HANDBOOK ON GREEN INFORMATION
AND COMMUNICATION SYSTEMS
Chapter 15
Energy Efficient MIMO-OFDM Systems
Zimran Rafique and Boon-Chong Seet
Auckland University of Technology
New Zealand
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Table of Contents
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INTRODUCTION
 Due to multimedia applications, wireless systems with
higher data rate are required
 Higher data rates necessitate more energy per bit for a
given bit error rate (BER)
 Thus, overall system energy consumption will increase
 Corresponding increase in CO2 emission: threatens climate
change and contributes to global warming
 Energy efficient designs for high data-rate wireless systems
is a crucial issue to be addressed
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INTRODUCTION
Multi-Input-Multi-Output (MIMO) systems
 In late 1990s, MIMO techniques were proposed to
achieve higher data rates and smaller BER with the
same transmit power and bandwidth required by
single antenna system
Orthogonal Frequency Division Multiplexing
(OFDM)
 OFDM is a multi carrier modulation technique which
has the capability to mitigate the effect of inter-symbolinterference (ISI) at the receiver side
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INTRODUCTION
Fourier based OFDM
(FOFDM)
Wavelet based OFDM
(WOFDM)
 In conventional OFDM, complex  In WOFDM, wavelet bases are
exponential Fourier bases are used
used to generate orthogonal
to generate orthogonal subcarriers
carriers. These bases are
consist of a series of orthogonal
generated using symmetric or
sine/cosine functions
asymmetric QMF structure of
delay or delay-free type
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INTRODUCTION
MIMO-OFDM
 MIMO techniques are used with OFDM (MIMO-OFDM) to
enhance the system performance
 MIMO-OFDM systems are capable of increasing the channel
capacity even under severe channel conditions
 Provide two dimensional space-frequency coding (SFC) in space
and frequency using individual subcarriers of an OFDM symbol or
three dimensional coding called space-time-frequency coding (STFC) to
achieve larger diversity and coding gains
 OFDM can also be used in multi-user cooperative communication
system by assigning subcarrier to different users for overall
transmit power reduction
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MULTIPLE ANTENNA SYSTEM
More than one antennas are used on transmitting
and/or receiving side
By using spatial multiplexing, data rate can be
increased
By using spatial diversity, BER can be improved
SNR can be improved at the receiver and
co-channel interference (CCI) can be eliminated
along with beam forming techniques
MIMO wireless communication system
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MULTIPLE ANTENNA SYSTEM
Spatial Multiplexing Techniques
The number of users, or data rate of a single user, can be increased by the factor of number
of transmitting antennas (Nt) for the same transmission power and bandwidth
Individual transmitter antenna power is scaled by 1/ Nt, thus the total power remains
constant and independent of number of Nt
At the receiver, the transmitted signals are retrieved from received sequences (layers)
by using detection algorithms
Spatial multiplexing system architecture with Nt transmitting and Nr receiving antennas
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MULTIPLE ANTENNA SYSTEM
,
Spatial Multiplexing Techniques
D-BLAST
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MULTIPLE ANTENNA SYSTEM
Spatial Multiplexing Techniques
D-BLAST
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MULTIPLE ANTENNA SYSTEM
Spatial Multiplexing Techniques
D-BLAST
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MULTIPLE ANTENNA SYSTEM
Spatial Multiplexing Techniques
V-BLAST
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MULTIPLE ANTENNA SYSTEM
Spatial Multiplexing Techniques
V-BLAST
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MULTIPLE ANTENNA SYSTEM
Spatial Multiplexing Techniques
V-BLAST
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MULTIPLE ANTENNA SYSTEM
Spatial Multiplexing Techniques
V-BLAST
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MULTIPLE ANTENNA SYSTEM
Spatial Multiplexing Techniques
V-BLAST
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MULTIPLE ANTENNA SYSTEM
Spatial Multiplexing Techniques
Turbo-BLAST
