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MIMO Mode Table for 802.11n

MIMO Mode Table for 802.11n. Ravi Mahadevappa, ravi@realtek-us.com Stephan ten Brink, stenbrink@realtek-us.com Realtek Semiconductors, Irvine, CA. DCN 802.11-04/553r0. May 2004. Overview. Why Different MIMO Modes Preliminaries, MIMO Modes Maximum ratio combining (MRC)

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MIMO Mode Table for 802.11n

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  1. MIMO Mode Table for 802.11n Ravi Mahadevappa, ravi@realtek-us.com Stephan ten Brink, stenbrink@realtek-us.com Realtek Semiconductors, Irvine, CA DCN 802.11-04/553r0 May 2004 Ravi Mahadevappa, Stephan ten Brink, Realtek

  2. Overview • Why Different MIMO Modes • Preliminaries, MIMO Modes • Maximum ratio combining (MRC) • „Circular Alamouti“ (CIRCAL) versus orthogonal space/time block codes (OSTBC) • MIMO mode table • „Circular SMX“ (CIRCSMX) • Example, discussion 4x4 • Conclusions • Appendix, results 1x1 to 4x4 Ravi Mahadevappa, Stephan ten Brink, Realtek

  3. Why Different MIMO Modes • We should allow both • Small/low cost terminals (moderate speed) with e.g. 2 TX-ant. (for use in handhelds, digital cameras etc.) • And high speed terminals with e.g. up to 4 TX-ant. (for use in laptop computers etc.) • Thus, there will be equipment with a variety of number of TX/RX antennas out there operating under the 802.11n-“umbrella” • Solution: Switch between MIMO modes depending on available number of TX and RX antennas of the equipment involved • Spatial multiplex (SMX): • High data rates, short range; optimal detection tends to be complex • Space time block codes (STBC), e.g. Alamouti 2x1 • Long range, lower data rates; optimal detection is simple • Should be transparent, 11a to 11n modes • From today’s perspective: Max. NT=4 TX antennas, NR=4 RX antennas reasonable (full RF chain TX, RX antennas) Ravi Mahadevappa, Stephan ten Brink, Realtek

  4. Preliminaries, MIMO Modes • General scenario: NTxNR • Obvious: For 1xNR use MRC at receiver • For NT>NR, in particular, for NTx1: Use simple TX diversity schemes based on space/time block codes • No general construction known • 2x1: Alamouti (perfect; full diversity, “rate 1”) • Should 3x1, 4x1, full diversity, “rate 3/4”-codes be used? • For NT>NR, NR>1 • use STBC and MRC at receiver • Or, use SMX with subset of TX antennas • For NT<=NR: use SMX for high rate Ravi Mahadevappa, Stephan ten Brink, Realtek

  5. 70 60 50 40 Rate (Mbps) 30 20 10 0 -10 -5 0 5 10 15 20 25 30 SNR for 10% PER (dB) 1x1 up to 1x4 MRC 1x4 MRC 1x2 MRC 1x1 Code Rates 1/4, 1/3, 1/2, 2/3, 3/4, 7/8 • Code rates 1/4, 1/3, 1/2, 2/3, 3/4, 7/8 • Modulation QPSK, 16QAM, 64QAM • Performance measure: required SNR for 10% PER • Packet length: 1000 bits • exponential decay, Trms = 60ns • For simulation: Perfect • Channel estimation • Packet detection, synchronization • foff estimation • No clipping DAC/finite precision ADC • No front-end filtering 64QAM 16QAM QPSK 1x3 MRC More receive antennas improve SNR (range) Ravi Mahadevappa, Stephan ten Brink, Realtek

  6. MIMO Mode Table (I) TX ant. RX ant. Table specifies the allowed MIMO modes depending on NT, NR NT=1, simple MRC for any NR Ravi Mahadevappa, Stephan ten Brink, Realtek

  7. TX Diversity with “Circular Alamouti” • NTx1 Space/Time Block Codes (STBC) • Orthogonal STBC (OSTBC) allow simple ML detection • For NTx1, no general construction of OSTBC known with full spatial diversity and full rate • Moreover, it can be proved that no full rate OSTBC exists with NT>2 • 2x1, Alamouti: only known OSTBC with full diversity and “rate 1” • 3x1, 4x1, full diversity, spatial “rate 3/4” codes known • We can easily build orthogonal NTx1 STBC based on the 2x1 Alamouti code with spatial “rate 1”; however, no full diversity • “circular Alamouti” 2(NT)x1 CIRCAL: • For each channel symbol, only use 2 TX antennas out of the NT available ones • Cycle through all NT!/(2! (NT-2)!) combinations (2 out of NT) • Example: NT=3, cycle period is 2.3=6 combinations; NT=4, cycle period is 2.6=12 combinations • Experiment: Compare performance of 3x1, 4x1 full diversity rate 3/4 OSTBC with 2(3)x1, 2(4)x1 rate 1 CIRCAL for MIMO-OFDM Ravi Mahadevappa, Stephan ten Brink, Realtek

