1. doc.: IEEE 802.11-04/792r1 Submission Slide 1 André Bourdoux (IMEC) July 2004 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

2. doc.: IEEE 802.11-04/792r1 Submission Slide 2 André Bourdoux (IMEC) July 2004 Need for 4G High-Speed WLANs 5 m 1 Mbps10 Mbps100 Mbps1 Gbps Maximum Data rate 100 kbps 50 m 500 m Range Higher data rates Larger range More users 1G WLAN 802.11 1-2 Mbps 3G WLAN 802.11a/g 6-54 Mbps 2G WLAN 802.11b 5.5-11 Mbps 4G WLAN 802.11n > 100 Mbps

3. doc.: IEEE 802.11-04/792r1 Submission Slide 3 André Bourdoux (IMEC) July 2004 MIMO-OFDM boosts performances in frequency selective environments MIMO offers: Higher capacity SDM, SDMA Higher robustness Diversity (MRC, STBC) Frequency Magnitude

4. doc.: IEEE 802.11-04/792r1 Submission Slide 4 André Bourdoux (IMEC) July 2004 A smart MIMO system adapts to scene and actual user needs SDMA multiplies cell capacity SDM brings higher throughput in DL/UL STBC brings robustness MRC brings robustness MIMO-TX !

5. doc.: IEEE 802.11-04/792r1 Submission Slide 5 André Bourdoux (IMEC) July 2004 A wide variety of MIMO schemes are available SDMA s1s1 s2s2 s1s1 s2s2 RX-SDMA SDM s1s1 s2s2 s1s1 s2s2 RX-SDM MRC s1s1 s1s1 RX-MRC STBC s1s1 s1s1 Uplink SDM s1s1 s2s2 s1s1 s2s2 TX-SDM SDMA s1s1 s2s2 s1s1 s2s2 TX-SDMA MRC s1s1 s1s1 TX-MRC STBC s1s1 s1s1 s1s1 s1s1 stbc Downlink HHH “MIMO-TX” schemes, focus of this presentation

6. doc.: IEEE 802.11-04/792r1 Submission Slide 6 André Bourdoux (IMEC) July 2004 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 h S1S1 H MIMO TX MRC … MIMO with TX pre-processing S1S1 … … H S1S1 H MIMO TX SDM(A) … … MIMO with TX pre-processing SNSN S1S1 SNSN

7. doc.: IEEE 802.11-04/792r1 Submission Slide 7 André Bourdoux (IMEC) July 2004 Example of Channel estimation and TX processing UL1 AP UT1 UL2 AP UT2 Channel estimation, AGC couples H H with FE. C. Spatial pre-filter DL 2 s2s2 AP s1s1 s1s1 s2s2 UT1 UT2 DL 1 Time Spatial dimension

8. doc.: IEEE 802.11-04/792r1 Submission Slide 8 André Bourdoux (IMEC) July 2004 Front-end non-reciprocity can be solved by calibration Base Station Receiver Front-end From modulator To demodulator Terminal Transmitter Front-end Terminal Receiver Front-end From modulator To demodulator Base Station Transmitter Front-end H D TX,AP D TX,MT D RX,AP D RX,MT Propagation Channel Uplink: Downlink: H DL  (H UL ) T The channel includes: the propagation channel ( H ) front-end circuits (filters, etc..) linear and non linear ( D xx,yy )

9. doc.: IEEE 802.11-04/792r1 Submission Slide 9 André Bourdoux (IMEC) July 2004 Non-perfect reciprocity  MUI Downlink model (for Inversion) : Not diagonal anymore  Multi-user interference

10. doc.: IEEE 802.11-04/792r1 Submission Slide 10 André Bourdoux (IMEC) July 2004 The Base Station Transceiver alone is responsible for the MUI Only the base station creates MUI (D TX,BS & D RX,BS ) The terminal effects (D TX,MT & D RX,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. doc.: IEEE 802.11-04/792r1 Submission Slide 11 André Bourdoux (IMEC) July 2004 OFDM-MIMO Demo Set-up Access Point with 2 antennas 2 Terminals with 1 antenna each

12. doc.: IEEE 802.11-04/792r1 Submission Slide 12 André Bourdoux (IMEC) July 2004 Our advise for 802.11n  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)