Use of MIMO in 802.11nUse of MIMO in 802.11n

ByBy

Chaitanya T KChaitanya T K

Email:tkchaitanya@tataelxsi.co.inEmail:tkchaitanya@tataelxsi.co.in

When you are in light, When you are in light,

Everything will follow you...... Everything will follow you......

But when you enter dark, But when you enter dark,

Even your shadow will not follow you...... Even your shadow will not follow you......

This is LIFE!!! This is LIFE!!!

Enjoy!!!Enjoy!!!

ObjectivesObjectives

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:

History of MIMOHistory of MIMO Understanding the Key words Understanding the Key words What is MIMO?What is MIMO? Different Techniques used in MIMODifferent Techniques used in MIMO MIMO-OFDMMIMO-OFDM MIMO Applications MIMO Applications How it is useful in 802.11n?How it is useful in 802.11n?

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 AdvancesWireless LAN Technology Advances

Wireless LAN technology has seen rapid Wireless LAN technology has seen rapid advancementsadvancements 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 .11n

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 StandardsExisting 802.11 WLAN Standards

Key words used in MIMOKey words used in MIMO

Multi path or Raleigh fadingMulti path or Raleigh fading Antenna gainAntenna gain Diversity gainDiversity gain SNR and SNIRSNR and SNIR Co-channel and adjacent channel Co-channel and adjacent channel

interferenceinterference Delay spreadDelay spread

Hurdles in wirelessHurdles in wireless

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 I

In 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

Multi Path Vs CapacityMulti Path Vs Capacity

Channel capacityChannel capacity

For SISO,For SISO,

C = B*log2(1+x)C = B*log2(1+x)

For MIMOFor MIMO

C = C = ΣB*log2(1+x/n*y)ΣB*log2(1+x/n*y)

Where,Where,

X-SNR X-SNR

y-Singular values of Radio channel matrix y-Singular values of Radio channel matrix

N- Number of Tx-Rx antenna pairs.N- Number of Tx-Rx antenna pairs.

MIMO TechniquesMIMO Techniques

These are the basic types of MIMO technology:These are the basic types of MIMO technology:

Pre-codingPre-coding DiversityDiversity

Transmitter DiversityTransmitter Diversity Receiver diversityReceiver diversity

Maximum Ratio combiningMaximum Ratio combining SDMA (Space division Multiple Access)SDMA (Space division Multiple Access) Spatial-multiplexing MIMOSpatial-multiplexing MIMO

Allows even higher data rates by transmitting parallel Allows even higher data rates by transmitting parallel data streams in the same frequency spectrumdata streams 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 Requires new standard (11n) for standards-based

operation operation Proprietary modes possible but cannot help legacy Proprietary modes possible but cannot help legacy

devicesdevices

PRE-CODINGPRE-CODING In MIMO along with ISI there is anotehr type of

interference developed due to the use of Multiple antennas, known as MSI (Multi-stream interference). To remove this MSI we use precoding at Tx and Rx.

The output of the space-time encoder is weighted by the pre-coding matrix,before being Tx from the antenna.but this approach requires periodic feedback of the actual complex elements of the weight matrix.

This can be achieved by using many Precoding algorithms. (with full feedback/limited feedback)

E.g. Tomlinson---Harashima precoding (THP) algorithm

Diversity MIMO OverviewDiversity 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 diversityReceive diversity / combining / combining boosts reception of boosts reception of standard 802.11 signalsstandard 802.11 signals

Phased array transmit diversity to focus energy to each receiver

Radio

DSP

BitsRadio

RX

BitsTX

BitsRXRadio

DSP

BitsRadio

TX

Radio

Radio

Diversity in DetailDiversity in Detail

DiversityDiversity —In MIMO systems, the same —In MIMO systems, the same information can be transmitted from multiple information can be transmitted from multiple transmit antennas and received at multiple transmit antennas and received at multiple receive antennas simultaneously. receive antennas simultaneously.

