MIMO in 4G Wireless

MIMO in 4G Wireless
 MIMO Introduction
 Realizing Benefits from MIMO
 Antenna Diversity, Beamforming
and SDM
Applications of MIMO in WiFi,
WiMax and LTE
 Future of MIMO

Copyright © USPurtek LLC, 2012 All Rights Reserved. No part of this publication may be reproduced without the prior written permission of USPurtek LLC, uspurtek.com

Introduction
 Multiple Input Multiple Output
o Multiple Tx & Rx Antennas
- Multiple radio channels
1

1

2

2

Tx

Rx
M

N


Introduction
 Multiple Input Multiple Output
o Multiple Tx & Rx Antennas
- Multiple radio channels


What came before MIMO?
 SISO
o Single Input Single Output

1

Tx

1

Rx


 SISO
o Single Input Single Output


 SIMO
o Single Input Multiple Output
1

1

2

Tx

Rx
N


 SIMO
o Single Input Multiple Output

Rx

Tx

 MISO
o Multiple Input Single Output
1

1

2

Tx

Rx
M


 MISO
o Multiple Input Single Output


Finally MIMO!
 MIMO
o Multiple Input Multiple Output


Interactive Question #1
 Which Antenna configuration is depicted by the
following figure?
1.
2.
3.
4.

SISO
SIMO
MISO
MIMO

Rx

Rx

Rx

Tx

Rx


Promises of MIMO
 Robust Radio Channel
o Effects of fading and multipath interference mitigated
o No breaks in voice calls or data
 Higher Throughput
o Faster downloads
o More Mbps with existing spectrum and power
 Enables 4G Wireless Broadband applications
o WLAN (IEEE 802.11n/ad)
o WiMAX (IEEE 802.16m)
o LTE-A (3GPP Rel 10)

Is this handset in
I
your future?


Realizing MIMO Promises
 Antenna Diversity
o Receive Diversity
o Transmit Diversity
 Beamforming
 Space Division Multiplexing (SDM)


Multipath Propagation

Path 1

20 -30 dB
I
Fading

Path 2
Path 3

+

=

Tx

Rx

+

=

no
signal


Multipath Propagation

Inter Symbol
I
Interference
(ISI)

Path 1
Path 2
Path 3

s1

s2

Path 3

Tx
Rx

Path 2
Path 1

+

s1, s2

+

s1

s2
s2

time

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

λ/2

Tx

Signals combined
I
from multiple
antennas

λ/2

Rx


Receive Diversity

Selection
I
Combining
λ/2

λ/2

Rx

Tx

Receive Diversity

Equal Gain
I
Combining
λ/2

λ/2

Rx

Tx

Receive Diversity

Maximal Ratio
I
Combining
λ/2

λ/2

Rx

Tx

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
 MISO Configuration

Ant 3

Ant 2
Ant 1
time

 What is not a benefit of Antenna Diversity?
1.
2.
3.
4.

Diversity Gain
Enhanced Signal to Noise Ratio
Increased Bandwidth
Redundant Copies of Signal


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


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)
1

λ
/
2

1

M X N MIMO
2

2

Tx

λ
/
2

Rx
M

N


 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
1

h11

1
h21

h1N

λ
/
2

M X N MIMO
2

2
h22

Tx

λ
/
2

Rx
hM2
M

hMN

N


 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
Rx1

h11

h21

•

•

hM1

Tx1

h21

h22

•

•

hM2

Tx2

•

•

•

•

•

•

•

•

•

•

•

•

•

RxN

hM1

hM2

•

•

Rx2
•

R
Received
I
Signals

₌

H
I
MIMO Channel

hMN

TxM

T
Transmitted
I
Signals


 Which technique will you recommend when the radio
channel is very noisy (SNR is low)?
1.
2.
3.
4.

