Z1(t) P # b1(t t1) # C1(t t1) P # b2(t t1) # C1Qt t1
T
2 R# cos [fe]
fe
352 CHAPTER SEVEN
X
C2(t) = C1(t ??“ T/2)
b2(t)
X
C1(t)
b1(t)
User #1
User #2
X
S1(t)
X
S2(t)
BS
2P . cos[2pfct]
2P . cos[2pfct]
FIGURE 7.12 Uplink spreading example.
FIGURE 7.13 Uplink receiver structure for the uplink spreading example.
X
Z1(t)
X LPF
V1(t) X1(t)
X
Z2(t)
X LPF
V2(t)
X2(t)
MS
#1
MS
#2
User #1
User #2
I1(t) = b1(t ??“ t1) ?† ?†
I2(t) = b2(t ??“ t2) ?† ?†
C1(t ??“ t1) ?†
C2(t ??“ t2) ?†
2P . cos[2pfct ??“ f1]
2P . cos[2pfct ??“ f2]
PG
. Tc
dt
0
??«
PG
. Tc
dt
0
??«
In the first part of the despreader, we have (omitting the AWGN terms)
(7.22)
The second part of the descrambling is given after integration.
(7.23)
Using the same approach as in the previous subsection allows us to write the following:
(7.24)
The first integration on the RHS represents the autocorrelation of the PN sequence evaluated at a
lag of zero. The second integration on the RHS also represents the autocorrelation, except that this is
for a lag of T/2, half the PN code period.
(7.25)
The interference component of the second summation can be minimized by proper choice of the
PN codes with excellent autocorrelation properties.
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