Bi-level Heterogeneous Learning for Time Series Foundation Models: A Federated Learning Approach
Organizations: Australian AI Institute, University of Technology Sydney · Robotics Institute, University of Technology Sydney
Abstract
Heterogeneity in time series data is more pronounced than in vision or language, as temporal dynamics vary substantially across domains and tasks. Existing efforts on training time series foundation models (TSFMs) from scratch are often trained with mixed-batch strategies that merge large-scale datasets, which can cause gradient conflicts and degrade representation quality. To address this, we propose a fine-grained learning method that distills invariant knowledge from heterogeneous series while reducing cross-domain interference. We characterize heterogeneity at two levels: inter-domain and intra-domain. To tackle this bi-level heterogeneity, we design a federated learning method that mitigates intra-domain conflicts by enforcing domain-invariant and semantically consistent representations through local regularization, and addresses inter-domain discrepancies by enhancing cross-domain collaboration via domain-aware aggregation. Experiments across diverse benchmarks show that TSFMs trained with our method consistently outperform both centralized and federated TSFM baselines in point and probabilistic forecasting, while also achieving competitive zero-shot performance at scale, offering a flexible pathway for training TSFMs from scratch in heterogeneous environments.
Figures & tables
| Ours | Federated Self-supervised † | Federated FMs | Centralized | |||||||||||||
| Methods | FedTRL | SimMTM | PatchTST | TimeMAE | CoST | FFTS | FedAvg | All Mixed | ||||||||
| Metric | MSE | MAE | MSE | MAE | MSE | MAE | MSE | MAE | MSE | MAE | MSE | MAE | MSE | MAE | MSE | MAE |
| ETTh1 | 0.448 | 0.472 | 0.495 | 0.512 | 0.478 | 0.495 | 0.502 | 0.518 | 0.521 | 0.540 | 0.463 | 0.485 | 0.476 | 0.495 | 0.458 | 0.488 |
| ETTh2 | 0.382 | 0.414 | 0.442 | 0.468 | 0.410 | 0.432 | 0.455 | 0.474 | 0.471 | 0.490 | 0.395 | 0.419 | 0.410 | 0.433 | 0.399 | 0.424 |
| ETTm1 | 0.375 | 0.402 | 0.415 | 0.439 | 0.386 | 0.408 | 0.421 | 0.444 | 0.436 | 0.455 | 0.380 | 0.406 | 0.399 | 0.406 | 0.372 | 0.398 |
| ETTm2 | 0.278 | 0.330 | 0.324 | 0.352 | 0.296 | 0.340 | 0.330 | 0.360 | 0.345 | 0.369 | 0.290 | 0.338 | 0.299 | 0.341 | 0.286 | 0.336 |
| Models | FedTRL | TimeMixer | TimeXer | iTransformer | PatchTST | TimesNet | DLinear | Autoformer | Stationary | LightTS | ||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Metrics | MSE | MAE | MSE | MAE | MSE | MAE | MSE | MAE | MSE | MAE | MSE | MAE | MSE | MAE | MSE | MAE | MSE | MAE | MSE | MAE |
