This is sometimes called open loop transmit diversity
(for reasons we will see later). Here we have 2 transmit antennas and group the input symbols into
a block of 2. The STTD encoding operations performed at the transmitter is shown in Fig. 5.69.
PERFORMANCE IMPROVEMENT TECHNIQUES 281
STTD
Encoder
d*1
??“d*2
d2
d1
d1 d2 ??¤
??¤
???
??¤
??¤
???
FIGURE 5.69 STTD encoding operations for M2 antennas.
The transmitted signal can be written in matrix form as
(5.141)
It is very easy to see the determinant is defined as , and for nonzero data symbols,
allows the signal matrix to be nonsingular.
Assuming a single receive antenna, we can draw the transmit diversity communication system
block diagram shown in Fig. 5.70.
det (S) Zd1 Z2 Zd2 Z2
S cs1
s2 d c d1 d2
d*2
d*1
d
STTD
Encoder
d1 d2
Decoder
r
h1
h2
d?†
FIGURE 5.70 STTD encoder and decoder communication block diagram.
Let r1 and r2 be the 2 received symbols in 2 consecutive symbol intervals and are given below
assuming .
@ t nTs (5.142)
@ t (n 1)Ts (5.143)
Here we assumed the multipath fading is constant over 2 consecutive symbols and can represent the
above equations in matrix notation.
(5.144)
(5.145)
Before we present the STTD decoder equations, we would like to state the decoder consists of two
functions: channel estimation and linear combiner, as shown in Fig.
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