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.

Click to enter your title

MIMO Technology for MIMO Technology for Advanced Wireless Local Area NetworksAdvanced Wireless Local Area Networks

Dr. Won-Joon ChoiDr. Won-Joon ChoiDr. Qinfang SunDr. Qinfang Sun

Dr. Jeffrey M. Gilbert Dr. Jeffrey M. Gilbert Atheros CommunicationsAtheros Communications

2005 Design Automation Conference – June 15, 20052005 Design Automation Conference – June 15, 2005

AgendaAgenda

This presentation will give an overview of This presentation will give an overview of MIMO technology and its future in Wireless MIMO technology and its future in Wireless LAN: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 statusNext-generation 11n overview and status

MIMO fundamentalsMIMO fundamentals BeamformingBeamforming Spatial MultiplexingSpatial Multiplexing

MIMO scalabilityMIMO scalability BandwidthBandwidth Number of spatial streamsNumber of spatial streams

Office

Email / Info anywhereVoice over IP

“Hot-spots”

Hot-spot coverageMetro-Area Networks

Home

Internet everywhereMultimedia

The Wireless LAN ExplosionThe Wireless LAN Explosion

The Wireless LAN / Wi-Fi market has exploded!

New technology is enabling new applications:

Wireless LAN Technology Wireless LAN Technology AdvancesAdvances

Wireless LAN technology has seen rapid advancementsWireless 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

802.11b802.11b 802.11a802.11a 802.11g802.11g 802.11n802.11n

Standard ApprovedStandard Approved Sept. 1999Sept. 1999 Sept. 1999Sept. 1999 June June 20032003 ??

Available BandwidthAvailable Bandwidth 83.5 MHz83.5 MHz 580 MHz580 MHz 83.5 MHz83.5 MHz 83.5/58083.5/580MHzMHz

Frequency Band of Frequency Band of Operation Operation 2.4 GHz2.4 GHz 5 GHz5 GHz 2.4 GHz2.4 GHz 2.4/5 GHz2.4/5 GHz

# Non-Overlapping # Non-Overlapping Channels (US) Channels (US) 33 2424 33 3/243/24

Data Rate per ChannelData Rate per Channel 1 – 11 1 – 11 MbpsMbps

6 – 54 6 – 54 MbpsMbps

1 – 54 1 – 54 MbpsMbps

1 – 600 1 – 600 MbpsMbps

Modulation TypeModulation Type DSSS, CCKDSSS, CCK OFDMOFDMDSSS, DSSS, CCK,CCK,

OFDMOFDM

DSSS, DSSS, CCK,CCK,

OFDM,OFDM,MIMOMIMO

Existing 802.11 WLAN Existing 802.11 WLAN StandardsStandards

What Is Being Proposed for What Is Being Proposed for 802.11n?802.11n?

Main FeaturesMain Features PHYPHY

MIMO-OFDMMIMO-OFDM BeamformingBeamforming Spatial MultiplexingSpatial Multiplexing

Extended bandwidth (40MHz)Extended bandwidth (40MHz) Advanced codingAdvanced coding

MACMAC AggregationAggregation Block ACKBlock ACK CoexistenceCoexistence Power savingPower saving

0

10

20

30

40

50

60

1 2 3 4 5 6 7 8 9 10 11 12

Range

Th

rou

gh

pu

t

Data Rate 1

Data Rate 2

Wireless Fundamentals IWireless Fundamentals IIn order to successfully decode data, signal strength needs In order to successfully decode data, signal strength needs

to be greater than noise + interference by a certain to be greater than noise + interference by a certain amountamount Higher data rates require higher SINR (Signal to Noise and Higher data rates require higher SINR (Signal to Noise and

Interference Ratio)Interference Ratio) Signal strength decreases with increased range in a Signal strength decreases with increased range in a

wireless environmentwireless environment

Wireless Fundamentals IIWireless Fundamentals II

Ways to increase data rate:Ways to increase data rate: Conventional single tx and rx radio systemsConventional single tx and rx radio systems

Increase transmit powerIncrease transmit power Subject to power amplifier and regulatory limitsSubject to power amplifier and regulatory limits Increases interference to other devicesIncreases interference to other devices Reduces battery lifeReduces battery life

Use high gain directional antennasUse 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 spectrumUse more frequency spectrum Subject to FCC / regulatory domain constraintsSubject to FCC / regulatory domain constraints

Advanced MIMO: Use multiple tx and / or rx Advanced MIMO: Use multiple tx and / or rx radios!radios!

