Hence the signal contains the desired signal plus
interference plus noise components.
Let us take a moment to provide a brief summary of what has been discussed thus far. Both examples
showed how the desired signal can be extracted. The first example showed the interference components
to be dependent on the cross-correlation properties, while the second example stressed the
autocorrelation properties of the PN sequence. This choice of the PN sequence with proper statistical
properties is essential. Recall these equations have been derived assuming a frequency flat fading
channel with AWGN.
7.4 RAKE FINGER ARCHITECTURE AND PERFORMANCE
In the previous subsections, we have considered an example of downlink and uplink spreading. These
examples assumed a frequency flat fading channel; hence the receiver simply needed to calculate the
propagation time delay . In this subsection, we will discuss the FSF channel and its effects on the
receiver architecture. For sake of discussion, we have decided to choose the downlink spreading
example provided earlier. If we have a two-ray channel, then the received signal becomes
(7.26)
We can generalize this to the following:
(7.27) Xj(t) a2
k1
hj, k(t) # ea2
i1
Ci(t tj, k) # bi(t tj, k) f# cos [2pfc(t tj, k)] Nj (t)
X(t) h1(t) # S(t t1) h2(t) # S(t t2) N(t)
t^
I1(t) P # b1(t t1) # PG P # b2(t t1) cos [fe] # RccQT
2 R noise terms
P # b2(t t1) # cos [fe] # 3Tb
0
C1Qt t1
T
2 R# C1(t t1) dt
I1(t) P # b1(t t1) # 3Tb
0
C21
(t t1) dt
P # 3Tb
0
b2(t t1) # C1Qt t1
T
2 R# C1(t t^
1) # cos [fe] dt
I1(t) P # 3Tb
0
b1(t t1) # C1(t t1) # C1(t t^
1) dt
P # b2(t t1) # C1Qt t1
T
2 R# C1(t t^
1) # cos [fe]
V1(t) P # b1(t t1) # C1(t t1) # C1(t t^
1)
3G WIDEBAND CDMA 353
where the index j is used to denote the receiver user of interest number, the index k is used to denote
the multipath number, and the index i is used to denote the number of transmit users present.
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