mimo in 4g wireless

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MIMO Introduction Realizing Benefits from MIMO Antenna Diversity, Beamforming and SDMApplications of MIMO in WiFi, WiMax and LTE Future of MIMO

MIMO in 4G Wireless


Introduction Multiple Input Multiple Outputo Multiple Tx & Rx Antennas

Multiple radio channels

Tx Rx

1 1

2 2

M N


Introduction Multiple Input Multiple Outputo Multiple Tx & Rx Antennas

Multiple radio channels


What came before MIMO?

SISOo Single Input Single Output

Tx Rx

1 1



SISOo Single Input Single Output



SIMOo Single Input Multiple Output

Tx Rx

1 1

2

N



SIMOo Single Input Multiple Output

TxRx



MISOo Multiple Input Single Output

Tx Rx

1 1

2

M



MISOo Multiple Input Single Output


Finally MIMO! MIMOo Multiple Input Multiple Output


Interactive Question #1 Which Antenna configuration is depicted by the following figure?

1. SISO2. SIMO3. MISO4. MIMO

TxRx

Rx

Rx

Rx


Promises of MIMO Robust Radio Channel

o Effects of fading and multipath interference mitigatedo No breaks in voice calls or data

Higher Throughputo Faster downloadso More Mbps with existing spectrum and power

Enables 4G Wireless Broadband applicationso WLAN (IEEE 802.11n/ad)o WiMAX (IEEE 802.16m)o LTE-A (3GPP Rel 10)

IIs this handset in your future?


Realizing MIMO Promises

Antenna Diversityo Receive Diversityo Transmit Diversity

Beamforming Space Division Multiplexing (SDM)


Multipath Propagation

I20 -30 dB Fading

+ =no signal

TxRx

Path 3

Path 2

Path 1

+ =


Multipath Propagation

I Inter Symbol Interference (ISI)

time

Path 1

Path 2

Path 3

++

s1 s2

s1, s2 s2

s1 s2

TxRx

Path 3

Path 2

Path 1


Receive Diversity Mitigates Effects of Multipath Propagation Enhances Signal to Noise Ratio (SNR) SIMO Configuration

TxRx

λ/2 λ/2

ISignals combined from multiple antennas

TxRx

λ/2 λ/2


• • •

• Max SNR

ISelection Combining


TxRx

λ/2 λ/2


IEqual Gain Combining

• • •

• 1/3 1/3 1/3

Mitigates Effects of Multipath Propagation Enhances Signal to Noise Ratio (SNR) SIMO Configuration

Receive Diversity


TxRx

IMaximal Ratio Combining

• • •

• 3/6 2/6 1/6

λ/2 λ/2



Transmit Diversity Redundant copies of signal transmitted across space and time Space Time Block Codes (STBC) used

o 50 – 200 ns time delay inserted in transmission paths Mitigates Effects of Multipath Propagation Enhances Signal to Noise Ratio (SNR) MISO Configuration

time

Ant 1

Ant 2

Ant 3


Interactive Question #2 What is not a benefit of Antenna Diversity?

1. Diversity Gain2. Enhanced Signal to Noise Ratio3. Increased Bandwidth4. Redundant Copies of Signal


Beamforming

Radio Beam

Controls shape and direction of radio signals Used on Transmit or Receive Antenna Arrays Extends range of radio signals in a direction

o Signals from multiple antennas add up constructively to maximize receiver gain

Mitigates Effects of Multipath Propagation


Radio Beam

Beamforming Controls shape and direction of radio signals Used on Transmit or Receive Antenna Arrays Extends range of radio signals in a direction

o Signals from multiple antennas add up constructively to maximize receiver gain

Mitigates Effects of Multipath Propagation


Space Division Multiplexing (SDM) Different signals transmitted and received simultaneously over same RF bandwidth Exploits spatial separation provided by MIMO Configuration Achieves Higher Throughput Ideal for RF channels with High Signal to Noise Ratio (SNR)

Tx Rx

1 1

2 2

M N

M X N MIMOλ/2

λ/2


Space Division Multiplexing (SDM) Signal Path Coefficients (h11….hMN) represent amplitude and phase response for each signal path

o Determined during training sequence– Tx generates known training signal– Rx processes training signal to estimate path responses

Tx Rx

1 1

2 2

M N

M X N MIMO

h11

h1Nh21

h22

hM2

hMN

λ/2

λ/2


Space Division Multiplexing (SDM) MIMO channel represented as matrix of signal path coefficients, H Receivers use H-1 to spatially demultiplex the original transmitted signals

o T = H-1 R

IReceived Signals

IMIMO ChannelITransmitted

Signals

Rx1

Rx2

RxN

••

•

₌

h11 h21 • • hM1

h21 h22 • • hM2

• • • • •

• • • • •

hM1 hM2 • • hMN

Tx1

Tx2

TxM

••

•

R H T


Interactive Question #3 Which technique will you recommend when the radio channel is very noisy (SNR is low)?

