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Time-FFM: Towards LM-Empowered Federated Foundation Model for Time Series Forecasting
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Time-FFM builds a federated foundation model for time series forecasting by mapping time series to text-prototype tokens, adaptively selecting prompts from the LM's embeddings, and personalizing prediction heads over a frozen GPT-2 backbone.
Problem
Building foundation models for time series forecasting is hampered by data scarcity and privacy/copyright constraints on sharing cross-domain data, while existing LM-based time series models are centralized and need domain-specific parameters.
Approach
Combines cross-modality adaptation of a frozen GPT-2 (patch-based modality alignment plus attention-selected text-prototype prompts) with personalized federated training that shares encoder parameters globally and keeps prediction heads local.
Key results
- Time-FFM achieves average MSE 0.555 and MAE 0.434 over all forecasting windows, best among federated baselines (FedIT average 0.910) and better than UniTime (0.559 MSE), with 8 of 8 dataset-level best in TY1.
- In 5% few-shot forecasting, Time-FFM reports ~20% lower average MSE than UniTime (0.329 vs 0.411).
- In zero-shot forecasting (trained on ETTh1/ETTm1/ETTm2), Time-FFM average MSE is 0.310 vs 0.360 for the second-best FL method (FedIT).
Measured effects reported in the paper
| What was changed | Where | Measured | Effect |
|---|---|---|---|
| Use Time-FFM instead of the strongest listed baseline | Time-FFM · ETTh1 | MSE: 0.442 vs 0.440 | Mixed |
| Use Time-FFM instead of the strongest listed baseline | Time-FFM · ETTh2 | MSE: 0.382 vs 0.373 | Hurt |
| Use Time-FFM instead of the strongest listed baseline | Time-FFM · ETTm1 | MSE: 0.399 vs 0.383 | Hurt |
| Use Time-FFM instead of the strongest listed baseline | Time-FFM · ETTm2 | MSE: 0.286 vs 0.291 | Helped |
| Use Time-FFM instead of the strongest listed baseline | Time-FFM · Electricity | MSE: 0.216 vs 0.193 | Hurt |
| Use Time-FFM instead of the strongest listed baseline | Time-FFM · Weather | MSE: 0.270 vs 0.253 | Hurt |
| Use Time-FFM instead of the strongest listed baseline | Time-FFM · Exchange | MSE: 0.338 vs 0.354 | Helped |
| Use Time-FFM instead of the strongest listed baseline | Time-FFM · ILI | MSE: 2.107 vs 2.137 | Helped |
| add prompt adaption (ablation) | Time-FFM · ETTh1-336 | MSE: 0.495 -> 0.480 | Helped |
| replace manually written instructions with adaptive prompts (ablation) | Time-FFM · ETTh1-336 | MSE: 0.487 -> 0.480 | Helped |
| add personalized prediction heads (ablation) | Time-FFM · ETTh1-336 | MSE: 0.537 -> 0.480 | Helped |
| add federated aggregation to share common temporal knowledge (ablation) | Time-FFM · ETTh1-336 | MSE: 0.499 -> 0.480 | Helped |
Surprising findings
- Freezing the GPT-2 backbone performs comparably to full fine-tuning in the ablation, suggesting the modality alignment does most of the work.
- For all methods except UniTime, 10% few-shot results are worse than 5% few-shot results, which the authors attribute to frozen or partially tuned LMs retaining reasoning capability.
Limitations
- Training time is higher than the federated fine-tuning baselines (TY1).
- Performance is suboptimal in some cases compared with centralized methods.
- The modality alignment strategy and the correspondence between patch and word embeddings are not fully explored.
Experimental setup
Datasets: ETTh1 ETTh2 ETTm1 ETTm2 Electricity Weather Exchange ILI
Benchmarks: ETTh1 ETTh2 ETTm1 ETTm2 Electricity Weather Exchange ILI
Metrics: MSE MAE
Baselines: FedIT FedAdapter-H FedAdapter-P FedLoRA UniTime GPT4TS PatchTST TimesNet DLinear FEDformer Autoformer Informer
Builds on: UniTime GPT4TS PatchTST FedIT FedAdapter
Closest papers by meaning
- Federated Foundation Models on Heterogeneous Time Series (AAAI 2025 · similarity 0.90)
- Time-LLM: Time Series Forecasting by Reprogramming Large Language Models (ICLR 2024 · similarity 0.90)
- AutoTimes: Autoregressive Time Series Forecasters via Large Language Models (NeurIPS 2024 · similarity 0.88)
- $S^2$IP-LLM: Semantic Space Informed Prompt Learning with LLM for Time Series Forecasting (ICML 2024 · similarity 0.88)
- TimeCAP: Learning to Contextualize, Augment, and Predict Time Series Events with Large Language Model Agents (AAAI 2025 · similarity 0.87)
- TimeCMA: Towards LLM-Empowered Multivariate Time Series Forecasting via Cross-Modality Alignment (AAAI 2025 · similarity 0.87)
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