1,116 research outputs found

    Minimum Distance Distribution of Irregular Generalized LDPC Code Ensembles

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    In this paper, the minimum distance distribution of irregular generalized LDPC (GLDPC) code ensembles is investigated. Two classes of GLDPC code ensembles are analyzed; in one case, the Tanner graph is regular from the variable node perspective, and in the other case the Tanner graph is completely unstructured and irregular. In particular, for the former ensemble class we determine exactly which ensembles have minimum distance growing linearly with the block length with probability approaching unity with increasing block length. This work extends previous results concerning LDPC and regular GLDPC codes to the case where a hybrid mixture of check node types is used.Comment: 5 pages, 1 figure. Submitted to the IEEE International Symposium on Information Theory (ISIT) 201

    Grassroots initiated networked communities: A study of hybrid physical/virtual communities

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    Virtual communities have been the focus of research since the beginning of the Internet. A more recent phenomenon is the hybrid networked community: a physical community extended by a network infrastructure, seeking to enhance existing social interactions, storage and dissemination of knowledge using both online and offline channels of communication. This paper considers one specific form: grassroots initiated networked communities. These are communities of locality that have developed their own Internet and /or intranet infrastructure with minimal external support. They believe that establishing such a network will enhance communication and 'sense of community' within their geographically defined boundaries. These initiatives may offer a viable and sustainable method for overcoming multiple digital inequalities, support the development of social capital, and provide insights into the impact of near-ubiquitous social computing. We review a case study of five such projects in the UK, identifying characteristics, methods of function, and long term aims. An outline of this work is presented and indications of likely future developments offered

    Design of LDPC Code Ensembles with Fast Convergence Properties

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    The design of low-density parity-check (LDPC) code ensembles optimized for a finite number of decoder iterations is investigated. Our approach employs EXIT chart analysis and differential evolution to design such ensembles for the binary erasure channel and additive white Gaussian noise channel. The error rates of codes optimized for various numbers of decoder iterations are compared and it is seen that in the cases considered, the best performance for a given number of decoder iterations is achieved by codes which are optimized for this particular number. The design of generalized LDPC (GLDPC) codes is also considered, showing that these structures can offer better performance than LDPC codes for low-iteration-number designs. Finally, it is illustrated that LDPC codes which are optimized for a small number of iterations exhibit significant deviations in terms of degree distribution and weight enumerators with respect to LDPC codes returned by more conventional design tools.Comment: 6 pages, 5 figures, Submitted to the 3rd International Black Sea Conference on Communications and Networking (IEEE BlackSeaCom 2015

    Improving the Quality of Low Fat Cheddar Cheese

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    End of Project ReportThe aims of this study were to elucidate the contribution of fat to cheese biochemistry and texture and to improve the texture and flavour of half-fat Cheddar cheese by modifications in make procedure, the addition of a fat mimetic, and/or the use of novel starter cultures/bacterial culture adjuncts. The main conclusions were as follows: A 'Moorepark Process' has been established for the production of half-fat Cheddar cheese with improved sensory acceptability. The flavour and texture of half-fat (17% w/w) Cheddar was improved by modification of the cheesemaking procedure and/or ripening conditions and through the use of novel starter cultures and/or bacterial culture adjuncts. Extensive databases have been compiled on: the effects of fat on the compositional, microbiological, biochemical, rheological and sensory properties of, and the yield of, Cheddar cheese. the compositional, biochemical and sensory characteristics of commercial Cheddar cheeses of different fat levels, available on the Irish and UK markets. Reduction in the fat level of Cheddar cheese resulted in a marked deterioration both in texture and flavour due to: increases in cheese hardness and fracture stress, indicating that the cheese became more elastic, tough and less amenable to mastication. a higher ratio of secondary-to-primary proteolysis a reduction in the level of primary proteolysis and an increase in the concentration of hydrophobic peptides which are conducive to bitterness.Department of Agriculture, Food and the Marin
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