Eavesdropping in the synchronous CDMA channel: an EM-based approach

The problem of blind detection in a synchronous code division multiple access (CDMA) system when there is no knowledge of the users’ spreading sequences is considered. An expectation maximization (EM)-based algorithm that exploits the finite alphabet (FA) property of the digital communications source is proposed. Simulations indicate that this approach, which makes use of knowledge of the subspace spanned by the signaling multiplex, achieves the Cramér–Rao lower bound (CRB). The issues of subspace estimation and timing acquisition are also considered.