132
M. El Ghzaoui and S. Das
Fig. 4 PSD of GMSK and QPSK transmitters for bit rate of 15 Mbps
⎡
⎢
⎢
⎣
r 0
r 1
r
∗
2
r
∗
3
⎤
⎥
⎥
⎦ =
⎡
⎢
⎢
⎣
h 11
h 21
h 12
h 22
h
∗
12
h
∗
22
−h
∗
11
−h
∗
21
⎤
⎥
⎥
⎦
H
s 0
s 1
+
⎡
⎢
⎢
⎣
n 0
n 1
n 2
n 3
⎤
⎥
⎥
⎦
(5)
The advantage of the Alamouti coding scheme is that it creates an orthogonal MIMO channel structure; i.e., H
H H is diagonal matrix, which enables lowcomplexity maximum-likelihood (ML) symbol detection using the simple zero
forcing (ZF) decoding:
s
=
H
H H
−1 H
H r
(6)
The difficulty of this technique is that all four channel links, i.e., h 11 , h 12 , h 21 ,
and h 22 should be estimated to decode the received signal. As a result, it needs twice
pilots as much as that is needed for SISO system.
M. El Ghzaoui and S. Das
Fig. 4 PSD of GMSK and QPSK transmitters for bit rate of 15 Mbps
⎡
⎢
⎢
⎣
r 0
r 1
r
∗
2
r
∗
3
⎤
⎥
⎥
⎦ =
⎡
⎢
⎢
⎣
h 11
h 21
h 12
h 22
h
∗
12
h
∗
22
−h
∗
11
−h
∗
21
⎤
⎥
⎥
⎦
H
s 0
s 1
+
⎡
⎢
⎢
⎣
n 0
n 1
n 2
n 3
⎤
⎥
⎥
⎦
(5)
The advantage of the Alamouti coding scheme is that it creates an orthogonal MIMO channel structure; i.e., H
H H is diagonal matrix, which enables lowcomplexity maximum-likelihood (ML) symbol detection using the simple zero
forcing (ZF) decoding:
s
=
H
H H
−1 H
H r
(6)
The difficulty of this technique is that all four channel links, i.e., h 11 , h 12 , h 21 ,
and h 22 should be estimated to decode the received signal. As a result, it needs twice
pilots as much as that is needed for SISO system.