doc.: IEEE /229r1 Submission March 2004 Alexandre Ribeiro Dias - Motorola LabsSlide 1 Multiple Antenna OFDM solutions for enhanced PHY Presented by: Alexandre Ribeiro Dias Contributors: A. Ribeiro Dias, Stéphanie Rouquette-Léveil, Sébastien Simoens Motorola Labs Paris +33 (1)

doc.: IEEE /229r1 Submission March 2004 Alexandre Ribeiro Dias - Motorola LabsSlide 2 Introduction (1/2) PAR requirements: –Define modifications to both PHY and MAC so that a maximum throughput of at least 100Mbps at the MAC SAP is enabled Increase PHY performance (1/2): –If same bandwidth (proposed functional requirement) multiple antenna techniques are required to increase the peak data rate with good coverage (add advanced coding schemes?) –Which multiple antennas techniques should be used? –How many antennas can be considered?

doc.: IEEE /229r1 Submission March 2004 Alexandre Ribeiro Dias - Motorola LabsSlide 3 Introduction (2/2) Increase PHY data rate (2/2): –How does « 100Mbps at the MAC SAP » translates in terms of PHY data rate requirements (  depends on MAC efficiency  depends on MAC amendment)? Increase MAC SAP goodput: –How high can the throughput be with an enhanced PHY and or e MACs? –How can this efficiency be increased with backward compatibility constraints ?

doc.: IEEE /229r1 Submission March 2004 Alexandre Ribeiro Dias - Motorola LabsSlide 4 Multiple antenna techniques (1/5) How can multiple antennas at the AP be used to improve performance of legacy STAs? UL Maximum Ratio Combining (MRC) Transmit Selection (TS, per subcarrier, per antenna) Partial channel state information, Closed-Loop (CL) technique DL

doc.: IEEE /229r1 Submission March 2004 Alexandre Ribeiro Dias - Motorola LabsSlide 5 Multiple antenna techniques (2/5) Space Time Block Codes (STBC) to benefit from spatial diversity (with MRC) –Increase communication reliability/coverage –Not optimal for high data rates

doc.: IEEE /229r1 Submission March 2004 Alexandre Ribeiro Dias - Motorola LabsSlide 6 Multiple antenna techniques (3/5) Spatial Division Multiplexing (SDM): –Data rate multiplied by number of transmit antennas –Transmit diversity not exploited In general (depending on decoder) Nr  Nt ML, ZF, MMSE, SIC… based receivers … S/P …

doc.: IEEE /229r1 Submission March 2004 Alexandre Ribeiro Dias - Motorola LabsSlide 7 Multiple antenna techniques (4/5) Hybrid schemes: increase data rate and exploit transmit diversity for higher robustness/good range SDM combined with STBCs (Open Loop OL) S/P SDM combined with TS (Closed-Loop CL) Transmit Selection (TS, per subcarrier, per antenna) S/P N<Nt data streams

doc.: IEEE /229r1 Submission March 2004 Alexandre Ribeiro Dias - Motorola LabsSlide 8 Multiple antenna techniques (5/5) Open-Loop vs Closed-Loop? CL techniques known to provide substantial gain but how CSI can be obtained at the TX? –Reciprocity assumption in TDD systems? Are RF front-ends identical on UL and DL? Additional overhead for calibration? Delay between UL and DL needs to be controlled –Feedback link? Needs to be implemented and additional overhead…

doc.: IEEE /229r1 Submission March 2004 Alexandre Ribeiro Dias - Motorola LabsSlide 9 Multiple antenna PHY example How many antennas should be used? –Antenna configuration should depend on STA size (laptop, mobile handset) –Ex: fixed number of antennas at the AP, several number of antennas (hence multiple antenna techniques) at the STA depending on dimensions/legacy AP 4 antennas, STA 1 antenna (legacy) AP 4 antennas, STA 2 antennas (mobile handset) AP 4 antennas, STA 4 antennas (laptop) TechniquesMRC, TS?STBC, SDM, Hybrid? ModesxQAM+code rate?

doc.: IEEE /229r1 Submission March 2004 Alexandre Ribeiro Dias - Motorola LabsSlide 10 Alternative OFDM modulators Cyclic Prefix OFDM (CP-OFDM) is an interesting option with simple equalisation scheme: BUT: –Zero Padded OFDM (ZP-OFDM, CP replaced by zeros) solves the sensibility to channel zeros locations –Pseudo-Random Postfix OFDM (PRP-OFDM, CP replaced by pseudo-randomly weighted known postfix): Keeps all advantages of ZP-OFDM Low complexity channel/synchronisation estimation and tracking possible, support for increased mobility (longer packets?) Alternative OFDM modulators worth being considered

doc.: IEEE /229r1 Submission March 2004 Alexandre Ribeiro Dias - Motorola LabsSlide 11 PHY simulation results (1/2) Simulation parameters: –256QAM investigated to increase spectral efficiency –NLOS TGn D channels (no spatial correlation, ≠ path loss model) –Packet size: 512Bytes, 23dBm transmit power –ZF receiver when SDM techniques (not optimal but least complex) –Perfect MIMO channel estimation All IEEE802.11a functional blocks are kept: Multiple Antenna System Processing mappinginterleavercoderscrambler OFDM modulation IEEE802.11a blockNew block Legend:

doc.: IEEE /229r1 Submission March 2004 Alexandre Ribeiro Dias - Motorola LabsSlide 12 PHY simulation results (2/2) Hybrid schemes for reliability and high data rate? –Hybrid schemes: range increase not very important, however reduces constraints on SNR requirements

doc.: IEEE /229r1 Submission March 2004 Alexandre Ribeiro Dias - Motorola LabsSlide 13 MAC simulation results Simulation Assumptions: –.11e MAC with Group Acknowledgement –1500 byte payload –16 MPDU per Group Simulation Results: –Only 100 Mbps effective vs 162Mbps theoretical with 3 streams and 64QAM –MAC Efficiency is of only 54% for the 216Mbps mode –.11e with Group Ack is too inefficient !

doc.: IEEE /229r1 Submission March 2004 Alexandre Ribeiro Dias - Motorola LabsSlide 14 Possible MAC improvements Need to increase the PHY burst size by aggregating numerous packets (without SIFS between each packet) Keep individual FCS per packet for SR-ARQ Possibility to rely on the Contention Free Period of.11e to introduce more efficient TDD/TDMA MAC, to reduce constraints on PHY

doc.: IEEE /229r1 Submission March 2004 Alexandre Ribeiro Dias - Motorola LabsSlide 15 Conclusions.11e MAC not efficient with high data rate PHY Increasing the MAC efficiency would relax the constraint on PHY peak data rate Number of antennas/techniques used should be chosen to reduce constraints on SNR requirements and keep reasonable range Antenna configurations should depend on STA size (set of different cost/performance trade-offs)