RoFi: Rotation-Aware WiFi Channel Feedback

Multiple-input multiple-output (MIMO) provides high throughput for WiFi networks, but it also leads to high overhead due to channel state information (CSI) feedback. Based on experiment measurements, this paper shows that MIMO has different feedback requirements when the receiver is rotating compared with when the receiver is in other mobility scenarios. Experiments of four popular Android games show that device rotation accounts for around 50% of the running time for these games, which implies that rotation-awareness could improve WiFi efficiency significantly for these games. We propose rotation-aware WiFi (RoFi) channel feedback to eliminate unnecessary CSI feedback while maintaining high throughput. We show the failure of existing mobility-aware methods, including CSI similarity, time-of-flight (ToF), and compression noise, in distinguishing the mobility status of rotation and mobile. RoFi calculates power delay profile (PDP) similarity for rotation detection and performs feedback compression and rate selection accordingly. To deal with false rotation detection and status transition between rotation and static, RoFi uses the power of the strongest path, which is calculated from PDP, to further refine CSI feedback when necessary. The RoFi design is compatible with legacy 802.11 protocols and is easy to be deployed on existing WiFi systems. Evaluation results show that RoFi reduces 25%-40% overhead with negligible signal-to-noise ratio decrease in rotation scenarios. RoFi also consumes 29%-69% less energy compared with state-of-the-art feedback compression and rate selection algorithms.