  Recent works have shown the potential of diffusion models in computer vision
and natural language processing. Apart from the classical supervised learning
fields, diffusion models have also shown strong competitiveness in
reinforcement learning (RL) by formulating decision-making as sequential
generation. However, incorporating temporal information of sequential data and
utilizing it to guide diffusion models to perform better generation is still an
open challenge. In this paper, we take one step forward to investigate
controllable generation with temporal conditions that are refined from temporal
information. We observe the importance of temporal conditions in sequential
generation in sufficient explorative scenarios and provide a comprehensive
discussion and comparison of different temporal conditions. Based on the
observations, we propose an effective temporally-conditional diffusion model
coined Temporally-Composable Diffuser (TCD), which extracts temporal
information from interaction sequences and explicitly guides generation with
temporal conditions. Specifically, we separate the sequences into three parts
according to time expansion and identify historical, immediate, and prospective
conditions accordingly. Each condition preserves non-overlapping temporal
information of sequences, enabling more controllable generation when we jointly
use them to guide the diffuser. Finally, we conduct extensive experiments and
analysis to reveal the favorable applicability of TCD in offline RL tasks,
where our method reaches or matches the best performance compared with prior
SOTA baselines.
