One-Shot Federated Learning with Classifier-Guided Diffusion Models

One-shot federated learning (OSFL) has gained attention in recent years due to its low communication cost. However, most of the existing methods require auxiliary datasets or training generators, which hinders their practicality in real-world scenarios. In this paper, we explore the novel opportunities that diffusion models bring to OSFL and propose FedCADO, utilizing guidance from client classifiers to generate data that complies with clients' distributions and subsequently training the aggregated model on the server. Specifically, our method involves targeted optimizations in two aspects. On one hand, we conditionally edit the randomly sampled initial noises, embedding them with specified semantics and distributions, resulting in a significant improvement in both the quality and stability of generation. On the other hand, we employ the BN statistics from the classifiers to provide detailed guidance during generation. These tailored optimizations enable us to limitlessly generate datasets, which closely resemble the distribution and quality of the original client dataset. Our method effectively handles the heterogeneous client models and the problems of non-IID features or labels. In terms of privacy protection, our method avoids training any generator or transferring any auxiliary information on clients, eliminating any additional privacy leakage risks. Leveraging the extensive knowledge stored in the pre-trained diffusion model, the synthetic datasets can assist us in surpassing the knowledge limitations of the client samples, resulting in aggregation models that even outperform the performance ceiling of centralized training in some cases, which is convincingly demonstrated in the sufficient quantification and visualization experiments conducted on three large-scale multi-domain image datasets.

Exploring One-shot Semi-supervised Federated Learning with A Pre-trained Diffusion Model

Federated learning is a privacy-preserving collaborative learning approach. Recently, some studies have proposed the semi-supervised federated learning setting to handle the commonly seen real-world scenarios with labeled data on the server and unlabeled data on the clients. However, existing methods still face challenges such as high communication costs, training pressure on the client devices, and distribution differences among the server and the clients. In this paper, we introduce the powerful pre-trained diffusion models into federated learning and propose FedDISC, a Federated Diffusion Inspired Semi-supervised Co-training method, to address these challenges. Specifically, we first extract prototypes from the labeled data on the server and send them to the clients. The clients then use these prototypes to predict pseudo-labels of the local data, and compute the cluster centroids and domain-specific features to represent their personalized distributions. After adding noise, the clients send these features and their corresponding pseudo-labels back to the server, which uses a pre-trained diffusion model to conditionally generate pseudo-samples complying with the client distributions and train an aggregated model on them. Our method does not require local training and only involves forward inference on the clients. Our extensive experiments on DomainNet, Openimage, and NICO++ demonstrate that the proposed FedDISC method effectively addresses the one-shot semi-supervised problem on Non-IID clients and outperforms the compared SOTA methods. We also demonstrate through visualization that it is of neglectable possibility for FedDISC to leak privacy-sensitive information of the clients.

Cross-domain Federated Adaptive Prompt Tuning for CLIP

Federated learning (FL) allows multiple parties to collaboratively train a global model without disclosing their data. Existing research often requires all model parameters to participate in the training procedure. However, with the advent of powerful pre-trained models, it becomes possible to achieve higher performance with fewer learnable parameters in FL. In this paper, we propose a federated adaptive prompt tuning algorithm, FedAPT, for cross-domain federated image classification scenarios with the vision-language pre-trained model, CLIP, which gives play to the strong representation ability in FL. Compared with direct federated prompt tuning, our core idea is to adaptively unlock specific domain knowledge for each test sample in order to provide them with personalized prompts. To implement this idea, we design an adaptive prompt tuning module, which consists of a global prompt, an adaptive network, and some keys. The server randomly generates a set of keys and assigns a unique key to each client. Then all clients cooperatively train the global adaptive network and global prompt with the local datasets and the frozen keys. Ultimately, the global aggregation model can assign a personalized prompt to CLIP based on the domain features of each test sample. We perform extensive experiments on two multi-domain image classification datasets. The results show that FedAPT can achieve better performance with less than 10\% of the number of parameters of the fully trained model, and the global model can perform well in different client domains simultaneously.

Cross-domain Federated Object Detection

Detection models trained by one party (server) may face severe performance degradation when distributed to other users (clients). For example, in autonomous driving scenarios, different driving environments may bring obvious domain shifts, which lead to biases in model predictions. Federated learning that has emerged in recent years can enable multi-party collaborative training without leaking client data. In this paper, we focus on a special cross-domain scenario where the server contains large-scale data and multiple clients only contain a small amount of data; meanwhile, there exist differences in data distributions among the clients. In this case, traditional federated learning techniques cannot take into account the learning of both the global knowledge of all participants and the personalized knowledge of a specific client. To make up for this limitation, we propose a cross-domain federated object detection framework, named FedOD. In order to learn both the global knowledge and the personalized knowledge in different domains, the proposed framework first performs the federated training to obtain a public global aggregated model through multi-teacher distillation, and sends the aggregated model back to each client for finetuning its personalized local model. After very few rounds of communication, on each client we can perform weighted ensemble inference on the public global model and the personalized local model. With the ensemble, the generalization performance of the client-side model can outperform a single model with the same parameter scale. We establish a federated object detection dataset which has significant background differences and instance differences based on multiple public autonomous driving datasets, and then conduct extensive experiments on the dataset. The experimental results validate the effectiveness of the proposed method.