Multi-Source Collaborative Contrastive Learning for Decentralized Domain Adaptation

Unsupervised multi-source domain adaptation aims to obtain a model working well on the unlabeled target domain by reducing the domain gap between the labeled source domains and the unlabeled target domain. Considering the data privacy and storage cost, data from multiple source domains and target domain are isolated and decentralized. This data decentralization scenario brings the difficulty of domain alignment for reducing the domain gap between the decentralized source domains and target domain, respectively. For conducting domain alignment under the data decentralization scenario, we propose Multi-source Collaborative Contrastive learning for decentralized Domain Adaptation (MCC-DA). The models from other domains are used as the bridge to reduce the domain gap. On the source domains and target domain, we penalize the inconsistency of data features extracted from the source domain models and target domain model by contrastive alignment. With the collaboration of source domain models and target domain model, the domain gap between decentralized source domains and target domain is reduced without accessing the data from other domains. The experiment results on multiple benchmarks indicate that our method can reduce the domain gap effectively and outperform the state-of-the-art methods significantly.