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What Is Being Proposed for 802.11n?

MIMO Technology for Advanced Wireless Local Area Networks Dr. Won- Joon Choi Dr. Qinfang Sun Dr. Jeffrey M. Gilbert Atheros Communications MIMO RAKE Antenna Technology for Advanced MIMO Wireless WAN and LAN Pr. Jean-Claude Ducasse Hypercable Telecommunications.

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What Is Being Proposed for 802.11n?

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  1. MIMO Technology for Advanced Wireless Local Area NetworksDr. Won-JoonChoiDr. Qinfang Sun Dr. Jeffrey M. Gilbert Atheros Communications MIMO RAKE Antenna Technology for Advanced MIMO Wireless WAN and LAN Pr. Jean-Claude Ducasse Hypercable Telecommunications

  2. What Is Being Proposed for 802.11n? Main Features • PHY • MIMO-OFDM • Beamforming • Spatial Multiplexing • Extended bandwidth (40MHz) • Advanced coding • MAC • Aggregation • Block ACK • Coexistence • Power saving

  3. Wireless Fundamentals I In order to successfully decode data, signal strength needs to be greater than noise + interference by a certain amount • Higher data rates require higher SINR (Signal to Noise and Interference Ratio) • Signal strength decreases with increased range in a wireless environment

  4. Wireless Fundamentals II Ways to increase data rate: • Conventional single tx and rx radio systems • Increase transmit power • Subject to power amplifier and regulatory limits • Increases interference to other devices • Reduces battery life • Use high gain directional antennas • Fixed direction(s) limit coverage to given sector(s) • Use more frequency spectrum • Subject to FCC / regulatory domain constraints • Advanced MIMO: Use multiple tx and / or rx radios!

  5. channel Conventional (SISO) Wireless Systems Conventional “Single Input Single Output” (SISO) systems were favored for simplicity and low-cost but have some shortcomings: • Outage occurs if antennas fall into null • Switching between different antennas can help • Energy is wasted by sending in all directions • Can cause additional interference to others • Sensitive to interference from all directions • Output power limited by single power amplifier Bits DSP DSP Radio Radio Bits TX RX

  6. channel MIMO Wireless Systems Multiple Input Multiple Output (MIMO) systems with multiple parallel radios improve the following: • Outages reduced by using information from multiple antennas • Transmit power can be increased via multiple power amplifiers • Higher throughputs possible • Transmit and receive interference limited by some techniques Radio Radio DSP DSP Bits Bits Radio Radio TX RX

  7. MIMO Alternatives There are two basic types of MIMO technology: • Beamforming MIMO • Standards-compatible techniques to improve the range of existing data rates using transmit and receive beamforming • Also reduces transmit interference and improves receive interference tolerance • Spatial-multiplexing MIMO • Allows even higher data rates by transmitting parallel data streams in the same frequency spectrum • Fundamentally changes the on-air format of signals • Requires new standard (11n) for standards-based operation • Proprietary modes possible but cannot help legacy devices

  8. Beamforming MIMO Overview Consists of two parts to make standard 802.11 signals “better Uses multiple transmit and/or receive radios to form coherent 802.11a/b/g compatible signals • Receive beamforming / combiningboosts reception of standard 802.11 signals Radio DSP Bits Bits Radio TX Radio RX • Phased array transmit beamforming to focus energy to each receiver DSP Radio Bits Bits Radio Radio RX TX

  9. Benefits of Beamforming Benefits • Power gain (applicable only to transmit beamforming) • Power from multiple PA’s simultaneously (up to regulatory limits) • Relaxes PA requirements, increases total output power delivered • Array gain: “dynamic high-gain antenna” • Interference reduction • Reduce co-channel inter-cell interference • Diversity gain: combats fading effects • Multipath mitigation • Per- subcarrier beamforming to reduce spectral nulls

