Let us start with one of
the early proposals for the RAKE receiver shown in Fig. 7.19 [3].
The time separation between the PN code correlations is sec. Recall from our earlier discussion
on the RAKE:We placed fingers at each significant time-of-arrival multipath. There was no mention
of preserving a distance constraint between each finger, as shown in Fig. 7.19.
3G WIDEBAND CDMA 357
FIGURE 7.19 General RAKE receiver block diagram using the MRC method.
X *
RAKE
Output
hN(t)
X X X X
. . .
. . .
+
X *
X *
h2(t) h3(t) h1(t)
X *
. . .
Received
Signal
PN
Code
PG
. Tc
dt
0
??«
PG
. Tc
dt
0
??«
PG
. Tc
dt
0
??«
PG
. Tc
dt
0
??«
??† ??†
??†
In [7], a generalized RAKE receiver called GRAKE was presented, and we have provided a block
diagram in Fig. 7.20. This is a generalized version of the RAKE diagram shown in Fig. 7.19. The only
difference being the combining weight calculation.
Note that with this technique, a group of N fingers can be placed contiguously in time, in order to
despread multipaths arriving within a group of N multipaths.
The RAKE output is given as . In the GRAKE, the weight is calculated using the following
(assuming the MSINR cost function is used):
(7.
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