Conventional (SISO) Conventional (SISO) Wireless SystemsWireless Systems

Conventional “Single Input Single Output” Conventional “Single Input Single Output” (SISO) systems were favored for simplicity (SISO) systems were favored for simplicity and low-cost but have some shortcomings:and low-cost but have some shortcomings: Outage occurs if antennas fall into nullOutage occurs if antennas fall into null

Switching between different antennas can helpSwitching between different antennas can help Energy is wasted by sending in all directionsEnergy is wasted by sending in all directions

Can cause additional interference to othersCan cause additional interference to others Sensitive to interference from all directionsSensitive to interference from all directions Output power limited by single power amplifierOutput power limited by single power amplifier

channelRadioDSPBits

TX

Radio DSP Bits

RX

MIMO Wireless SystemsMIMO Wireless Systems

Multiple Input Multiple Output (MIMO) systems with multiple Multiple Input Multiple Output (MIMO) systems with multiple parallel radios improve the following:parallel radios improve the following: Outages reduced by using information from multiple antennasOutages reduced by using information from multiple antennas Transmit power can be increased via multiple power amplifiersTransmit power can be increased via multiple power amplifiers Higher throughputs possibleHigher throughputs possible Transmit and receive interference limited by some techniquesTransmit and receive interference limited by some techniques

channel

Radio

DSP

Bits

TX

Radio

Radio

DSP

Bits

RX

Radio

MIMO AlternativesMIMO Alternatives

There are two basic types of MIMO technology:There are two basic types of MIMO technology:

Beamforming MIMOBeamforming MIMO Standards-compatible techniques to improve the range of Standards-compatible techniques to improve the range of

existing data rates using transmit and receive beamformingexisting data rates using transmit and receive beamforming Also reduces transmit interference and improves receive Also reduces transmit interference and improves receive

interference toleranceinterference tolerance

Spatial-multiplexing MIMOSpatial-multiplexing MIMO Allows even higher data rates by transmitting parallel data Allows even higher data rates by transmitting parallel data

streams in the same frequency spectrumstreams in the same frequency spectrum Fundamentally changes the on-air format of signalsFundamentally 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 devicesProprietary modes possible but cannot help legacy devices

Beamforming MIMO OverviewBeamforming MIMO Overview

Consists of two parts to make standard 802.11 signals “betterConsists of two parts to make standard 802.11 signals “better Uses multiple transmit and/or receive radios to form coherent Uses multiple transmit and/or receive radios to form coherent 802.11a/b/g compatible signals802.11a/b/g compatible signals

Receive beamformingReceive beamforming / combining / combining boosts reception of boosts reception of standard 802.11 signalsstandard 802.11 signals

Phased array transmit beamforming to focus energy to each receiver

Radio

DSP

BitsRadio

RX

BitsTX

BitsRXRadio

DSP

BitsRadio

TX

Radio

Radio

Benefits of BeamformingBenefits of BeamformingBenefitsBenefits

Power gain (applicable only to transmit Power gain (applicable only to transmit beamforming)beamforming)

Power from multiple PA’s simultaneously Power from multiple PA’s simultaneously (up to regulatory limits)(up to regulatory limits)

Relaxes PA requirements, increases total Relaxes PA requirements, increases total output power deliveredoutput power delivered

Array gain: Array gain: “dynamic high-gain antenna”“dynamic high-gain antenna”

Interference reductionInterference reduction Reduce co-channel inter-cell interferenceReduce co-channel inter-cell interference

Diversity gain: Diversity gain: combats fading effectscombats fading effects

Multipath mitigationMultipath mitigation Per- subcarrier beamforming to reduce spectral Per- subcarrier beamforming to reduce spectral

nullsnulls

Multipath MitigationMultipath Mitigation

Multiple transmit and receive radios allow compensation of Multiple transmit and receive radios allow compensation of notches on one channel by non-notches in the othernotches on one channel by non-notches in the other

Same performance gains with Same performance gains with either either multiple tx or rx radios multiple tx or rx radios and greater gains with and greater gains with bothboth multiple tx and rx radios multiple tx and rx radios

