I. Introduction  
II. Overview of IEEE 802.11n and IEEE 802.11ac Enhancements  
IV. Impact of One New Feature of IEEE 802.11n/ac  
V. Impact of Two New Features of IEEE 802.11n/ac  
VI. Impact of Three Enhanced Features of IEEE 802.11n/ac  
VII. Impact of All New Features of IEEE 802.11n/ac  
VIII. Works that Considered Impact of Only IEEE 802.11ac Related Works  
IX. Future Research Directions on the Design of IEEE 802.11n Based Networks  
X. Future Research Directions for IEEE 802.11ac Networks  
XI. General Research Challenges: Directions for Future HT-WLAN Developments  
XII. Conclusion  