| ETTh1 | 0.372 | 0.399 | 0.448 | 0.443 | 0.491 | 0.489 | 0.474 | 0.476 | 0.413 | 0.430 | 0.458 | 0.450 | 0.422 | 0.437 | 0.496 | 0.487 | 0.570 | 0.537 | 0.491 | 0.479 |
| ETTh2 | 0.330 | 0.383 | 0.364 | 0.394 | 0.356 | 0.398 | 0.372 | 0.411 | 0.330 | 0.379 | 0.414 | 0.427 | 0.431 | 0.446 | 0.450 | 0.459 | 0.526 | 0.516 | 0.602 | 0.543 |
| ETTm1 | 0.316 | 0.369 | 0.381 | 0.395 | 0.381 | 0.402 | 0.368 | 0.396 | 0.351 | 0.380 | 0.400 | 0.406 | 0.357 | 0.378 | 0.588 | 0.517 | 0.481 | 0.456 | 0.435 | 0.437 |
| ETTm2 | 0.257 | 0.313 | 0.275 | 0.323 | 0.275 | 0.329 | 0.271 | 0.331 | 0.255 | 0.315 | 0.291 | 0.333 | 0.267 | 0.333 | 0.327 | 0.371 | 0.306 | 0.347 | 0.409 | 0.436 |
| Electricity | 0.143 | 0.247 | 0.175 | 0.272 | 0.171 | 0.273 | 0.161 | 0.256 | 0.161 | 0.252 | 0.192 | 0.295 | 0.188 | 0.295 | 0.227 | 0.338 | 0.193 | 0.296 | 0.229 | 0.329 |
| Models | FedTRL | Time-MoE b | Time-MoE l | Time-MoE u | Moirai s | Moirai b | Moirai l | TimesFM | Moment | Chronos s | Chronos b | Chronos l | ||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Metrics | MSE | MAE | MSE | MAE | MSE | MAE | MSE | MAE | MSE | MAE | MSE | MAE | MSE | MAE | MSE | MAE | MSE | MAE | MSE | MAE | MSE | MAE | MSE | MAE |
| ETTh1 | 0.399 | 0.420 | 0.400 | 0.424 | 0.394 | 0.419 | 0.412 | 0.426 | 0.428 | 0.427 | 0.417 | 0.419 | 0.480 | 0.439 | 0.473 | 0.443 | 0.683 | 0.566 | 0.545 | 0.472 | 0.591 | 0.468 | 0.588 | 0.466 |
| ETTh2 | 0.350 | 0.380 | 0.366 | 0.404 | 0.405 | 0.415 | 0.371 | 0.399 | 0.361 | 0.384 | 0.362 | 0.382 | 0.367 | 0.377 | 0.392 | 0.406 | 0.361 | 0.409 | 0.424 | 0.430 | 0.405 | 0.410 | 0.455 | 0.427 |
| ETTm1 | 0.349 | 0.383 | 0.394 | 0.415 | 0.376 | 0.405 | 0.356 | 0.391 | 0.436 | 0.410 | 0.406 | 0.385 | 0.422 | 0.391 | 0.433 | 0.418 | 0.670 | 0.536 | 0.640 | 0.499 | 0.645 | 0.500 | 0.555 | 0.465 |
| ETTm2 | 0.282 | 0.330 | 0.317 | 0.365 | 0.316 | 0.361 | 0.288 | 0.344 | 0.307 | 0.347 | 0.311 | 0.337 | 0.329 | 0.343 | 0.328 | 0.346 | 0.316 | 0.365 | 0.349 | 0.380 | 0.310 | 0.350 | 0.295 | 0.338 |
| Weather | 0.238 | 0.279 | 0.265 | 0.297 | 0.270 | 0.300 | 0.270 | 0.300 | 0.275 | 0.286 | 0.287 | 0.281 | 0.264 | 0.273 | – | – | 0.294 | 0.326 | 0.300 | 0.318 | 0.292 | 0.315 | 0.279 | 0.306 |
| Type | Statistical Methods | Supervised Task-Specific Models | Zero-Shot Models | Zero-Shot Models (FL) | ||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Model | Naïve | Seasonal | Auto | Auto | DeepAR | TiDE | N-BEATS | PTST. | iTrans. | TimesFM | TabPFN | Chronos | Moirai | FedAvg | FFTS | FedTRL |