1. Space Division Multiplexing (SDM)2. Transmit Antenna Diversity3. Space Time Block Codes (STBC)4. Time Division Multiplexing (TDM)


Multiplexing Rate in MIMO

Base Station

1 1

22

3

Single User

3 X 2 MIMOMultiplexing Rate = 2

Multiplexing Rate o Number of distinctive data streams that can be received correctly and simultaneously

– For MxN MIMO, it is the min (M,N)


Multiplexing Rate in MIMO Multiplexing Rate

o Number of distinctive data streams that can be received correctly and simultaneously


Base Station

1 1

22

3


Single User



Base Station

1 1

22

3

Single User






Base Station

1 1

22

3


Single User




Diversity Gain in MIMO For narrow band system with slow fadingo Product of M & N

Base Station

1 1

22

3

Single User

3 X 2 MIMODiversity Gain = 6


Trade Off is Possible For 5x4 MIMO oCase 1: Reliable Mode

– Multiplexing Rate = 2– Diversity Gain = 3x2 = 6

Multiplexing & Diversity Combo


Multiplexing & Diversity Combo

Trade Off is Possible For 5x4 MIMO oCase 2: High Rate Mode

– Multiplexing Rate = 3– Diversity Gain = 2x1 = 2


MIMO in WiFi IEEE 802.11n standard has adopted MIMOo Antenna Diversity upto 4 x 4o Tx Beamformingo Space Division Multiplexing (SDM)

2.4/5 GHz ISM bando 20/40 MHz Bandwidth

PHY Data rates upto 600 Mbpso Throughput > 200 Mbps

Extended Rangeo Indoor 70 mo Outdoor 250 m


MIMO in WiFi Antennas for Access Pointo Narrowband Monopole

λ/2 λ/2

λ/4


MIMO in WiFi Antennas for Access Pointo Multiband Compact

Top View

2.4 GHz5 GHz

RF Cable

Ground

Multiband Antenna Element

Antenna Element


MIMO in WiFi Antennas for Portable Deviceso Tradeoffs between design, performance and placement

Antenna Feed Point

Ground Plane

Antenna Configuration: Case1


MIMO in WiFi Antennas for Portable Deviceso Tradeoffs between design, performance and placement

Antenna Feed Point

Ground Plane

Antenna Configuration: Case2


Interactive Question #4 What is the recommended physical separation between Antenna elements of a MIMO system?

1. λ/42. Depends on the wireless standard3. Minimum λ/24. Does not matter


MIMO in WiMax IEEE 802.16m has full featured MIMOo Antenna Diversity o Beamformingo Space Division Multiplexing (SDM)

2.3-2.4, 3.3-3.4 GHz (country specific)o 5-10 MHz Bandwidth

Enhanced Throughputo 1 Gbps for fixed stationso 100 Mbps for mobile stations

Single or Multi User MIMOo SU-MIMOo MU-MIMO


MIMO in LTE-A 3GPP Rel 10 (LTE-A) has full featured MIMOo Antenna Diversity o Beamformingo Space Division Multiplexing (SDM)

22 Freq. bands covering 698-3600 MHzo Scalable Bandwidth (20-100 MHz)

Enhanced Throughputo 1 Gbps Downlinko 500 Mbps Uplink

Single or Multi User MIMOo SU-MIMOo MU-MIMO


SU-MIMO Single User gets the benefit of full

Throughput

Base Station

1 1

22

3

3 X 2 MIMO

Single User


SU-MIMO

1

1

2

2

3

3 X 2 MIMO

Base Station

Single User

Single User gets the benefit of full Throughput


MU-MIMO Multiple Users share full Throughput

11

22

3

Base Station Multiple

Users

3


A Glimpse of the Future Massive MIMO & WiGig (IEEE 802.11ad)o 60 GHz unlicensed band

– 4 channels of 2 GHz eacho Upto 7 Gbps data rateso mm Wave MIMO Antenna Arrays

– small λ ( 5 mm) means very small antenna

λ /2 = 2.5 mmDistance between elements

1 cm


A Glimpse of the Future

256 elements

16 elements

Massive MIMO & WiGig (IEEE 802.11ad)o 60 GHz unlicensed band

– 4 channels of 2 GHz eacho Upto 7 Gbps data rateso mm Wave MIMO Antenna Arrays

– small λ ( 5 mm) means very small antenna


Bibliography“An Introduction to MU-MIMO Downlink” IEEE Communications Magazine, October 2004 “MIMO-OFDM based air interface” IEEE Communications Magazine, January 2005 “Downlink MIMO in LTE-A” IEEE Communications Magazine, February 2012 “Understanding IEEE 802.11n amendment” IEEE Circuits and Systems Magazine 1Q 2008 “Advancement of MIMO in WiMax” IEEE Communications Magazine June 2009 “MIMO in WiMax and LTE” IEEE Communications Magazine May 2010 “MIMO-OFDM Wireless Systems” IEEE Wireless Communications August 2006 “Antennas for WiFi Connectivity” Proceedings of the IEEE July 2012 “Overview of Mobile WiMax – Technology and Evolution” IEEE Communications Magazine October 2008 The ARRL Handbook for Radio Communications, 2010

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