This paper presents a subspace blind method to estimate the direction of arrival (DOA) of direct sequence code division multiple access (DS-CDMA) signals in a multipath fading environment. The proposed method is based on a signal/noise subspace approach that exploits the structure of the desired signal, self-interference, and multiple access interference simultaneously. The main idea is based on fitting the extended subspace spanned by the desired signature waveform in all different paths into the estimated extended signal subspace. Unlike conventional methods that require knowledge of all users' signature waveforms and timings, the proposed method is blind in the sense that it utilizes only the desired user's code and its corresponding path delays. The problem is formulated as an optimization that can be solved using generalized eigendecomposition, considering both signal and noise subspaces for enhanced performance. The method demonstrates better performance at low SNR compared to existing projection-based methods in the literature, approaching the Cramer-Rao lower bound. Additionally, we propose a method for estimating the relative power of different paths in multipath CDMA signals, which can be used for maximal ratio combining at the receiver.
Comparison of the proposed algorithm with the relevant methods in literature. The root mean square error (RMSE) of DOA estimation is plotted versus SNR for the first path of user no. 5 in a multipath CDMA system with 8 users. The proposed mixed subspace optimization method outperforms projection-based methods (Olfat IET 2004), joint channel and DOA estimation methods (Lamare IET 2011), and parallel MUSIC approaches (Chiang Trans. Antennas and Propagation 2003), particularly at lower SNR values. The simulation uses a uniform linear antenna array with 5 elements, GOLD sequences with processing gain of 31, and 3 paths per user.
This paper presents a subspace blind method to estimate the direction of arrival of direct sequence code division multiple access signals in a multipath fading environment. The proposed method is based on signal/noise subspace approach. For enhancing the results, the problem is formulated based on both signal and noise subspaces to exploit structures of desired signal, self interference and multiple access interference simultaneously. The main idea in this paper is based on fitting the extended subspace spanned by the desired signature waveform in all different paths into the estimated extended signal subspace. The proposed method is blind in the sense that it utilizes only the desired user’s code and its corresponding path delays. The performance of the proposed method is compared to the Cramer–Rao lower bound. We also propose a method for estimating relative power of different paths in multipath code division multiple access signals.
@article{ghasemian2023subspace,title={Subspace based DOA estimation of DS-CDMA signals},author={Ghasemian, Amir and Olfat, Ali and Amiri, Mojtaba},journal={Telecommunication Systems},pages={1--12},year={2023},publisher={Springer},project={/projects/DOA_CDMA/}}
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