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Fendy Santoso
Department of Electrical and Computer Systems Engineering, Monash University, VIC, 3800, Melbourne, Australia
Computer Science & IT

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Uniform and NonUniform Optimum Scalar Quantisers: A Comparative Study Fendy Santoso
Journal of ICT Research and Applications Vol. 2 No. 1 (2008)
Publisher : LPPM ITB

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.5614/itbj.ict.2008.2.1.1

Abstract

The aim of this research is to investigate source coding, the representation of information source output by finite R bits/symbol. The performance of optimum quantisers subject to an entropy constraint has been studied. The definitive work in this area is best summarised by Shannon's source coding theorem, that is, a source with entropy H can be encoded with arbitrarily small error probability at any rate R (bits/source output) as long as R>H. Conversely, If R<H the error probability will be driven away from zero, independent of the complexity of the encoder and the decoder employed. In this context, the main objective of engineers is however to design the optimum code. Unfortunately, the ratedistortion theorem does not provide the recipe for such a design. The theorem does, however, provide the theoretical limit so that we know how close we are to the optimum. The full understanding of the theorem also helps in setting the direction to achieve such an optimum. In this research, we have investigated the performances of two practical scalar quantisers, i.e., a LloydMax quantiser and the uniformly defined one and also a wellknown entropy coding scheme, i.e., Huffman coding against their theoretically attainable optimum performance due to Shannon's limit R. It has been shown that our uniformly defined quantiser could demonstrate superior performance. The performance improvements, in fact, are more noticeable at higher bit rates.
Computer Simulations of Welch Based Denoising Technique for a Set of Chirp Signals Corrupted by Gaussian Noises Fendy Santoso
Journal of ICT Research and Applications Vol. 2 No. 2 (2008)
Publisher : LPPM ITB

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.5614/itbj.ict.2008.2.2.3

Abstract

The aim of this research is to investigate the performance of Welch based de-noising technique for a set of chirp signals corrupted by Gaussian noises. In telecommunications, chirp signals are widely studied, particularly for sonar, radar and spread spectrum applications. However, unlike conventional signals, chirp signals are typical of time varying frequency signals. It sweeps linearly from a low to a high frequency. It is in fact a signal in which its frequency increases or decreases with time. Results indicate that Welch based de-noising technique has effectively inhibited the noise. Nevertheless, this method works satisfactory only below its threshold point. Beyond this limit, the signal-to-noise ratio of the desired signal is not acceptable. Figuratively, radar can only detect the presence of the aircraft only at a certain limited distance only. As soon as the aircraft moves further apart, the transmitted signal becomes substantially weaker before the noise can completely overwhelm it. It turns out that the presence of the aircraft is no longer perceptible.
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