Abstract: This paper proposes an approximate calculation for correction function of Log-MAP algorithm and obtaines a well turbo decoding in AWGN channel.The algorithm mainly uses segmenting and fitting method for correction function by spline function.The kind of the method has solved the difficulties and obstacles resulting from inaccessible calculation of correction function with exponential and logarithm operations.It shows that error correction performance of turbo decoder with the interpolation function calculating correction function is the same as that with Log-MAP algorithm，and the former algorithm complexity is much obviously lower than the latter.

Key words: Turbo codes, MAP algorithm, quadratic spline functions, Hermite interpolation

摘要： 提出用插值函数来计算Log-MAP算法中的校正函数，并在AWGN信道上采用分段差值方法实现了Turbo译码。该算法解决了校正函数计算复杂度较大的问题，消除了译码计算中的指数和对数运算。仿真结果表明：用2段二次样条函数实现的Turbo译码器，其译码性能与Log-MAP算法等价，而计算的复杂度明显降低，运算时间大幅度减少。

关键词: Turbo码, MAP算法, 二次样条函数, Hermite插值