| Summary: | 博士 === 國立清華大學 === 電機工程學系 === 85 === The digital joint estimators for carrier phase, symbol
timing,and the detection of data sequence with different
modulations are proposed in this dissertation.In communication
systems, the synchronization including both carrier phase
andsymbol timing is important for data detection.Basically, the
synchronization is an estimator which estimates carrier phase
and/or symbol timing.In most systems, these functions are
usually separated.However, it is expected that the receiver with
joint estimation would be betterthan the one with separated
estimations of parameters. Otherwise, it is the trend to use
the digital circuit in applicationbecause it is usually more
stable than its analog counter counterpartand can implement the
complex algorithms.These estimators are derived from the maximum
likelihood estimation (MLE)theorem. First, the scheme for
BPSK modulation is derived.According to the derivation, a
recursive scheme applying the decision directedmethod is
proposed.In order to simplify the structure, the Sample-
Correlate-Choose-Largest (SCCL)algorithm is used in the
estimation of carrier phase.With the similar derivation, the
proposed scheme is applied to the $\frac{\pi}{4}$-DQPSK
modulation.Because the peculiarity of $\frac{\pi}{4}$-DQPSK, the
estimation of carrierphase is omitted. The direct sequence
spread spectrum (DSSS) communication systems have receiveda lot
attention because many signals can be transmitted in the same
frequencyband and in the same time.With the similar method, the
similar scheme for DSSS systems can be obtained.However, the
timing candidates are too many to implement.To solve this
problem, the SCCL algorithm is also applied in timing
estimation.The whole scheme becomes a modified two dimensional
SCCL schemeand the two dimensional SCCL scheme also have
efficient performance. The synchronization of DSSS systems
includes two steps.The first step is acquisition and the second
step is tracking.The mean acquisition time for single dwell and
multi dwell scheme in slow Rayleighfading channels are analyzed.
With some modifications in the proposed tracking scheme
described above,A new acquisition scheme is obtained.Because the
new acquisition scheme applies the same algorithm as the
tracking scheme,the whole receiver scheme may be simpler than
the traditional one.Simulation results have shown to prove its
efficient performance.
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