This document provides an overview of a course on multi-antenna techniques and their applications. It discusses the use of multiple antennas to combat fading through diversity combining and spatial multiplexing to achieve higher data rates. It notes that while more antennas can improve performance, there are diminishing returns due to factors like mutual coupling between closely spaced antennas. The document also compares spatial multiplexing and diversity, noting that multiplexing transmits multiple streams for higher throughput while diversity transmits one stream redundantly for better reliability.

1. About this course:
Multi-Antenna Techniques and Their Applications
Prerequisites: Principle of Communications,
Probabilities, linear algebra, antennas
References:
1. David Tse and Pramod Viswanath. Fundamentals of
Wireless Communication, Cambridge University Press,
2005.
2. A. Paulraj, R. Nabar and D. Gore. Introduction to
Space-Time Wireless Communication, Cambridge
University Press, 2003.
3. Massimo Franceschetti. Wave Theory of Information,
Cambridge University Press, 2018.

2. Lecture 1
Introduction of Multi-Antenna Systems
-- Part 1: Antenna Diversity
Xiaoming Chen
School of Information and
Communications Engineering

3. antennas
Why are there multiple antennas in WiFi router？

4. Tx antennas
Rx antennas
Multipath propagation
location
Rx
Power
Fading channel
How do we cope
with fading?

5. Antenna Diversity
Div. combin.
Rx
SNR
Selection combining
(SC)
Maximum ratio combining
(MRC)

6. CDF
P{X<=x}
x (dB)
The more antennas the better？
Diversity
gain
Diminishing
return！
Rx power: X

7. For a fixed terminal, more antennas mean
less antenna spacing…
Half-wavelength dipoles：
I1=1, I2=-Z12/(Zd+Zs) Larger Z12 means larger mutual coupling,
larger losses…

8. 2 cos( / 2cos )
ˆ
( , ) exp( sin sin )
sin 2
k i
i
C d
G jk
k
  
    


 
,1 1 1 2 2
,2 1 2 2 1
( , ) ( , ) ( , )
( , ) ( , ) ( , )
emb
emb
G G I G I
G G I G I
     
     
  
  
 
 
*
* ,1 ,2
1 2 4
2 2 2 2
,1 ,2
1 2
4 4
( )
| | | |
emb emb
emb emb
G G d
E S S
G d G d
E S E S

 


 
 
 
     
   

 
Correlation indicates the similarity
between two random signals
Assuming isotropic
scattering

9. d (λ)
Correlation
d (λ)
Antenna
efficiency
d (λ)
DG
DG decreases as
antenna spacing
reduces!
Diversity gain
(DG)

10. Summary
• Multipath propagation results in fading
• Fading can be combated by diversity antenna
• For a fixed array size, increasing antennas
may not necessarily improve performance
Diminishing return，mutual coupling，correlation

11. Introduction of Multi-Antenna Systems
-- Part 2: Spatial Multiplexing

12. What does MIMO stands for?
MIMO: Multiple-input multiple-output

13. Spatial Multiplexing in MIMO System
Tx H Rx
x y
Received signals are coupled.
 
y Hx n
After decoding W (& precoding P), parallel channels are formed:
P
s x H y W r

14. P
s x H y W r
s r
σ1
σ2
1 1 1 1
2 2 2 2
0
0
r s n
r s n


       
 
       
       
Spatial Multiplexing and Correlation
Correlation ρ tends to reduce σ2.
ρ1, σ2 0: the 2nd data stream will not be supported.
2
1
2
2
1 1
* 1 1
  
  
 
 
    
 
R
E.g.

15. What is the difference between spatial
multiplexing and diversity?
Spatial multiplexing transmit more than one data
stream over the spatial domain  higher data rate
Spatial diversity transmit one data stream and
receive multiple copies of it  higher reliability
Generally speaking, both spatial multiplexing and
diversity can be regarded as MIMO techniques.

16. Spatial Multiplexing vs. Diversity
-20 -15 -10 -5 0 5 10 15 20 25 30
0
0.2
0.4
0.6
0.8
1
Normalized SNR (dB)
User-distributed
detection
probability
0 stream
1 stream
2 streams
2X2 MIMO
-20 -15 -10 -5 0 5 10 15 20 25 30
0
0.2
0.4
0.6
0.8
1
Normalized SNR (dB)
User-distributed
detection
probability
0
1
2
3
4 streams
4X4 MIMO
Probability
of
detection

17. Tput
Spatial Multiplexing vs. Diversity
Adaptative MCS & layer
Adaptative MCS for a single layer
Throughput of an 5G smartphone

18. MIMO is ubiquitous in modern
telecommunication systems.
Example?
WiFi or WLNA (IEEE
802.11n, 802,11ac)
4G base station, mobile
phone (LTE, LTE-A)

19. What are the differences between
3G, 4G, and 5G?

20. 5G is not just about data rate
• Lower latency
• Lower power consumption?
So 5G is good! No worries 

21. Massive MIMO for 5G
Traditional BS 5G massive MIMO BS
In theory:
1) propagation losses are mitigated by beamforming;
2) Inter-user interference is easily mitigated by the high
beamforming;
3) low-complexity signal processing algorithms are
asymptotically optimal.

22. Massive MIMO for 5G
In practice, the system can be very complicated:
1) Clock distribution
2) Mutual coupling
3) Impairments of PA, ADC/DAC
…

23. Form of Final Exam
• Oral Presentation
• Project-oriented
• The audience can ask questions
• I will ask questions about topics/concepts
covered in the lectures

24. Grading Criteria of Final Exam
• Pass: literature survey of MIMO papers
• Higher score: complete a mutually agreed project,
or solid comprehension of a theoretical paper
(less support from Prof., higher score)
• Attendance rate will be a weighting factor

25. Rule of Final Exam
• Literature survey should be completed by
individuals.
• Project can be carried out in a group of max. 4
students.
Please choose your team members carefully :-)
• 20 min Presentation + 10 min questions
(everybody should attend and ask questions).
• Score + bonus points cannot exceed 100.

26. Examples of Assigned Projects
……

27. Final Presentation Times
• In the last ~2 weeks approximately

28. Computer Exercises
• Laptop?
• Matlab?
• ……