| Summary: | 博士 === 國立臺灣大學 === 電機工程學系研究所 === 86 === Spread spectrum techniques have been rapidly developed and used in many commun
ication systems in the recent past. Due to the diverse types of channel envir
onments, the study of new techniques for coping with various wireless communic
ation issues have been intensive for years. Among many issues being studied so
far, synchronization playsan essential role in establishing reliable communic
ation systems. Usually, in direct sequence spread spectrum, the process of cod
e synchronization is performed in twosteps: code acquisition and then code tra
cking. And both are essential parts for designing code synchronization scheme.
In our thesis, there are two chaptersin discussing acquisition receivers and
two chapters in discussing tracking receivers. In Chapter 2, based on a PN ac
quisition receiver with parallel I-Q matched filter and presumed data bit tran
sition, we employ the parallelsearch strategy to improve acquisition process f
or PN sequence under data modulation. In Chapter 3,by employing the property o
f shift-and-add of PN code, we propose a differentially coherent acquisition s
cheme that has a simple structure similar to noncoherent square-law receiver.
In Chapter 4, a novel differen tially coherent delay-locked loop (DCDLL) for a
ccuratecode tracking is proposed for direct sequence spread spectrum systems.
Due to the use of the differentialdecoder and exactly one correlator, the pro
posed scheme avoids the problems of gain imbalance. The tracking errorvariance
and mean time to lose lock (MTLL) are derived by linear and nonlinear ana
lysis. W hen the proposed DCDLL scheme is considered to be applied in ranging,
the performance of the proposed DCDLL scheme is better than that of tau-dithe
r loop(TDL) in the AWGN environment.In Chapter 5, we consider the effect of ve
ry fast Rayleigh fading on the proposed DCDLL. The derived results provide a t
ool to determine the design parameters in the tracking system.
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