# Survey on Quality of Experience Evaluation for Cloud-Based Interactive Applications
## 3 Categories of CIAs
### Cloud Gaming  
Cloud gaming services are also a category of CIAs. In cloud gaming, users access a remote video game as if it were local. Similar to remote desktops, processing and rendering take place on the remote server, and the user device collects user interactions with the controller, sends them to the server, and displays the resulting screen updates. Using these services, players do not require expensive video consoles with large computational resources. The user device can be a smartphone, tablet, PC, laptop, or even a traditional video console. This flexibility allows the user to play in the cloud from anywhere and resume their games from other devices. In cloud gaming CIAs, there may be increased sensitivity to delay for some types of games. CIAs allow video game developers and publishers to use the cloud resources of cloud gaming platforms. This simplifies their deployment, maintenance, and costs. Additionally, game developers can develop games for a single platform instead of multiple platforms. There are commercial cloud gaming deployments such as Nvidia GeForce NOW [72], Amazon Luna Cloud Gaming [73], PlayStation Now [74], and Xbox Cloud Gaming [75]. The cloud gaming industry is expected to reach a value of USD 3856 million by 2025, which represents an increase of 54.1% from 2019 [76].  
The three human perceptions described in Section 2 influence the final QoE perceived by the user of a cloud-based game. The player wants to play a video game as if it were running on their game console and not a remote server. There are two main components of a cloud gaming platform: (1) the game logic, responsible for transforming user inputs into actions, and (2) the scene renderer, responsible for generating the screen updates in real time. A scene in a video game is composed of all the elements present at a specific time and in a specific position. On the client's computer, the command interpreter captures the user interactions that are then sent to the server. The video capture must capture the scenes of the video game rendered on the server and make a video stream that is later compressed to save bandwidth. Compression influences human perceptions when it is lossy. In multiplayer sessions, each player's game scenes can be used together to perform compression, taking advantage of the redundant information and compressing multiple users' streams together [25]. Additionally, cloud gaming platforms can detect the regions of the game scene of interest to use compression with more bits and, therefore, higher quality [77; 78]. Other compression strategies use information from the rendering of video games to estimate movements and save compression time [29]. Graphics compression strategies generate a 3D coordinate space with information on the points of the objectsthat make up the scene and the 2D texts that cover them [79]. The server compresses this scene and sends it to the client, who must render that information. This strategy is more demanding for the client since it has to perform rendering in the case of the server compressing the video. Lossy compression influences the visual quality perceived by the player and adds a delay to communication.  
In gaming, the user expects the service to respond graphically as quickly as possible with good interactivity. The game should quickly execute actions, such as rotating a geometric figure or moving a player, so that the user does not perceive the involvement of a remote cloud platform. The codec directly influences the time spent on compression and, therefore, the perceived interactivity. The cloud server sends an audio stream alongside the video stream. Human perception of audio quality is more important in cloud gaming services than in remote desktop CIAs. Compression, network packet losses, and network packet delays affect audio quality. Furthermore, sound stimuli produced in response to player actions must be presented in a synchronised way.