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11ac: 5G WiFi

11ac: 5G WiFi. The trigger for 5GHz everywhere Led by Apple and other consumer specialists In-home device sync, video, backup, etc “Gigabit WiFi ” on retail shelves 11ac’s best feature is that it is 5GHz only!. 11ac Throughputs. 11ac Potential Data Rates vs 11n. 11ac. Wave 1

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11ac: 5G WiFi

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  1. 11ac: 5G WiFi • The trigger for 5GHz everywhere • Led by Apple and other consumer specialists • In-home device sync, video, backup, etc • “Gigabit WiFi” on retail shelves • 11ac’s best feature is that it is 5GHz only!

  2. 11ac Throughputs 11ac Potential Data Rates vs 11n

  3. 11ac Wave 1 • 80MHz channels • 256QAM modulation • Potentially could be added to 2.4GHz • MAC improvements • Ubiquitous support on TX-BF (hopefully) Wave 2 • MU-MIMO • 160MHz channels • non adjacent (future?)

  4. 11ac: wider channels • 80 MHz Channels More spectrum coming soon • 160 MHz (potentially noncontiguous) channels in ~2014? WLAN - 160 MHz Radar Radar WLAN WLAN 80 MHz WLAN 80 MHz U-NII 1 U-NII 2 U-NII Worldwide U-NII 3 J

  5. Dynamic bandwidth (BW) operation • Currently channel must be free on whole 40MHz even if using 20MHz only • Wider channel increases likelihood of interfering signal in extension • Dynamic BW capability is desired to utilize BW more efficiently • Not required, but most vendors support it • Meeting spectral mask is challenging • Operating mode change requires 10s of milliseconds Secondary 40MHz Primary 20MHz Secondary 20MHz 36+40 44 48 Mode 1 Mode 2 Mode 3

  6. 11ac: 256QAM QPSK 256QAM 6

  7. 11ac MAC Changes • Frame size and MAC efficiency • Dynamic bandwidth operation • CCA thresholds differently handled • New RTS/CTS rules

  8. MAC efficiency Random backoff AIFS t Overhead Effective Note: BestEffortQoS is assumed

  9. 11ac strengthened Clear Channel Assessment (CCA) requirement • Must detect WiFi signals with energy level above threshold on all channel widths • Preamble detection not required • Different back-off thresholds for WiFivs non-WiFi signals • Device must be either smart enough to differentiate WiFi signals vs other energy or use lowest threshold for all

  10. RTS/CTS in 11ac • Under 11n RTS/CTS rules for wider channels, a responder responds with CTS using full wide channel • If a transmitter receives a CTS on 20MHzchannel, it responds with data using full width channel (20/40/80MHz etc.) • This rule does not account for possible interference on the wider channels BA Primary RTS CTS time Secondary20 RTS CTS BA time RTS CTS BA Secondary40 time RTS CTS BA time SIFS Interference at responder

  11. Wave 2 – Multi-User (MU-MIMO)

  12. 11ac : DL-MU-MIMO 2 streams PC 1 stream Phone AP 1 stream PC 2 streams Phone Down-link Multi-User MIMO (spatial division multiple access) Makes use of multiple physical paths through the environment to enable multiple simultaneous transmissions to different receivers Impressive capacity improvements if you can fit 8-16 antennas per band on an AP. 12

  13. DL-MU: basic parameters • Max. # of users per packet : 4 • Max. # of space-time streams per user : 4 • Collision free maximum# of space-time streams for SU packet = 8 • Max. total # of space-time streams over all users: 8

  14. DL-MU – Spatial Multiplexing Single-User MIMO (11n) Stream 1 • Historically • Access pointsand clients were using same/similar baseband • MU requires different designs • AP complexity increased due to MU support in both HW and SW • MU capability costs likely to push market to different AP and client BB silicon Stream 2 Stream 3 Stream 4 Multi-User MIMO (11ac) Stream 1 Stream 2 Stream 3 Stream 4

  15. DL-MU: Sequential Block ACK • Sequential Ack is used because no UL-MU support • One user send immediate BA • Other users are polled using BAR STA 1 BAR BAR AP STA 2 STA 3 SIFS SIFS SIFS SIFS SIFS PIFS BA STA 1 BA STA 2 STA 3 Error Recovery (same for sounding) BA

  16. DL-MU: TXOP sharing • After random back off the winning AC will be allowed to transmit • Other ACs are allowed to piggy back in MU packet as long as it doesn’t extend the TXOP • If primary AC is voice, max TXOP is 1.5 seconds • If primary AC is video, max TXOP is 3 seconds Video Voice (primary AC) Data

  17. Thank You

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