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A novel, robust and practical method for active user enumeration in asynchronous CDMA in multipath channel condition is proposed in this paper. Most of the previous works do not consider the fact that in practical case, user's signals with the help of receiver arrive asynchronously. The proposed method can be used practically in blind multi-user detection such as eavesdropping; moreover, the method is based on information theory criteria which outperform other methods. Minimum description length (MDL) has better performance than all other information criteria used in such scenarios. Unlike most of the pervious works, we do not exploit array antenna to gather necessary data of the users. However our proposed method needs a simple omnidirectional antenna which simplifies receiver's structure and reduces its costs. Also, this exploitation provides us the ability to use our proposed algorithm in coherent signal case. Similar to some other information criterion based methods, our method exploits the users' code length as an input which is not appropriate for blind active user enumeration. A novel Pseudo Noise (PN) code detection approach is also presented in this paper to tackle this problem. Presented numerical results confirm our claims and focus on efficiency of algorithm in detection and exact enumeration of active users in low SNRs and multipath environment.