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Technology and Use Cases for TGac

Technology and Use Cases for TGac. Date: 2009-07-13. Authors:. Introduction. We look at various technologies for TGac, map the technologies to use cases and conclude that most of the gain is achieved with simple extensions to TGn For use cases, we reference

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Technology and Use Cases for TGac

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  1. Technology and Use Cases for TGac Date: 2009-07-13 Authors:

  2. Introduction • We look at various technologies for TGac, map the technologies to use cases and conclude that most of the gain is achieved with simple extensions to TGn • For use cases, we reference • WiFi Alliance (WFA) VHT Study Group Usage Models presented in 07/2988r4

  3. Possible technologies • Wider channels • Higher order modulation and code rate • More spatial streams • Multi-user MIMO • OFDMA

  4. Wider Channels • Possible approaches • Bond adjacent channels to form 80 MHz channel • Simultaneous transmission on non-adjacent channels • Advantage • Doubles the PHY data rate (sticker on the box still sells) • Negligible increase in cost over 11n • Issues • Bonding • Coexistence with 11n 20MHz & 40MHz • Non-adjacent channels • Significant receiver complexity to deal with OBSS • Frequency reuse • The number of available non-overlapping bonded channels will be lower • One 80MHz channel in 5.15-5.25 GHz band • One 80MHz channel in 5.25-5.35 GHz band • Can increase co-channel interference • Unknown whether a single channel can span multiple regulatory bands

  5. Higher order modulation and code rate • Higher order modulation • 256 QAM (was almost adopted in 11n) • 1024 QAM • Higher code rate • 7/8 (was almost adopted in 11n) • Advantage • Architecturally simple addition to the standard • Issues • Reduces robustness • Requires tighter Tx and Rx specs (e.g. phase noise)

  6. More Spatial Streams • Go beyond four steams in 11n, perhaps eight • Advantage • data rate increases as a function of number spatial streams • Issues • Size/power constrained devices may not be capable of supporting additional antennas • Antenna correlation/coupling if antennas need to be packed closer together • As we have seen in 11n, mobile/portable devices unlikely to support a large number of antennas

  7. Multi-user MIMO • 11n MIMO • Spatial division multiplexing (SDM) – STA simultaneously transmits multiple streams to another STA • Multi-user MIMO • STA simultaneously transmits multiple streams to several other STAs • E.g. 4 antenna AP transmits two streams to STA1 and two streams to STA2 • Advantage • Increases network capacity with client devices that only have few antennas • Issues • Multi-user MIMO on the downlink from AP to STA has higher complexity than 11n Tx Beamforming • Multi-user MIMO has very high complexity on uplink - would require precise transmit packet synchronization between STAs and transmit power control (similar to that required in CDMA cellular system) • Scheduling • As yet not well know how time variant is the channel

  8. OFDMA • Subdivide OFDM subcarriers to several STAs • Used in cellular systems like Wimax • Advantage • More efficient method in usages with multiple lower rate clients, e.g. voice • Efficient uplink technique for ACK packets in response to downlink MU-MIMO packet • Issues • Has very high complexity on uplink - would require precise transmit packet synchronization between STAs and transmit power control • Scheduling • Does not increase maximum data rate or network capacity, only improves efficiency with multiple lower rate clients

  9. 3a 1c 1b 2a 2b 1d 3b 1a 6a 2d 3d 4a 4b 3e 2c 1f 5b 1e 5a 2e 3c WFA VHT Usage Models mapped to market volume and timing* RelativelyHigh Highlight these use cases on the next slide Market Volume Rela-tivelyLow Later Sooner Anticipated Market Timing For Mainstream Market * from 07/2988r4

  10. WFA VHT Usage Models mapped to technologies Slide 10

  11. Summary • Wider channel benefits almost all applications • 2x improvement • MCS enhancements benefit short range, direct link applications • Almost 2x improvement possible • Downlink MU-MIMO provides increased network efficiency for some applications • Only when long term, simultaneous traffic flows are present (e.g. video) • < 2x improvement; dependent on uplink/downlink traffic mix • Not clear that 2 hop MU-MIMO is better than direct link • More spatial streams may provide some benefit in certain environments • Cost and form factor prohibitive for most devices due to antenna requirements • Downlink OFDMA provides little benefit • Power saving and performance gain questionable • Uplink space/frequency multiplexing techniques • No compelling use case, especially considering complexity

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