Since the fading for each link between a pair of transmit Since the fading for each link between a pair of transmit and receive antennas can usually be considered as and receive antennas can usually be considered as independent, the probability that the information is independent, the probability that the information is detected accurately is increased. detected accurately is increased.

spatial diversity, spatial diversity, temporal diversity temporal diversity frequency diversityfrequency diversity if the replicas of the faded signals are received in the if the replicas of the faded signals are received in the

form ofform of redundancy in the temporal and frequencyredundancy in the temporal and frequency domains.domains.

The simplest way of achieving the diversity in The simplest way of achieving the diversity in MIMO systems is through repetition coding that MIMO systems is through repetition coding that sends the same information symbol at different sends the same information symbol at different time slots from different Tx antennas. time slots from different Tx antennas.

A more BW Efficient coding is ST coding, where a A more BW Efficient coding is ST coding, where a block of different symbols are Tx in a different block of different symbols are Tx in a different order from each antenna.order from each antenna.

Spatial MultiplexingSpatial Multiplexing

It is widely recognized that the capacity of a MIMO system is much higher than a single-antenna system. Fora rich scattering environment , in a MIMO system with Mt transmit antennas and Mr

receive antennas, the capacity will grow proportionally withmin(Mt,Mr).MIMO systems provide more spatial freedoms or spatial multiplexing, so that different information can be Tx simultaneously over multiple antennas, thereby boosting the system throughput.

SM needs a dedicated algorithm at the Rx to sort out the Rx signals. E.g. V-BLAST.

Multipath Mitigation with MRCMultipath Mitigation with MRC

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 ConceptSpatial Multiplexing MIMO Concept

Spatial multiplexing concept:Spatial multiplexing concept:

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

However, there are cross-paths between However, there are cross-paths between antennasantennas

Radio

Radio

DSP

DSP

BitSplit

BitsBit

Merge

TX

Radio

RadioRX

GarbageDSP

DSP

Spatial Multiplexing MIMO RealitySpatial Multiplexing MIMO Reality

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 TheorySpatial Multiplexing MIMO Theory 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 equationsExample 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

Trade-off b/w Diversity and spatial Trade-off b/w Diversity and spatial MultiplexingMultiplexing

Depending on the channel conditions and Depending on the channel conditions and type of clients you have u can go for either type of clients you have u can go for either diversity/SM.diversity/SM.

But there are some grouping techniques at But there are some grouping techniques at the Rx using which we achieve optimal the Rx using which we achieve optimal diversity-multiplexing trade off. E.g. GZF diversity-multiplexing trade off. E.g. GZF (ZF+ML) and ,GSIC (Interference (ZF+ML) and ,GSIC (Interference Cancellation+ML) and LAST (Lattice space-Cancellation+ML) and LAST (Lattice space-time coding/decoding).time coding/decoding).

Different Implementations of spatial Different Implementations of spatial MultiplexingMultiplexing

Vertical encodingVertical encoding Horizontal encodingHorizontal encoding Vertical Bell Labs Layered Space time Vertical Bell Labs Layered Space time

architecture (V-BLAST)architecture (V-BLAST)

Space Time Coding in MIMOSpace Time Coding in MIMO A A space–time codespace–time code (STC) is a method employed to (STC) is a method employed to

improve the reliability of data transmission in improve the reliability of data transmission in wireless communication systems using multiple wireless communication systems using multiple transmit antennas. STCs rely on transmitting transmit antennas. STCs rely on transmitting multiple, redundant copies of a data stream to the multiple, redundant copies of a data stream to the receiver in the hope that at least some of them may receiver in the hope that at least some of them may survive the physical path between transmission and survive the physical path between transmission and reception in a good enough state to allow reliable reception in a good enough state to allow reliable decoding.decoding.

