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# [MARC: Multipolicy and Risk-aware Contingency Planning for Autonomous Driving](https://arxiv.org/abs/2308.12021) | ||
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_June 2024_ | ||
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tl;dr: Generating safe and non-conservative behaviors in dense dynamic environment, by combining multipolicy decision making and contigency planning. | ||
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#### Overall impression | ||
This is a continuation of work in [MPDM](mpdm.md) and [EUDM](eudm.md). It introduces dynamic branching based on scene-level divergence, and risk-aware contingency planning based on user-defined risk tolerance. | ||
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POMDP provides a theoretically sounds framework to handle dynamic interaction, but it suffers from curse of dimensionality and making it infeasible to solve in realtime. | ||
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* [MPDM](mpdm.md) prunes belief trees heavily and decomposes POMDP into a limited number of closed-loop policy evaluations. MPDM has only one ego policy over planning horizon (8s). Mainly BP. | ||
* EUDM improves by having multiple (2) policy in planning horizon, and performs DCP-Tree and CFB (conditoned focused branching) to use domain specific knowledge to guide branching in both action and intention space. Mainly BP. | ||
* MARC performs risk-aware contigency planning based on multiple scenarios. And it combines BP and MP. | ||
* All previous MPDM-like methods consider the optimal policy and single trajectory generation over all scenarios, resulting in lack of gurantee of policy consistency and loss of multimodality info. | ||
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#### Key ideas | ||
- Planning is hard from uncertainty and interaction (inherently multimodal intentions). | ||
- For interactive decision making, MDP or POMDP are mathematically rigorous formulations for decision processes in stochastic environments. | ||
- For static (non-interactive) decision making, the normal trioka of planninig (sampling, searching, optimization) would suffice. | ||
- *Contigency planning* generates deterministic behavior for mulutiple future scenarios. In other words, it plans a short-term trajectory that ensures safety for all potential scenarios. | ||
- Scenario tree construction | ||
- generating policy-conditioned critical scenario sets via closed-loop forward simulation (similar to CFB in EUDM?). | ||
- building scenario tree with scene-level divergence assessment. Determine the latest timestamp at which the scenario diverge. Delaying branching time as much as possble. | ||
- State variables in trajectory optimization decreases | ||
- Smooth handling of different potential outcomes, more robust to disturbance (more mature driver-like). | ||
- Trajectory tree generation with RCP | ||
- RCP (risk-aware contingency planning) considers tradeoff beween conservativeness and efficiency. | ||
- RCP generates trajectories that are optimal in multiple future scenarios under user-defined risk-averse levels. --> This can mimic human preference. | ||
- Evalution | ||
- Selection based on both policy tree and trajectory tree (new!), ensuring consistency of policies | ||
- MARC are more robust under uncertain interactions and fewer unexpected policy switches | ||
- can handle cut-in with smoother decel, and can handle disturbance (prediciton noise, etc) | ||
- with better effiency (avg speed) and riding comfort (max decel/acc). | ||
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#### Technical details | ||
- Summary of technical details, such as important training details, or bugs of previous benchmarks. | ||
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#### Notes | ||
- Questions and notes on how to improve/revise the current work | ||
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