Trellis-based channel estimation for asynchronous IDMA with superimposed pilots

In this paper, we investigate channel estimation for Interleave-Division Multiple Access (IDMA) in an asynchronous multiuser system, by deploying superimposed pilots. As the superimposed pilots are the a priori known spreading sequences, the initial channel estimates can be obtained by separating the users with respect to the corresponding code-division orthogonality. Within the inherent IDMA iterations, a trellis-based channel estimator is integrated, which can significantly enhance the channel estimation during the iterations, by exploiting the superimposed pilots. Notice that the so-called turbo-effect can be clearly observed, in which both data detection and channel estimation are jointly improved between consecutive iterations.