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3/8/01 3
CDMA Era
T. Ojanpera and R. Prasad, Wideband CDMA for Third Generation Mobile Communications, Artech House
3/8/01 5
Why Spread Spectrum?
• Multiple access capability– CDMA
• Interference suppression– Jammer can be reduced on all/few signal coordinates
• Energy density reduction– Low probability of intercept (LPI)– Low probability of detection (LPD), LPPF, LPSE
• Finite time resolution– High resolution ranging– Accurate universal timing– Multipath resolution
3/8/01 7
Spread Spectrum Types
• Signal dimensionality ⇒
D↑ ⇒ W ↑ or T ↑
• Direct sequence (DS) ⇒ W ↑• Frequency hopping (FH) ⇒ W ↑• Time hopping (TH) T ↑• Hybrids
WTD 2≈
∫
≠=
=T
kj kjkj
dttt0
*
,0,1
)()( ϕϕ TWk 2,,2,1 K=
3/8/01 8
IMT-2000 / UMTS
( )[ ]∑ −= +
nh
tfj nTtpetC nn )()( 2 φπ
∑ −=n
hn nTtpctC )()(
∑
+−=
ns
t
n TMa
ntptC )()(
∏=i
i tctC )()( )(