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Chapter 18

High Throughput (HT) and 802.11n. Chapter 18. Outline. 802.11n History MIMO HT Channels HT PHY HT MAC. 802.11n History. The main objective of the 802.11n draft amendment is to increase the data rates and the throughput in both the 2.4GHz and 5GHz frequency bands

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Chapter 18

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  1. High Throughput (HT) and 802.11n Chapter 18

  2. Outline • 802.11n History • MIMO • HT Channels • HT PHY • HT MAC

  3. 802.11n History • The main objective of the 802.11n draft amendment is to increase the data rates and the throughput in both the 2.4GHz and 5GHz frequency bands • The 802.11n defines a new operation knows as High Throughput (HT) • HT provides PHY and MAC enhancements to provide for data rates potentially as high as 600 Mbps

  4. 802.11n History • 802.11n Draft Amendment • 802.11n draft defines HT clause 20 radios that use multiple-input multiple-output (MIMO) technology in unison with OFDM technology • The beneficial consequences of using MIMO are increased throughput and even greater range • Enhancements to the MAC sublayer of the Data-Link layer • HT technology can be used in both the 2.4GHz and 5GHz

  5. 802.11n History • Wi-Fi Alliance Certification • The Wi-Fi Alliance currently has a vendor certification program called Wi-Fi CERTIFIEDTM802.11n draft 2.0 • All certified products must also support both Wi-Fi Multimedia (WMM) Quality-of-Service mechanisms and WPA/WPA2 security mechanisms

  6. MIMO • Radio Chains • Radio chain is defined as a single radio and all of its supporting architecture including mixers, amplifiers, and analog/digital converters • A MIMO system consists of multiple radio chains, with each radio chain having its own antenna • MIMO system is characterized by the number of transmitters and receivers used by the multiple radio chains

  7. MIMO • Spatial Multiplexing (SM) • MIMO radios transmit multiple radio signal at the same time and take advantage of multipath • Each independent signal is known as a spatial stream • Each unique radio can contain different data than the other streams transmitted by one or more of the other radios • Each stream will also travel a different path • The space between the transmitting antennas is known as spatial diversity

  8. MIMO • Spatial Multiplexing (SM) • Sending multiple independent streams of unique data using spatial diversity is often also referred to as spatial multiplexing (SM) • When using spatial multiplexing, both the transmitter and receiver must be MIMO systems • The benefits of sending multiple unique data streams is that throughput is drastically increased

  9. MIMO • MIMO Diversity • MIMO systems employ advanced antenna diversity capabilities that are analogous to having multiple ears • When receive diversity is used, the signals may also be linearly combined by using a signal processing technique called maximal ratio combining (MRC) • MRC algorithms are used to combine multiple received signals by looking at each unique signal and optimally combining the signals in a method that is additive as opposed to destructive

  10. MIMO • Transmit Beamforming (TxBF) • The 802.11n draft amendment also proposes an optional PHY capability called transmit beamforming (TxBF) • Beamforming technology is also known as a phased-array antenna system and is often referred to as smart antenna technology • Two major types of smart antenna • Switched antenna array uses a number of fixed beam patterns • Adaptive antenna array maneuvers the beam in the direction of targeted receiver

  11. HT Channels • 20MHz Non-HT and HT Channels • 802.11a and 802.11g use 20MHz OFDM channel, each channel consists of 52 subcarriers • 48 of the subcarriers transmit data • 4 of the subcarriers are used as pilot tones for dynamic calibration between the transmitter and receiver • The 20MHz channels used by HT radio have 4 extra subcarriers and can carry a little more data than a non-HT

  12. HT Channels • 20MHz Non-HT and HT Channels • 802.11a and 802.11g use 20MHz OFDM channel, each channel consists of 52 subcarriers • 48 of the subcarriers transmit data • 4 of the subcarriers are used as pilot tones for dynamic calibration between the transmitter and receiver • The 20MHz channels used by HT radio have 4 extra subcarriers and can carry a little more data than a non-HT

  13. HT Channels • 40MHz Channels • 108 of the subcarriers transmit data • 6 of the subcarriers are used as pilot tones for dynamic calibration between the transmitter and receiver

  14. HT MAC • A-MSDU • Aggregate MAC Service Data Unit • Multiple MSDUs can be aggregate into a single frame transmission • A-MPDU • Aggregate MAC Protocol Data Unit • Multiple MPDU can be can be aggregate into a single frame transmission

  15. HT MAC • MTBA • Multiple traffic ID block ACK frame • Block ACK are also needed to cover the multiple MPDU that are aggregated inside a single A-MPDU transmission • RIFS • Reduced interframe space (RIFS) • SIFS interval: 16µ • RIFS interval: 2µ

  16. The END Chapter 18

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