# Quality of Experience in 6G Networks: Outlook and Challenges
## 1 Introduction
The GSMA expectation for subscriber growth (in terms of compound annual growth rate, or CAGR) during 2019-2025, for example, is at 1.9% [4]. However, this figure translates to 5.8 billion subscribers in 2025. Meanwhile, connectivity challenges will be more prominent in the context of the Internet of Things (IoT), where 24.6 billion \"things\" (e.g., devices) are expected to be connected in 2025. In addition to these increasing numbers, connectivity requirements are also becoming more demanding. For instance, there is a rising emphasis on time-sensitive communications in contexts ranging from tactile Internet, to intelligent transport systems (ITS) and to industrial IoT (or Industry 4.0). In 5G networks, accommodations have been made through massive machine type communications (mMTC) or massive IoT (mIoT), and ultra-reliable and low-latency communications (URLLC). Therefore, the expectation is that 6G networks will offer solutions capable of handling these increasingly complex demands and capabilities [20]. Visions on 6G networks have yielded detailed descriptions touching on various aspects [6, 13], but there is a lack of discussions on managing user experience in the literature. 6G will deliver enhanced mobile experiences (through more capable \"devices\") and individualized mobile experiences. Realizing these objectives entails harmonizing network resources in an end-to-end and cross-layer fashion to match individual user requirements and expectations. A harmonized and individualized delivery is another definite by-product of capitalizing on AI-based network management. Nevertheless, specific considerations for user quality of experience (QoE) are yet to be addressed in the context of 6G networks. The notion, practicalities, and applications of QoE have considerably evolved since its inception in the telecommunication context [21]. Defined at the time as the \"the overall acceptability of an application or service, as perceived subjectively by the end-user\", QoE was understood to include \"end-to-end system effects\" and that it \"may be influenced by user expectations and context\". The evolution of QoE inference and use have included improvements on the manually aggregated scores, e.g., the mean opinion score (MOS); standardizing QoE mappings to network measurements of service delivery; association/correlation studies with user-end observations and responses; and more [22]. This evolution came in tandem with enhanced network delivery performance, especially after introducing IP-based services and smartphones in 2007. In light of the ongoing deliberations on 6G networks, QoE aspects take on new dimensions that have not been previously accounted for, especially with the projected user context cyberphysical enrichment through augmented reality (AR) and virtual reality (VR), in addition to tactile experiences. Streamlining QoE investigation towards relevant and usable techniques thus becomes necessary. The objective of this work is to address this void. Specifically, we aim to identify the critical characteristics of user experience in 6G networks. We also highlight how the evolutions in the relevant areas will enhance the understanding and use of QoE inferences. Finally, we elaborate on the challenges expected in QoE and allude to viable opportunities in both emerging and expected technologies. The remainder of this paper is organized as follows. In Section 2, we discuss the evolution of cellular networks through 5G. We then discuss the enabling technologies and projected services of 6G networks in Sections 3 and 4, respectively. Next, we expand on QoE aspects in 6G networks in Section 5 and discuss the outlook, challenges, and opportunities. Finally, we conclude the work in Section 6.