Downlink Precoding for Cell-free FBMC/OQAM Systems With Asynchronous Reception

In this work, an efficient precoding design scheme is proposed for downlink cell-free distributed massive multiple-input multiple-output (DM-MIMO) filter bank multi-carrier (FBMC) systems with asynchronous reception and highly frequency selectivity. The proposed scheme includes a multiple interpolation structure to eliminate the impact of response difference we recently discovered, which has better performance in highly frequency-selective channels. Besides, we also consider the phase shift in asynchronous reception and introduce a phase compensation in the design process. The phase compensation also benefits from the multiple interpolation structure and better adapts to asynchronous reception. Based on the proposed scheme, we theoretically analyze its ergodic achievable rate performance and derive a closed-form expression. Simulation results show that the derived expression can accurately characterize the rate performance, and FBMC with the proposed scheme outperforms orthogonal frequency-division multiplexing (OFDM) in the asynchronous scenario.Comment: 16pages, 4 figure

Color-Perception-Guided Display Power Reduction for Virtual Reality

Battery life is an increasingly urgent challenge for today's untethered VR and AR devices. However, the power efficiency of head-mounted displays is naturally at odds with growing computational requirements driven by better resolution, refresh rate, and dynamic ranges, all of which reduce the sustained usage time of untethered AR/VR devices. For instance, the Oculus Quest 2, under a fully-charged battery, can sustain only 2 to 3 hours of operation time. Prior display power reduction techniques mostly target smartphone displays. Directly applying smartphone display power reduction techniques, however, degrades the visual perception in AR/VR with noticeable artifacts. For instance, the "power-saving mode" on smartphones uniformly lowers the pixel luminance across the display and, as a result, presents an overall darkened visual perception to users if directly applied to VR content. Our key insight is that VR display power reduction must be cognizant of the gaze-contingent nature of high field-of-view VR displays. To that end, we present a gaze-contingent system that, without degrading luminance, minimizes the display power consumption while preserving high visual fidelity when users actively view immersive video sequences. This is enabled by constructing a gaze-contingent color discrimination model through psychophysical studies, and a display power model (with respect to pixel color) through real-device measurements. Critically, due to the careful design decisions made in constructing the two models, our algorithm is cast as a constrained optimization problem with a closed-form solution, which can be implemented as a real-time, image-space shader. We evaluate our system using a series of psychophysical studies and large-scale analyses on natural images. Experiment results show that our system reduces the display power by as much as 24% with little to no perceptual fidelity degradation