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Adaptive Gradient Clipping for Robust Federated Learning
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Proposes ARC, an adaptive pre-aggregation gradient clipping rule for Byzantine-robust distributed/federated SGD that clips a number of largest gradients tied to f/n, and proves improved error bounds under heterogeneity near the breakdown point.
Problem
Robust federated/distributed learning with Byzantine workers under data heterogeneity, where static pre-aggregation gradient clipping gives inconsistent robustness across heterogeneity levels and attacks.
Approach
Replace static clipping thresholds with an adaptive threshold chosen so that a fixed fraction lambda = zeta*f/n of input gradients (the largest ones) is clipped, guaranteeing at least one honest unclipped vector among any n-f subset; combined with NNM and robust aggregators, this yields provably better error under (G,B)-gradient dissimilarity near the breakdown point.
Key results
- ARC with NNM outperforms vanilla Robust-DSGD on MNIST under extreme heterogeneity with one Byzantine worker among 10 honest workers, with ARC matching Byzantine-free DSGD under good initialization.
- No single static clipping threshold among {0.02, 0.2, 2, 20} performs consistently well across heterogeneity levels and attacks, whereas ARC adapts without tuning.
- Theorem 5.2 shows ARC yields a strictly better learning error bound than the lower bound for (G,B)-gradient dissimilarity when f/n approaches the breakdown point and initial honest gradients are bounded.
Measured effects reported in the paper
| What was changed | Where | Measured | Effect |
|---|---|---|---|
| Add ARC to Robust-DSGD with good initialization (μ=1) | Robust-DSGD · MNIST, extreme heterogeneity, α = 0.1, f = 1 | accuracy | Helped |
| Degrade initialization from μ=1 toward μ=5 while using ARC-enhanced Robust-DSGD (ablation) | ARC-enhanced Robust-DSGD · MNIST, extreme heterogeneity, α = 0.1, f = 1 | accuracy | Hurt |
| Add ARC to Robust-DSGD with poor initialization (μ=5) | Robust-DSGD · MNIST, extreme heterogeneity, α = 0.1, f = 1 | accuracy | No clear effect |
| Use ARC instead of static clipping thresholds C = 0.2 or C = 0.02 | Robust-DSGD · MNIST, moderate heterogeneity (Dirichlet α = 1) | performance | Helped |
| Use ARC instead of static clipping thresholds C = 2 or C = 20 | Robust-DSGD · MNIST, moderate heterogeneity (Dirichlet α = 1) | performance | No clear effect |
| Vary the static clipping threshold across C ∈ {0.02, 0.2, 2, 20} (ablation) | Robust-DSGD with static clipping · MNIST, different heterogeneity levels and Byzantine attacks | robust performance | Mixed |
| Use ARC instead of static clipping across the tested settings | Robust-DSGD · MNIST, different heterogeneity levels and Byzantine attacks | robust performance | Helped |
| Set ARC parameter ζ to 2 (ablation) | ARC · Experiments across tested settings | performance | Helped |
| Add ARC to Robust-DSGD | Robust-DSGD · Fashion-MNIST and CIFAR-10, tested settings | performance | Helped |
Surprising findings
- ARC's advantage over vanilla Robust-DSGD diminishes with worse model initialization, though it still matches vanilla performance at the worst tested initialization.
Limitations
- Experiments limited to small-scale setups (10-17 workers) and simple datasets (MNIST, Fashion-MNIST, CIFAR-10); larger-scale results promised but not in the text.
- Theoretical improvement shown only in regime where f/n is close to the breakdown point and requires bounded honest gradients at initialization.
- Linear dependence on model dimension d and additional cost compared to simple aggregators.
Experimental setup
Datasets: MNIST Fashion-MNIST CIFAR-10
Benchmarks: MNIST Fashion-MNIST CIFAR-10
Metrics: test accuracy
Baselines: static gradient clipping vanilla Robust-DSGD Byzantine-free DSGD NNM
Builds on: Robust-DGD nearest neighbor mixing Robust-DSGD Byzantine-robust learning under heterogeneity (Allouah et al.)
Closest papers by meaning
- Byzantine-Robust Federated Learning: Impact of Client Subsampling and Local Updates (ICML 2024 · similarity 0.86)
- Byzantine Robustness and Partial Participation Can Be Achieved at Once: Just Clip Gradient Differences (NeurIPS 2024 · similarity 0.85)
- CLIP-Guided Federated Learning on Heterogeneity and Long-Tailed Data (AAAI 2024 · similarity 0.85)
- From Inexact Gradients to Byzantine Robustness: Acceleration and Optimization under Similarity (NeurIPS 2026 · similarity 0.85)
- To Clip or not to Clip: the Dynamics of SGD with Gradient Clipping in High-Dimensions (ICLR 2025 · similarity 0.85)
- How Does the Smoothness Approximation Method Facilitate Generalization for Federated Adversarial Learning? (AAAI 2025 · similarity 0.84)
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