| Summary: | As technology improves, customers' expectations become higher every day. With such
technologies as the Super-VHS video recording and laserdisc player, customers compare
these against the quality of the video received over the cable system.
Distortions in the image are mainly caused by the nonlinearity of the underground
cascaded amplifiers in the cable TV system. Moreover, the addition of new channels on
the congested transmission system will increase present interference levels or create new
interferences causing picture quality degradation.
There are two approaches for combatting impairments. First, these can be prevented
by modifying hardware components in the cable TV system such as amplifiers, converters
among others. The other approach is to deal with the distortion itself through the use of
image processing and filtering techniques. The idea of this approach is, if not to totally
cancel the distortion, to reduce it until it becomes less visible to the human eye.
This thesis deals with the second approach that consists of reducing/cancelling and measuring
impairments such as the single frequency intermodulation, narrowband and wideband
CSO (Composite Second Order) distortion. This would complement the automatic detection
for a complete monitoring process of impairments. Our approach would fit in an automatic
system since it employs non-intrusive methods that do not involve the use of a test signal
and hence, no interruption in the transmission would be needed.
In this thesis, several filtering methods for cancellation and reduction of single frequency
intermodulation, narrowband and wideband CSO are studied and compared. Among these
methods are the FIR Linear Filtering, Interpolation in the frequency domain and the Alpha
Trimmed Filter. Results show that a combination of the last two methods reduces the single
frequency intermodulation considerably. In addition, results also show that the interpolation
in the frequency domain perform better than the other methods for narrowband CSO
cancellation and reduction. In the case of wideband CSO, a combination of the interpolation
in the frequency domain and the Alpha Trimmed filter reduces the impairment considerably. In the area of SNR measurements, different algorithms are proposed for each impairment.
For the single frequency intermodulation, the interpolation in the frequency domain algorithm
provides acceptable SNR measurements of less than 0.5 dB margin error. For the narrowband
CSO, algorithms consisting of the interpolation in the frequency domain and the block
averaging are proposed. These two algorithms provide acceptable results. For the wideband
CSO, several algorithms that involve the one-dimensional and two-dimensional Discrete
Fourier transform are proposed. The two-dimensional algorithms provide more accurate
results than the one-dimensional approach giving a margin error of less than 2 dB for SNR
measurements of up to 53 dB. === Applied Science, Faculty of === Electrical and Computer Engineering, Department of === Graduate
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