  8. 2x1 Orthogonal Design (“Alamouti”) • Provides TX diversity • NT=2 TX antennas, NR=1 RX antennas • 2 channel uses, 2 symbols transmitted; thus, spatial rate 1 • To read as • At time 1, transmit s1 from antenna 1, s2 from antenna 2 • At time 2, transmit -s2* from antenna 1, s1* from antenna 2 • Repeat pattern with new symbols s1, s2 Ravi Mahadevappa, Stephan ten Brink, Realtek

  9. 3x1 Orthogonal Design • Provides TX diversity • NT=3 TX antennas, NR=1 RX antennas • 4 channel uses, 3 symbols transmitted; thus, spatial rate 3/4 Ravi Mahadevappa, Stephan ten Brink, Realtek

  10. 4x1 Orthogonal Design • Provides TX diversity • NT=4 TX antennas, NR=1 RX antennas • 4 channel uses, 3 symbols transmitted; thus, rate 3/4 Ravi Mahadevappa, Stephan ten Brink, Realtek

  11. Example: 2(3)x1 CIRCAL • Based on 2x1 Alamouti (full diversity, spatial rate 1) • Cycling for averaging good/bad MIMO subchannels • NT=3 TX antennas, 2 used at a time, NR=1 RX antennas • 6 channel uses, 6 symbols transmitted; thus, „rate 1“ (or any other wayof cycling through 2 TX antennas used at a time) Ravi Mahadevappa, Stephan ten Brink, Realtek

  12. Example: 2(4)x1 CIRCAL • Based on 2x1 Alamouti (full diversity, spatial rate 1) • Cycling for averaging good/bad MIMO subchannels • NT=4 TX antennas, 2 used at a time, NR=1 RX antennas • 12 channel uses, 12 symbols transmitted; thus, „rate 1“ (or any other wayof cycling through 2 TX antennas used at a time) Ravi Mahadevappa, Stephan ten Brink, Realtek

  13. 2(NT)xNR CIRCAL • Based on 2x1 Alamouti (full diversity, spatial rate 1) • Rotation for averaging good/bad MIMO subchannels • NT TX antennas, nT=2 used at a time, NR RX antennas • Use MRC (maximum ratio combining) for NR receive antennas • Cycling through all PCIRCAL = NT!/(nT! (NT-nT)!) combinations on a per OFDM symbol basis • since two OFDM symbols per Alamouti code are used, the cycle period in OFDM symbols is 2. PCIRCAL • For better averaging in OFDM systems, TX antenna cycling can be applied over both, time index and subcarrier index Ravi Mahadevappa, Stephan ten Brink, Realtek

  14. 3x1: 2(3)x1 CIRCAL versus OSTBC 70 3x1 60 • Code rates 1/4, 1/3, 1/2, 2/3, 3/4, 7/8 • Modulation QPSK, 16QAM, 64QAM • 3x1 STBC: „full diversity“, but (spatial) rate 3/4, rate loss • 2(3)x1 CIRCAL outperforms 3x1 STBC • suffers no rate loss • cycling/rotating compensates some of the diversity losses 50 40 2(3)x1 CIRCAL Rate (Mbps) STBC “full diversity” Rate 3/4 30 20 10 0 -5 0 5 10 15 20 25 SNR for 10 % PER (dB) 2(3)x1 CIRCAL better than 3x1 OSTBC Ravi Mahadevappa, Stephan ten Brink, Realtek

  15. 4x1: 2(4)x1 CIRCAL versus OSTBC 70 4x1 60 • 4x1 STBC: „full diversity“, but (spatial) rate 3/4, rate loss • 2(4)x1 CIRCAL outperforms 4x1 STBC • suffers no rate loss • cycling/rotating compensates some of the diversity losses • 2(NT)x1 CIRCAL better than known OSTBC • 2(NT)xNR CIRCAL by using MRC at the RX 2(4)x1 CIRCAL 50 40 Rate (Mbps) STBC “full diversity”Rate 3/4 30 20 10 0 -5 0 5 10 15 20 25 SNR for 10% PER (dB) 2(4)x1 CIRCAL better than 4x1 OSTBC Ravi Mahadevappa, Stephan ten Brink, Realtek

