Interleave-Division Multiple Access from a Multiuser Theory Point of View

Interleave-Division Multiple Access (IDMA) has recently been proposed by a number of authors. By means of Monte Carlo simulations, a performance close to the capacity limit has been demonstrated. In this paper, we investigate IDMA from a multiuser theory point of view using known concepts for the Gaussian multiple-access channel. Specifically, we proof that binary code words are sufficient. For all layers the same encoder should be used. We show that IDMA with a sufficiently large number of superimposed code words, with optimum power allocation, and in conjunction with a suitable receiver is capacity achieving. As a side effect, the optimum power allocation scheme for IDMA with non-Gaussian chips in conjunction with a successive interference cancellation receiver is derived. As a reference, the optimum rate allocation for an IDMA-like transmission scheme with equal powers per layer is obtained for the same receiver. Finally, some remarks on the code design for IDMA systems are made.