In this paper, we study the optimal wireless streaming of a multi-quality
tiled 360 virtual reality (VR) video from a multi-antenna server to multiple
single-antenna users in a multiple-input multiple-output (MIMO)-orthogonal
frequency division multiple access (OFDMA) system. In the scenario without user
transcoding, we jointly optimize beamforming and subcarrier, transmission
power, and rate allocation to minimize the total transmission power. This
problem is a challenging mixed discretecontinuous optimization problem. We
obtain a globally optimal solution for small multicast groups, an
asymptotically optimal solution for a large antenna array, and a suboptimal
solution for the general case. In the scenario with user transcoding, we
jointly optimize the quality level selection, beamforming, and subcarrier,
transmission power, and rate allocation to minimize the weighted sum of the
average total transmission power and the transcoding power. This problem is a
two-timescale mixed discrete-continuous optimization problem, which is even
more challenging than the problem for the scenario without user transcoding. We
obtain a globally optimal solution for small multicast groups, an
asymptotically optimal solution for a large antenna array, and a low-complexity
suboptimal solution for the general case. Finally, numerical results
demonstrate the significant gains of proposed solutions over the existing
solutions. significant gains of proposed solutions over the existing solutions.

本文研究了多输入多输出正交频分多址系统中从多天线服务器到多个单天线用户的多质量瓷砖 360 虚拟现实（VR）视频的最优无线传输。我们在无需用户转码的情况下共同优化波束成形和子载波、传输功率和速率分配以减少总传输功率，并获得了小组播放、大天线阵列和一般情况下的全局最优解、渐进最优解和次优解。在存在用户转码的情况下，我们共同优化了质量级别选择、波束成形和子载波、传输功率和速率分配，以最小化平均总传输功率和转码功率的加权和，获得了小组播放、大天线阵列和一般情况下的全局最优解、渐进最优解和低复杂度的次优解。最后，数值结果表明，所提出的解决方案的显著优于现有解决方案。