  16. 2x1, 2(3)x1, 2(4)x1 CIRCAL 70 64QAM 60 Code Rates 1/4, 1/3, 1/2, 2/3, 3/4, 7/8 • 2(3)x1 CIRCAL improves over 2x1 AL by about 0.5dB • 2(4)x1 CIRCAL improves over 2x1 AL by about 1dB • Only 2 antennas used at a time, but rotated through all combinations • The antenna cycling captures more of the available diversity in the system • More transmit antennas improve diversity, even if only used in rotation with Alamouti code 2(4)x1 CIRCAL 2(3)x1 CIRCAL 2x1 AL 50 40 Rate (Mbps) 16QAM 30 20 QPSK 10 0 0 5 10 15 20 25 SNR for 10% PER (dB) Gains of 2(NT)x1 CIRCAL over 2x1 AL saturate for NT=4 and more Ravi Mahadevappa, Stephan ten Brink, Realtek

  17. MIMO Mode Table (II) TX ant. RX ant. Table specifies the allowed MIMO modes depending on NT, NR NT>=NR, low rate: Use Circular AL (CIRCAL) and MRC Ravi Mahadevappa, Stephan ten Brink, Realtek

  18. Circular SMX • When NT>NR, we use same idea as with CIRCAL: • collect diversity by cycling through TX antennas • nT(NT) CIRCSMX: • Use nT TX antennas per channel use for SMX, out of NT>nT available antennas at transmitter • Cycle through all PCIRCSMX=NT!/(nT! (NT-nT)!) combinations on a per OFDM symbol basis • The cycle period in OFDM symbols is PCIRCSMX • For example, say we have NT=3 TX antennas, but only NR=2 RX antennas • Possible cycling for 2(3)x2 CIRCSMX: • at time 1, transmit from antennas 1, 2 • at time 2, transmit from antennas 1, 3 • at time 3, transmit from antennas 2, 3 • repeat the pattern Ravi Mahadevappa, Stephan ten Brink, Realtek

  19. 140 120 100 80 Rate (Mbps) 60 40 20 0 -5 0 5 10 15 20 25 30 SNR for 10% PER (dB) 2x2 SMX, 2(3)x2, 2(4)x2 CIRCSMX 2x2 2(4)x2 CIRCSMX • Code rates 1/4, 1/3, 1/2, 2/3, 3/4, 7/8 • Modulation QPSK, 16QAM, 64QAM • CIRCSMX improves TX diversity • 2(4)x2 SMX gains about 1dB over 2x2 SMX • CIRCAL curves given as references 2(3)x2 CIRCSMX 2x2 SMX 64QAM 64QAM 16QAM 2(4)x2 CIRCAL/MRC 2(3)x2 CIRCAL/MRC 2x2 AL/MRC QPSK For NT>NR: NR(NT)xNR CIRCSMX better than NRxNR SMX Ravi Mahadevappa, Stephan ten Brink, Realtek

  20. MIMO Mode Table (III) TX ant. RX ant. Any NT, NR, high rate: SMX, or Circular SMX (CIRCSMX) Ravi Mahadevappa, Stephan ten Brink, Realtek

  21. 300 250 200 Rate (Mbps) 150 100 50 0 -10 -5 0 5 10 15 20 25 30 35 SNR for 10 % PER (dB) Example, Discussion of 4x4 4x4 • Code rates 1/4, 1/3, 1/2, 2/3, 3/4, 7/8 • Modulation QPSK, 16QAM, 64QAM • The rate/SNR envelope includes • 2(4)x4 CIRCAL for lowest rates • 2(4)x4 CIRCSMX • 3(4)x4 CIRCSMX • 4x4 SMX for highest rate • To simplify: • Omit 2(4)x4 CIRCSMX • Use 4x4 SMX for highest two rates • Use 2(4)x4 CIRCAL for lowest 4x4 SMX 3(4)x4 CIRCSMX 2(4)x4 CIRCSMX 2(4)x4CIRCAL/MRC For NT>NR: NR(NT)xNR CIRCSMX better than NRxNR SMX Ravi Mahadevappa, Stephan ten Brink, Realtek

