Figure 3.18 essentially
describes the FSF criteria in the time domain. Next we present the similar description in the frequency
domain.
Now that we have a quantitative expression for the BWof the wireless channel, we wish to compare
it to the occupied BW of the transmitted signal. If the transmitted BW is much larger than the
CBWthen the received signal will experience FSF. On the other hand, if the transmitted BW is much
smaller than the CBW, then the received signal will experience frequency flat fading. It is actually the
same channel; however, how the varying baud rates relate to this gives rise to the above used notation.
Let us assume a PDP with the following exponential profile.
(3.43) P(t)
1
2p # tRMS
# e
t
tRMS
CBW
1
(2p) # (0.575sec)
> 277 kHz
tRMS ?…0.4
1.1
c0.2
1.1 d2
0.575sec
t2
(1) # (0)2 (0.1) # (2)2
1 0.1
0.4
1.1
0.36sec
132 CHAPTER THREE
0 2 msec
P(t)
P(t1) = 0 dB
P(t2) = ??“10 dB
?„
FIGURE 3.17 Two-ray multipath PDP example.
Then the envelope correlation coefficient of two signals separated in time by t seconds and in
frequency by f Hz is equal to the following [1].
(3.44)
This is a very interesting result since it allows us to gain insight into a few properties.
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