Hi @urczf ,
As you can see in the study pointed by @Katherine_Scott , Fast DDS is the best implementation in terms of latency, when you setup for sync publishing.
Until now, ROS2 has the requirement to be Async, and Fast DDS is configured that way for ROS2. CycloneDDS does not support this mode, and it is just sync, which favors a better latency.
See here for more information: RMW Fast DDS Publication Mode: Sync vs Async and how to change it
I think your study should take this into account.