  22. MIMO Mode Table (IV), any NT, NR TX RX Ravi Mahadevappa, Stephan ten Brink, Realtek

  23. Conclusions • Use 2(NT)x1 CIRCAL rather than full diversity, spatial rate 3/4 STBC for NT=3, 4 • Always use all receive antennas • Not always use all transmit antennas • Only when very high rates are desired • For medium rates, it is better to use less antennas, but higher modulation/rate; to have at least one excess antenna at receiver • CIRCSMX NR(NT)xNR always better (slightly) than SMX NRxNR • For low-complexity, suboptimal MIMO detection, excess antennas pay off • For example 3x3 • for medium rate, use 2(3)x3 CIRCSMX (high rate code/modulation) rather than 3x3 SMX (medium code rate/modulation) • Only use 3x3 SMX when really high rates are desired Ravi Mahadevappa, Stephan ten Brink, Realtek

  24. Appendix • Rate versus SNR-charts for NTxNR = 1x1 to 4x4 Ravi Mahadevappa, Stephan ten Brink, Realtek

  25. Performance Criteria/Abbreviations • Receiver sensitivity for 10% PER • Abbreviations: • SEL: selection diversity at RX • MRC: maximum ratio combining at RX • AL/MRC: Alamouti Space/Time with MRC at RX [7,8] • SMX: spatial multiplexing (i.e. MIMO mode, [4,5,6]) • nT(NT) CIRCAL: “circular Alamouti”, using nT=2 antennas per channel use, out of NT>nT available antennas at transmitter, and cycling through all PCIRCAL = NT!/(nT! (NT-nT)!) combinations on a per OFDM symbol basis; since two OFDM symbols per Alamouti code are used, the cycle period in OFDM symbols is 2. PCIRCAL • nT(NT) CIRCSMX: “circular SMX”, using nT transmit antennas per channel use for SMX, out of NT>nT available antennas at transmitter, and cycling through all PCIRCSMX=NT!/(nT! (NT-nT)!) combinations on a per OFDM symbol basis; the cycle period in OFDM symbols is PCIRCSMX • MIMO detection used in following plots • ZF and APP post processing • Note: ZF with APP post processing provides close to optimal performance for higher order modulation (increasing number of excess antennas); for small constellations (QPSK), i.e., low-rate communication, ZF/APP suffers significant performance loss; that’s the main reason why AL-type of STBC are a good choice for low-rate communication Ravi Mahadevappa, Stephan ten Brink, Realtek

  26. Simulation Environment/Assumptions • 802.11a PHY simulation environment, plus • Higher order QAM constellations • Higher/lower channel code rates • TX/RX diversity/MIMO OFDM • ZF detection and soft post processing (shown in plots) • APP and reduced APP detection • Perfect channel knowledge/synchronization • Idealized multipath MIMO channel • Sub-channels independent; exponential decay, Trms = 60ns • Quasi static (channel stays constant during one packet) • Packet length: 1000 bits • Perfect • Channel estimation • Packet detection, synchronization • foff estimation • No clipping DAC/finite precision ADC • No front-end filtering Ravi Mahadevappa, Stephan ten Brink, Realtek

  27. 70 60 50 40 Rate (Mbps) 30 20 10 0 -10 -5 0 5 10 15 20 25 30 SNR for 10% PER (dB) 1x1 up to 1x4 MRC 1x4 MRC 1x2 MRC 1x1 • Code rates 1/4, 1/3, 1/2, 2/3, 3/4, 7/8 • Modulation QPSK, 16QAM, 64QAM • More receive antennas improve SNR (range) Code Rates 1/4, 1/3, 1/2, 2/3, 3/4, 7/8 64QAM 16QAM QPSK 1x3 MRC Ravi Mahadevappa, Stephan ten Brink, Realtek

  28. 2x1 Alamouti STBC 70 2x1 AL 60 Code Rates 1/4, 1/3, 1/2, 2/3, 3/4, 7/8 64QAM • Code rates 1/4, 1/3, 1/2, 2/3, 3/4, 7/8 • Modulation QPSK, 16QAM, 64QAM 50 40 Rate (Mbps) 16QAM 30 20 QPSK 10 0 0 5 10 15 20 25 SNR for 10% PER (dB) Ravi Mahadevappa, Stephan ten Brink, Realtek

  29. 2x2 140 2x2 120 • Code rates 1/4, 1/3, 1/2, 2/3, 3/4, 7/8 • Modulation QPSK, 16QAM, 64QAM • Low rate: AL/MRC • High rate: SMX 2x2 SMX 100 80 Rate (Mbps) 60 40 2x2 AL/MRC 20 0 -5 0 5 10 15 20 25 30 SNR for 10% PER (dB) Ravi Mahadevappa, Stephan ten Brink, Realtek