Spatial Multiplexing MIMO Spatial Multiplexing MIMO ConceptConcept

Spatial multiplexing concept:Spatial multiplexing concept:

Form multiple independent links (on same channel) Form multiple independent links (on same channel) between transmitter and receiver to communicate at between transmitter and receiver to communicate at higher total data rateshigher total data rates

Radio

Radio

DSP

DSP

BitSplit

BitsBit

Merge

TX

Radio

RadioRX

BitsDSP

DSP

Spatial Multiplexing MIMO Spatial Multiplexing MIMO DifficultiesDifficulties

Spatial multiplexing concept:Spatial multiplexing concept:

Form multiple independent links (on same channel) Form multiple independent links (on same channel) between transmitter and receiver to communicate at between transmitter and receiver to communicate at higher total data rateshigher total data rates

However, there are cross-paths between antennasHowever, there are cross-paths between antennas

Radio

Radio

DSP

DSP

BitSplit

BitsBit

Merge

TX

Radio

RadioRX

GarbageDSP

DSP

Spatial Multiplexing MIMO Spatial Multiplexing MIMO RealityReality

Radio

Radio

DSP

DSP

DSP

BitSplit

BitsBit

Merge

TX

Radio

Radio

Bits

RX

Spatial multiplexing concept:Spatial multiplexing concept:

Form multiple independent links (on same channel) Form multiple independent links (on same channel) between transmitter and receiver to communicate at between transmitter and receiver to communicate at higher total data rateshigher total data rates

However, there are cross-paths between antennasHowever, there are cross-paths between antennas

The correlation must be decoupled by digital signal The correlation must be decoupled by digital signal processing algorithmsprocessing algorithms

Spatial Multiplexing MIMO Spatial Multiplexing MIMO TheoryTheory

High data rateHigh data rate Data rate increases by the minimum of number of Data rate increases by the minimum of number of

transmit and receive antennastransmit and receive antennas Detection is conceptually solving equationsDetection is conceptually solving equations

Example of 2-by-2 system: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 succeedNeed more equations than unknowns to succeed

High spectral efficiencyHigh spectral efficiency Higher data rate in the same bandwidthHigher data rate in the same bandwidth

21, xx21, yy

2221212

2121111

xhxhy

xhxhy22211211 ,,, hhhh

Moore’s lawMoore’s law Doubling transistors every couple of yearsDoubling transistors every couple of years

MIMOMIMO Increases number of streamsIncreases number of streams Higher performance/speedHigher performance/speed Higher complexityHigher complexity

MIMO is the bridge to allow us to MIMO is the bridge to allow us to exploit Moore’s law to get higher exploit Moore’s law to get higher performanceperformance

MIMO ScalabilityMIMO Scalability

NotationNotation 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 streamsNs: number of spatial streams NNRR: number of Rx chains: number of Rx chains NNTT: number of Tx chains: number of Tx chains

MIMO ScalabilityMIMO Scalability

Data RatesData Rates R = Es * Bw * Ns -> ScalesR = Es * Bw * Ns -> Scales with bandwidth with bandwidth

and the number of spatial streamsand the number of spatial streams ExampleExample

11a/g: Es = 2.7; Bw = 20MHz; Ns=1; R = 11a/g: Es = 2.7; Bw = 20MHz; Ns=1; R = 54Mbps54Mbps

Spatial multiplexing MIMOSpatial multiplexing MIMOEs = 3.75; Bw=40MHz;Ns = 2; R = 300MbpsEs = 3.75; Bw=40MHz;Ns = 2; R = 300Mbps

Number of Tx/Rx chainsNumber of Tx/Rx chains At least as many chains as NsAt least as many chains as Ns

Ns = min(NNs = min(NRR, N, NTT))

MIMO ScalabilityMIMO Scalability

MIMO Transmitter (parallelism and data rate scaling)MIMO Transmitter (parallelism and data rate scaling)

MIMO Hardware RequirementsMIMO Hardware Requirements

FECStreamSplit

MOD

MOD

SpatialMapping

IFFT

IFFT

RF

RF

1 *O(Bw*Es*Ns)

Ns *O(Bw*Es)

1*O(Bw*Es*Ns*NT)

NT*O(Bw*Es)

