Blind subspace-based signature waveform estimation in BPSK-modulated DS-CDMA systems with circular noise

A new blind subspace-based algorithm for signature waveform estimation in binary phase-shift-keying (BPSK)-modulated direct-sequence code-division multiple-access (DS-CDMA) systems is proposed. Our approach can be viewed as a modification of the popular blind technique by Liu and Xu (LX), which additionally exploits noncircularity of the transmitted signals and circularity of noise to increase the dimension of the observation space twice while keeping the dimension of the signal subspace unchanged. This enables us to improve the performance substantially and to apply the proposed algorithm to scenarios with an increased number of active users and lengthier user channels as compared with the original LX algorithm. The theoretical analysis of the identifiability of the proposed technique is provided, which shows that it enjoys more relaxed identifiability conditions than the LX algorithm. Analytical expressions for the mean-square error (MSE) of the proposed algorithm are also derived. Numerical examples verify the advantages of the proposed algorithm over the LX technique and validate our analytical results