| Naïve | ARIMA | Theta | (Ours) | |||||||||||||
| MASE | 1.260 | 1.000 | 0.964 | 0.978 | 1.206 | 0.980 | 0.842 | 0.762 | 0.802 | 0.680 | 0.748 | 0.786 | 0.809 | 0.872 | 0.766 | 0.675 |
| CRPS | 1.383 | 1.000 | 0.770 | 1.051 | 0.721 | 0.652 | 0.689 | 0.496 | 0.524 | 0.465 | 0.480 | 0.551 | 0.515 | 0.700 | 0.521 | 0.460 |
| Rank | 28.072 | 26.175 | 21.515 | 24.031 | 18.938 | 18.557 | 21.381 | 10.052 | 11.320 | 8.237 | 8.268 | 14.309 | 10.175 | 18.231 | 9.787 | 8.676 |
| Tasks | In-domain | Full-shot | Zero-shot | ||||
|---|---|---|---|---|---|---|---|
| Variants | MSE | MAE | MSE | MAE | MSE | MAE | |
| ETTh1 | FedTRL | 0.448 | 0.472 | 0.372 | 0.399 | 0.399 | 0.420 |
| w/o GRL | 0.464 | 0.486 | 0.377 | 0.400 | 0.407 | 0.435 | |
| w/o Proto | 0.458 | 0.482 | 0.382 | 0.410 | 0.417 | 0.432 | |
| w/o DaG | 0.472 | 0.494 | 0.394 | 0.421 | 0.436 | 0.459 | |
| ETTm1 | FedTRL | 0.375 | 0.402 | 0.316 | 0.369 | 0.350 | 0.380 |
| Model | ETTh1 | ETTm1 | Weather | Traffic | ||||
|---|---|---|---|---|---|---|---|---|
| MSE | MAE | MSE | MAE | MSE | MAE | MSE | MAE | |
| SimMTM † | 0.495 | 0.512 | 0.415 | 0.439 | 0.285 | 0.310 | 0.472 | 0.315 |
| + FedTRL | 0.476 | 0.501 | 0.401 | 0.430 | 0.263 | 0.301 | 0.459 | 0.305 |
| Improvement (%) | 3.84 | 2.15 | 3.37 | 2.05 | 7.88 | 2.48 | 2.82 | 3.13 |
| PatchTST † | 0.478 | 0.495 | 0.386 | 0.408 | 0.260 | 0.295 | 0.438 | 0.295 |
| + FedTRL | 0.461 | 0.487 | 0.378 | 0.404 | 0.252 | 0.288 | 0.430 | 0.291 |
Appendix figures & tables20 assets
Supplementary material from the paper’s appendix.
Appendix
| Dataset | Domain | # Channels | Frequency | Size | Forecast Length | SE † | ACF † | Proxy † |
|---|---|---|---|---|---|---|---|---|
| ETTh1 | Power | 7 | Hourly | (8545, 2881, 2881) | 0.523 | 20.372 | 0.857 | |
| ETTh2 | Power | 7 | Hourly | (8545, 2881, 2881) | 0.652 | 35.940 | 0.943 | |
| ETTm1 | Power | 7 | 15 Minute | (34465, 11521, 11521) | 0.580 | 24.335 | 0.949 | |
| ETTm2 | Power | 7 | 15 Minute | (34465, 11521, 11521) | 0.696 | 40.276 | 0.978 | |
| Electricity | Energy | 321 | Hourly | (17805, 2537, 5166) | 0.706 | 12.137 | 0.814 | |
| Traffic | Transportation | 862 | Hourly | (11673, 1661, 3413) | 0.567 | 6.977 | 0.681 |
| Dataset | Region | # Channels | Frequency | Size | Forecast Length | SE † | ACF † | Proxy † |
|---|---|---|---|---|---|---|---|---|
| RW-1 | Yuzhno-Sakhalinsk | 10 | Hourly | January 2022 - August 2025 | 0.438 | 17.089 | 0.682 | |