NT*Analog RF

MIMO Receiver (parallelism and data rate scaling)MIMO Receiver (parallelism and data rate scaling)

MIMO Hardware RequirementsMIMO Hardware Requirements

1*O(Bw*Es*Ns)

DECStreamMerge

Demod

Demod

MIMOEqualizer

FFT

FFT

RF

RF

NR*Analog RF

1*O(Bw*Es*NR*Ns2)

NR*O(Bw*Es)

Ns*O(Bw*Es)

Ns*O(Bw*Es)

ConclusionsConclusions

The next generation WLAN uses MIMO technologyThe next generation WLAN uses MIMO technology Beamforming MIMO technologyBeamforming MIMO technology

Extends range of existing data rates by transmit and Extends range of existing data rates by transmit and receive beamformingreceive beamforming

Spatial-multiplexing MIMO technologySpatial-multiplexing MIMO technology Increases data rates by transmitting parallel data Increases data rates by transmitting parallel data

streamsstreams

MIMO allows system designers to leverage Moore’s MIMO allows system designers to leverage Moore’s law to deliver higher performance wireless law to deliver higher performance wireless systemssystems

Circuit Implications of MIMOCircuit Implications of MIMO CrystalCrystal

Common crystal is required Common crystal is required SynthesizerSynthesizer

Common synthesizer is preferredCommon synthesizer is preferred PAPA

Allow additional flexibility Allow additional flexibility With total power limit, PA requirements With total power limit, PA requirements

relaxedrelaxed With PA limit, total power increased.With PA limit, total power increased.

Cross-talk/ CouplingCross-talk/ Coupling Need to minimize coupling between Need to minimize coupling between

antennasantennas

Circuit Circuit Impairments/CorrectionsImpairments/Corrections Timing offsetTiming offset

Common across multiple chainsCommon across multiple chains Frequency offsetFrequency offset

Common across multiple chainsCommon across multiple chains Phase noisePhase noise

Common with common synthesizerCommon with common synthesizer With independent synthesizers, a new With independent synthesizers, a new

tracking algorithm may be needed.tracking algorithm may be needed. Other impairmentsOther impairments

1/f noise, I/Q mismatch, spurs, etc. 1/f noise, I/Q mismatch, spurs, etc. Estimated and corrected for each chainEstimated and corrected for each chain

Backup SlidesBackup Slides

0.18um 0.18um standard standard digital digital CMOSCMOS

7.2x7.2 7.2x7.2 mmmm2 2 die sizedie size

15x15mm15x15mm22 BGA with BGA with 261 balls261 balls

Ref: Ref: ISSCC’05ISSCC’05

Backup SlidesBackup Slides

MIPS R4Kc, 16kB I and D MIPS R4Kc, 16kB I and D cachescaches

180 MHz180 MHz

16b SDRAM interface16b SDRAM interface 100 MHz100 MHz

9b ADCs (4x)9b ADCs (4x) < 0.65 LSB INL&DNL, -48dB < 0.65 LSB INL&DNL, -48dB SNDR, 27mWSNDR, 27mW

9b DACs (4x)9b DACs (4x) <0.25 LSB INL&DNL, -51dB <0.25 LSB INL&DNL, -51dB SNDR, 20mWSNDR, 20mW

Total power, PCI mode, CPU Total power, PCI mode, CPU offoff

690 mW690 mW

Total power, MPEG-TS mode, Total power, MPEG-TS mode, CPU onCPU on

1.8W1.8W

Supports 802.11 a, b, g, 20 Supports 802.11 a, b, g, 20 and 40 MHz channel BWand 40 MHz channel BW

1 to 108 Mb/s raw data rates1 to 108 Mb/s raw data rates

Backup SlidesBackup Slides

2.4/5 GHzTransceiverRx

Tx

2.4/5 GHzTransceiverRx

Tx

AD

Cs

DA

Cs

SDRAM Controllerand Memory

Interface

MIPS Processor

WLAN MAC

MRC/BF

OFDM Mod/Demod

Radio Control

MPEG-TS

Local Bus

I2C

PCI

UART

PeripheralInterface

IR Interface

SDRAM andFlash

VideoEncoder/Decoder

Host System

RS232

LED Control

GPIOs

IR RemoteControl

WLAN SOC