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 1
Mar 27, 2015
HANDBOOK ON GREEN INFORMATION AND COMMUNICATION SYSTEMS
Chapter 15
Energy Efficient MIMO-OFDM Systems
Zimran Rafique and Boon-Chong Seet
Auckland University of TechnologyNew 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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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)
In conventional OFDM, complex exponential Fourier bases are used to generate orthogonal subcarriers consist of a series of orthogonal sine/cosine functions
Wavelet based OFDM (WOFDM)
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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INTRODUCTION
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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
MULTIPLE ANTENNA SYSTEMSpatial Multiplexing Techniques
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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 bandwidthIndividual 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 SYSTEMSpatial Multiplexing Techniques
D-BLAST
,
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MULTIPLE ANTENNA SYSTEMSpatial Multiplexing Techniques
D-BLAST
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MULTIPLE ANTENNA SYSTEMSpatial Multiplexing Techniques
D-BLAST
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MULTIPLE ANTENNA SYSTEMSpatial Multiplexing Techniques
V-BLAST
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MULTIPLE ANTENNA SYSTEM
Spatial Multiplexing TechniquesV-BLAST
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MULTIPLE ANTENNA SYSTEM
Spatial Multiplexing TechniquesV-BLAST
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MULTIPLE ANTENNA SYSTEM
Spatial Multiplexing TechniquesV-BLAST
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MULTIPLE ANTENNA SYSTEM
Spatial Multiplexing TechniquesV-BLAST
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MULTIPLE ANTENNA SYSTEM
Spatial Multiplexing TechniquesTurbo-BLAST
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MULTIPLE ANTENNA SYSTEM
Spatial Multiplexing TechniquesTurbo-BLAST
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MULTIPLE ANTENNA SYSTEM
Spatial Multiplexing TechniquesTurbo-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 SYSTEMSpace Time Coding Techniques
Alamouti STC Technique
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MULTIPLE ANTENNA SYSTEMSpace Time Coding Techniques
Alamouti STC Technique
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MULTIPLE ANTENNA SYSTEMSpace Time Coding Techniques
Space-Time Trellis Coding ( STTC) Technique
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MULTIPLE ANTENNA SYSTEMSpace Time Coding Techniques
Space-Time Trellis Coding ( STTC) Technique
Time-delay diversity with 2 antennas
PSK 4-state space-time code with two transmitting antennas
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MULTIPLE ANTENNA SYSTEMSpace Time Coding Techniques
Orthogonal Space-Time Block Coding ( OSTBC) Technique
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MULTIPLE ANTENNA SYSTEMSpace Time Coding Techniques
Orthogonal Space-Time Block Coding ( OSTBC) Technique
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MULTIPLE ANTENNA SYSTEMSpace Time Coding Techniques
Space-Time Vector Coding ( STVC) Technique
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MULTIPLE ANTENNA SYSTEMSpace Time Coding Techniques
Space-Time Vector Coding ( STVC) Technique
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MULTIPLE ANTENNA SYSTEMBeam-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 SYSTEMBeam-Forming
Delay-Sum Beam-Former
A Simple Delay-Sum Beam-Former
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MULTIPLE ANTENNA SYSTEMBeam-Forming
V-BLAST MIMO System with Beam-Former
V-BLAST MIMO system with beam-former
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MULTIPLE ANTENNA SYSTEMMulti-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 SYSTEMVirtual MIMO (V-MIMO) Systems
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
Models
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MULTIPLE ANTENNA SYSTEMVirtual MIMO Systems
Models
Virtual-MIMO system models
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MULTIPLE ANTENNA SYSTEMVirtual MIMO Systems
Transmission-Delay for Model-d
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MULTIPLE ANTENNA SYSTEMEnergy Efficiency of MIMO Systems
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MULTIPLE ANTENNA SYSTEMEnergy Efficiency of MIMO Systems
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MULTIPLE ANTENNA SYSTEMEnergy Efficiency of MIMO Systems
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MULTIPLE ANTENNA SYSTEMEnergy Efficiency of MIMO Systems
Transmitter and receiver architecture (In-Phase/Quadrature-Phase) for FOFDM and QAM (analog)
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MULTIPLE ANTENNA SYSTEMEnergy Efficiency of MIMO Systems
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MULTIPLE ANTENNA SYSTEMEnergy Efficiency of MIMO Systems
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MULTIPLE ANTENNA SYSTEMEnergy Efficiency of MIMO Systems
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OFDM & WOFDMOFDM
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OFDM & WOFDMOrthogonality Principle of OFDM
Comparison of the bandwidth utilization for FDM and OFDM
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OFDM & WOFDMFourier based OFDM (FOFDM)
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OFDM & WOFDMFourier based OFDM (FOFDM)
A basic FOFDM based communication system
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OFDM & WOFDMFourier based OFDM (FOFDM)
FOFDM modulator and demodulator with filter bank structure
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OFDM & WOFDMWavelet based OFDM (WOFDM)
Constellation Diagram of WOFDM
-5 -4 -3 -2 -1 0 1 2 3 4 5-1
-0.8
-0.6
-0.4
-0.2
0
0.2
0.4
0.6
0.8
1
In-Phase
Qua
drat
ure-
Phas
e
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OFDM & WOFDMWavelet based OFDM (WOFDM)
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OFDM & WOFDMWavelet based OFDM (WOFDM)
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OFDM & WOFDMWavelet based OFDM (WOFDM)
WOFDM modulator and demodulator using symmetric QMF filter bank structure
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OFDM & WOFDMWavelet 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 SYSTEMSMIMO Techniques with FOFDM
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MULTIPLE ANTENNA OFDM SYSTEMSMIMO Techniques with FOFDM
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MULTIPLE ANTENNA OFDM SYSTEMSMIMO Techniques with FOFDM
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MULTIPLE ANTENNA OFDM SYSTEMSMIMO Techniques with FOFDM
Co-operative communication in a multi user scenario using FOFDM
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MULTIPLE ANTENNA OFDM SYSTEMSMIMO 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