Received May 30, 2016, accepted June 13, 2016, date of publication August 8, 2016, date of current version November 18, 2016. Digital Object Identifier 10.1109/ACCESS.2016.2590500 A Survey on Cloud Gaming: Future of Computer Games WEI CAI1, (Member, IEEE), RYAN SHEA2, (Member, IEEE), CHUN-YING HUANG3, (Member, IEEE), KUAN-TA CHEN4, (Senior Member, IEEE), JIANGCHUAN LIU2, (Senior Member, IEEE), VICTOR C. M. LEUNG1, (Fellow, IEEE), AND CHENG-HSIN HSU5, (Senior Member, IEEE) 1Department of Electrical and Computer Engineering, The University of British Columbia, Vancouver, BC V6T 1Z4, Canada 2School of Computing Science, Simon Fraser University, Burnaby, BC V5A 1S6, Canada 3Department of Computer Science, National Chiao Tung University, Hsinchu 300, Taiwan 4Institute of Information Science, Academia Sinica, Taipei 115, Taiwan 5Department of Computer Science, National Tsing Hua University, Hsinchu 300, Taiwan Corresponding author: C.-H. Hsu ([email protected]) This work was supported in part by the University of British Columbia through the Four Year Doctoral Fellowship, in part by the Natural Sciences and Engineering Research Council of Canada under Grant STPGP 447524, in part by the National Natural Science Foundation of China under Grant 61271182, in part by the Ministry of Science and Technology of Taiwan under Grant 102-2221-E-007-062-MY3, Grant 103-2221-E-009-230-MY2, Grant 104-2221-E-009-200-MY3, and Grant 103-2221-E-001-023-MY2, in part by an NSERC E.W.R. Steacie Memorial Fellowship, in part by an NSERC Strategic Project Grant, and in part by a Discovery Grant. ABSTRACT Cloud gaming is a new way to deliver high-quality gaming experience to gamers anywhere and anytime. In cloud gaming, sophisticated game software runs on powerful servers in data centers, rendered game scenes are streamed to gamers over the Internet in real time, and the gamers use light-weight software executed on heterogeneous devices to interact with the games. Due to the proliferation of high-speed networks and cloud computing, cloud gaming has attracted tremendous attentions in both the academia and industry since late 2000's. In this paper, we survey the latest cloud gaming research from different aspects, spanning over cloud gaming platforms, optimization techniques, and commercial cloud gaming services. The readers will gain the overview of cloud gaming research and get familiar with the recent developments in this area. INDEX TERMS Clouds, distributed computing, video coding, quality of service, computer graphics. I. INTRODUCTION all implemented as parts of the cloud gaming platform. Cloud gaming refers to a new way to deliver computer As shown in this figure, the cloud gaming platform sends the games to users, where computationally complex games are video frames to, and receives user inputs from thin clients executed on powerful cloud servers, the rendered game used by gamers for playing games. It is a thin client, because scenes are streamed over the Internet to gamers with thin only two low-complexity components are required: (i) com- clients on heterogeneous devices, and the control events from mand receiver, which connects to the game controllers, such input devices are sent back to cloud servers for interactions. as gampads, joysticks, keyboards, and mouses, and (ii) video Figure 1 presents how cloud gaming services work. In the decoder, which can be realized using massively produced cloud, a cloud gaming platform is hosted on cloud servers (inexpensive) decoder chips. The communications between in one or multiple data centers. The cloud gaming platform the cloud game platform and thin clients are over the best- runs computer game programs, which can be roughly divided effort Internet, which in turn makes supporting real-time into two major components: (i) game logic that is responsible computer games quite challenging. to convert gamer commands into in-game interactions, and In late 2000's, we started to see cloud gaming services (ii) scene renderer that generates game scenes in real-time. offered by startups, such as OnLive [67], Gaikai [27], The gamer commands come from the command interpreter, G-cluster [26], and Ubitus [93]. We also witnessed that Gaikai and the game scenes are captured by video capturer into was acquired by SONY,which is a major game console devel- videos, which are then compressed by video encoder. The oper [86]. This was followed by the competition between command interpreter, video capturer, and video encoder are Sony's PlayStation Now (PS Now) [68] and Nvidia's Grid 2169-3536 2016 IEEE. Translations and content mining are permitted for academic research only. VOLUME 4, 2016 Personal use is also permitted, but republication/redistribution requires IEEE permission. 