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TraXion: Rethinking Pre-training Frameworks for Mobility and Beyond
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Proposes TraXion, a pre-training framework for multi-entity spatiotemporal event streams (MESES) combining a noise-detection objective, an entity-prototype contrastive objective, and a factorized transformer with a co-occurrence axis, evaluated on six mobility datasets, LANL auth logs, and eICU mortality.
Problem
Existing pre-training recipes for mobility and event streams import language-modeling objectives (next-token, masked-token) that ignore tuple-valued events, persistent entity signatures, and cross-entity co-occurrence structure.
Approach
Three axioms (joint-attribute density, entity-coupled representation, shared context) motivate a pre-training recipe pairing context/time perturbation detection with an InfoNCE loss on learned entity prototypes that also serve as input tokens, on a backbone with an added co-occurrence attention axis.
Key results
- Visit-level anomaly AP on NUMOSIM-LA reaches .2512 (TraXion) and .6020 agent-level (TraXion w/o co-occurrence) vs. best baseline ICAD .0283 visit-level and .0329 agent-level.
- Social link AP on Foursquare-Tokyo .9354 vs. strongest baseline H3GNN .9138, tops 8 of 9 columns.
- On LANL, TraXion w/o co-occurrence reaches event-level AP .0315 vs. LogBERT .0076 and AUROC .9402 vs. .8861.
Surprising findings
- Generic causal and masked-token pre-training (C4, C5) fall below no pre-training on LANL log AD and next-visit T±60.
- Removing the co-occurrence sub-layer at fine-tune improves several tasks (UA-Berlin/Atlanta, NUMOSIM agent-level, next-visit), so the co-occurrence axis is not uniformly beneficial.
Limitations
- Discriminative only; trails on next-visit time prediction (T±60) against TPP-style and Mobility-LLM baselines.
- Co-occurrence sub-layer is chosen per dataset on validation rather than learned.
- One checkpoint per dataset rather than a unified multi-instance MESES backbone.
Experimental setup
Datasets: NUMOSIM-LA Urban Anomalies Berlin Urban Anomalies Atlanta Foursquare-Tokyo Gowalla-Stockholm Gowalla-Austin LANL unified host-and-network authentication log PhysioNet eICU-CRD demo
Benchmarks: NUMOSIM-LA Urban Anomalies Berlin Urban Anomalies Atlanta Foursquare-Tokyo Gowalla-Stockholm Gowalla-Austin LANL eICU-CRD demo
Metrics: AP Max F1 AUROC Sens@Sp.9 H@10 H@20 MRR T±60
Baselines: CoBAD DeepBayesic USTAD ICAD UniTraj GETNext LoTNext MobTCast COAST TAPT TrajGPT Mobility-LLM
Builds on: ELECTRA InfoNCE Space2Vec Time2Vec UniTraj
Closest papers by meaning
- RHYTHM: Reasoning with Hierarchical Temporal Tokenization for Human Mobility (NeurIPS 2025 · similarity 0.85)
- Taming the Long Tail in Human Mobility Prediction (NeurIPS 2024 · similarity 0.84)
- Spatial-Temporal Interplay in Human Mobility: A Hierarchical Reinforcement Learning Approach with Hypergraph Representation (AAAI 2024 · similarity 0.83)
- Large Language Models as Urban Residents: An LLM Agent Framework for Personal Mobility Generation (NeurIPS 2024 · similarity 0.83)
- UniMTS: Unified Pre-training for Motion Time Series (NeurIPS 2024 · similarity 0.82)
- Correlation-Attention Masked Temporal Transformer for User Identity Linkage Using Heterogeneous Mobility Data (AAAI 2025 · similarity 0.82)
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