Multi-Rate Communications Using Layered Interleave-Division Multiple Access with Power Allocation

Interleave-division multiple-access (IDMA) has recently been proposed as a multiuser scheme where users are separated by unique interleaver sequences. When used with low-complexity iterative receivers, IDMA has been shown to outperform coded CDMA. In this paper we consider a multi-rate system where high data- rate transmitters are constructed by combining several IDMA layers together, and transmitting the composite layered signal from a single antenna. Each layer is of equal rate, but unequal power. Assignment of different powers to the different layers has been shown to significantly improve the performance of iterative decoder receivers. Using Variance Transfer (VT) charts, we derive an optimal power allocation scheme for the IDMA layers. In a Rayleigh flat-fading environment, simulation results demonstrate that the performance of this proposed system is close to the theoretical limit.