Improved Turbo Decoding With Multivariable Taylor Series Expansion

In this letter, a new method is proposed to approximate n-input (n > 2) max* operation. Bi-variable Taylor series expansion, for the first time, is applied to approximate the correction term of n-input (n > 2) max* operation. It avoids the recursive computation of bi-variable Jacobian logarithm. To improve the approximation performance, multiple expansion points are considered. The proposed method is evaluated for 3GPP LTE turbo codes. The simulation results show that the approximation with five expansion points, applied with scaling factor to extrinsic information, has performance degradation of 0.01 dB compared with radix-4 Log-MAP algorithm. Furthermore, the approximation with three expansion points will bring minor performance loss but almost the same computational complexity compared with five expansion points.