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High Throughput (HT) and 802.11n Module-10B

High Throughput (HT) and 802.11n Module-10B. Jerry Bernardini Community College of Rhode Island . Presentation Reference Material. CWNA Certified Wireless Network Administration Official Study Guide (PWO-104), David Coleman, David Westcott, 2009, Chapter-18

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High Throughput (HT) and 802.11n Module-10B

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  1. High Throughput (HT) and 802.11nModule-10B Jerry Bernardini Community College of Rhode Island CCRI J. Bernardini

  2. Presentation Reference Material • CWNA Certified Wireless Network Administration Official Study Guide (PWO-104), David Coleman, David Westcott, 2009, Chapter-18 • 802.11n Demystified Companion Guide, Xirrus Inc • USING MIMO-OFDM TECHNOLOGY TO BOOST WIRELESS LAN PERFORMANCE TODAY - DATACOMM RESEARCH COMPANY Wireless Networking J. Bernardini

  3. 802.11 Summary Characteristics CCRI J. Bernardini

  4. 802.11n Requirements Backward compatible with 802.11abg Higher throughput than 802.11abg Mixed mode operation CCRI J. Bernardini

  5. Review 802.11g Protection • Before an 802.11g client can transmit to an 802.11g AP it must reserve the medium. • Must transmit so 802.11b will understand. • Two Protection Methods • CTS-to self at 802.11b modulation (slow Clear to Send) • RTS-CTS at 802.11b modulation • CTS-to-self is more efficient but may not be seen by hidden-node • RTS-CTS is more reliable but has more overhead • Both Methods dramatically reduce the 802.11g throughput CCRI J. Bernardini

  6. 802.11b/g Mixed Mode Operation Station802.11g Station802.11g AP 802.11g Station802.11b 1-Slow CTS 2-Slow CTS 2-Slow CTS 3-Fast Data 3-Fast Data 3-Fast Data CCRI J. Bernardini

  7. Protection Throughput Effect CCRI J. Bernardini

  8. 802.11g Conclusions • 802.11g is significantly faster then 802.11b for all conditions • 802.11b station associating with a 802.11g network drops throughput due to protection • 802.11b station does not have to be active to reduce throughput (just associated ) • Mixed 802.11b/g deployments are likely to be common for the foreseeable future • Mixed 802.11b/a deployments will have higher throughput • 802.11b/g/n will also have to provide protection CCRI J. Bernardini

  9. 802.11n History • In 2004 IEEE 802.11 Group-n formed to improve 802.11 standards • 2009 802.11n draft • Main objectives • Increase data rates and throughput • Operate in 2.4 GHz and 5 GHz bands • 802.11n Draft defines High Throughput (HT) • Defines PHY and MAC enhancements • Can provide data rates up to 600Mbps • Wi-Fi Alliance Certification CCRI J. Bernardini

  10. 802.11n Draft Amendment • Defines HT • Uses Multiple-input Multiple-output (MIMO) • OFDM • MAC layer enhancements • Backward compatible to 802.11abg Wireless Networking J. Bernardini

  11. Wi-Fi Alliance Certification802.11n • Most vendors say draft 2.0 software can be upgraded to 802.11n final • Two spatial stream support-mandatory • Two spatial receive stream support-mandatory • A-MPDU and A-MSDU support- mandatory • Block ACK support-mandatory • Dual Band support-optional • 40 MHz band support-optional • Greenfield support –optional • Short guard interval-optional • Concurrent 2.4 GHz and 5Ghz--optional Wireless Networking J. Bernardini

  12. MIMO • Multiple-input Multiple-output (MIMO) • Takes advantage of multipath • Multiple radios and antennas Transmitter x Receiver MIMO TxRxMIMO 2 3 2x3 3 3 3x3 4 4 4x4 CCRI J. Bernardini

  13. Antenna Beamforming and Diversity Beamforming (beam steering) employs two transmit antennas to deliver the best multipath signal Diversity (receive combining) uses two receive antennas to capture the best multipath signal Wireless Networking J. Bernardini

  14. Multi-Antenna Systems not the Same Multi-antennas beam steering/diversity approach, only one signal is sent over the channel. MIMO uses multiple transmitters, receivers and antennas to send multiple signals over the same channel, multiplying spectral efficiency. Wireless Networking J. Bernardini

  15. MIMO and Multi-path • Normally when a signal is transmitted from A to B the signal will reach the receiving antenna via multiple paths, causing interference. • MIMO uses this multipath propagation to increase the data rate by using a technique known as spatial division multiplexing. • The data is split into a number of spatial streams and these are transmitted through separate antennas to corresponding antennas at the receiver. • Doubling the number of spatial streams doubles the raw data rate, enabling a far greater utilization of the available bandwidth. • The current 802.11n standard allows for up to four spatial streams. Wireless Networking J. Bernardini