7605 See http://www.ieee.org/publications_standards/publications/rights/index.html for more information. W. Cai et al.: Survey on Cloud Gaming: Future of Computer Games FIGURE 1. Typical cloud gaming services. Game Streaming Service [65], which further heats up the performance evaluations. The evaluations include measure- cloud gaming market. In fact, a 2014 report from Strategy ments on Quality of Service (QoS) metrics, such as energy Analytics [75] indicates that the number of cloud gaming consumption and network metrics, and Quality of Experi- users increases from 30 millions in 2014 to 150 millions ence (QoE) metrics, such as gamer perceived experience. in 2015. The same report also predicts that other leading Building platforms and testbeds, designing the test scenarios, game console manufactures will soon join the cloud gaming and carrying out the evaluations, require significant efforts, market. while analyzing the complex interplay between QoS and QoE The tremendous popularity of cloud gaming may be metrics is even more difficult. attributed to several potential advantages to gamers, game Second, the resulting platforms and evaluation procedures developers, and service providers. For gamers, cloud gaming allow the research community to optimize various compo- enables them to: (i) have access to their games anywhere and nents, such as cloud servers and communication channels. anytime, (ii) purchase or rent games on-demand, (iii) avoid More specifically, optimization techniques for: (i) better regularly upgrading their hardware, and (iv) enjoy unique fea- resource allocation and distributed architecture are possible tures such as migrating across client computers during game at cloud servers, and (ii) optimal content coding and adaptive sessions, observing ongoing tournaments, and sharing game transmissions are possible in communication channels. replays with friends. For game developers, cloud gaming Third, computer games are of various game genres [19]. allows them to: (i) concentrate on a single platform, which in These genres can be categorized on the basis of two elements: turn reduces the porting and testing costs, (ii) bypass retailers viewpoint and theme. Viewpoint is how a gamer observe for higher profit margins, (iii) reach out to more gamers, and the game scene. It determines the variability of rendered (iv) avoid piracy as the game software is never downloaded video on the screen. Most commonly seen viewpoints include to client computers. For service providers, cloud gaming: first-person, second-person, third-person, and omnipresent. (i) leads to new business models, (ii) creates more demands on First-person games adopt graphical perspectives rendered already-deployed cloud resources, and (iii) demonstrates the from the viewpoint of the in-game characters, such as in potential of other/new remote execution applications, since Counter-Strike. Second-person games are rendered from the cloud gaming imposes the strictest constraints on various back of the in-game characters, so that gamers can see the computing and networking resources. characters on the screen, like in Grand Theft Auto. Third- Despite the great opportunities of cloud gaming, person games fix the gamers' views on 3D scenes, projected several crucial challenges must be addressed by the research onto 2D spaces. Modern third-person games usually adopts community before it reaches its full potentials to attract more the sky view, also known as God view. Classic third-person gamers, game developers, and service providers. We summa- games include Diablo, Command & Conquer, FreeStyle, rize the most important aspect as follows. First, cloud gaming and etc. Last, omnipresent enables gamers to fully control platforms and testbeds must be built up for comprehensive views on the region of interest (RoI) from different angels 7606 VOLUME 4, 2016 W. Cai et al.: Survey on Cloud Gaming: Future of Computer Games and distances. Many recent war games, e.g., Age of other systems areas, is to put up basic platforms, Empires 3, Stronghold 2, and Warcraft III, fall into this cate- based on existing tools. We summarize such gory. Game theme determines how gamers interact with game system integration efforts, which serve as corner- content. Common themes include shooting, fighting, sports, stones of related research. turn-based role-playing (RPG), action role-playing (ARPG), b) Quality of Service Evaluations (Section III-B): turn-based strategy, real-time strategy (RTS), and manage- We survey the studies on objective metric evalua- ment simulation. Although the viewpoint may be restricted by tions, which algorithmically quantify the system game theme, but generally a game genre can be describe by performance, i.e., without subject assessments. a pair of viewpoint and theme, such as first-person shooting,