  30. 2x3 140 2x3 120 • Code rates 1/4, 1/3, 1/2, 2/3, 3/4, 7/8 • Modulation QPSK, 16QAM, 64QAM • Low rate AL/MRC • High rate SMX 2x3 SMX 100 80 Rate (Mbps) 60 40 2x3AL/MRC 20 0 -10 -5 0 5 10 15 20 25 SNR for 10 % PER (dB) Ravi Mahadevappa, Stephan ten Brink, Realtek

  31. 2x4 140 2x4 120 • Code rates 1/4, 1/3, 1/2, 2/3, 3/4, 7/8 • Modulation QPSK, 16QAM, 64QAM • Low rate AL/MRC • High rate SMX • Almost all rates can be covered with SMX only 2x4 SMX 100 80 Rate (Mbps) 60 40 2x4AL/MRC 20 0 -10 -5 0 5 10 15 20 SNR for 10 % PER (dB) Ravi Mahadevappa, Stephan ten Brink, Realtek

  32. 3x1 70 3x1 60 • Code rates 1/4, 1/3, 1/2, 2/3, 3/4, 7/8 • Modulation QPSK, 16QAM, 64QAM • 3x1 STBC: „full diversity“, but (spatial) rate 3/4, rate loss • 2(3)x1 CIRCAL outperforms 3x1 STBC (suffers no rate loss; no significant loss due to smaller diversity; circulating/rotating compensates some of the diversity losses, see next slide) 50 40 2(3)x1 CIRCAL Rate (Mbps) STBC “full diversity” Rate 3/4 30 20 10 0 -5 0 5 10 15 20 25 SNR for 10 % PER (dB) Ravi Mahadevappa, Stephan ten Brink, Realtek

  33. 3x2 140 3x2 120 • Code rates 1/4, 1/3, 1/2, 2/3, 3/4, 7/8 • Modulation QPSK, 16QAM, 64QAM • 2(3)x2 CIRCAL/MRC better for low data rates • 2(3)x2 CIRCSMX better for higher data rates (no rate loss); for low data rates: loss due to ZF/APP detection for small constellation size 2(3)x2 CIRCSMX 100 80 Rate (Mbps) 60 40 2(3)x2CIRCAL/MRC 20 0 -5 0 5 10 15 20 25 30 SNR for 10 % PER (dB) Ravi Mahadevappa, Stephan ten Brink, Realtek

  34. 3x3 200 180 3x3 • Code rates 1/4, 1/3, 1/2, 2/3, 3/4, 7/8 • Modulation QPSK, 16QAM, 64QAM • 3x3 SMX only for high rate • 2(3)x3 CIRCSMX better for medium rate (easier detection since excess antenna) 3x3 SMX 160 140 120 100 Rate (Mbps) 80 2(3)x3 CIRCSMX2 60 40 2(3)x3CIRCAL/MRC 20 0 -10 -5 0 5 10 15 20 25 30 35 SNR for 10 % PER (dB) Ravi Mahadevappa, Stephan ten Brink, Realtek

  35. 3x4 200 180 3x4 • Code rates 1/4, 1/3, 1/2, 2/3, 3/4, 7/8 • Modulation QPSK, 16QAM, 64QAM • 3x4: highest rate • 2(3)x4: medium rate • 2(3)x4 CIRCAL/MRC: lowest rate 160 3x4 SMX 140 120 Rate (Mbps) 100 80 2(3)x4 CIRCSMX 60 40 2(3)x4CIRCAL/MRC 20 0 -10 -5 0 5 10 15 20 25 SNR for 10 % PER (dB) Ravi Mahadevappa, Stephan ten Brink, Realtek

  36. 4x1 70 4x1 60 • Code rates 1/4, 1/3, 1/2, 2/3, 3/4, 7/8 • Modulation QPSK, 16QAM, 64QAM • 4x1 STBC: „full diversity“, but (spatial) rate 3/4, rate loss (as with 3x1 STBC case) • 2(4)x1 CIRCAL outperforms 4x1 STBC (suffers no rate loss; no significant loss due to smaller diversity; circulating/rotating compensates some of the diversity losses, see next slide) 2(4)x1 CIRCAL 50 40 Rate (Mbps) STBC “full diverity” Rate 3/4 30 20 10 0 -5 0 5 10 15 20 25 SNR for 10% PER (dB) Ravi Mahadevappa, Stephan ten Brink, Realtek

