Cosmo: Contrastive Fusion Learning with Small Data for Multimodal Human Activity Recognition

Human activity recognition (HAR) is a key enabling technology for a wide range of emerging applications. Although multimodal sensing systems are essential for capturing complex and dynamic human activities in real-world settings, they bring several new challenges including limited labeled multimodal data. In this paper, we propose Cosmo, a new system for contrastive fusion learning with small data in multimodal HAR applications. Cosmo features a novel two-stage training strategy that leverages both unlabeled data on the cloud and limited labeled data on the edge. By integrating novel fusion-based contrastive learning and quality-guided attention mechanisms, Cosmo can effectively extract both consistent and complementary information across different modalities for efficient fusion. Our evaluation on a cloud-edge testbed using two public datasets and a new multimodal HAR dataset shows that Cosmo delivers significant improvement over state-of-the-art baselines in both recognition accuracy and convergence delay.