Blind identification of co-existing synchronous and asynchronous users for CDMA systems

In a code-division multiple access (CDMA) system, if all users are either bit-synchronous or bit-asynchronous, the number of active users can be easily estimated from the dimension of the signal subspace, and users can be correspondingly identified. However, identification of co-existing synchronous and asynchronous users has not been addressed in the literature. In this letter, a subspace-based blind identification approach is presented by exploring correlations of relevant data vectors and evaluating projection of possible code vectors onto the noise subspace.