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 terms 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.