This document discusses multiple input multiple output (MIMO) systems. MIMO uses multiple antennas at both the transmitter and receiver to improve communication performance. It achieves spatial diversity to increase signal quality and reduce fading, and spatial multiplexing to increase data rates by sending independent data streams over the same frequency band. The capacity of MIMO systems grows linearly with the number of antennas and can be several times more than single input single output systems. MIMO provides higher signal to noise ratio and lower error probability compared to SISO, SIMO and MISO through exploitation of spatial diversity and multiplexing gains.

1. MULTIPLE INPUT MULTIPLE
OUTPUT
By
XXXXX
(12XXXXXXX)
Under the guidance of
XXXXXX, XXXX
Lecturer

2. 1. INTRODUCTION
MIMO Systems:
• use multiple inputs and multiple outputs from a single
channel.

3. SPATIAL DIVERSITY AND SPATIAL MULTIPLEXING
1. Spatial Diversity
• Signal copies are transferred from multiple antennas
or received at more than one antenna
1. Spatial Multiplexing
• the system is able to carry more than one data stream
over one frequency, simultaneously

4. Why MIMO....?
1. There is always a need for increase in performance in wireless
systems
• Significant increase in spectral efficiency and data rates
• Wide coverage, etc.
1. Wireless channel that we are using is very unfriendly
• Suffers from Co–channel interference and signal level fading
• power falls off with distance

5. MIMO System solutions
1. By using Multiple Output Multiple Input (MIMO) systems
• Diversity gain mitigates the fading and increases
coverage and improves QOS
• Array gain results in an increase in average receive SNR.
1. Spatial Diversity and Spatial Multiplexing can be
conflicting goals

6. Spatial Multiplexing
1. 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.

7. MEMO capacity on fading channels
1. 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]
)
2
1(
2
log hsnrBC ⋅+=
)
1
2
1(
2
log ∑
=
⋅+=
m
n
n
hsnrBC

8. 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
B) If the channel is known at the transmitter
)
2
2
1(
2
log
n
h
N
s
E
NC ⋅








+=
σ
∑= 







⋅








+=
N
n n
hn
E
C
1
)
2
2
1(
2
log
σ

9. MEMO capacity on fading channels
• With the channel known at the
transmitter, the total power
allocation the each channel
will be based on watterfilling.
Where σN
2
= σ2
/ h│ n
2
│

10. Average capacity of a MIMO Rayleigh
fading channel
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]
AverageCapacity[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

11. Spatial Diversity
• Improves the signal quality and achieves a higher
SNR at the receiver-side
xi
yi

12. 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):
Ninxhy iii ,2,1, =+=
∑=
N
i
hSNRhSNR
2
)(
2
1
1
SNR
Pe
+
≤
nhxy +=
2
2
2
)( hSNR
nE
hxE
hSNR == and
N
SNR
Pe






+
≤
2
1
1
and

13. 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:
ijij
M
j
i nxhy += ∑=1
2
2
)(
},min{
HSNRHSNR
MN
HSNR
≤≤
M
SNR
Pe






+
≤
2
1
1
nxhy j
M
j
j += ∑=1
∑=
=
M
j
jhSNRhSNR
1
2
)( and
MN
MN
SNR
Pe






+
≤
},min{2
1
1
and

14. Conclusion
• 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

15. References
[1] MIMO Architecture for Wireless Communication:
Intel Technology Journal, vol. 10, Issue 02, May
2006
[2] MIMO Systems and Transmit Diversity,
www.comm.utoronto.ca/~rsadve/Notes/DiversityT
ransmit.pdf
[3] R.A. Carrasco, Space-time Diversity Codes for
fading Channel,
Staffordshire University