1. INTRODUCTION

2. DATA ANALYSIS FOR HAR  
2.1 Visual-based System  
2.2 Non Visual-based System  

3. MULTIMODAL HUMAN ACTIVITY RECOGNITION  
3.1 Inter Multimodal HAR Approach  
3.2 Intra Multimodal HAR Approach  

4. CHALLENGES IN MULTIMODAL WEARABLE HAR SYSTEM  
4.1 Multimodal Dataset Challenge  
4.2 Heterogeneous Feature Alignment Challenge  
4.3 Model Deployment Challenge  

5. FUTURE RESEARCH DIRECTION  
5.1 Future Activity Prediction  
5.2 Identifying Unknown Activities  
5.3 New Foundation Models  
5.4 Unified Multimodal Systems  
5.5 Concurrent Activity Segmentation  
5.6 Personalization and Privacy  

6. CONCLUSION