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MULTIPLE ANTENNA SYSTEM
Spatial Multiplexing Techniques
Turbo-BLAST
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MULTIPLE ANTENNA SYSTEM
Spatial Multiplexing Techniques
Turbo-BLAST
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MULTIPLE ANTENNA SYSTEM
Space Time Coding Techniques
By using space and time (two-dimensional coding),
multiple antenna setups can be used to attain coding
gain and diversity gain for the same bit rate,
transmission power and bandwidth as compared
single antenna system
Information bits are transmitted according to
some pre-defined transmission sequence
At the receiver, the received signals are combined
by using optimal combining scheme followed by a
decision rule for maximum likelihood detection
Space-time coding system architecture
with Nt transmitting and Nr receiving
antennas
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MULTIPLE ANTENNA SYSTEM
Space Time Coding Techniques
Alamouti STC Technique
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MULTIPLE ANTENNA SYSTEM
Space Time Coding Techniques
Alamouti STC Technique
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MULTIPLE ANTENNA SYSTEM
Space Time Coding Techniques
Space-Time Trellis Coding ( STTC) Technique
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MULTIPLE ANTENNA SYSTEM
Space Time Coding Techniques
Space-Time Trellis Coding ( STTC) Technique
PSK 4-state space-time code with two transmitting antennas
Time-delay diversity with 2 antennas
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MULTIPLE ANTENNA SYSTEM
Space Time Coding Techniques
Orthogonal Space-Time Block Coding ( OSTBC) Technique
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MULTIPLE ANTENNA SYSTEM
Space Time Coding Techniques
Orthogonal Space-Time Block Coding ( OSTBC) Technique
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MULTIPLE ANTENNA SYSTEM
Space Time Coding Techniques
Space-Time Vector Coding ( STVC) Technique
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MULTIPLE ANTENNA SYSTEM
Space Time Coding Techniques
Space-Time Vector Coding ( STVC) Technique
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MULTIPLE ANTENNA SYSTEM
Beam-Forming
Multiple antennas capable of steering lobes and nulls of antenna beam
Co-channel interference cancellation can be done to improve SNR
and to reduce delay spread of the channel
A beam-former with Nt transmitting and Nr receiving antennas
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MULTIPLE ANTENNA SYSTEM
Beam-Forming
Delay-Sum Beam-Former
A Simple Delay-Sum Beam-Former
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MULTIPLE ANTENNA SYSTEM
Beam-Forming
V-BLAST MIMO System with Beam-Former
V-BLAST MIMO system with beam-former
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MULTIPLE ANTENNA SYSTEM
Multi-Functional MIMO Systems
 Capable for achieving multiplexing gain, diversity gain and beamforming gain
 Has Nt transmit antenna arrays (AAs) which are sufficiently apart to experience independent fading
LAA numbers of elements of each AA are spaced at a distance of λ/2 for achieving beamforming gain
 Receiver is equipped with Nr receiving antennas
Multi-functional MIMO system
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MULTIPLE ANTENNA SYSTEM
Virtual MIMO (V-MIMO) Systems
Models
Also known as cooperative MIMO systems
 Proposed primarily for energy and physically constrained wireless nodes (e.g. sensor nodes)
to realize the advantages of MIMO techniques, which is otherwise not possible
V-MIMO systems are distributed in nature because multiple nodes are placed at different
physical locations to cooperate with each other
V-MIMO systems may also have problems such as time and frequency asynchronism
Virtual-MIMO system models
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MULTIPLE ANTENNA SYSTEM
Virtual MIMO Systems
Models
Virtual-MIMO system models
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MULTIPLE ANTENNA SYSTEM
Virtual MIMO Systems
Transmission-Delay for Model-d
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MULTIPLE ANTENNA SYSTEM
Energy Efficiency of MIMO Systems
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MULTIPLE ANTENNA SYSTEM
Energy Efficiency of MIMO Systems
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MULTIPLE ANTENNA SYSTEM
Energy Efficiency of MIMO Systems
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MULTIPLE ANTENNA SYSTEM
