Volumetric video offers a highly immersive viewing experience, but poses challenges in ensuring quality of experience (QoE) due to its high bandwidth requirements. In this paper, we explore the effect of viewing distance introduced by six degrees of freedom (6DoF) spatial navigation on user's perceived quality. By considering human visual resolution limitations, we propose a visual acuity model that describes the relationship between the virtual viewing distance and the tolerable boundary point cloud density. The proposed model satisfies spatial visual requirements during 6DoF exploration. Additionally, it dynamically adjusts quality levels to balance perceptual quality and bandwidth consumption. Furthermore, we present a QoE model to represent user's perceived quality at different viewing distances precisely. Extensive experimental results demonstrate that, the proposed scheme can effectively improve the overall average QoE by up to 26% over real networks and user traces, compared to existing baselines.

翻译：体积视频提供了高度沉浸的观看体验，但由于其高带宽需求，在保障体验质量（QoE）方面面临挑战。本文探讨了六自由度（6DoF）空间导航中观看距离对用户感知质量的影响。通过考虑人类视觉分辨率的局限性，我们提出了一种视觉敏锐度模型，该模型描述了虚拟观看距离与可容忍边界点云密度之间的关系。该模型满足了6DoF探索过程中的空间视觉需求，同时能够动态调整质量等级以平衡感知质量与带宽消耗。此外，我们提出了一种QoE模型，用于精确表征用户在不同观看距离下的感知质量。大量实验结果表明，与现有基线方法相比，所提方案在实际网络和用户轨迹中能将总体平均QoE有效提升高达26%。