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Unified Uncertainty-Aware Diffusion for Multi-Agent Trajectory Modeling
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Proposes U2Diff, a unified diffusion model for multi-agent trajectory completion that jointly predicts state-wise uncertainty via an NLL loss augmentation and ranks sampled modes with a supervised RankNN to estimate per-mode error probabilities.
Problem
Multi-agent trajectory modeling has focused on forecasting, lacking unified trajectory completion, state-wise uncertainty estimates, and per-mode error probabilities for ranking multi-modal samples under the same prior.
Approach
Augment the DDPM denoising loss with the Gaussian negative log-likelihood of the predicted noise to learn per-state variance, propagate latent variance to state space during DDIM sampling, and add a Rank Neural Network (RankNN) that outputs softmax error probabilities over K sampled scene modes, trained with a differentiable Spearman correlation objective.
Key results
- On trajectory completion, U2Diff reduces minADE20 on Football-U from 3.55 (UniTraj) to 2.42 and on Soccer-U from 94.59 to 53.93, and gives about 27% better minSADE20 on Basketball-U.
- On NBA forecasting, U2Diff achieves minSADE20 1.48 vs 1.63 for LED, over 9% better in scene-level metric.
- RankNN achieves median Spearman correlation with SADE of 0.58 (NBA), 0.78 (Soccer-U) range, versus 0.25-0.35 for AvgUcty on the NBA and other datasets.
Measured effects reported in the paper
| What was changed | Where | Measured | Effect |
|---|---|---|---|
| add loss augmentation (λ > 0) (ablation) | U2Diff · Basketball-U | minADE20[60]: 4.68 -> 4.65 | Helped |
| add loss augmentation (λ > 0) (ablation) | U2Diff · Football-U | minADE20[60]: 2.53 -> 2.42 | Helped |
| add loss augmentation (λ > 0) (ablation) | U2Diff · Soccer-U | minADE20[60]: 54.41 -> 53.93 | Helped |
| add loss augmentation (λ > 0) (ablation) | U2Diff · Basketball-U | minSADE20: 3.10 -> 3.13 | Hurt |
| add loss augmentation (λ > 0) (ablation) | U2Diff · Football-U | minSADE20: 2.37 -> 2.35 | Helped |
| add loss augmentation (λ > 0) (ablation) | U2Diff · Soccer-U | minSADE20: 51.27 -> 51.14 | Helped |
| add loss augmentation (λ > 0) (ablation) | U2Diff · NBA | minADE20: 0.86 -> 0.85 | Helped |
| add loss augmentation (λ > 0) (ablation) | U2Diff · NBA | minFDE20: 1.11 -> 1.11 | No clear effect |
| add loss augmentation (λ > 0) (ablation) | U2Diff · NBA | minSADE20: 1.50 -> 1.48 | Helped |
| add loss augmentation (λ > 0) (ablation) | U2Diff · NBA | minSFDE20: 2.70 -> 2.68 | Helped |
| use RankNN error-probability ranking instead of AvgUcty ranking | U2Diff · Basketball-U | Spearman correlation with SADE: 0.27 / 0.29 -> 0.56 / 0.63 | Helped |
| use RankNN error-probability ranking instead of AvgUcty ranking | U2Diff · Football-U | Spearman correlation with SADE: 0.28 / 0.31 -> 0.59 / 0.65 | Helped |
Surprising findings
- Omitting the NLL loss augmentation (lambda=0) does not degrade minSADE20 performance, though it helps minADE20 under the UniTraj metric.
- Variance propagation works best when started at an intermediate denoising step (30 of 50) rather than from the first step.
Limitations
- NBA long-horizon forecasting shows lower AccRate and higher NLL, indicating weaker uncertainty calibration over long horizons.
- Basketball-U with five or more fully unseen agents is more challenging, with slightly lower AccRate.
- Covariance across state dimensions is approximated as null during variance propagation to avoid cost and instability.
Experimental setup
Datasets: NBA SportVU Basketball-U Football-U Soccer-U
Benchmarks: Basketball-U Football-U Soccer-U NBA
Metrics: minADE20 minFDE20 minSADE20 minSFDE20 AccRate NLL Spearman correlation minSADEk
Baselines: UniTraj LED AutoBots GroupNet MID SSSD GC-VRNN Naomi
Builds on: DDPM DDIM CSDI Mamba UniTraj
Closest papers by meaning
- Sports-Traj: A Unified Trajectory Generation Model for Multi-Agent Movement in Sports (ICLR 2025 · similarity 0.87)
- Improving Transferability for Cross-Domain Trajectory Prediction via Neural Stochastic Differential Equation (AAAI 2024 · similarity 0.86)
- Proper Scoring Rules for Agentic Uncertainty Quantification (NeurIPS 2026 · similarity 0.86)
- Event2Tracking: Reconstructing Multi-Agent Soccer Trajectories Using Long-Term Multimodal Context (AAAI 2025 · similarity 0.86)
- C2F-TP: A Coarse-to-Fine Denoising Framework for Uncertainty-Aware Trajectory Prediction (AAAI 2025 · similarity 0.86)
- SingularTrajectory: Universal Trajectory Predictor Using Diffusion Model (CVPR 2024 · similarity 0.86)
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