Bidirectional Buffer-Constrained Bitrate Adaptation for Layered 360-degree Video Streaming

By cutting the 360-degree video into temporal chunks and spacial tiles of different quality levels, layered 360-degree video streaming enables fine-grained bitrate adaptation. A critical challenge is whether to transmit the expected viewport at a higher quality level or pre-fetch the low-rate base layer while avoiding buffer overflow or rebuffering, given the fluctuated and constrained fronthaul bandwidth. In this work, we investigate this interplay to provision better quality of experience (QoE) while guaranteeing the smoothness of 360-degree video streaming. Specifically, an optimization problem is formulated to maximize the expected video quality under a bidirectional constraint on the long-term average buffer. To address this problem, we propose the Lyapunov Stable Point Optimization(LSPO), which is a Lyapunov optimization variant. LSPO achieves a near-optimal time-averaged QoE within an O(1/V )margin, while also upholding bidirectional buffer constraints. A buffer-based algorithm is then proposed and evaluated based on real-trace data. The results demonstrate superior performance in video quality and reduced rebuffering probability compared to existing algorithms.