However, if one expects a 16-finger RAKE actively demodulating 384-kbps
data services, then the chip-level buffer makes more sense. It is not the intention of this section to suggest
an architectural implementation, rather to inform the reader of choices that are available.
Fine Time Tracking. Once a multipath is found and assigned to a finger, certain time offset exists
due to the course resolution of the multipath searcher. Hence the finger must perform fine time code
tracking to not only reduce this potentially large initial time offset, but also to track time due to movement
and tolerances in the transmit and receive chip clocks. In this section, two fine??“time tracking
methods will be discussed.
Delay Locked Loop (DLL) Time Tracking. The first technique used for fine time tracking is the
DLL. This technique assumes the autocorrelation function of the received chip sequence is symmetrical.
The DLL has two parallel correlators: the first tracking the early time offset and the second
tracking the late time offset. The time corresponding to the center of the earlier and late offset is the
desired timing instance to be used by the finger despreader. This implies the received chip sequence
is oversampled to allow for tracking time offsets.
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