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Click to enter your title. MIMO Technology for Advanced Wireless Local Area Networks Dr. Won-Joon Choi Dr. Qinfang Sun Dr. Jeffrey M. Gilbert Atheros Communications 2005 Design Automation Conference – June 15, 2005. Agenda.

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  1. Click to enter your title

  2. MIMO Technology for Advanced Wireless Local Area NetworksDr. Won-Joon ChoiDr. Qinfang Sun Dr. Jeffrey M. Gilbert Atheros Communications2005 Design Automation Conference – June 15, 2005

  3. Agenda • This presentation will give an overview of MIMO technology and its future in Wireless LAN: • Wireless Local Area Networks (WLAN) • Current standards (11a/b/g) • Next-generation 11n overview and status • MIMO fundamentals • Beamforming • Spatial Multiplexing • MIMO scalability • Bandwidth • Number of spatial streams

  4. Email / Info anywhereVoice over IP Internet everywhereMultimedia Hot-spot coverageMetro-Area Networks The Wireless LAN Explosion The Wireless LAN / Wi-Fi market has exploded! New technology is enabling new applications: Office Home “Hot-spots”

  5. Wireless LAN Technology Advances Wireless LAN technology has seen rapid advancements • Standards: • Data rates: • Range / coverage: • Integration: • Cost: 802.11  .11b  .11a  .11g 2Mbps  100+ Mbps Meters  kilometers Multiple discretes  single chip solutions $100’s  $10’s (sometimes free w/rebates!) • How can this growth continue? • Previous advances have been limited to a single transmitting and receiving radio • The next generation exploits multiple parallel radios using revolutionary class of techniques called MIMO (Multiple Input Multiple Output) to send information farther and faster

  6. Existing 802.11 WLAN Standards

  7. 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

  8. 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

  9. 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!

  10. 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

  11. 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

  12. 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

  13. 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

  14. 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

  15. 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

  16. 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

  17. 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

  18. 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

  19. 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

  20. MIMO Scalability • Moore’s law • Doubling transistors every couple of years • MIMO • Increases number of streams • Higher performance/speed • Higher complexity MIMO is the bridge to allow us to exploit Moore’s law to get higher performance

  21. MIMO Scalability • Notation • R: data rates (Mbps) • Es: spectral efficiency (bps/Hz) • Bw: bandwidth (MHz) • Ns: number of spatial streams • NR: number of Rx chains • NT: number of Tx chains

  22. 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)

  23. 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

  24. 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)

  25. 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

  26. Circuit Implications of MIMO • Crystal • Common crystal is required • Synthesizer • Common synthesizer is preferred • PA • Allow additional flexibility • With total power limit, PA requirements relaxed • With PA limit, total power increased. • Cross-talk/ Coupling • Need to minimize coupling between antennas

  27. Circuit Impairments/Corrections • Timing offset • Common across multiple chains • Frequency offset • Common across multiple chains • Phase noise • Common with common synthesizer • With independent synthesizers, a new tracking algorithm may be needed. • Other impairments • 1/f noise, I/Q mismatch, spurs, etc. • Estimated and corrected for each chain

  28. Backup Slides • 0.18um standard digital CMOS • 7.2x7.2 mm2 die size • 15x15mm2 BGA with 261 balls • Ref: ISSCC’05

  29. Backup Slides

  30. Backup Slides

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