## 1 Introduction
To overcome the above-mentioned drawbacks, some researchers have shifted the focus to the cyclostationarity of the repetitive transients. The protrugram [32] and enhanced kurtogram [19] were proposed as a breakthrough attempt for the optimal band selection, where the kurtosis of the envelope spectrum is adopted as an indication of repetitive transients. The main innovation is that it takes advantage of the cyclostationarity of repetitive transients in the frequency domain, that is, its envelope spectrum shows an impulsiveness with a series of harmonics. However, new drawback is exposed with in-depth research that it may invalid when the discrete harmonic components, produced by uncorrelated excitation sources, are dominant in the envelope spectrum compared with fault characteristic frequencies [22]. To further utilize the traits of repetitive transients, another attractive method, named Infogram, was proposed by [PERSON] [31], where the negentropy of the squared envelope and squared envelope spectrum (SES) are respectively generated to measure both the impulsiveness and the cyclostationarity of the repetitive transients. After that, some excellent improvements were proposed to extend the original Infogram. The pareto optimal solution [33] and a grey strategy [34] have been utilized to balance the contributions due to the spectral negentropys generated from two evaluation domains, differ from simply synthesize by the equal weight adopted in original Infogram. Nonetheless, the above-improved methods still inherit the drawbacks that the negentropyof the squared envelope is prone to be disturbed by the large impulse interference and the negentropy of the SES is easily affected by discrete harmonic components. Recently, one of the exciting attempts was proposed Autogram [22], which adopts the kurtosis of AC of the squared envelope of the filtered time signal as an evaluation strategy to determine the IFB. The intensity of the fault-induced repetitive transients is enhanced and the uncorrelated background noise is further decreased after the AC process. However, the Autogram only depicts the impulsiveness of AC of the squared envelope signal through the evaluation indicator of kurtosis. Another significant merit, the periodic property of AC, has not been fully utilized in Autogram, which suggests that it will be sensitive to the discrete harmonic interferences generated by other sources such as shafts, gears and so on. Therefore, although the above methods pay attention to the cyclostationarity of fault-induced repetitive transients and avoid the interference of large impulses, they still can't avoid the influence of discrete harmonic interference. According to the above discussion, it can be seen that the determination of IFB is still not a simple matter when there are multiple complex interferences in the faulty signal, such as large impulse interference and discrete harmonic interference. However, influenced by the complex wheel/rail excitation and the complex vibration transmission, the wheelset bearing faulty signal usually contains multiple complex interferences. In order to decrease the effect of multiple complex interferences on the selection of the IFB, a novel approach, named Mkurtogram, is proposed for the railway wheelset bearings fault diagnosis in this paper. It takes the Mkurt [35; 36] of unbiased AC of the squared envelope signal generated from sub-bands as assessment indicator for the first time. The AC process is firstly used to decrease the large impulses interference and enhance the strength of the fault-induced repetitive transients. Then, based on the regular periodic distribution of fault-related peaks in AC domain, a unified representation of the impulsiveness and periodicity is performed by Mkurt, thus, the influence of irrelevant discrete harmonic interferences is further eliminated. Moreover, based on the periodic directivity of Mkurt, the proposed method also can be applied to the compound faults diagnosis of the wheelset bearing.