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.11g and .11b Collision Avoidance

Explore a bandwidth-efficient proposal to tackle collisions between 11g and 11b Wi-Fi devices, optimizing system throughput. This approach introduces an OFDM Contention Period within the CFP, eliminating the need for RTS/CTS exchanges and improving network efficiency.

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.11g and .11b Collision Avoidance

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  1. .11g and .11b Collision Avoidance Olaf Hirsch*, Atul Garg*, Sunghyun Choi+, Brian de Bart*, and Paul Gruijters* *Philips Semiconductors and +Philips Research Olaf Hirsch, et al., Philips

  2. Assumptions • .11g and .11b STAs co-exist in a BSS. • BSS Basic Rate set is equal to or a subset of .11b DSSS/CCK rates. Olaf Hirsch, et al., Philips

  3. Collision Avoidance of OFDM and CCK • Legacy .11b STAs may not correctly see a pure OFDM frame as a busy channel. • RTS/CTS exchange before OFDM transmission was proposed in 01/646r0. Olaf Hirsch, et al., Philips

  4. Comments on RTS/CTS • It is a plausible solution apparently! • But, this will lead to high overhead and reduce the maximum system throughput compared to the pure OFDM network. • One should use RTS/CTS even if there is no .11b STA in the BSS as it may be problematic when a new .11b STA wants to enter a .11g BSS without any .11b STA at the moment otherwise. • But, can we mandate using RTS/CTS in .11g BSS? Olaf Hirsch, et al., Philips

  5. Goal • To achieve a high throughput within BSS with co-existing .11b STAs. Olaf Hirsch, et al., Philips

  6. OFDM CP • Add OFDM Contention Period to CFP • During OFDM CP, .11g STAs contend with OFDM frames. • No RTS/CTS needed as NAV is set by .11b STAs. • .11g STAs do not contend during CP. • OFDM CP duration is coded in beacon frame. • Sizes of CP and OFDM CP can be adapted by the AP. Olaf Hirsch, et al., Philips

  7. Usage ElementID Order Length Information OFDM-CP Start Note OFDM-CP MaxDuration 11g 16 OFDM Frame parameter set The OFDM Frame parameter set is only present in a 11g network and shall be evaluated by 11g capable devices only New Element Beacon Frame OFDM Frame parameter set OFDM-CP Start, OFDM-CP MaxDuration given in TUs Olaf Hirsch, et al., Philips

  8. Conclusion • Our proposal is very bandwidth-efficient! • Will allow some room for .11b STAs to associate when the network is heavily loaded by pure OFDM traffic Olaf Hirsch, et al., Philips

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