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Subspace-based channel estimation for CDMA downlink with aperiodic spreading codes and multiple subchannels

We consider a downlink CDMA system with aperiodic spreading codes and multipath propagation. Assisted by either multiple antennas or oversampling, multiple subchannels are created. Then a subspace technique can be applied directly to estimate all channel parameters, based only on the channel output. The proposed method does not require either the spreading codes of the users or pre-processing of the received data. It is also applicable to an overloaded system. These appealing features make our method significantly different from existing subspace approaches.