As stated earlier, in the above uplink and downlink finger-block diagrams, we have assumed fine
time tracking is performed elsewhere and relevant timing info is passed to these fingers. One of
the most important functions in the RAKE finger is CE. As one would expect, various options exist
to the system designer. What has been presented thus far is averaging a combination of the present
and past instantaneous channel estimates. This type of signal processing is called causal estimation.
Next we provide an alternative estimator where future estimates are additionally used, at the expense
of delay through the finger output.
z(k) j # K # Zh(k) Z2 # d(k)
z(k) 5PG # d(k) # h(k)65j # PG # Np # h*(k)6 z(k) r2(k) # r ~
1 *
(k)
r2(k) PG # d(k) # h(k) n ~
(k)
jaSF
t1
ZScr(k) Z2 # p(k) # CCCH(k) # CDCH(k) # h(k) n(k)
r2(k) aSF
t1
ZScr(k) Z2 # ZCDCH(k) Z2 # d(k) # h(k)
3G WIDEBAND CDMA 395
FIGURE 7.66 WCDMA uplink RAKE finger-block diagram using time division??“multiplexed dedicated pilot bits.
CCH Despreader
X MA
Scr
X X
CCCH p*
X
CDCH
( )*
r
X
jhi(t)
h(t)
DCH Despreader
Channel
Compensation
Depilot & Channel
Estimation
Finger Output
Pilot
Gating
SF
??
256
??
Recall, on the uplink, we have the quadrature-multiplexed physical channels shown in Fig.
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