| Summary: | 碩士 === 國立清華大學 === 電機工程學系 === 85 === In this thesis we discuss the receiver performance of two
types of optical coherent communication system , i.e. , homodyne
PSK systems and heterodyne CPFSK systems . In the first part of
this study , which deals with homodyne PSK systems , we
emphasize the effect of signal waveform distortion on system
performance , although other effects such as the effects of
laser phase noise and shot noise are accounted for . In contrast
to the conventional discussion in which the received signal
data is a sequence of square pulses , this study for the first
time investigates the problem encountered in BPSK homodyne
communication systems with Costas PLL's as the received signal
data is not a sequence of square pulses but is a sequence of
distorted pulses . The signal waveform distortion induces
additional amount of phase error variance and henceforth an
increase in bit-error rate , resulting in a more stringent laser
linewidth requirement . Ths laser linewidth requirement is
evaluated here taking into account such an effect of signal
waveform distion . Then in the second part , we analyze the
system performance of optical CPFSK receivers with AFC loops .
The effects of loop gain , bandwidth of IF band-pass filter ,
and postdetection filters are taken into account . The KL
(Karhunen-Loeve) expansion and the GQR ( Gaussian quadure rule )
method are used to deal with the laser phase noise
characteristics in computing the bit-error rates . With
different closed loop gains , we show the improvement of system
performance compared with the system without AFC .
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