# Optimal Multi-Quality Multicast for 360 Virtual Reality Video

## TL;DR

This paper develops optimized algorithms for multi-quality multicast transmission of 360 VR videos, enhancing efficiency by joint quality, time, and power allocation under network constraints.

## Contribution

It introduces two low-complexity algorithms for joint optimization of quality, time, and power in multi-quality VR video multicast, addressing a complex mixed discrete-continuous problem.

## Key findings

- Proposed algorithms outperform baseline methods in simulation.
- Joint optimization improves overall user utility.
- Algorithms effectively handle quality smoothness constraints.

## 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 opti-mization 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.