Paper Detail

Breaking the Structural Identity: Personalized Federated LoRA Fine-tuning under Rank Heterogeneity

Lei Wang, Jieming Bian, Letian Zhang, Jie Xu

arxiv Score 9.3

Published 2026-09-01 · First seen 2026-09-03

General AI

Abstract

Large Language Models (LLMs) have achieved remarkable success across diverse domains, but their adaptation to privacy-sensitive, distributed datasets remains a challenge. While Federated Learning (FL) combined with Low-Rank Adaptation (LoRA) provides a resource-efficient paradigm for collaborative fine-tuning, practical deployments are hindered by the dual challenges of resource heterogeneity and data heterogeneity. Existing rank-heterogeneous methods primarily focus on bridging dimension mismatches for aggregation but typically provide a unified global model for all clients sharing the same rank, failing to capture client-specific features in non-IID scenarios. In this paper, we propose FedRoRA (Federated Rank-wise Personalized LoRA), a novel framework that enables fine-grained personalization within rank-heterogeneous federations. FedRoRA decouples adaptation into shared global directions and personalized rank-wise magnitudes governed by learnable diagonal scales. On the server side, it extracts a global subspace via singular value decomposition (SVD) and redistributes client-specific initializations through a personalized projection and top-$k$ selection mechanism. Extensive experiments on NLU and NLG benchmarks demonstrate that FedRoRA consistently outperforms state-of-the-art methods.

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BibTeX

@article{wang2026breaking,
  title = {Breaking the Structural Identity: Personalized Federated LoRA Fine-tuning under Rank Heterogeneity},
  author = {Lei Wang and Jieming Bian and Letian Zhang and Jie Xu},
  year = {2026},
  abstract = {Large Language Models (LLMs) have achieved remarkable success across diverse domains, but their adaptation to privacy-sensitive, distributed datasets remains a challenge. While Federated Learning (FL) combined with Low-Rank Adaptation (LoRA) provides a resource-efficient paradigm for collaborative fine-tuning, practical deployments are hindered by the dual challenges of resource heterogeneity and data heterogeneity. Existing rank-heterogeneous methods primarily focus on bridging dimension mismat},
  url = {https://arxiv.org/abs/2609.00632},
  keywords = {cs.LG, cs.AI},
  eprint = {2609.00632},
  archiveprefix = {arXiv},
}

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