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

Table of Contents

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

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

Fourier based OFDM (FOFDM) Wavelet based OFDM (WOFDM) 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

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

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 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

Multiple Antenna System Spatial Multiplexing Techniques , D-BLAST

Multiple Antenna System Spatial Multiplexing Techniques D-BLAST

Multiple Antenna System Spatial Multiplexing Techniques D-BLAST

Multiple Antenna System Spatial Multiplexing Techniques V-BLAST

Multiple Antenna System Spatial Multiplexing Techniques V-BLAST

Multiple Antenna System Spatial Multiplexing Techniques V-BLAST

Multiple Antenna System Spatial Multiplexing Techniques V-BLAST

Multiple Antenna System Spatial Multiplexing Techniques V-BLAST

Multiple Antenna System Spatial Multiplexing Techniques Turbo-BLAST

Multiple Antenna System Spatial Multiplexing Techniques Turbo-BLAST

Multiple Antenna System Spatial Multiplexing Techniques Turbo-BLAST

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

Multiple Antenna System Space Time Coding Techniques Alamouti STC Technique

Multiple Antenna System Space Time Coding Techniques Alamouti STC Technique

Multiple Antenna System Space Time Coding Techniques Space-Time Trellis Coding ( STTC) Technique

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

Multiple Antenna System Space Time Coding Techniques Orthogonal Space-Time Block Coding ( OSTBC) Technique

Multiple Antenna System Space Time Coding Techniques Orthogonal Space-Time Block Coding ( OSTBC) Technique

Multiple Antenna System Space Time Coding Techniques Space-Time Vector Coding ( STVC) Technique

Multiple Antenna System Space Time Coding Techniques Space-Time Vector Coding ( STVC) Technique

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

Multiple Antenna System Beam-Forming Delay-Sum Beam-Former A Simple Delay-Sum Beam-Former

Multiple Antenna System Beam-Forming V-BLAST MIMO System with Beam-Former V-BLAST MIMO system with beam-former

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

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

Multiple Antenna System Virtual MIMO Systems Models Virtual-MIMO system models

Multiple Antenna System Virtual MIMO Systems Transmission-Delay for Model-d

Multiple Antenna System Energy Efficiency of MIMO Systems

Multiple Antenna System Energy Efficiency of MIMO Systems

Multiple Antenna System Energy Efficiency of MIMO Systems

Multiple Antenna System Energy Efficiency of MIMO Systems Transmitter and receiver architecture (In-Phase/Quadrature-Phase) for FOFDM and QAM (analog)

Multiple Antenna System Energy Efficiency of MIMO Systems

Multiple Antenna System Energy Efficiency of MIMO Systems

Multiple Antenna System Energy Efficiency of MIMO Systems

OFDM & WOFDM OFDM

OFDM & WOFDM Orthogonality Principle of OFDM Comparison of the bandwidth utilization for FDM and OFDM

Fourier based OFDM (FOFDM) OFDM & WOFDM Fourier based OFDM (FOFDM)

Fourier based OFDM (FOFDM) OFDM & WOFDM Fourier based OFDM (FOFDM) A basic FOFDM based communication system

OFDM & WOFDM Fourier based OFDM (FOFDM) FOFDM modulator and demodulator with filter bank structure

Wavelet based OFDM (WOFDM) Constellation Diagram of WOFDM

Wavelet based OFDM (WOFDM)

Wavelet based OFDM (WOFDM)

Wavelet based OFDM (WOFDM) WOFDM modulator and demodulator using symmetric QMF filter bank structure

Wavelet based OFDM (WOFDM)

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

Multiple Antenna OFDM Systems MIMO Techniques with FOFDM

Multiple Antenna OFDM Systems MIMO Techniques with FOFDM

Multiple Antenna OFDM Systems MIMO Techniques with FOFDM

Multiple Antenna OFDM Systems MIMO Techniques with FOFDM Co-operative communication in a multi user scenario using FOFDM

Multiple Antenna OFDM Systems MIMO Techniques with WOFDM Transmitter and receiver architecture for WOFDM (analog)

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

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