Energy Efficiency of MIMO Systems
Transmitter and receiver architecture (In-Phase/Quadrature-Phase) for FOFDM and
QAM (analog)
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MULTIPLE ANTENNA SYSTEM
Energy Efficiency of MIMO Systems
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MULTIPLE ANTENNA SYSTEM
Energy Efficiency of MIMO Systems
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MULTIPLE ANTENNA SYSTEM
Energy Efficiency of MIMO Systems
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OFDM & WOFDM
OFDM
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OFDM & WOFDM
Orthogonality Principle of OFDM
Comparison of the bandwidth utilization for FDM and OFDM
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OFDM & WOFDM
Fourier based OFDM (FOFDM)
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OFDM & WOFDM
Fourier based OFDM (FOFDM)
A basic FOFDM based communication system
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OFDM & WOFDM
Fourier based OFDM (FOFDM)
FOFDM modulator and demodulator with filter bank structure
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OFDM & WOFDM
Wavelet based OFDM (WOFDM)
1
0.8
0.6
Quadrature-Phase
0.4
0.2
0
-0.2
-0.4
-0.6
-0.8
-1
-5
-4
-3
-2
-1
0
1
2
3
4
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In-Phase
Constellation Diagram of WOFDM
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OFDM & WOFDM
Wavelet based OFDM (WOFDM)
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OFDM & WOFDM
Wavelet based OFDM (WOFDM)
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OFDM & WOFDM
Wavelet based OFDM (WOFDM)
WOFDM modulator and demodulator using symmetric QMF filter bank structure
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OFDM & WOFDM
Wavelet based OFDM (WOFDM)
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MULTIPLE ANTENNA OFDM SYSTEMS
Most of the MIMO techniques have been developed with the assumption of
flat fading channel
For broadband frequency selective wireless channel, the combination of MIMO and
OFDM (MIMO-OFDM) was proposed to mitigate the effect of ISI and ICI
In MIMO techniques, CSI is usually required at transmitter and/or receive side,
thus OFDM is also used in MIMO systems to estimate CSI
MIMO-OFDM system with Nt transmitting and Nr receiving Antennas
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MULTIPLE ANTENNA OFDM SYSTEMS
MIMO Techniques with FOFDM
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MULTIPLE ANTENNA OFDM SYSTEMS
MIMO Techniques with FOFDM
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MULTIPLE ANTENNA OFDM SYSTEMS
MIMO Techniques with FOFDM
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MULTIPLE ANTENNA OFDM SYSTEMS
MIMO Techniques with FOFDM
Co-operative communication in a multi user scenario using FOFDM
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MULTIPLE ANTENNA OFDM SYSTEMS
MIMO Techniques with WOFDM
Transmitter and receiver architecture for WOFDM (analog)
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CONCLUSION
The underlying principles and techniques of MIMO-OFDM systems for energy efficient
wireless communications are presented
Multi-antenna systems with spatial multiplexing, space-time coding and beamforming
techniques are introduced
 To improve BER, SNR, throughput, and energy efficiency, multi-functional MIMO and
virtual MIMO systems are discussed along with energy efficiency analysis
 The basic principles of FOFDM and WOFDM and their applications in true (co-located)
and virtual (cooperative) MIMO wireless systems are described
MIMO-OFDM is a promising solution for energy efficient high data rate wireless networks
WOFDM can be used for SFC, STFC, as well as cooperative communication systems
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CONCLUSION
 Potential directions for future work:
• New wavelet basis can be designed according to wireless channel conditions to
improve the overall system performance
• Multifunctional MIMO performance can be evaluated using WOFDM/FOFDM
• True and virtual MIMO-OFDM systems can be implemented to verify the theoretical results
• Physical layer architecture performance of MIMO-OFDM system along with medium
access control (MAC) layer protocols can be explored
• New MAC layer protocols can be proposed for true and virtual MIMO-OFDM systems
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