asynchronous variable processing gain direct-sequence

Recently, blind multi-user detection has become an important topic in code division multiple access (CDMA) systems. Direct-Sequence Spread Spectrum (DSSS) signals are well-known due to their low probability of detection, and secure communication. In this article, the problem of blind multi-user detection is studied in variable processing gain direct-sequence code division multiple access (VPG DS-CDMA). The method based on the fluctuations of autocorrelation estimators,which previously described in a single and multi-user context, is extended to an asynchronous variable processing gain (VPG) DS/CDMA systems without restrictions on the processing gains in multi-path channel condition. According to the proposed algorithm, not only the presence of the common peaks in the second-order statistic of the received signal is proved, but the relationship between these peaks and the spreading code length is also derived. The simulation results show that the proposed algorithm even in the presence a very low signal-to-noise ratio (SNR) is completely efficient in signal detection. It is remarkable that  the minimum description length (MDL) method is used to determine the number of users.