In an FSF channel, many multipaths can be found, and this could result in many fingers being used
in the demodulation process.
A high layer of control over the assignment and de-assignment of multipaths is the role of the finger
management. Although not shown, it is responsible for the handling of the birth/death scenarios
discussed in the channel modeling section of Chap. 3. Another role of the EPM is to perform course
time synchronization, say within Tc/2. Once this multipath is assigned to a finger, then fine time tracking
(i.e., DLL) will be activated to track moving propagation environments. One of the roles of the
finger manager is to always have at least one finger actively demodulating a multipath, so there are
no time gaps of symbols at the RAKE combiner output.
3G WIDEBAND CDMA 355
FIGURE 7.16 Two-finger RAKE receiver with CE block diagram.
X X LPF
X
CE
X
*
Time
Deskew
&
Combine
CE
X
*
RAKE
Output
PG. Tc
dt
0
??«
PG. Tc
dt
0
??«
C1(t ??“ t12) ?†
b(t ??“ t12) ?† ?†
b(t ??“ t11) ?† ?†
C1(t ??“ t11) ?† 2P . cos[2pfct]
Lastly, this RAKE receiver provides BER performance improvements due to the time diversity of
the received symbols. An example of the performance improvement is given in Fig.
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