Discussions on the access control mechanisms for WLAN NG

1. Discussions on the access control mechanisms for WLAN NG Yasuhiko Inoue, Satoru Hori, Tetsu Sakata and Masahiro Morikura NTT Access Network Service Systems Laboratories mailto:yinoue@ansl.ntt.co.jp Y.Inoue, NTT

2. HDR more than 100M bit/s • Our initial analysis shows that it is difficult to achieve data rate of 100M bit/s with 20MHz (02/159r1) • Combination with new techniques • MIMO, Link aggregation • Increase the bandwidth for a channel • High efficiency is required for MAC protocol • Access control mechanism • TDMA based • CSMA based • Additional functions topic of this presentation Y.Inoue, NTT

3. ISP AP AP Scenario • Multi-cell environment • Example: • hotspot, flat, etc. • may experience sever interference • Single-cell environment • Example: • SOHO, etc • no need to consider interference Interference C o f f e e AP same channel same channel Y.Inoue, NTT

4. Multi-cell environment • Channel selection: • may not be always done ideally • Problem: co-channel interference degrades throughput • To avoid interference: • Channel separation: • Prepare enough number of channels to satisfy C/I requirement. • Channel sharing: • Share the same frequency channel with other areas AP AP AP AP AP AP AP AP AP AP AP AP AP AP AP AP Y.Inoue, NTT

5. f2 f2 f2 f2 f2 f7 f7 f7 f7 f7 f3 f3 f3 f3 f3 f1 f2 f3 f4 f5 f6 f7 f1 f1 f1 f1 f1 f6 f6 f6 f6 f6 f4 f4 f4 f4 f4 f5 f5 f5 f5 f5 Freq. Channel separation • Channel separation: • Basically the same idea as cellular systems. • Prepare enough number of channels to satisfy C/I requirement when the channel is reused. • Problem: Do we have enough bandwidth? Example of 7 channels Y.Inoue, NTT

6. Channel sharing • Channel sharing: • Basically the same idea as current 802.11. • Share the same channel with other area autonomously. • Problem: Hidden terminal problem. • Other mechanism something like CDMA also be considered. Y.Inoue, NTT

7. TDMA Based Access Protocol • Channel separation: • C/I requirements: • have an effect on the radius of a service area (BSA) • determines necessary number of the channels for stable operation • Channel sharing: • mechanism for channel sharing will be required. • Problem: • Autonomous synchronization of the time frame between APs • Autonomous scheduling for transmission between APs, etc. TDMA based protocol will work well if enough number of channels are available Y.Inoue, NTT

8. CSMA Based Access Mechanism • Channel separation: • The effect of hidden terminal problem will greatly decreased. • Channel sharing: • CSMA based protocol basically provides this mechanism • Problem: • Hidden terminals causes throughput degradation • RTS/CTS procedure may not enough to prevent inter-cell interference CSMA based protocol can be adopted for both scenarios Y.Inoue, NTT

9. TDMA TDMA TDMA CSMA CSMA time Coexistence with legacy systems in UNII band • TDMA based protocol • Additional mechanism will be required for coexistence. • High efficiency of the new protocol may not be seen as far as coexisting with the legacy system. • CSMA based protocol • Good solution considering coexistence. • Backward compatibility will be achieved. • CDMA may be used with this mechanism. Y.Inoue, NTT

10. Summary • TDMA based access control: • High efficiency • Needs a number of channels to satisfy C/I requirement. • CSMA based access control: • Good channel sharing mechanism if hidden terminal problem is avoided. • flexible configuration • lower efficiency than TDMA based mechanism, but it can be improved by additional mechanism. CSMA based protocol will be a better solution for WLAN NG Y.Inoue, NTT