Download - MIMO in 15 minutes
Use of MIMO in 802.11nUse of MIMO in 802.11n
ByBy
Chaitanya T KChaitanya T K
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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?