1. 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

2. Table of Contents

3. 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

4. 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

5. 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

6. 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

7. 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

8. 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

9. Multiple Antenna System Spatial Multiplexing Techniques,
D-BLAST

10. Multiple Antenna System Spatial Multiplexing Techniques
D-BLAST

11. Multiple Antenna System Spatial Multiplexing Techniques
D-BLAST

12. Multiple Antenna System Spatial Multiplexing Techniques
V-BLAST

13. Multiple Antenna System Spatial Multiplexing Techniques
V-BLAST

14. Multiple Antenna System Spatial Multiplexing Techniques
V-BLAST

15. Multiple Antenna System Spatial Multiplexing Techniques
V-BLAST

16. Multiple Antenna System Spatial Multiplexing Techniques
V-BLAST

17. Multiple Antenna System Spatial Multiplexing Techniques
Turbo-BLAST

18. Multiple Antenna System Spatial Multiplexing Techniques
Turbo-BLAST

19. Multiple Antenna System Spatial Multiplexing Techniques
Turbo-BLAST

20. 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

21. Multiple Antenna System Space Time Coding Techniques
Alamouti STC Technique

22. Multiple Antenna System Space Time Coding Techniques
Alamouti STC Technique

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

24. 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

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

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

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

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

29. 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

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

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

32. 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

33. 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

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

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

36. Multiple Antenna System Energy Efficiency of MIMO Systems

37. Multiple Antenna System Energy Efficiency of MIMO Systems

38. Multiple Antenna System Energy Efficiency of MIMO Systems

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

40. Multiple Antenna System Energy Efficiency of MIMO Systems

41. Multiple Antenna System Energy Efficiency of MIMO Systems

42. Multiple Antenna System Energy Efficiency of MIMO Systems

43. OFDM & WOFDM
OFDM

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

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

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

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

48. Wavelet based OFDM (WOFDM)
Constellation Diagram of WOFDM

49. Wavelet based OFDM (WOFDM)

50. Wavelet based OFDM (WOFDM)

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

52. Wavelet based OFDM (WOFDM)

53. 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

54. Multiple Antenna OFDM Systems MIMO Techniques with FOFDM

55. Multiple Antenna OFDM Systems MIMO Techniques with FOFDM

56. Multiple Antenna OFDM Systems MIMO Techniques with FOFDM

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

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

59. 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

60. 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