  37. 4x2 140 4x2 120 2(4)x2 CIRCSMX • Code rates 1/4, 1/3, 1/2, 2/3, 3/4, 7/8 • Modulation QPSK, 16QAM, 64QAM • 2(4)x2 CIRCAL/MRC better for low data rates 100 80 Rate (Mbps) 60 40 2(4)x2CIRCAL/MRC 20 0 -5 0 5 10 15 20 25 30 SNR for 10% PER (dB) Ravi Mahadevappa, Stephan ten Brink, Realtek

  38. 4x3 200 3(4)x3 CIRCSMX 180 4x3 • Code rates 1/4, 1/3, 1/2, 2/3, 3/4, 7/8 • Modulation QPSK, 16QAM, 64QAM • 2(4)x3 CIRCAL/MRC better for low data rates (hardly) • 2(4)x3 CIRCSMX better for medium data rates • 3(4)x3 CIRCSMX better for high data rates • Note for all SMX at low data rates: loss due to ZF/APP detection for small constellation size; that is why 2(4)x3 CIRCSMX better than 3(4)x3 CIRCSMX at medium data rates 160 140 120 2(4)x3 CIRCSMX 100 Rate (Mbps) 80 60 40 2(4)x3 CIRCAL/MRC 20 0 -10 -5 0 5 10 15 20 25 30 35 SNR for 10% PER (dB) Ravi Mahadevappa, Stephan ten Brink, Realtek

  39. 300 250 200 150 Rate (Mbps) 100 50 0 -10 -5 0 5 10 15 20 25 30 35 SNR for 10 % PER (dB) 4x4 4x4 • Code rates 1/4, 1/3, 1/2, 2/3, 3/4, 7/8 • Modulation QPSK, 16QAM, 64QAM • Similar situation as for 3x3 • 4x4 SMX only for highest rates 4x4 SMX 3(4)x4CIRCSMX 2(4)x4 CIRCSMX 2(4)x4CIRCAL/MRC Ravi Mahadevappa, Stephan ten Brink, Realtek

  40. Other Designs Considered • Linear dispersion (LD) codes [9] • Very general set-up • Powerful codes designed using an optimization algorithm • Good performance for any NT, NR • However, generally requires ML/APP detection (e.g. Sphere detection); complexity is an issue • Delay diversity • good for MIMO-OFDM since guard interval eliminates need for multi-tap channel equalizer • However, it has been shown that to obtain „full diversity“, the delay needs to be bigger than the guard interval (and, in turn, would require a multi-tap channel equalizer, counteracting the benefits of OFDM transmission) Ravi Mahadevappa, Stephan ten Brink, Realtek

  41. Some References [1] IEEE Std 802.11a-1999, Part 11: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) Specifications, High-speed Physical Layer in the 5 GHz Band [2] S. Sandhu, M. Ho, “Transmit diversity for MIMO OFDM”, IEEE 802.11-03/847r0, Nov. 2003 [3] H. Sampath, R. Narasimhan, “Advantages and drawbacks of circular delay diversity for MIMO-OFDM”, IEEE 802.11-04/075r1 [4] J. H. Winters, J. Salz, R. D. Gitlin, “The impact of antenna diversity on the capacity of wireless communication systems”, IEEE Trans. Commun., vol. 42, no. 2/3/4, pp. 1740-1751, Feb./Mar./Apr. 1994 [5] G. J. Foschini, “Layered space-time architecture for wireless communication in a fading environment when using multi-element antennas”,Bell Labs. Tech. J., vol. 1, no. 2, pp. 41-59, 1996 [6] H. Sampath, S. Talwar, J. Tellado, V. Erceg, A. Paulraj, “A fourth-generation MIMO-OFDM broadband wireless system: Design, performance, and field trial results”, IEEE Commun. Mag., pp. 143-149, Sept. 2002 [7] S. M. Alamouti, “A simple transmit diversity technique for wireless communications”, IEEE J. on Select. Areas in Commun., vol. 16, pp. 1451-1458, Oct. 1998 [8] V. Tarokh, H. Jafarkani, A. R. Calderbank, “Space-time block codes from orthogonal designs”, IEEE Trans. Inform. Theory, vol. 45, pp. 1456-1467, July 1999 [9] B. Hassibi, B. M. Hochwald, “High-rate codes that are linear in space and time,” IEEE Transactions on Information Theory, July 2002. Ravi Mahadevappa, Stephan ten Brink, Realtek

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