以DiffusionDriveV2为例，解析自动驾驶中强化学习的使用

Core Viewpoint - The rapid development of large models has propelled reinforcement learning (RL) to unprecedented prominence, becoming an essential part of post-training in the autonomous driving sector. The shift to end-to-end (E2E) learning necessitates the use of RL to address challenges that imitation learning cannot solve, such as the centering problem in driving behavior [1]. Understanding Reinforcement Learning Algorithms in Autonomous Driving - Proximal Policy Optimization (PPO) and Generalized Recurrent Policy Optimization (GRPO) are currently the most prevalent algorithms in the field. The article emphasizes the importance of understanding reward optimization through classic algorithms [2]. PPO and GRPO Algorithm Insights - The classic PPO algorithm, particularly the PPO CLIP variant, is discussed with a focus on its application in autonomous driving. The formula for the algorithm is provided, highlighting the interaction between the system and the environment over multiple steps [3]. - The evaluation of actions in trajectory generation is based on overall trajectory quality rather than individual points, which is crucial for effective RL training [3]. RL Loss and DiffusionDriveV2 Architecture - The RL loss function is composed of three parts: anchor design, group design from GRPO, and the denoising process of diffusion. Each component plays a critical role in trajectory generation and optimization [9]. - The denoising process is framed as a Markov Decision Process (MDP), where each denoising step represents a decision-making step within the MDP framework [10]. Intra-Anchor and Inter-Anchor GRPO - Intra-Anchor GRPO modifies the group concept to ensure that each anchor has its own group, which is essential for distinguishing different driving behaviors. This prevents the dominance of straight driving data over other behaviors [12]. - Inter-Anchor GRPO addresses the risk of lacking global constraints between different anchors, optimizing the advantage calculation further [13]. Additional Improvements - The article discusses improvements such as trajectory noise management and the introduction of a model selector, which are crucial for ensuring the reliability and effectiveness of the RL approach in autonomous driving [15]. Conclusion - The article uses DiffusionDriveV2 to elucidate the application of reinforcement learning in autonomous driving, indicating that the current state of RL in this field is still evolving. The expectation is for advancements in closed-loop simulation and deeper applications of RL [15].