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UBC Theses and Dissertations

Cancellation of arbitrary tone interference for all-digital high definition television transmitted over coaxial cable networks Marsland, Ian D.


In this thesis a novel canceller of a completely unknown tone which is interfering with a digital quadrature amplitude modulation (QAM) signal operating in an additive white Gaussian noise (AWGN) environment is proposed, analysed and evaluated. This canceller can be applied to protect all-digital high definition television (HDTV) signals from tone interference, which arises from intermodulation products, a common source of distortion in cable television networks. Expressions for the optimal weights for the linear minimum mean-square enor (MMSE) filter, consisting of L delay elements, for cancelling the tone interference are derived, under the condition that the tone’s frequency and power are known to the canceller. It is shown that the MMSE is directly proportional to the combined power of the QAM signal and the Gaussian noise, and inversely proportional to L. Furthermore, as the characteristics of the tone are assumed to be completely unknown, novel fast Fourier transform (FFT) based methods for estimating the frequency and power of the tone are proposed and analysed. By using these estimates in place of the true values for the optimal weights, a suboptimal filter is derived. Performance evaluation results have shown that the performance of the suboptimal canceller is, for all practical purposes, identical to the optimal one. To improve the performance further, without increasing the number of the filter’s delay elements, a decision feedback mechanism is employed to reduce the power of the data signal. Through a combination of analytical and computer simulated performance evaluation it is found that for all practical purposes the proposed decision feedback tone canceller removes the tone interference completely.

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