Hybrid action space, which combines discrete choices and continuous parameters, is prevalent in domains such as robot control and game AI. However, efficiently modeling and optimizing hybrid discrete-continuous action space remains a fundamental challenge, mainly due to limited policy expressiveness and poor scalability in high-dimensional settings. To address this challenge, we view the hybrid action space problem as a fully cooperative game and propose a Cooperative Hybrid Diffusion Policies (CHDP) framework to solve it. CHDP employs two cooperative agents that leverage a discrete and a continuous diffusion policy, respectively. The continuous policy is conditioned on the discrete action's representation, explicitly modeling the dependency between them. This cooperative design allows the diffusion policies to leverage their expressiveness to capture complex distributions in their respective action spaces. To mitigate the update conflicts arising from simultaneous policy updates in this cooperative setting, we employ a sequential update scheme that fosters co-adaptation. Moreover, to improve scalability when learning in high-dimensional discrete action space, we construct a codebook that embeds the action space into a low-dimensional latent space. This mapping enables the discrete policy to learn in a compact, structured space. Finally, we design a Q-function-based guidance mechanism to align the codebook's embeddings with the discrete policy's representation during training. On challenging hybrid action benchmarks, CHDP outperforms state-of-the-art method by up to 19.3% in success rate.

In order to support diverse applications in intelligent transportation, intelligent connected vehicles (ICVs) need to send multiple types of messages, such as periodic messages and event-driven messages with different frame specifications. However, existing researches often concentrate on the transmission of single-message types, overlooking hybrid communication scenarios where multiple types of messages coexist, posing challenges in meeting the diverse transmission needs of different message types. To optimize the Quality of Service (QoS) in such scenarios, we take the perspective of ICVs and formulate their decision making as a multi-agent reinforcement learning problem. More specifically, we propose a cooperative individual rewards assisted multi-agent reinforcement learning (CIRA) framework. The transformer structure in CIRA is used to avoid mutual interference during the transmission of different vehicles. Besides, the introduction of individual rewards and the dual-layer architecture of CIRA contribute to providing ICVs with more forward-looking message dissemination scheme. Finally, we set up a simulator to create dynamic traffic scenarios reflecting different real-world conditions. We conduct extensive experiments to evaluate the proposed CIRA framework’s performance. The results show that CIRA can significantly improve the packet reception rates and ensure low communication delays in various scenarios.