HANDBOOK ON GREEN INFORMATION AND COMMUNICATION SYSTEMS

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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-symbol-interference (ISI) at the
  receiver side

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INTRODUCTION

• Fourier based OFDM (FOFDM)

• Wavelet based OFDM (WOFDM)

• In conventional OFDM, complex exponential Fourier
  bases are used to generate orthogonal subcarriers
  consist of a series of orthogonal sine/cosine
  functions

• In WOFDM, wavelet bases are used to generate
  orthogonal carriers. These bases are generated
  using symmetric or 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 ?/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)
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