Analysis and Optimization of Interleave-Division Multiple-Access Communication Systems

The recently proposed interleave-division multiple-access (IDMA) system is a flexible spread-spectrum air-interface technique featuring low receiver complexity and high spectral efficiency. In IDMA, each user's chip sequence is interleaved by a distinct chip-level interleaver. The receiver employs a simple chip-level iterative multiuser detector to decode the user's data. Here we focus on the analysis and optimization of such an IDMA system. We show that IDMA can be viewed as a limit case of the conventional CDMA employing repetition code and random spreading. Two analytical tools, namely, the large-system performance approximation and the EXIT chart technique are tailored in the context of IDMA chip-level iterative detector to facilitate the system performance analysis and optimization. The spectral efficiencies of a low-rate coded IDMA system with equal power setting in both single-cell and multi-cell scenarios are then analyzed, from which it is seen that the coded IDMA system with turbo receiver is a spectral efficient multiple-access scheme. Finally, we consider optimal power allocation among users in IDMA to maximize the spectral efficiency with finite-alphabet constellation. The differential evolution technique for nonlinear optimization is adopted to solve the power profile optimization problem. With optimized power profiles, the low-rate coded IDMA system can approach the optimal spectral efficiency with finite input constellations.