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Transmit processing: a viable scheme for MIMO-OFDM in 802.11n

Transmit processing: a viable scheme for MIMO-OFDM in 802.11n. André Bourdoux Bart Van Poucke Liesbet Van der Perre IMEC, Wireless Research bourdoux@imec.be. 802.11 1-2 Mbps. 802.11a/g 6-54 Mbps. 4G WLAN. 1G WLAN. 2G WLAN. 3G WLAN. 500 m. 802.11b 5.5-11 Mbps. 802.11n

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Transmit processing: a viable scheme for MIMO-OFDM in 802.11n

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  1. Transmit processing:a viable schemefor MIMO-OFDM in 802.11n André Bourdoux Bart Van Poucke Liesbet Van der Perre IMEC, Wireless Research bourdoux@imec.be

  2. 802.11 1-2 Mbps 802.11a/g 6-54 Mbps 4G WLAN 1G WLAN 2G WLAN 3G WLAN 500 m 802.11b 5.5-11 Mbps 802.11n > 100 Mbps Range 50 m 5 m 100 kbps 1 Mbps 10 Mbps 100 Mbps 1 Gbps Maximum Data rate Need for 4G High-Speed WLANs • Higher data rates • Larger range • More users

  3. Higher capacitySDM, SDMA Higher robustnessDiversity (MRC, STBC) Magnitude Frequency MIMO-OFDM boosts performancesin frequency selective environments MIMOoffers:

  4. SDMA multiplies cell capacity SDMbrings higher throughput in DL/UL MIMO-TX ! MIMO-TX ! MIMO-TX ! STBC brings robustness MRC brings robustness A smart MIMO system adapts to scene and actual user needs

  5. s1 s2 s1 s2 s1 s1 s1 Downlink H H H SDM SDMA MRC STBC STBC STBC stbc s1 s2 s1 s2 s1 s1 s1 TX-SDM TX-SDMA TX-MRC STBC STBC s1 s2 s1 s2 s1 s1 Uplink “MIMO-TX”schemes, focus of this presentation SDM SDMA MRC STBC STBC s1 s2 s1 s2 s1 s1 RX-SDM RX-SDMA RX-MRC STBC A wide variety of MIMO schemes are available

  6. S1 S1 h H MIMOTX SDM(A) MIMOTX MRC … … … S1 S1 … SN … SN MIMO with TX pre-processing H H MIMO with TX pre-processing MIMO-TX requires “TX-CSI” • Simpler receiver (no MIMO processing needed, SISO equalizer needed) • Transmitter processing: low complexity (Zero-forcing, MMSE, MRC) • Channel H needed at TX ( “TX-CSI” ) • Option 1: by feedback • Option 2: from channel estimation in reverse link, reciprocity needed only works for TDD set-ups • Reciprocity: • Propagation channel: OK if delay kept short • Front-ends: not OK, calibration needed to measure transfer function of the front-ends

  7. UT1 UT1 s1 s1 AP AP AP UT2 s2 UT2 s2 DL 1 UL1 UL2 DL 2 H Spatial pre-filter H with FE. C. Channel estimation,AGC couples Example of Channel estimation and TX processing Spatialdimension Time

  8. Base StationTransmitterFront-end TerminalTransmitterFront-end Frommodulator Frommodulator H DTX,AP DTX,MT Propagation Channel DRX,AP DRX,MT Base StationReceiverFront-end TerminalReceiverFront-end Todemodulator Todemodulator Uplink: HDL (HUL)T Downlink: Front-end non-reciprocity can be solved by calibration The channel includes: • the propagation channel ( H ) • front-end circuits (filters, etc..) linear and non linear ( Dxx,yy )

  9. Downlink model (for Inversion) : Not diagonal anymore  Multi-user interference Non-perfect reciprocity  MUI

  10. The Base Station Transceiver aloneis responsible for the MUI • Only the base station creates MUI (DTX,BS & DRX,BS) • The terminal effects (DTX,MT & DRX,MT) only create scalar complex multiplication, can be equalized • H includes all common (reciprocal) terms, including antenna coupling • Common LO is mandatory • Valid for all pre-filtering technique, including MIMO-TX, beamforming, SVD

  11. OFDM-MIMO Demo Set-up Access Point with 2 antennas 2 Terminals with 1 antenna each

  12. MIMO-TX and MIMO-RX schemes are both interesting for 802.11n MIMO-TX needs channel knowledge at TX side Estimation in reverse link has lower latency Delay between reverse link estimation and MIMO-TX transmission must be minimized must be supported by MAC Protocol MIMO-TX has been demonstrated Real-time (VHDL, 5GHz band) Wireless, 2x2 antennas MIMO-OFDM-SDM (108 Mbps) and MIMO-OFDM-MRC (8 dB SNR improvement) Our advise for 802.11n

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