Transmit Antenna Diversity
Space Time Block Codes (STBC)
Time Division Multiplexing (TDM)


Multiplexing Rate in MIMO
 Multiplexing Rate
o Number of distinctive data streams that can
be received correctly and simultaneously
– For MxN MIMO, it is the min (M,N)
1

Base
Station

2

3

1

2

Single
User
3 X 2 MIMO
Multiplexing
Rate = 2


Diversity Gain in MIMO
 For narrow band system with
slow fading
o Product of M & N
1

Base
Station

2

3

1

2

Single
User
3 X 2 MIMO
Diversity
Gain = 6


Multiplexing & Diversity Combo
 Trade Off is Possible
 For 5x4 MIMO
oCase 1: Reliable Mode
– Multiplexing Rate = 2
– Diversity Gain = 3x2 = 6


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 MIMO
o Antenna Diversity upto 4 x 4
o Tx Beamforming
o Space Division Multiplexing (SDM)
 2.4/5 GHz ISM band
o 20/40 MHz Bandwidth
 PHY Data rates upto 600 Mbps
o Throughput > 200 Mbps
 Extended Range
o Indoor 70 m
o Outdoor 250 m


MIMO in WiFi
 Antennas for Access Point
o Narrowband Monopole
λ
/
4

λ/2

λ/2


MIMO in WiFi
 Antennas for Access Point
o Multiband Compact
Multiband Antenna Element
5 GHz

2.4 GHz

Antenna Element

Top View

Ground

RF Cable


MIMO in WiFi
 Antennas for Portable Devices
o Tradeoffs between design, performance and placement

Antenna Configuration: Case1

Ground Plane

Antenna Feed Point


MIMO in WiFi
 Antennas for Portable Devices
o Tradeoffs between design, performance and placement

Antenna Configuration: Case2

Ground Plane

Antenna Feed Point


 What is the recommended physical separation
between Antenna elements of a MIMO system?
1.
2.
3.
4.

λ/4
Depends on the wireless standard
Minimum λ/2
Does not matter


MIMO in WiMax
 IEEE 802.16m has full featured MIMO
o Antenna Diversity
o Beamforming
 2.3-2.4, 3.3-3.4 GHz (country specific)
o 5-10 MHz Bandwidth
 Enhanced Throughput
o 1 Gbps for fixed stations
o 100 Mbps for mobile stations
 Single or Multi User MIMO
o SU-MIMO
o MU-MIMO


MIMO in LTE-A
 3GPP Rel 10 (LTE-A) has full featured MIMO
o Antenna Diversity
o Beamforming
 22 Freq. bands covering 698-3600 MHz
o Scalable Bandwidth (20-100 MHz)
 Enhanced Throughput
o 1 Gbps Downlink
o 500 Mbps Uplink
 Single or Multi User MIMO
o SU-MIMO
o MU-MIMO


SU-MIMO
 Single User gets the benefit of full
Throughput
1

Base
Station

2

1

2

Single
User
3 X 2 MIMO

3


SU-MIMO
 Single User gets the benefit of full
Throughput
1

3 X 2 MIMO

Base
Station

2
1

2

Single
User

3


MU-MIMO
 Multiple Users share full Throughput
1
1

Base
Station

2

2

Multiple
Users

3
3


A Glimpse of the Future
 Massive MIMO & WiGig (IEEE 802.11ad)
o 60 GHz unlicensed band
– 4 channels of 2 GHz each
o Upto 7 Gbps data rates
o mm Wave MIMO Antenna Arrays
– small λ ( 5 mm) means very small
antenna

Distance between elements
λ /2 = 2.5 mm
1 cm


A Glimpse of the Future
 Massive MIMO & WiGig (IEEE 802.11ad)
o 60 GHz unlicensed band
– 4 channels of 2 GHz each
o Upto 7 Gbps data rates
o mm Wave MIMO Antenna Arrays
– small λ ( 5 mm) means very small antenna
256 elements

16 elements


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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