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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) 69 35 48 32 alexandre.ribeirodias@motorola.com. Presentation Outline. Introduction
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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) 69 35 48 32 alexandre.ribeirodias@motorola.com Alexandre Ribeiro Dias - Motorola Labs
Presentation Outline • Introduction • Multiple antenna techniques • Multiple antenna PHY example • Alternative OFDM modulators • PHY simulation results • MAC simulation results • Possible MAC improvements • Conclusion Alexandre Ribeiro Dias - Motorola Labs
Introduction (1/2) • PAR requirements: • Define modifications to both 802.11 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? Alexandre Ribeiro Dias - Motorola Labs
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 802.11 or 802.11e MACs? • How much can this efficiency be increased with backward compatibility constraints ? Alexandre Ribeiro Dias - Motorola Labs
UL Maximum Ratio Combining (MRC) Multiple antenna techniques (1/5) • How can multiple antennas at the AP can be used to improve performance of legacy STAs? Partial channel state information, Closed-Loop (CL) technique Transmit Selection (TS, per subcarrier, per antenna) DL Alexandre Ribeiro Dias - Motorola Labs
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 Alexandre Ribeiro Dias - Motorola Labs
ML, ZF, MMSE, SIC… based receivers S/P … … 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 Alexandre Ribeiro Dias - Motorola Labs
SDM combined with STBCs (Open Loop OL) • SDM combined with TS (Closed-Loop CL) N<Nt data streams Transmit Selection (TS, per subcarrier, per antenna) S/P S/P Multiple antenna techniques (4/5) • Hybrid schemes: increase data rate and exploit transmit diversity for higher robustness/range Alexandre Ribeiro Dias - Motorola Labs
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 impairments identical on UL and DL? • Delay between UL and DL needs to be controlled • Feedback link? • Needs to be implemented and additional overhead… Alexandre Ribeiro Dias - Motorola Labs
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 Alexandre Ribeiro Dias - Motorola Labs
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 estimation and tracking possible • Support for increased mobility (longer packets?) • Alternative OFDM modulators worth being considered Alexandre Ribeiro Dias - Motorola Labs
Multiple Antenna System Processing OFDM modulation OFDM modulation scrambler coder interleaver mapping IEEE802.11a block New block Legend: PHY simulation results (1/3) • Simulation parameters: • 256QAM investigated to increase spectral efficiency • NLOS TGn D channels (no spatial correlation) • Packet size: 512Bytes, 23dBm transmit power • ZF receivers when SDM-based techniques • All IEEE802.11a functional blocks are kept: Alexandre Ribeiro Dias - Motorola Labs
PHY simulation results (2/3) • Use of STBCs for increased reliability: • Important range increase, even with legacy STAs Alexandre Ribeiro Dias - Motorola Labs
PHY simulation results (3/3) • Hybrid schemes for reliability and high data rate? • Hybrid schemes: range increase not very important, however reduces constraints on SNR requirements Alexandre Ribeiro Dias - Motorola Labs
MAC simulation results • Simulation Assumptions: • .11e MAC with Group Acknowledgement • 1500 byte payload • 16 MPDU per Group • Simulation Results: • Only 100 Mbit/s effective vs 162 Mbit/s theoretical with 3 streams and 64 QAM • MAC Efficiency is of only 54% for the 120 Mbit/s mode • .11e with Group Ack is too inefficient ! Alexandre Ribeiro Dias - Motorola Labs
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 Alexandre Ribeiro Dias - Motorola Labs
Conclusion • .11e MAC not efficient with high data rate PHY • With enhanced MAC, PHY data rate of 162Mbps might be sufficient (which is the best solution?) • Antenna configurations should depend on STA size • Number or antennas/techniques used should be chosen to reduce constraints on SNR requirements and keep reasonable range Alexandre Ribeiro Dias - Motorola Labs