# Survey on Quality of Experience Evaluation for Cloud-Based Interactive Applications
## 2 Related Works
### QoE and Human Perceptions Related to CIAs  
The stimuli perceived by the user influence the quality of experience provided by a CIA. In this section, we discuss the human perceptions considered crucial in the state of the art for quantifying QoE in CIAs. In the literature, these human perceptions, also referred to as physiological aspects, play a significant role in shaping the user experience [28]. Three primary human perceptions have been identified: visual quality, audio quality, and interactivity or responsiveness. In most digital systems, audio and video signals are fundamental components [24]. Subjective evaluations of audiovisual quality are widely regarded as the most accurate method to reflect human perception [32]. However, given the idiosyncrasies of the applications under review in this study (interactive applications), the tools and methodologies for QoE quantification also require metrics that evaluate the strict temporal requirements between user interactions and system responses.  
Visual quality encompasses the aspects of an image perceived by the human perceptual system, significantly influencing the end-user experience. Content may experience degradation, such as a decrease in the quality of textures in a video game, pixelation of the remote desktop screen, or missing video frames, compared to the original or expected content. This degradation can impact visual quality. Researchers have proposed various metrics to quantify these degradation artefacts.  
A second human perception that the tools evaluate is the audio quality of the services. Equivalent to video quality, audio quality is understood as the aspects of the audio signal perceived by the human auditory system, which impact the final user experience. Similar to visual quality, audio quality can be impaired by the degradation of the sonorous content compared to the expected or original content (e.g., clarity of the sounds of a video game hosted in the cloud). In this area, we present the efforts made to obtain metrics that quantify the quality or degradation of the audio.  
Audio and visual quality have varying degrees of relevance depending on the service being consumed [24]. This is why the research works studied in this article may emphasise varying degrees of emphasis on the quantification of each perception, depending on the scope of their target services.  
Finally, given that the present taxonomy is aimed at CIAs, the third human perception evaluated by the tools and methodologies is the responsiveness or interactivity of the services. The QoE perceived by users is influenced by the time it takes to perceive a response to interactions with the service. This responsiveness can be translated in many ways. There are several temporal references that can influence it, depending on the service or application consumed (e.g., opening time of a window in a remote desktop, deployment time of a field in an online form, agile movement of a player in a cloud gaming service). Again, researchers have made efforts to quantify this interactivity in different applications and services, and we explore them throughout this paper.  
The efforts of academia and industry seek to quantify one or more of these human perceptions with particular output metrics depending on the type of CIA.