The evolution of wireless communications has been significantly influenced by remarkable advancements in multiple access (MA) technologies over the past five decades, shaping the landscape of modern connectivity. Within this context, a comprehensive tutorial review is presented, focusing on representative MA techniques developed over the past 50 years. The following areas are explored: i) The foundational principles and information-theoretic capacity limits of power-domain non-orthogonal multiple access (NOMA) are characterized, along with its extension to multiple-input multiple-output (MIMO)-NOMA. ii) Several MA transmission schemes exploiting the spatial domain are investigated, encompassing both conventional space-division multiple access (SDMA)/MIMO-NOMA systems and near-field MA systems utilizing spherical-wave propagation models. iii) The application of NOMA to integrated sensing and communications (ISAC) systems is studied. This includes an introduction to typical NOMA-based downlink/uplink ISAC frameworks, followed by an evaluation of their performance limits using a mutual information (MI)-based analytical framework. iv) Major issues and research opportunities associated with the integration of MA with other emerging technologies are identified to facilitate MA in next-generation networks, i.e., next-generation multiple access (NGMA). Throughout the paper, promising directions are highlighted to inspire future research endeavors in the realm of MA and NGMA.

翻译：过去五十年间，无线通信的演进深受多址接入（MA）技术卓越进步的显著影响，这些技术塑造了现代连接的面貌。在此背景下，本文提出了一篇全面的教程综述，聚焦于过去50年间发展的代表性MA技术。探讨领域包括：i）功率域非正交多址接入（NOMA）的基础原理与信息论容量极限，及其在多输入多输出（MIMO）-NOMA中的扩展；ii）利用空间域的多种MA传输方案，涵盖传统空分多址（SDMA）/MIMO-NOMA系统以及采用球面波传播模型的近场MA系统；iii）NOMA在集成感知与通信（ISAC）系统中的应用，包括基于NOMA的典型下行/上行ISAC框架介绍，并利用基于互信息（MI）的分析框架评估其性能极限；iv）识别MA与其他新兴技术整合中的主要问题与研究机遇，以促进下一代网络中的多址接入，即下一代多址接入（NGMA）。全文强调了有前景的方向，以激励未来在MA与NGMA领域的研究努力。