| RW-2 | Tokyo | 10 | Hourly | January 2022 - August 2025 | 0.438 | 17.090 | 0.682 | |
| RW-3 | Beijing | 10 | Hourly | January 2022 - August 2025 | 0.431 | 16.660 | 0.711 | |
| RW-4 | Mumbai/Santacruz | 10 | Hourly | January 2022 - August 2025 | 0.398 | 16.474 | 0.706 | |
| RW-5 | Ho Chi Minh City | 10 | Hourly | January 2022 - August 2025 | 0.462 | 17.292 | 0.768 | |
| RW-6 | Cairo | 10 | Hourly | January 2022 - August 2025 | 0.456 | 16.912 | 0.734 |
| Category | Configuration | Configuration |
|---|---|---|
| (In-domain Forecasting) | (Large Foundation Model) | |
| Optimizer | Adam | Adam |
| Batch Size | 128 | 2048 |
| Local Epochs | 10 | 100 |
| Global Rounds | 200 | 10,000 |
| Learning Rate (Local Updating) | 0.0001 | 0.0005 |
| Method | FedTRL | Time-MoE | Moirai | MOMENT | LLMTime | Chronos | Lag-Llama | TimesFM |
|---|---|---|---|---|---|---|---|---|
| (Ours) | ( 2024 ) | ( 2024 ) | ( 2024 ) | ( 2024 ) | ( 2024 ) | ( 2023 ) | ( 2023b ) | |
| Architecture | Encoder | Decoder | Encoder | Encoder | Decoder | EncDec | Decoder | Decoder |
| Model Size | 113M | 14M | 40M | 46M | 17M | |||
| 302M | 453M | 91M | 125M | – | 200M | 200M | 70M | |
| 2.4B | 311M | 385M | 710M | 200M | ||||
| Pre-training Scale | 300B | 300B | 231B | 1.13B | – | 84B | 0.36B | 100B |
| Dataset | FedTRL | FFTS | FedAvg | FedProx | FedPer | FedRep | pFedMe |
|---|---|---|---|---|---|---|---|
| ETT-h1 | 0.448 | 0.463 | 0.476 | 0.477 | 0.492 | 0.482 | 0.499 |
| ETT-m1 | 0.375 | 0.380 | 0.399 | 0.395 | 0.405 | 0.401 | 0.414 |
| Weather | 0.241 | 0.252 | 0.264 | 0.262 | 0.281 | 0.280 | 0.287 |
| Ours | Federated Unsupervised † | Federated FMs | Centralized | ||||||||||||||
| Methods | FedTRL | SimMTM | PatchTST | TimeMAE | CoST | FFTS | FedAvg | All Mixed | |||||||||
| Metric | MSE | MAE | MSE | MAE | MSE | MAE | MSE | MAE | MSE | MAE | MSE | MAE | MSE | MAE | MSE | MAE | |
| ETTh1 | 96 | 0.367 | 0.441 | 0.399 | 0.477 | 0.391 | 0.462 | 0.410 | 0.485 | 0.414 | 0.498 | 0.387 | 0.456 | 0.393 | 0.462 | 0.372 | 0.454 |
| 192 | 0.433 | 0.464 | 0.466 | 0.503 | 0.449 | 0.482 | 0.476 | 0.507 | 0.500 | 0.531 | 0.444 | 0.481 | 0.454 | 0.490 | 0.437 | 0.478 | |
| 336 | 0.467 | 0.482 | 0.519 | 0.523 | 0.504 | 0.508 | 0.531 | 0.530 | 0.550 | 0.555 | 0.479 | 0.491 | 0.495 | 0.502 | 0.485 | 0.500 | |
| 720 | 0.525 | 0.501 | 0.595 | 0.546 | 0.569 | 0.528 | 0.591 | 0.549 | 0.620 | 0.576 | 0.542 | 0.511 | 0.562 | 0.527 | 0.539 | 0.520 | |
