Joint Blind User Identification and Synchronization in Non-Cooprative CDMA Systems at Slow Flat Fading Channels

Number of active users estimation and synchronization have important roles in eavesdropping of multi-user direct sequence spread spectrum (DS_SS) systems. In this paper the subspace method is used for joint number of active users estimation and synchronization. Signal of each user is synchronized by maximizing modified FROBENIOUS square norm of estimated received signals covariance matrix, active users are discriminated from noise and number of those is determined using Eigen analysis of received signal covariance matrix by help of an adaptive threshold. The proposed method for number of active users estimation has lower computational complexity relative to the traditional methods, such as minimum description length (MDL) and Akaike's information criterion (AIC). Furthermore the proposed algorithm has good detection performance in low signal to noise ratio (SNR) and is resistant against carrier frequency offset of received signals. Moreover, the synchronization criterion is analyzed for K active users with unequal power signals. Theoretical results of synchronization analysis are verified using computer simulations. It is shown that the synchronization method is also robust against carrier frequency offset of active users

کلیدواژه ها:

CDMA ، Blind Detection ، Synchronization ، adaptive threshold ، modified FROBENIOUS square norm ، Subspace