I. INTRODUCTION  
A. LoRa Surveys  
B. Motivation and Contributions  
C. Paper Organization  

II. SYSTEM MODEL AND CSS SCHEMES CATEGORIZATION  
A. System Model  
B. CSS Schemes Taxonomy  
C. CSS-based Schemes for LPWANs  
D. Design Methodologies  
E. Detection Principles  

III. CSS-BASED PHY LAYER WAVEFORM DESIGN AND DETECTION PRINCIPLES  
A. Single Carrier CSS Schemes  
B. Multiple Carrier CSS Schemes  
C. Multiple Carrier with Index Modulation CSS Schemes  

IV. PERFORMANCE ANALYSIS  
A. Spectral Efficiency Analysis  
B. Spectral Efficiency vs Energy Efficiency Performance  
C. Bit-Error Rate Performance  
D. Bit-Error Performance considering Phase Offset  
E. Bit-Error Performance considering Frequency Offset  
F. General Summary  

V. MERITS AND LIMITATIONS OF DIFFERENT WAVEFORM DESIGNS  
A. Important Characteristics for Waveform Design  
B. Analysis of Characteristics for Different Waveform Design  
C. Takeaways  
D. Analysis of Characteristics for CSS Schemes  

VII. CONCLUSIONS