Mimo

1. www.studymafia.org
Submitted To: Submitted By:
www.studymafia.org www.studymafia.org
Seminar
On
MULTIPLE INPUT
MULTIPLE OUTPUT
SYSTEMS (MIMO)

2.  Introduction
 What is MIMO?
 Spatial Diversity and Spatial Multiplexing
 MEMO capacity on fading channels
 Benefits of MIMO
 Drawbacks of MIMO
 Conclusion
Content

3. MIMO Systems:
 use multiple inputs and multiple outputs from a
single channel
 are defined by Spatial Diversity and Spatial
Multiplexing
Introduction

4. As we know MIMO is multiple antenna
technology in which more than one antennas
are used at transmitter and receiver stations.
What is MIMO?

5.  Spatial Diversity
◦ Signal copies are transferred from multiple
antennas or received at more than one antenna
◦ redundancy is provided by employing an array of
antennas, with a minimum separation of λ/2
between neighbouring antennas
 Spatial Multiplexing
◦ the system is able to carry more than one data
stream over one frequency, simultaneously
Spatial Diversity and Spatial Multiplexing

6.  There is always a need for increase in performance in
wireless systems
◦ Significant increase in spectral efficiency and data
rates
◦ High Quality of Service (QoS)
◦ Wide coverage, etc.
 Wireless channel that we are using is very unfriendly
◦ Suffers from Co–channel interference and signal
level fading
◦ It provides a limited bandwidth
◦ power falls off with distance
Why MIMO?

7.  By using Multiple Output Multiple Input (MIMO)
systems
◦ Diversity gain mitigates the fading and increases
coverage and improves QoS
◦ Multiplexing gain increases capacity and spectral
efficiency with no additional power or bandwidth
expenditure
◦ Array gain results in an increase in average receive
SNR.
 Spatial Diversity and Spatial Multiplexing can be
conflicting goals
MIMO System solutions

8.  MIMO channels can be decomposed into a number of R parallel
independent channels Multiplexing Gain
→
◦ Principle: Transmit independent data signals from different antennas
to increase the throughput, capacity.
Spatial Multiplexing
Source: An Overview of MIMO Systems in Wireless Communications
www.iet.ntnu.no/projects/beats/Documents/mimo.pdf

9. MEMO capacity on fading channels
 The capacity increase can be seen by comparing MEMO
systems with SISO, SIMO, and MISO systems
◦ SISO:capacity is given by Shannon’s classical formula:
Where B is the BW and h is the fading gain
◦ SIMO (with M transmitting antennas), the capacity is given by
[2]
◦ MISO (with M transmitting antennas), the capacity is given by
[2]
)
2
1
(
2
log h
snr
B
C 


)
1
2
1
(
2
log 




m
n
n
h
snr
B
C
)
1
2
1
(
2
log 










N
n
n
h
N
snr
B
C

10. MEMO capacity on fading channels
 The capacity for MIMO systems can have the following forms
(Assuming Tx antennas = Rx antennas = N):
A) If the channel is not known at the transmitter:
◦ Where Es is the total power, σ2
is noise level of AWGN
◦ Hence the power is equally shared by each channel
◦ The capacity grows linearly with the number of antennas
B) If the channel is known at the transmitter
)
2
2
1
(
2
log
n
h
N
s
E
N
C 












 


















N
n n
h
n
E
C
1
)
2
2
1
(
2
log


11.  With the channel known at the transmitter, the total power
allocation the each channel will be based on watterfilling.
◦ Watterfilling: Strong Sub-channel, with low noise power level will be
assigned with a higher signal power.
Where σ 2
= σ2
/ h
│ 2
│
MEMO capacity on fading channels
Illustrating Watterfilling
Source: MIMO Systems and Transmit Diversity,
www.comm.utoronto.ca/~rsadve/Notes/DiversityTransmit.pdf

12. 0
5
10
15
20
25
30
35
40
45
50
55
60
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25
SNR [dB]
Average
Capacity
[bits/sec/Hz]
N=1 M=1 N=2 M=1 N=1 M=2 N=2 M=2 N=2 M=4 N=2 M=6 N=4 M=4 N=8 M=8
Average capacity of a MIMO Rayleigh
fading channel []
Source: Space-time Diversity Codes for Fading Channels, [3]

13.  Improves the signal quality and achieves a higher SNR at the
receiver-side
 Principle of diversity relies on the transmission of structured
redundancy
Spatial Diversity
xi
yi

14. MIMO Diversity and Reliability
 The performance improvement in SNR and error probability
for MIMO can be compared with SISO, SIMO, and MISO
 The detailed calculation for SNR and Pe is shown in [1]
◦ SISO:
◦ Receive Diversity (SIMO):
N
i
n
x
h
y i
i
i 
,
2
,
1
, 




N
i
h
SNR
h
SNR
2
)
(
2
1
1
SNR
Pe


n
hx
y 

2
2
2
)
( h
SNR
n
E
hx
E
h
SNR 
 and
N
SNR
Pe








2
1
1
and

15. MIMO Diversity and Reliability
 The values for SNR and Pe for:
◦ Transmit Diversity (MISO):
◦ Transmit/Receive Diversity (MIMO):
 The received signal at antenna i will be:
 H is the channel fading matrix
i
j
ij
M
j
i n
x
h
y 


1
2
2
)
(
}
,
min{
H
SNR
H
SNR
M
N
H
SNR


M
SNR
Pe








2
1
1
n
x
h
y j
M
j
j 


1



M
j
j
h
SNR
h
SNR
1
2
)
( and
MN
M
N
SNR
Pe










}
,
min{
2
1
1
and

16. ➨There is lower susceptibility of tapping by
unauthorized persons due to multiple antennas and
algorithms.
The systems with MIMO offers high QoS (Quality of
➨
Service) with increased spectral efficiency and data
rates.
The wide coverage supported by MIMO system
➨
helps in supporting large number of subscribers per
cell.
The MIMO based system is widely
➨
Benefits of MIMO

17. ➨The hardware resources increase power
requirements. Battery gets drain faster due to
processing of complex and computationally intensive
signal processing algorithms. This reduces battery
lifetime of MIMO based devices.
MIMO based systems cost higher compare to single
➨
antenna based system due to increased hardware
and advanced software requirements.
Drawbacks of MIMO

18.  The capacity of Receive or Transmit Diversity grows
logarithmically with the number of antennas
 Capacity of MEMO increases linearly with the number of
antennas
 Using Spatial Diversity:
◦ The SNR increases and Pe decreases when using MIMO
 Spatial Multiplexing and Spatial Diversity are conflicting
objectives
Conclusion

19. Reference
 www.google.com
 www.wikipedia.com
 www.studymafia.org

20. THANKS