diff --git a/README.md b/README.md
index 09fa996..e4db81e 100644
--- a/README.md
+++ b/README.md
@@ -50,3 +50,11 @@ ros2 bag play -s rosbag_v2 test.bag
 ![demo](./images/demo_ekfl.gif)    
 blue:initial pose, red:gnss pose, green: fusion pose
 
+## references
+
+- K Feng,"A New Quaternion-Based Kalman Filter",2017
+- Joan Solà,"Quaternion kinematics for the error-state Kalman filter",2017
+- Daniel Choukroun et al,"A Novel Quaternion Kalman Filter",2006
+- An Improved EKF - The Error State Extended Kalman Filter
+- Weikun Zhen, Sam Zeng, and Sebastian Scherer. "Robust Localization and Localizability Estimation with a Rotating Laser Scanner" , 2017.
+