Time-Smooth Wireless Transmission of Probabilistic Slicing VR 360 Video in MISO-OFDM Systems

Abstract

The multiple-input and single-output (MISO)-orthogonal frequency-division multiplexing (OFDM) systems afford low latency and high reliability for virtual reality (VR) 360 video in multi-user scenarios. Motivated by the goal of maintaining time-smoothness while holding acceptably low complexity, a crucial factor in VR video transmission, we conduct a comprehensive study that integrates the characteristics of VR video with the strategies for subcarrier assignment and power allocation. By analyzing the pre-transmitted tile-segments, the missing tile-segments, and the video frame structure, we propose two probabilistic slicing schemes (PSPs) to minimize the size of required tile-segments of VR video scenes. In time-smoothness maximization, the desired discrete encoding rate set, discrete subcarrier assignment, continuous power allocation, and fixed total power constraint make it a challenging mixed-integer nonlinear programming (MINLP) problem. Unlike the straightforward relaxation-recovery method, we firstly prove that a near-optimal recovered encoding rate is the discrete value closest to the optimal relaxed-continuous encoding rate. We then propose a Two-step Encoding Rate Maximization (TERM) method, including the relaxed-continuous sum-rate maximization and the discrete encoding rate recovery, to achieve the near-optimal subcarrier assignment and the power allocation with low complexity. Simulation results on real-world VR video dataset validate that the two PSPs can effectively minimize the number of transmitted tile-segments. The proposed TERM with PSPs can maintain time-smoothness of VR 360 video with an acceptably low level of complexity in MISO-OFDM systems.