5.65).
In the above block diagram we see the antenna weights are adaptively controlled by either minimizing
or maximizing the chosen cost function. Two commonly used cost functions are Minimum
Mean Squared Error (MMSE) and Maximal Signal to Interference plus Noise Ratio (MSINR). It has
been shown that in a CCI limited environment, OC performs better than MRC [63]. The received signal
vector is given as
(5.114)
where T is used to denote the transpose operation. The weight vector is defined as, , so the AAA output
signal as
(5.115)
where * is used to denote the complex conjugate transpose operation.
MMSE and MSINR Cost Functions. In this section we will present the two cost functions used to
derive the array weights, namely MSINR and MMSE. The array weights must be adaptively controlled
to track the time varying, multipath fading channel.
y w* # x
w
x [x1 x2cxM]T
PERFORMANCE IMPROVEMENT TECHNIQUES 275
BPSK MRC, SC, SC2, and SC3 Comparison
0 5 10 15 20
Eb/No (dB)
MRC (M = 1)
MRC (M = 3)
MRC (M = 4)
SC2 (M = 3)
SC3 (M = 4)
1.E??“06
1.E??“05
1.E??“04
1.E??“03
1.E??“02
1.E??“01
BER
FIGURE 5.64 BPSK BER performance for MRC, SC, SC2, and SC3 combining.
First, the array weights that minimize the MSE will be denoted as and are defined as follows:
(5.
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