MULTIPLE INPUT MULTIPLE OUTPUT By XXXXX (12XXXXXXX) Under the guidance of XXXXXX, XXXX Lecturer
MULTIPLE INPUT MULTIPLE OUTPUT
By
XXXXX (12XXXXXXX)
Under the guidance of XXXXXX, XXXX Lecturer
1. INTRODUCTION
MIMO Systems:• use multiple inputs and multiple outputs from a single
channel.
SPATIAL DIVERSITY AND SPATIAL MULTIPLEXING
1. Spatial Diversity• Signal copies are transferred from multiple
antennas or received at more than one antenna
2. Spatial Multiplexing• the system is able to carry more than one data
stream over one frequency, simultaneously
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.
2. Wireless channel that we are using is very unfriendly
• Suffers from Co–channel interference and signal level fading
• power falls off with distance
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.
2. Spatial Diversity and Spatial Multiplexing can be
conflicting goals
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.
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]
)21(2log hsnrBC
)1
21(2log
m
n nhsnrBC
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
21(2log nhNsENC
N
n nhnEC
1
)2
21(2log
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 σN2 = σ2 / h│ n
2│
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]
Ave
rage
Cap
acity
[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
Spatial Diversity
• Improves the signal quality and achieves a higher SNR at the receiver-side
xiyi
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)(
21
1SNRPe
nhxy
22
2
)( hSNRnE
hxEhSNR and
NSNRPe
21
1and
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
ji nxhy
1
22
)(},min{
HSNRHSNRMNHSNR
MSNRPe
21
1
nxhy j
M
j
j 1
M
j
jhSNRhSNR1
2)( and
MN
MNSNR
Pe
},min{21
1and
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
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/DiversityTransmit.pdf
[3] R.A. Carrasco, Space-time Diversity Codes for fading Channel,Staffordshire University