbo codes. The introduction of a precoder provides a degree of freedom for code optimisation. As a result, an optimised rate-1/2 precoded turbo code with a threshold of 0.28 dB is designed using the EXIT chart.
S. Tong, H. Zheng & B. Bai, "Precoded turbo code within 0.1dB of Shannon limit," Electronics Letters, vol. 47, (8) pp. 521-522, 2011.