| Models | Ours | Pretrained Time Series Foundation Models (Zero-shot) | |||||||||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| FedTRL | Time-MoE base | Time-MoE large | Time-MoE ultra | Moirai small | Moirai base | Moirai large | TimesFM | Moment | Chronos small | Chronos base | Chronos large | ||||||||||||||
| Metrics | MSE | MAE | MSE | MAE | MSE | MAE | MSE | MAE | MSE | MAE | MSE | MAE | MSE | MAE | MSE | MAE | MSE | MAE | MSE | MAE | MSE | MAE | MSE | MAE | |
| ETTh1 | 96 | 0.346 | 0.381 | 0.357 | 0.381 | 0.350 | 0.382 | 0.349 | 0.379 | 0.401 | 0.402 | 0.376 | 0.392 | 0.349 | 0.379 | 0.414 | 0.404 | 0.688 | 0.557 | 0.466 | 0.409 | 0.440 | 0.393 | 0.441 | 0.390 |
| 192 | 0.386 | 0.407 | 0.384 | 0.404 | 0.388 | 0.412 | 0.395 | 0.413 | 0.388 | 0.412 | 0.412 | 0.413 | 0.434 | 0.415 | 0.465 | 0.434 | 0.688 | 0.560 | 0.530 | 0.450 | 0.492 | 0.426 | 0.502 | 0.424 | |
| 336 | 0.420 | 0.443 | 0.411 | 0.434 | 0.411 | 0.430 | 0.447 | 0.453 | 0.433 | 0.428 | 0.433 | 0.428 | 0.495 | 0.445 | 0.503 | 0.456 | 0.675 | 0.563 | 0.570 | 0.486 | 0.550 | 0.462 | 0.576 | 0.467 | |
| 720 | 0.444 | 0.449 | 0.449 | 0.477 | 0.427 | 0.455 | 0.457 | 0.462 | 0.439 | 0.454 | 0.447 | 0.444 | 0.611 | 0.510 | 0.511 | 0.481 | 0.683 | 0.585 | 0.615 | 0.543 | 0.882 | 0.591 | 0.835 | 0.583 | |
| Models | Ours | Pretrained Time Series Foundation Models (Zero-shot) | |||||||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| FedTRL | Time-MoE base | Time-MoE large | Moirai small | Moirai base | Moirai large | TimesFM | Moment | Chronos small | Chronos base | Chronos large | |||||||||||||
| Metrics | MSE | MAE | MSE | MAE | MSE | MAE | MSE | MAE | MSE | MAE | MSE | MAE | MSE | MAE | MSE | MAE | MSE | MAE | MSE | MAE | MSE | MAE | |
| RW1 | 96 | 0.508 | 0.453 | 0.510 | 0.460 | 0.505 | 0.455 | 0.885 | 0.547 | 0.879 | 0.529 | 0.986 | 0.530 | 0.883 | 0.703 | 0.674 | 0.594 | 0.850 | 0.581 | 0.879 | 0.589 | 0.873 | 0.583 |
| 192 | 0.528 | 0.473 | 0.540 | 0.492 | 0.532 | 0.485 | 0.950 | 0.569 | 0.896 | 0.546 | 1.011 | 0.548 | 0.903 | 0.711 | 0.717 | 0.600 | 0.917 | 0.620 | 0.979 | 0.634 | 0.950 | 0.623 | |
| 336 | 0.546 | 0.488 | 0.566 | 0.519 | 0.556 | 0.505 | 1.148 | 0.588 | 0.813 | 0.552 | 0.868 | 0.560 | 0.889 | 0.708 | 0.913 | 0.700 | 0.957 | 0.649 | 1.047 | 0.667 | 0.973 | 0.646 | |
| 720 | 0.552 | 0.497 | 0.643 | 0.580 | 0.568 | 0.519 | 1.869 | 0.667 | 0.958 | 0.602 | 1.259 | 0.625 | 0.877 | 0.705 | 1.740 | 1.019 | 1.089 | 0.708 | 1.142 | 0.715 | 1.012 | 0.687 | |
| Dataset/Model | FedTRL (Ours) | VisionTS | Sundial (94B) | Sundial (230B) | Sundial (1032B) |
|---|---|---|---|---|---|
| ETTh1 | 0.399 | 0.412 | 0.402 | 0.403 | 0.411 |
| ETTh2 | 0.350 | 0.365 | 0.377 | 0.364 | 0.333 |