Space time codes may be split into two main types:Space time codes may be split into two main types: Space–time trellis codes (STTCs)Space–time trellis codes (STTCs) distribute a trellis distribute a trellis

code over multiple antennas and multiple time-slots code over multiple antennas and multiple time-slots and provide both coding gain and diversity gain. and provide both coding gain and diversity gain.

Space–time block codes (STBCs)Space–time block codes (STBCs) act on a block of act on a block of data at once (similarly to block codes) and provide data at once (similarly to block codes) and provide only diversity gain, but are much less complex in only diversity gain, but are much less complex in implementation terms than STTCs.implementation terms than STTCs.

STC may be further subdivided according to STC may be further subdivided according to whether the receiver knows the channel whether the receiver knows the channel impairments. impairments.

In coherent STC, the receiver knows the channel In coherent STC, the receiver knows the channel impairments through training or some other form of impairments through training or some other form of estimation. These codes have been studied more estimation. These codes have been studied more widely because they are less complex than their widely because they are less complex than their non-coherent counterparts. non-coherent counterparts.

In noncoherent STC the receiver does not know the In noncoherent STC the receiver does not know the channel impairments but knows the statistics of the channel impairments but knows the statistics of the channel. In differential space–time codes neither the channel. In differential space–time codes neither the channel nor the statistics of the channel are channel nor the statistics of the channel are available.available.

ST CodingST Coding

SF CodingSF Coding

SF CodingSF Coding

STF CodingSTF Coding

Modulation and Coding schemesModulation and Coding schemes

To vary the data rate, one can consider the following options:

1.Decreasing the channel spacing or increasing the number of samples within one second 2.Decreasing the guard band overhead, i.e. increasing the number of data sub carriers out of total number of sub carriers. 3.Increasing the constellation size, i.e. choosing higher QAM 4.Decreasing the channel coding rate and 5.Decreasing the guard time, i.e. decreasing the cyclic prefix 6.Number of Spatial Streams7.Number of Encoded streams

Different Modulation SchemesDifferent Modulation Schemes

Symbol error rate comparisonSymbol error rate comparison

MIMO-OFDM Tx Block Diagram for .11nMIMO-OFDM Tx Block Diagram for .11n

MIMO-OFDM Rx Block diagram for .11nMIMO-OFDM Rx Block diagram for .11n

Transmit processing techniquesTransmit processing techniques

Receive Processing techniquesReceive Processing techniques

What Is Being Proposed for What Is Being Proposed for 802.11n?802.11n?Main FeaturesMain Features

PHYPHY MIMO-OFDMMIMO-OFDM DiversityDiversity Spatial MultiplexingSpatial Multiplexing Pre-codingPre-coding Maximum Ratio CombiningMaximum Ratio Combining Extended bandwidth (40MHz)Extended bandwidth (40MHz) Advanced coding techniquesAdvanced coding techniques BeamformingBeamforming

MACMAC AggregationAggregation Block ACKBlock ACK CoexistenceCoexistence Power savingPower saving

Frame formats changed to Frame formats changed to accommodate MIMOaccommodate MIMO

ConclusionsConclusions

The next generation WLAN uses MIMO technologyThe next generation WLAN uses MIMO technology It is menu of options, which can make It is menu of options, which can make

interoperability difficult to achieve. (depending on interoperability difficult to achieve. (depending on cost and usage) cost and usage)

Power saving is very critical in MIMO.Power saving is very critical in MIMO. The beauty of MIMO is it has every option to suit all The beauty of MIMO is it has every option to suit all

scenarios.scenarios. Diversity MIMO technologyDiversity MIMO technology

Extends range of existing data rates by transmit and Extends range of existing data rates by transmit and receive diversitiesreceive diversities

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

Destiny is no matter of chance, it is a Destiny is no matter of chance, it is a matter of choice. It is not a thing to be matter of choice. It is not a thing to be waited for, it is a thing to be achievedwaited for, it is a thing to be achieved

Queries?Queries?