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This position paper explores the challenges and opportunities for high-quality immersive volumetric video streaming for multiple users over millimeter-wave (mmWave) WLANs. While most of the previous work has focused on single-user streaming, there is a growing need for multi-user immersive applications such as virtual collaboration, classroom education, teleconferencing, etc. While mmWave wireless links can provide multi-gigabit per second data rates, they suffer from blockages and high beamforming overhead. This paper investigates an environment-driven approach to address the challenges. It presents a comprehensive research agenda that includes developing a collaborative 3D scene reconstruction process, material identification, ray tracing, blockage mitigation, and cross-layer multi-user video rate adaptation. Our preliminary results show the feasibility and identify the limitations of existing solutions. Finally, we discuss the open challenges of implementing a practical system based on the proposed research agenda. 

Striking a balance between minimizing bandwidth consumption and maintaining high visual quality stands as the paramount objective in volumetric content delivery. However, achieving this ambitious target is a substantial challenge, especially for mobile devices with constrained computational resources, given the voluminous amount of 3D data to be streamed, strict latency requirements, and high computational load. Inspired by the advantages offered by neural radiance fields (NeRF), we propose, for the first time, to deliver volumetric videos by utilizing neural-based content representations. We delve deep into potential challenges and explore viable solutions for both video-on-demand (VOD) and live video streaming services, in terms of the end-to-end pipeline, real-time and high-quality streaming, rate adaptation, and viewport adaptation. Our preliminary results lend credence to the feasibility of our research proposition, offering a promising starting point for further investigation. 

While recent work explored streaming volumetric content on-demand, there is little effort on live volumetric video streaming that bears the potential of bringing more exciting applications than its on-demand counterpart. To fill this critical gap, in this paper, we propose MetaStream, which is, to the best of our knowledge, the first practical live volumetric content capture, creation, delivery, and rendering system for immersive applications such as virtual, augmented, and mixed reality. To address the key challenge of the stringent latency requirement for processing and streaming a huge amount of 3D data, MetaStream integrates several innovations into a holistic system, including dynamic camera calibration, edge-assisted object segmentation, cross-camera redundant point removal, and foveated volumetric content rendering. We implement a prototype of MetaStream using commodity devices and extensively evaluate its performance. Our results demonstrate that MetaStream achieves low-latency live volumetric video streaming at close to 30 frames per second on WiFi networks. Compared to state-of-the-art systems, MetaStream reduces end-to-end latency by up to 31.7% while improving visual quality by up to 12.5%.