I. INTRODUCTION  
  
III. BACKGROUND: NARROWBAND AND COOPERATIVE SPECTRUM SENSING  
  
IV. NYQUIST MULTIBAND SPECTRUM SENSING  
  
V. COMPRESSIVE SUB-NYQUIST WIDEBAND SENSING  
  
VI. ALIAS-FREE-BASED SUB-NYQUIST WIDEBAND SPECTRUM SENSING  
  
VII. COMPARISON BETWEEN SUB-NYQUIST SPECTRUM SENSING ALGORITHMS  
  
VIII. CONCLUSIONS AND OPEN RESEARCH CHALLENGES