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Thoughts on High Data Rate 802.11

Thoughts on High Data Rate 802.11. Jim Tomcik QUALCOMM, Incorporated 5775 Morehouse Drive San Diego, CA, 92121 +1 (858)-658-3231 jtomcik@qualcomm.com. Note: The Text Associated with this Presentation Appears in the Power Point Notes Page View. WLAN Service Drivers and Requirements.

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Thoughts on High Data Rate 802.11

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  1. Thoughts onHigh Data Rate 802.11 Jim Tomcik QUALCOMM, Incorporated 5775 Morehouse Drive San Diego, CA, 92121 +1 (858)-658-3231 jtomcik@qualcomm.com Note: The Text Associated with this Presentation Appears in the Power Point Notes Page View James D. Tomcik, QUALCOMM, Incorporated

  2. WLAN Service Drivers and Requirements • Extensions of Wireless Operator’s Network • Video • High Fidelity Audio • Toll quality voice • Potential Offload of Cellular/PCS Network • Data Rate Requirements: • voice: 32 kbps • audio: > 192 kbps • video: 1.2 mbps (MPEG1) to 35 mbps (HDTV) • Service Requirements • Delay - minimize buffering (e.g. interleaving, processing) • Jitter - minimize delay variations • Guaranteed QoS –perhaps via bandwidth reservation • Potentially “Many” Users James D. Tomcik, QUALCOMM, Incorporated

  3. Data Rate Requirements James D. Tomcik, QUALCOMM, Incorporated

  4. 802.11- DCF Mode James D. Tomcik, QUALCOMM, Incorporated

  5. 802.11 PCF mode • Contention-free period uses short interframe space • Every packet ACK’ed James D. Tomcik, QUALCOMM, Incorporated

  6. 802.11e HCF mode • Single ACK for up to 16 packets James D. Tomcik, QUALCOMM, Incorporated

  7. Can Reservation Based Systems do Better?HiperLAN2 Frame Format Example • Data portion of frame remains ~fixed • Roughly 80% efficient James D. Tomcik, QUALCOMM, Incorporated

  8. 802.11a/HiperLAN High Rate Performance Achieved Throughput (Mbps) • Extrapolated rates of 128-384Mbps • OFDM symbol packing inefficiency not included • Fraction of OFDM symbol wasted at end of 1500-byte ethernet packet *- 300msec frame required, long delay for initiating transfer **- 54byte LCF packet must be modified for 128-384Mbps rates James D. Tomcik, QUALCOMM, Incorporated

  9. 802.11- MAC Key Issues • DCF Mode (asynchronous): • inefficient for high data rates • fraction of “dead” air-time increases • e.g. 54 Mbps rate in 802.11a has < 50% thruput efficiency • For higher rates: • < 25% thruput efficiency for rates exceeding 100 Mbps • PCF Mode (polled) efficiency increased marginally • 3msec contention period required (802.11a) • ACK still follows each packet • HCF Mode (802.11e, standard work in progress) • Polled mode with burst ACK improves efficiency • Still has significant dead air time • QoS is best effort, not guaranteed • Turn-around times are short • real time decoding becomes problematic at high speeds • Decoding more bits – tougher to do James D. Tomcik, QUALCOMM, Incorporated

  10. Conclusions • Advanced Service Offerings Require High Data Rates to Serve Reasonable Numbers of Users • Typical “hotspot” application may entail 20-50 users or more • NG WLAN system requires an Improved MAC • maintain efficiency for high data rates • guaranteed QoS • low delay & jitter • Random Access Protocols can be Inefficient • wasted capacity (dead air time) is the main cause • “dead air time” makes it easier to decode ever increasing numbers of bits, however! • Reservation-based Structures: • Can maintain efficiency as data rate scales • May meet QOS Constraints More Directly • Efficiency reduced with increased user loads (initiation of transfer difficult) James D. Tomcik, QUALCOMM, Incorporated

  11. James D. Tomcik, QUALCOMM, Incorporated

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