  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.
