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2. 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

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

4. Office Email / Info anywhere Voice over IP “Hot-spots” Hot-spot coverage Metro-Area Networks Home Internet everywhere Multimedia The Wireless LAN Explosion The Wireless LAN / Wi-Fi market has exploded! New technology is enabling new applications:

5. Wireless LAN Technology Advances Wireless LAN technology has seen rapid advancements Standards: Standards: Data rates: Data rates: Range / coverage: Range / coverage: Integration: Integration: Cost: Cost: 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 802.11 .11b .11a .11g

6. 802.11b802.11a802.11g802.11n Standard Approved Sept. 1999 June2003? Available Bandwidth 83.5 MHz 580 MHz 83.5 MHz 83.5/580MHz Frequency Band of Operation 2.4 GHz 5 GHz 2.4 GHz 2.4/5 GHz # Non-Overlapping Channels (US) 32433/24 Data Rate per Channel 1 – 11 Mbps 6 – 54 Mbps 1 – 54 Mbps 1 – 600 Mbps Modulation Type DSSS, CCK OFDM DSSS, CCK, OFDM OFDM,MIMO Existing 802.11 WLAN Standards

7. What Is Being Proposed for 802.11n? Main Features PHY PHY MIMO-OFDM MIMO-OFDM Beamforming Beamforming Spatial Multiplexing Spatial Multiplexing Extended bandwidth (40MHz) Extended bandwidth (40MHz) Advanced coding Advanced coding MAC MAC Aggregation Aggregation Block ACK Block ACK Coexistence Coexistence Power saving 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) Higher data rates require higher SINR (Signal to Noise and Interference Ratio) Signal strength decreases with increased range in a wireless environment 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 Conventional single tx and rx radio systems Increase transmit power Increase transmit power Subject to power amplifier and regulatory limits Subject to power amplifier and regulatory limits Increases interference to other devices Increases interference to other devices Reduces battery life Reduces battery life Use high gain directional antennas Use high gain directional antennas Fixed direction(s) limit coverage to given sector(s) Fixed direction(s) limit coverage to given sector(s) Use more frequency spectrum Use more frequency spectrum Subject to FCC / regulatory domain constraints Subject to FCC / regulatory domain constraints Advanced MIMO: Use multiple tx and / or rx radios! Advanced MIMO: Use multiple tx and / or rx radios!

10. 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 Outage occurs if antennas fall into null Switching between different antennas can help Switching between different antennas can help Energy is wasted by sending in all directions Energy is wasted by sending in all directions Can cause additional interference to others Can cause additional interference to others Sensitive to interference from all directions Sensitive to interference from all directions Output power limited by single power amplifier Output power limited by single power amplifier channel Radio DSP Bits TX Radio DSP Bits RX

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

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

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

14. Benefits of Beamforming Benefits Power gain (applicable only to transmit beamforming) Power gain (applicable only to transmit beamforming) Power from multiple PA’s simultaneously (up to regulatory limits) Power from multiple PA’s simultaneously (up to regulatory limits) Relaxes PA requirements, increases total output power delivered Relaxes PA requirements, increases total output power delivered Array gain: “dynamic high-gain antenna” Array gain: “dynamic high-gain antenna” Interference reduction Interference reduction Reduce co-channel inter-cell interference Reduce co-channel inter-cell interference Diversity gain: combats fading effects Diversity gain: combats fading effects Multipath mitigation Multipath mitigation Per- subcarrier beamforming to reduce spectral nulls 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 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 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 Form multiple independent links (on same channel) between transmitter and receiver to communicate at higher total data rates Radio DSP Bit Split Bits Bit Merge TX Radio RX Bits DSP

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 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 However, there are cross-paths between antennas Radio DSP Bit Split Bits Bit Merge TX Radio RX Garbage DSP

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

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

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

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

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

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

24. MIMO Receiver (parallelism and data rate scaling) MIMO Hardware Requirements 1* O(Bw*Es*Ns) DEC Stream Merge Demod MIMO Equalizer FFT RF N R * Analog RF 1* O(Bw*Es*N R *Ns 2 ) N R * O(Bw*Es) N s * O(Bw*Es) N s * O(Bw*Es)

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

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

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

28. Backup Slides 0.18um standard digital CMOS 0.18um standard digital CMOS 7.2x7.2 mm 2 die size 7.2x7.2 mm 2 die size 15x15mm 2 BGA with 261 balls 15x15mm 2 BGA with 261 balls Ref: ISSCC’05 Ref: ISSCC’05

29. Backup Slides MIPS R4Kc, 16kB I and D caches 180 MHz 16b SDRAM interface 100 MHz 9b ADCs (4x) < 0.65 LSB INL&DNL, -48dB SNDR, 27mW 9b DACs (4x) <0.25 LSB INL&DNL, -51dB SNDR, 20mW Total power, PCI mode, CPU off 690 mW Total power, MPEG-TS mode, CPU on 1.8W Supports 802.11 a, b, g, 20 and 40 MHz channel BW 1 to 108 Mb/s raw data rates

30. Backup Slides