Will Dynamic Foveation Boost Cloud VR Gaming Experience?

Cloud Virtual Reality (VR) gaming offloads the computationally-intensive rendering tasks from resource-limited Head-Mounted Displays (HMDs) to cloud servers, which consume a staggering amount of bandwidth for high-quality gaming experiences. One way to cope with such high bandwidth demands is to capitalize on human vision systems by allocating a higher bitrate to the foveal region of HMD viewport, which is known as foveation in the literature. Although foveation was employed by remote VR gaming, existing open-source projects all adopt static foveation, in which the HMD gamer gaze position is assumed to be fixed at the viewport center. In this paper, we construct the very first cloud VR gaming system that supports dynamic foveation. That is, the real-time gaze positions of gamers are streamed from eye-trackers on HMDs to cloud servers, which in turn adjust the foveation parameters, such as foveal region size/location and peripheral region quality degradation, accordingly. Using our developed cloud VR gaming system, we design and carry out a user study using a game called Fruit Ninja VR 2 to find the foveation parameters in static and dynamic foveation for maximizing the gaming Quality of Experience (QoE) in Mean Opinion Score (MOS). With the chosen foveation parameters, we found that, compared to cloud VR gaming without foveation, static foveation leads to a MOS increase of 0.60 and a bitrate reduction of 8.71%. Furthermore, adopting dynamic foveation results in an additional 0.60 increase on MOS while saving 9.81% bitrate, compared to static foveation. Our findings demonstrate the potential of dynamic foveation in cloud VR gaming, which dictates both high visual quality and short response time. The optimization techniques developed in this and follow-up work could benefit other cloud-rendered applications that typically have less strict requirements than cloud VR gaming.