Subspace-based delay estimation for CDMA communication systems

We consider a subspace-based approach to delay estimation for code division multiple access communication systems. By exploiting the eigenstructure of the received signal´s sample correlation matrix, the observation space is partitioned into a signal subspace and a noise subspace without prior knowledge of the users´ delays. The delay estimate is formed by maximizing the likelihood of the projection of a given user´s spreading waveform into the estimated noise subspace, thus decomposing the multiuser delay estimation problem into a series of single user problems. This subspace-based approach requires no preamble for acquisition, is near-far resistant, and is robust to changing channel conditions