IDMA Using Non-Gray Labelled Modulation

Interleave-division multiple-access (IDMA) is a multiple-access technique, which uses an elementary signal estimator (ESE) to achieve simple chip-by-chip detection. In this paper, we propose a new ESE which can be calculated directly based on the two-dimensional received signals. Hence, the proposed ESE can be applied to IDMA using signal modulation with either Gray labelling or non-Gray labelling. In contrast, the original ESE is calculated either based on the one-dimensional received signals or separately based on the real parts and the imaginary parts of the two-dimensional received signals. In fact, the original ESE can only be applied to IDMA using BPSK or Gray-labelled QPSK. From the proposed ESE, we can predict that the IDMA using the non-Gray labelling will be superior to the IDMA using the Gray labelling at the high signal-to-noise ratio (SNR) region. With EXIT (extrinsic information transfer) chart analysis, we can estimate the SNR region for which there is advantage of using non-Gray labelling for IDMA. The simulation results fit well with the theoretical analysis.