In order to solve the defects which are poor error tolerance and large amount of calculation in current algorithms in recognition of the RSC encoder

a fast iterative recognition algorithm which has excellent performance was proposed. Firstly

according to the linear constraint relation between RSC symbols

the concept of hyperbolic tangent conformation was defined; this can measure the possibility of the linear relationship between the symbols under a certain polynomial parameter. Secondly

the total hyperbolic tangent coincidence value of the intercepted symbol was used as a cost function

and then the probability value of the polynomial parameters were regarded as the cost function independent variable and the problem of RSC code identification was transformed into the maximum value of the multivariate function. Finally

the variable step gradient method was used to solve the maximum value of the cost function in the continuous probability space at the finite iteration. The proposed algorithm has a fast and stable convergence speed. In addition to the strong adaptive ability of low SNR

the computational complexity increases squarely with the number of encoder registers and the number of symbols. The simulation experiment showed that the proposed algorithm could achieve the convergence of the parameters at most fifth iterations

while have strong ability to suit to the low SNR. Even the SNR is 0dB

the correct identification rate of RSC code can reach more than 90%. Compared with the existing algorithm

the proposed algorithm improved the adaptive capacity of low SNR by nearly 3dB

at the same time

the time consuming is greatly reduced.