THE NONENGINEER’S INTRODUCTION TO MIMO AND
MIMOOFDM
http://www.mimo.ucla.edu
Various schemes that employ multiple antennas at the transmitter and receiver are being
considered to improve the range and performance of communication systems. By far the most
promising multiple antenna technology today happens to be the so called multipleinput
multipleoutput (MIMO) system. MIMO systems employ multiple antennas at both the
transmitter and receiver as shown in Figure .
Data
1:N
DEMUX
MODULATOR
MODULATOR
MODULATOR
MIMO
Receiver
ENCODER
x
1
(t)
x
2
(t)
x
3
(t)
r
1
(t) = h
11
x
1
(t)+h
12
x
2
(t)+h
13
x
3
(t)
r
3
(t) = h
31
x
1
(t)+h
32
x
2
(t)+h
33
x
3
(t)
Figure 1 A Generic MIMO system
They transmit independent data (say
x
1
, x
2
, …, x
N
) on different transmit antennas simultaneously
and in the same frequency band. At the receiver, a MIMO decoder users M
≥
N antennas.
Assuming N receive antennas, and representing the signal received by each antenna as
r
j
we
have:
N
NN
N
N
N
N
N
N
N
x
h
x
h
x
h
r
x
h
x
h
x
h
r
x
h
x
h
x
h
r
+
+
+
=
+
+
+
=
+
+
+
=
L
M
L
L
2
2
1
1
2
2
22
1
21
2
1
2
12
1
11
1
As can be seen from the above set of equations, in making their way from the transmitter to the
receiver, the independent signals {x1, x2, …, xN} are all combined. Traditionally this
“combination” has been treated as interference. However, by treating the channel as a matrix, we
can in fact recover the independent transmitted streams {xi}. To recover the transmitted data
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 Spring '10
 attkin
 Orthogonal frequencydivision multiplexing, MIMO MIMO Receiver

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