Following the trends of index modulated (IM) techniques for optical communications, in the last few years several new waveform proposals have been made, aiming at conveying a higher density of information by driving different signal properties. One of these proposals mixes multi-pulse pulse-position modulation (MPPM) and quadrature amplitude modulation (QAM) in a system called QAM-MPPM. We present here a new way to demodulate its compound waveform, and, for the non-turbulent free space optical (FSO) channel, we provide accurate analytical expressions for its error probabilities, both in the case of the traditional and the new detector. Based on these analytical derivations, we also provide simplified expressions for the estimation of the error probabilities. We show that the new detector offers a gain of some tenths of dB in signal-to-noise ratio with respect to the previously defined one without an increase in complexity, and that our error probability estimations are more accurate than previously published results. To the best of our knowledge, this work is the first to provide simulation results validating the study of the error probability performance of QAM-MPPM.

翻译：近年来，随着光通信中索引调制（IM）技术的发展，为通过驱动不同信号特性来传递更高密度的信息，研究者们提出了多种新型波形方案。其中一种方案将多脉冲脉冲位置调制（MPPM）与正交幅度调制（QAM）相结合，形成QAM-MPPM系统。本文提出了一种对其复合波形进行解调的新方法，并针对非湍流自由空间光（FSO）信道，分别给出了传统检测器与新型检测器下误码率的精确解析表达式。基于这些解析推导，我们还提供了误码率估计的简化表达式。研究表明，与先前定义的检测器相比，新型检测器在信噪比上可实现约十分之几分贝的增益，且复杂度未增加；同时，我们的误码率估计结果比已发表文献更为精确。据我们所知，本文首次通过仿真结果验证了QAM-MPPM误码率性能的研究。