RCMixer: Radar-camera fusion based on vision transformer for robust object detection

In real-world object detection applications, the camera would be affected by poor lighting conditions, resulting in a deteriorate performance. Millimeter-wave radar and camera have complementary advantages, radar point cloud can help detecting small objects under low light. In this study, we focus on feature-level fusion and propose a novel end-to-end detection network RCMixer. RCMixer mainly includes depth pillar expansion(DPE), hierarchical vision transformer and radar spatial attention (RSA) module. DPE enhances radar projection image according to perspective principle and invariance assumption of adjacent depth; The hierarchical vision transformer backbone alternates the feature extraction of spatial dimension and channel dimension; RSA extracts the radar attention, then it fuses radar and camera features at the late stage. The experiment results on nuScenes dataset show that the accuracy of RCMixer exceeds all comparison networks and its detection ability of small objects in dark light is better than the camera-only method. In addition, the ablation study demonstrates the effectiveness of our method.