Optimal Multi-Quality Multicast for 360 Virtual Reality Video

Abstract

A 360 virtual reality (VR) video, recording a scene of interest in every direction, provides VR users with immersive viewing experience. However, transmission of a 360 VR video which is of a much larger size than a traditional video to mobile users brings a heavy burden to a wireless network. In this paper, we consider multi-quality multicast of a 360 VR video from a single server to multiple users using time division multiple access (TDMA). To improve transmission efficiency, tiling is adopted, and each tile is pre-encoded into multiple representations with different qualities. We optimize the quality level selection, transmission time allocation and transmission power allocation to maximize the total utility of all users under the transmission time and power allocation constraints as well as the quality smoothness constraints for mixed-quality tiles. The problem is a challenging mixed discrete-continuous optimization problem. We propose two low-complexity algorithms to obtain two suboptimal solutions, using continuous relaxation and DC programming, respectively. Finally, numerical results demonstrate the advantage of the proposed solutions.Index Terms-virtual reality, 360 video, multi-quality multicast, convex optimization, difference of convex programming.

Optimal Transmission of Multi-Quality Tiled 360 VR Video by Exploiting Multicast Opportunities

“…In our previous work [9], we study the optimal quality level selection to maximize the total utility of all users under communications resource constraints and quality smoothness constraints for adjacent tiles. In contrast with [8], in [9] we partition the set of tiles to be transmitted into subsets with different subsets for different user groups, and consider the optimization with respect to the subsets of tiles to effectively reduce computational complexity. Note that [8], [9] neglect the fact that channel conditions of users change much faster than their FoVs.…”

“…In contrast with [8], in [9] we partition the set of tiles to be transmitted into subsets with different subsets for different user groups, and consider the optimization with respect to the subsets of tiles to effectively reduce computational complexity. Note that [8], [9] neglect the fact that channel conditions of users change much faster than their FoVs. Hence, the proposed single timescale solutions in [8], [9] may not yield desired performance in practical systems.…”

“…In this paper, we would like to investigate fundamental impacts of multicast opportunities on efficient transmission of a multi-quality tiled 360 VR video to multiple users in the cases with and without transcoding at each user. In contrast with [8], [9], we ensure that all tiles in a user's FoV are played at the same quality, and we consider the practical scenario where users' channel conditions and FoVs change at two timescales. First, we introduce an elegant notation system for partitioning all tiles into subsets, each for a particular group of users, and specifying the relation between a subset of tiles and their target user group.…”

Vantage

“…Prioritization in multimedia. Several previous works have developed transport protocols [17] and application-specific optimizations (e.g., 360-video [13,20,28,29]) which prioritize multimedia to improve quality. Vantage uses a similar technique (of selective prioritization) to prioritize real-time frames over retransmissions.…”

Power-Efficient Wireless Streaming of Multi-Quality Tiled 360 VR Video in MIMO-OFDMA Systems

“…Nevertheless, the obtained quality levels of adjacent tiles may vary significantly, leading to poor viewing experiences [15]- [17]. In [18], the authors impose some constraints on quality variation while maximizing the total utility of all users to address this issue. Although the restrictions on quality variation in [18] can alleviate quality variation in an FoV to a certain extent, they cannot guarantee quality smoothness and are less mathematically tractable.…”