Abstract: In this paper, a robust and practical method for active user enumeration in asynchronous direct sequence code division multiple access (DS-CDMA) in multipath channel condition is proposed. The method is based on information theory criteria which outperforms other methods. There are two main categories of information criteria which are widely used in active user enumeration, Akaike Information Criterion (AIC) and Minimum Description Length (MDL) information theory criteria. The main difference between these two criteria is their penalty functions. Due to this difference, MDL is a consistent enumerator which has better performance in higher signal to noise ratios (SNR) but AIC is preferred in lower SNRs. In sequel, we propose a SNR compliance method based on subspace and training genetic algorithm to have the performance of both of them. Most of the previous works do not mention the fact that in practical case, user\'s signals arrive at receiver asynchronously. Moreover the proposed method needs a simple omni-directional antenna which simplifies receiver structure and reduces its costs. Numerical results confirm our claim and focus on efficiency of algorithm in detection and exact enumeration of active users in low SNRs and multipath environment.

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