  16. Spatial Multiplexing (SM or SDM) • MIMO employs multiple independent radio transmitter-receiver pairs • Radio pairs send independent signals • Transmitter antennas spaced by half-wave length or more – insuring different paths • Each independent signal is a spatial stream • Spatial streams are combined at the access point • Referred to as: • Spatial Multiplexing (SM) or • Spatial Diversity Multiplexing (SDM) Wireless Networking J. Bernardini

  17. MIMO Diversity • Increasing the number of receiving antennas can improve overall signal to noise • Pre-802.11n used switched diversity to select best multipath signal • Increasing antennas (3 or 4) increases the receiver choice for a “good” signal • MIMO maximal ratio combining (MRC) allows for additive effective of multipath signals – increasing signal to noise ratio Wireless Networking J. Bernardini

  18. Transmit Beamforming (TxBF) • 802.11n optional feature • Multiple transmitter antennas “focus” the signal to a receiver • Used by radar; phased-array antenna systems • Transmitter is the beamformer • Receiver is the beamformee • Feedback from the beamformee allows the beamformer to adjust the antennas and signal to improve SNR Wireless Networking J. Bernardini

  19. 802.11n HT Channel Technology • 802.11n uses OFDM (just as 802.11ag) • 802.11n has option to use 20 MHz and 40 MHz channels • 802.11n can use can combine channels for Channel Bonding • 802.11n can use variable Guard Interval (GI) • 802.11n can use various Modulation and Coding Schemes (MCS) CCRI J. Bernardini

  20. Non-HT and HT Channels (clause 20) • 802.11ag use 20 MHz OFDM channels • Each channel are made of 52 subcarriers • 48-subcarriers transmit data • 4-subcarriers transmit pilot tones for transmitter-receiver calibrations • 802.11n can use either 20 MHz or 40 MHz channels • Each HT 20 MHz channel has 56 subcarriers • 52-subcarriers transmit data • 4-subcarriers transmit pilot tones for transmitter-receiver calibrations • Each HT 40 MHz channel has 114 subcarriers • 108-subcarriers transmit data • 6-subcarriers transmit pilot tones for transmitter-receiver calibrations Wireless Networking J. Bernardini

  21. Channel Bonding • 40 MHz channels are formed by bonding two 20MHz channels • When bonding two channels there no need for a guard band • 5 GHz UNNI band allows twenty three 20 MHz channels to be bonded • 2.4 GHz ISM band allows only one bonding of two 20 MHz channels (only 3 non-overlapping channels) Wireless Networking J. Bernardini

  22. Channel Bonding Wireless Networking J. Bernardini

  23. Guard Interval (GI) • Digital Symbol is a collection of bits • If the bits overlap Inter-symbol Interference (ISI) is experienced • 802.11ag uses a 800 ns guard interval between symbols • 802.11n can use a 800 ns or 400 ns guard interval between symbols • 400 ns GI improves throughput by 10% • The 400 ns GI should only be used in a “good” RF environment Wireless Networking J. Bernardini

  24. Modulation and Coding Schemes (MCS) • 802.11n defines data rates as Modulation and Coding Schemes (MCS) • MCS are based upon • Modulation technique (BPSK, QPSK, 16-QAM, 64-QAM) • Spatial streams (1, 4) • Channel size (20 MHz, 40 MHz) • Guard Interval (400 ns, 800 ns) • 802.11n requires Eight mandatory 20 MHz MCSs • Total of 78 MCSs • Data rates vary from 6.5 Mbps to 600 Mbps Wireless Networking J. Bernardini

  25. HT PHY and MPDU • 802.11 frame is a MAC Protocol Data Unit (MPDU) • The payload is the MAC service Unit (MSDU) (layer 7-3 data) • MPDU is made up of the header and body • At the PHY layer is the Physical Layer Protocol Data Unit (PPDU) • PPDU = MPDU + PHY preamble-header • 802.11n defines three PHY preamble-headers • Legacy format, HT Mixed, HT Greenfield CCRI J. Bernardini

  26. HT PPDU Formats • Non-HT Legacy • Mandatory for 802.11n • Only 20 MHz channels • Same format as 802.11ag • HT Mixed • Two part preamble • First part can be decoded by 802.11ag • Second part can not be decoded by 802.11ag • HT Greenfield • Preamble can not be decoded by 802.11ag • Can use both 20 MHz and 40 MHz channels Wireless Networking J. Bernardini

  27. HT MAC CCRI J. Bernardini

  28. HT Operation • 20/40 Channel Operation • Legacy 802.11 communication using 20 MHz only • 802.11n can use 20MHz or 40 MHz • HT protection Modes • Four modes • Mode 0, 1, 2, 3 • Dual-CTS protection • Send both legacy and HT RTS/CTS combinations • Phased Coexistence Operation (PCO) • Time slices between 20MHz or 40 MHz channel usage CCRI J. Bernardini

  29. Through Put Comparison Wireless Networking J. Bernardini

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