An equal-probability symbolic analysis approach for mutual information function is proposed to improve routine symbolic analysis method.Firstly,the time series are rearranged according to the range from small to large.Then the rearranged time series are divided into several groups by equal-probability step and the number of groups are determined with empirical sub-formula.Finally,a critical point set of symbolic analysis method is made with boundary values of each group.Experiments of Lorenz and forced Brusselator show that this approach agrees well with Fraser' method while it is simplified significantly.

To improve noisepmof ability and stability of Lempel-Ziv complexity (LZC), LZC is calculated by an equiprobable coarse graining method. Relation between threshold of bi-quantified coarse graining and LZC is analyzed. An anti-jamming test is performed with 87 series generated by Logistic map. Correlation coefficients and relative variance coefficients of LZC series before and after noise inject are used to measure noiseproof ability of LZC indexes. 10 electroencephalograms are used to test stability of LZC. It shows that with equiprobable coarse graining, correlation coefficients are more than 0.998, relative variance coefficients are smaller and stability of LZC of electroencephalogram is good.