  10. Multipath Mitigation • Multiple transmit and receive radios allow compensation of notches on one channel by non-notches in the other • Same performance gains with either multiple tx or rx radios and greater gains with both multiple tx and rx radios

  11. Spatial Multiplexing MIMO Concept Spatial multiplexing concept: • Form multiple independent links (on same channel) between transmitter and receiver to communicate at higher total data rates Radio DSP Radio DSP BitMerge BitSplit Bits Bits DSP Radio DSP Radio RX TX

  12. MIMO RAKE Antenna Concept • Dual CircularPolarizationDiversity • Spatial Multiplexing • Multipath Mitigation • Spacediversity • Beamforming Radio Radio Radio Radio DSP DSP DSP DSP RX BitSplit BitSplit Radio Radio DSP DSP BitMerge BitMerge Bits TX TX DSP DSP Radio Radio GIGABIT I/O & POE RX Bits Bits Bits Bits

  13. Spatial Multiplexing MIMO Difficulties Spatial multiplexing concept: • Form multiple independent links (on same channel) between transmitter and receiver to communicate at higher total data rates • However, there are cross-paths between antennas Radio DSP Radio DSP BitMerge BitSplit Garbage Bits DSP Radio DSP Radio RX TX

  14. Spatial Multiplexing MIMO Reality Spatial multiplexing concept: • Form multiple independent links (on same channel) between transmitter and receiver to communicate at higher total data rates • However, there are cross-paths between antennas • The correlation must be decoupled by digital signal processing algorithms DSP Radio DSP Radio BitMerge BitSplit Bits Bits DSP Radio Radio RX TX

  15. MIMO RAKE Antenna Solution • Dual CircularPolarizationDiversity • Spatial Multiplexing • Multipath Mitigation • Spacediversity • Beamforming Radio Radio Radio Radio DSP DSP DSP DSP RX BitSplit BitSplit Radio Radio DSP DSP BitMerge BitMerge Bits TX TX DSP DSP Radio Radio GIGABIT I/O & POE RX Bits Bits Bits Bits

  16. Spatial Multiplexing MIMO Theory • High data rate • Data rate increases by the minimum of number of transmit and receive antennas • Detection is conceptually solving equations Example of 2-by-2 system: • Transmitted signal is unknown, • Received signal is known, • Related by the channel coefficients, • Need more equations than unknowns to succeed • High spectral efficiency • Higher data rate in the same bandwidth

  17. MIMO Scalability • Data Rates • R = Es * Bw * Ns -> Scales with bandwidth and the number of spatial streams • Example • 11a/g: Es = 2.7; Bw = 20MHz; Ns=1; R = 54Mbps • Spatial multiplexing MIMO Es = 3.75; Bw=40MHz;Ns = 2; R = 300Mbps • Number of Tx/Rx chains • At least as many chains as Ns Ns = min(NR, NT)

  18. MIMO Hardware Requirements MIMO Transmitter (parallelism and data rate scaling) IFFT MOD RF Stream Split Spatial Mapping FEC RF IFFT MOD 1 *O(Bw*Es*Ns) Ns *O(Bw*Es) 1* O(Bw*Es*Ns*NT) NT* O(Bw*Es) NT* Analog RF

  19. DEC FFT FFT MIMO Hardware Requirements MIMO Receiver (parallelism and data rate scaling) Demod RF Stream Merge MIMO Equalizer RF Demod NR* Analog RF NR* O(Bw*Es) 1* O(Bw*Es*NR*Ns2) Ns* O(Bw*Es) Ns* O(Bw*Es) 1* O(Bw*Es*Ns)

  20. Conclusions • The next generation WLAN uses MIMO technology • Beamforming MIMO technology • Extends range of existing data rates by transmit and receive beamforming • Spatial-multiplexing MIMO technology • Increases data rates by transmitting parallel data streams • MIMO allows system designers to leverage Moore’s law to deliver higher performance wireless systems

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