f. Quality of the channel estimate.
Tau-Dithered Loop (TDL) Time Tracking. In this section, we will present the second technique
used to perform fine time tracking. A simplified block diagram is shown in Fig. 7.85.
412 CHAPTER SEVEN
FIGURE 7.85 TDL block diagram.
X
Finger
Input
X
(??“1) (+1)
PN
Generator
LPF
E L
C(t ??“ t ??“ Tc/2) C(t ??“ t + Tc/2)
r(t) | |2
g(t)
??‘
This is a single correlator realization of the DLL (which, as shown above, uses two parallel correlators).
The received signal is alternatively correlated with the early and late PN codes. Alternatively
stated, this TDL can be viewed as a DLL with early and late correlations time sharing a single correlator.
The dithering signal is denoted as g(t) and shown in Fig. 7.86.
FIGURE 7.86 Dither control signal example.
+1
??“1 Td
BW
Td
>> Dither Frequency, fDither = 2
1
The dithering signal controls which of the two correlators, early or late, are to be used. The actual
subtracting functions are performed with the help of the inverter and the LPF.
Inner/Outer-Loop Power Control. In this section, we will present a mechanism that adjusts the
transmission power inversely proportional to the channel fading characteristics. This is called transmit
power control (TPC).
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