S. Lai et J. Conradi, THEORETICAL AND EXPERIMENTAL-ANALYSIS OF CLIPPING-INDUCED IMPULSIVE NOISE IN AM-VSB SUBCARRIER MULTIPLEXED LIGHTWAVE SYSTEMS, Journal of lightwave technology, 15(1), 1997, pp. 20-30
A new theoretical and experimental analysis of clipping-induced impuls
ive noise in directly modulated AM-VSB/digital hybrid lightwave system
s is presented. The theoretical model is based on asymptotic clipping
and shot noise theories, and the probability density of combined Gauss
ian and impulsive noise is obtained by performing a numerical inverse
Fourier transform on the closed-form characteristic function. Similar
analyzes in previously published work [3], [4] have resulted in closed
-form expressions for the BER in hybrid AM-VSB/QAM systems, but these
models, which do not use the numerical inverse Fourier transform, have
either required the use of an experimentally measured clipping rate u
sing a spectrum analyzer [3] or have had limited BER prediction accura
cy [4]. Application of our theory to experimental results for the BER
in a hybrid AM-VSB/64 QAM system demonstrates that the performance of
the model is better than the models of previously published works. The
oretical analysis of a similar hybrid system employing the N-VSB HDTV
digital modulation format rather than QAM indicates that an improvemen
t in BER is achieved if 8-VSB at double the symbol rate is used instea
d of 64 QAM. We also present the first experimental characterization o
f the amplitude and time distribution of 1) low-frequency bandpass and
2) down-converted impulsive noise and we show that the time interval
between clipping events has a high probability of being 167 mu s, 1.5
mu s, or 4 ms in an NTSC system with unmodulated carriers. These resul
ts have potential impact on forward error correcting codes used to ame
liorate the degrading effects of clipping.