| ETTm1 | 0.349 | 0.391 | 0.367 | 0.352 | 0.336 |
| ETTm2 | 0.282 | 0.296 | 0.280 | 0.273 | 0.258 |
| Weather | 0.238 | 0.303 | 0.254 | 0.252 | 0.234 |
| Count | 5 | 0 | 0 | 0 | 0 |
| Patch Size | Context Length | Prediction Length | Layers | Dimension | Heads | Total Parameters |
|---|---|---|---|---|---|---|
| 12 | M | |||||
| 16 | M | |||||
| 24 | M |
| Task / Report | Datasets / Metric | Pretraining Datasets Scale (Billion) | |||||
|---|---|---|---|---|---|---|---|
| 90B | 120B | 180B | 300B (Original) | 450B | 540B | ||
| Full-shot Forecasting | |||||||
| MSE Report | ETTh1 | 0.401 | 0.387 | 0.372 | 0.371 | 0.363 | 0.363 |
| ETTm1 | 0.343 | 0.336 | 0.328 | 0.316 | 0.312 | 0.310 | |
| Weather | 0.232 | 0.231 | 0.227 | 0.214 | 0.204 | 0.202 | |
| Zero-shot Point Forecasting | |||||||
| Method | ETTh1 | ETTm1 | Traffic | Weather |
|---|---|---|---|---|
| FedAvg | 0.511 | 0.433 | 0.488 | 0.295 |
| FFTS | 0.492 | 0.421 | 0.479 | 0.290 |
| Centralized All Mixed | 0.498 | 0.427 | 0.483 | 0.290 |
| FedTRL (Original) | 0.448 | 0.375 | 0.426 | 0.241 |
| FedTRL (Ours) | 0.472 | 0.411 | 0.477 | 0.282 |
| Method | ETTh1 | ETTm1 | Weather |
|---|---|---|---|
| FedAvg | 0.438 | 0.384 | 0.292 |
| FFTS | 0.427 | 0.380 | 0.282 |
| Centralized All Mixed | 0.431 | 0.382 | 0.288 |
| FedTRL (Original) | 0.399 | 0.349 | 0.238 |
| FedTRL | 0.418 ( 4.76%) | 0.366 ( 4.87%) | 0.269 ( 13.03%) |
| Method | Inter-domain Centroid Distance ( ) | Within-domain Variance ( ) |
|---|---|---|
| All Mixed (Centralized) | 1.08 | 0.91 |
| FedAvg | 1.06 | 0.85 |
| FFTS | 1.34 | 0.69 |
| FedTRL (Ours) | 1.27 | 0.53 |
| Method | Avg. Gradient Cosine Similarity ( ) | Gradient Norm Variance ( ) |
|---|---|---|
| All Mixed (Centralized) | 0.23 | 0.021 |
| FedAvg | 0.33 | 0.015 |
| FFTS | 0.37 | 0.013 |
| FedTRL (Ours) | 0.43 | 0.010 |
| Task Type / Dataset (Metric) | Method | Inter-domain Imbalance Level | ||
|---|---|---|---|---|
| Balanced (Simulated) | Mildly Imbalanced (Simulated) | Real Skew (Original Pretraining) | ||
| In-domain Forecasting (MSE on Weather) | All Mixed (Centralized) | 0.235 | 0.248 | 0.254 |
| FedAvg | 0.231 | 0.248 | 0.264 | |
| FFTS | 0.224 | 0.235 | 0.252 | |
| FedTRL (Ours) | 0.216 | 0.230 | 0.241 | |
| Full-shot Forecasting (MSE on Weather) | All Mixed (Centralized) | 0.227 | 0.235 | 0.238 |
Time-Series Foundation Models
Time-series foundation models are pretrained sequence models designed to transfer across forecasting, classification, anomaly detection, and other temporal tasks.
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