On the robustness of the subspace method for blind signature waveform estimation in asynchronous DS/CDMA systems

We study the performance of the mth-order subspace method for blind signature waveform estimation in asynchronous DS/CDMA systems using a perturbation analysis approach. By partitioning the true signature waveform into the mth-order significant part and the tails. We show that the mth-order subspace method estimates-a signature waveform that is close to the mth-order significant part. The closeness depends on the signature waveform matrix, the diversity of the mth-order significant part and the size of the tails. Furthermore, we show that if we try to model not only the large ten-ns but also some small terms, then the duality of the signature estimation may degrade dramatically; thus, we should avoid modeling small terms. Finally, we propose a two-step subspace (TSSS) method for blind signature waveform estimation, which can provide improved performance. The numerical results also support our claims.