Blind Estimation of PN Sequence of DS-CDMA Signals over Time Varying Flat Fading Channel

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Abstract

Spread spectrum signals are widely used for secure communications, as well as for multiple access interference (MAI). They have many interesting properties, including low probability of interception. Indeed, direct sequence spread spectrum systems (DSSSS) use a periodical pseudo-random sequence to modulate the baseband signal before transmission. Interception of DSSS signals is a difficult task due to the hiding of the PN sequence, especially if the accompanied noise is non-Gaussian and the channel is time varying. In this paper, a receiver is proposed to intercept asynchronous direct sequence code division multiple access (DS-CDMA) signals received from different users and estimate the PN sequences of each one of them. The signals are assumed to be transmitted over time varying flat fading channel and contaminated with Class-A impulsive noise. The proposed interception receiver is based on Independent Component Analysis (ICA). The proposed receiver is tested for different types of PN sequences including m sequence, Gold sequence, and Walsh codes. The results show that the interception receiver is not sensitive to the time variation of the channel and to the type of PN sequence. Moreover it is found that the receiver performs well for low signal to noise ratio and for any type of PN codes.

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