360Cast+: Viewport Adaptive Soft Delivery for 360-Degree Videos

The existing viewport-adaptive 360-degree video streaming schemes encode tiled 360-degree videos with digital-based compression. However, these schemes cause a cliff effect wherein the headset video quality drops when the channel signal-to-noise ratio (SNR) falls below a certain threshold. To realize high-quality wireless 360-degree video streaming, we propose a novel viewport-adaptive soft delivery scheme for 360-degree videos, called 360Cast+. 360Cast+ skips the non-linear operations in digital-based streaming and adopts power allocation and analog modulation to achieve graceful video quality improvement in unstable wireless links. In particular, 360Cast+ integrates the human vision system (HVS) and projection distortion as a perceptual weight in power allocation operations. A near-optimal low-complexity subcarrier matching algorithm was also adopted to extend 360Cast+ to fading channel environments. To reduce the effect of the prediction error, 360Cast+ uses dynamic linear regression (DLR) to predict the future orientation and future prediction error to extract the extension area around a viewport. The evaluation results demonstrated that the proposed 360Cast+ provides sophisticated video quality irrespective of the prediction error and channel conditions in orthogonal frequency-division multiplexing (OFDM)-based systems.