X X
X1(t)
LPF
X
b(t ??“ t11) . h11(t) ?† ?†
b(t ??“ t12) . h12(t) ?† ?†
2P . cos[2pfct]
PG. Tc
dt
0
??«
PG
. Tc
dt
0
??«
C1(t ??“ t11) ?†
C1(t ??“ t12) ?†
Finger #1
Finger #2
In this figure, the first finger is demodulating the path arriving at t 11 while the second finger is
demodulating the path arriving at t 12. We see the same information is present at both outputs,
except they are time skewed and independently Rayleigh faded. So the next function required is to
introduce the CE algorithm. The CE independently estimates the channel response for each arriving
ray and then performs CD (for this example). Depending on the relative time difference of the two rays
and its relation to the PG or SF, a time-deskewing buffer is needed to time align the despread symbols
prior to being added or combined to create a single, received RAKE combined output symbol.
Whether we study the uplink or the downlink, there will be some known pilot bits/symbols
that the receiver can use to estimate the channel response. If the pilot bits are time multiplexed,
then some sort of demultiplexing operation is needed to extract the pilot bits. If the pilot symbols
are code multiplexed, then a parallel despreader (at the same time of arrival) is needed to
determine the symbol.
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