As an evolving successor to the mobile Internet, the extended reality (XR) devices can generate a fully digital immersive environment similar to the real world, integrating integrating virtual and real-world elements. However, in addition to the difficulties encountered in traditional communications, there emerge a range of new challenges such as ultra-massive access, real-time synchronization as well as unprecedented amount of multi-modal data transmission and processing. To address these challenges, semantic communications might be harnessed in support of XR applications, whereas it lacks a practical and effective performance metric. For broadening a new path for evaluating semantic communications, in this article, we construct a multi-user uplink non-orthogonal multiple access (NOMA) system to analyze its transmission performance by harnessing a novel metric called age of incorrect information (AoII). First, we derive the average semantic similarity of all the users based on DeepSC and obtain the closed-form expressions for the packets' age of information (AoI) relying on queue theory. Besides, we formulate a non-convex optimization problem for the proposed AoII which combines both error-and AoI-based performance under the constraints of semantic rate, transmit power and status update rate. Finally, in order to solve the problem, we apply an exact linear search based algorithm for finding the optimal policy. Simulation results show that the AoII metric can beneficially evaluate both the error- and AoI-based transmission performance simultaneously.

中文翻译：

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NOMA 辅助 XR 应用的语义通信中的错误信息时代

作为移动互联网不断发展的继承者，扩展现实（XR）设备可以生成类似于现实世界的全数字沉浸式环境，将虚拟和现实世界元素融为一体。然而，除了传统通信遇到的困难之外，还出现了超海量接入、实时同步以及前所未有的多模态数据传输和处理等一系列新的挑战。为了应对这些挑战，可以利用语义通信来支持 XR 应用程序，但它缺乏实用且有效的性能指标。为了拓宽评估语义通信的新途径，在本文中，我们构建了一个多用户上行链路非正交多址（NOMA）系统，通过利用一种称为错误信息年龄（AoII）的新指标来分析其传输性能。首先，我们基于DeepSC推导所有用户的平均语义相似度，并依靠队列理论获得数据包信息年龄（AoI）的封闭式表达式。此外，我们为所提出的 AoII 制定了一个非凸优化问题，该问题在语义率、传输功率和状态更新率的约束下结合了基于错误和基于 AoI 的性能。最后，为了解决该问题，我们应用基于精确线性搜索的算法来寻找最优策略。仿真结果表明，AoII 度量可以有益地同时评估基于错误和基于 AoI 的传输性能。