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IEEE 802.11 session Hawaii November 2002

IEEE 802.11 session Hawaii November 2002. MIMO-OFDM for high throughput WLAN: experimental results. Alexei Gorokhov, Paul Mattheijssen, Manel Collados, Bertrand Vandewiele, Gunnar Wetzker Philips Research. PHY options for high throughput wireless LANs Right time and place for MIMO?

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IEEE 802.11 session Hawaii November 2002

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  1. IEEE 802.11 session Hawaii November 2002 MIMO-OFDM for high throughput WLAN: experimental results Alexei Gorokhov, Paul Mattheijssen, Manel Collados,Bertrand Vandewiele, Gunnar WetzkerPhilips Research PHY options for high throughput wireless LANs Right time and place for MIMO? Performance enhancement via antenna selection Experimental set-up and channel measurements MIMO architectures for high data rates Experimental results

  2. High data rates: challenges & solutions Possible solutions Requirements • Increase bandwidth per link • Higher order modulation • More powerful CODEC • TX / RX diversity • MIMO Higher data rates (> 100Mbps) Increased throughput Extended range Better coverage Higher network capacity

  3. High data rates: challenges & solutions Possible solutions Requirements • Increase bandwidth per link • Higher order modulation • More powerful CODEC • TX / RX diversity • MIMO • Higher data rates (> 100Mbps) • Increased throughput • Extended range • Better coverage • Higher network capacity • Currently  12 channels 2 x rate  6 channels

  4. High data rates: challenges & solutions Possible solutions Requirements • Increase bandwidth per link • Higher order modulation • More powerful CODEC • TX / RX diversity • MIMO • Higher data rates (> 100Mbps) • Increased throughput • Extended range • Better coverage • Higher network capacity • Over 64-QAM: severe requirements to analogue & mixed signal circuits

  5. High data rates: challenges & solutions Possible solutions Requirements • Increase bandwidth per link • Higher order modulation • More powerful CODEC • TX / RX diversity • MIMO • Higher data rates (> 100Mbps) • Increased throughput • Extended range • Better coverage • Higher network capacity • Iterative demodulation with “anti-Gray” maps • Turbo coded CODEC • Higher complexity: power & area

  6. High data rates: challenges & solutions Possible solutions Requirements • Increase bandwidth per link • Higher order modulation • More powerful CODEC • TX / RX diversity • MIMO • Higher data rates (> 100Mbps) • Increased throughput • Extended range • Better coverage • Higher network capacity

  7. High data rates: challenges & solutions Possible solutions Requirements • Increase bandwidth per link • Higher order modulation • More powerful CODEC • TX / RX diversity • MIMO • Higher data rates (> 100Mbps) • Increased throughput • Extended range • Better coverage • Higher network capacity

  8. MIMO transcievers RX Motivation • Theoretical throughput scales linearly w.r.t. the # of antennas: • Increased range / coverage in NLOS environments • Cheap RF-CMOS technology: fractional cost per RF front-end (5.x GHz) • Keep DSP complexity limited Constraint TX

  9. Receive antenna selection Need for extra degrees of freedom at RX to ensure enough diversity ( ) High incremental cost of adding RF front-end versus the cost of antenna RX • Use antennas and front-ends at RX, select adaptively a subset of antennas, select out of antennas • optimal selection is rather complex • simple sub-optimal selection possible TX

  10. MIMO test-bed • 4 TX chains • 4 RX chains • f ~ 5.8GHz • BW 20MHz • 14 bit ADC • 35 dB AGC Receiver Transmitter

  11. More on parts LNA mixer AGC+LPF DAC/ADC Monopoles

  12. 1 2 3 4 5 6 7 8 9 10 11 12 Measurements Total TX power 14dBm • “soft” walls, much glass • few heavy metallic constructions • lots of furniture • few concrete walls / blocks

  13. Signal-to-noise ratio and delay spread Signal-to-noise ratio per RX antenna versus range RMS delay spread versus range

  14. Space-frequency modulation & layered reception TX signal path cyclic extension pulse shaping FEC encoder interleaver mapper IFFT streamcycling DEMUX cyclic extension pulse shaping FEC encoder interleaver mapper IFFT RX signal path deinterleavedemap pulse shaping FEC encoder MMSE filter FFT sampling - MUX + deinterleavedemap pulse shaping FEC encoder sampling FFT MRC + - FEC encoder interleaver mapper latency of ~ one TX/RX cycle

  15. Space-frequency interleaving & MMSE TX signal path cyclic extension pulse shaping mapper IFFT space frequencyinterleaver FEC encoder cyclic extension pulse shaping mapper IFFT RX signal path pulse shaping sampling FFT space frequencyde-interleaver demapper 2 x 2MMSEfilter FEC decoder pulse shaping sampling demapper FFT

  16. MIMO channel versus layered transceiver MIMO channel S-F modulation / layered RX Outage capacities versus rangeoutage rate 1%optimal RX antenna selection

  17. MIMO channel versus MMSE transceiver MIMO channel S-F interleaving / MMSE Outage capacities versus rangeoutage rate 1%optimal RX antenna selection

  18. Layering versus MMSE S-F modulation / layered RX S-F interleaving / MMSE Outage capacities versus rangeoutage rate 1%optimal RX antenna selection

  19. Observations MIMO capacities • MIMO capacity scales almost linearly w.r.t. the number of TX/RX antennas • space-frequency modulation with layered RX : ~90% of theoretical limit • space-frequency interleaving with MMSE:~60% of theoretical limit • …………… with adaptive RX selection: ~80% of theoretical limit Feasibility aspects channel processing beyond 2 x 2 system is hardly feasible (baseband) layered reception yields higher complexity & processing latency, seems prohibitive beyond 2 x 2 systems sub-optimal RX antenna selection looks attractive

  20. Layering versus MMSE: detailed S-F interleaving / MMSE S-F modulation / layered RX Outage capacities versus rangeoutage rate 1% • S-F modulation with MMSE receiver & sub-optimal RX selection looks attractive

  21. CODEC design Candidate FEC structures • Standard convolutional code • rate (1/2) 64-state code[133,171]8 • puncture to achieve mandatory / supplementary rate modes • soft-input Viterbi decoding at RX • easy to implement, IEEE 802.11 acceptance • expected to be sensitive to SINR discrepancy • Turbo- CODEC similar to that of UMTS • rate (1/3) PCCC with 8-state components [13,15]8 • puncture to achieve desired rates • iterative SISO decoding (Max-Log-MAP) • reduced SINR margin, less sensitive to SINR discrepancy • rather high complexity

  22. Outage performance of MIMO-MMSE Signalling 108Mbps  64QAM, rate 3/4 96Mbps  64QAM, rate 2/372Mbps  16QAM, rate 3/464Mbps  16QAM, rate 2/336Mbps  16QAM, rate 3/432Mbps  QPSK, rate 2/324Mbps  QPSK, rate 1/2

  23. Concluding remarks Observations • Maximum data rate scales linearly w.r.t. to the number of antennas • Receive antenna selection improves substantially maximum data rates (limited number of TX/RX chains) • 2 x 2 space division multiplexing with selection 2 of 4 RX antennas  200%-300% of single-antenna rates

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