Data compression methods in telematics applications on mobile machines Nowadays self propelled agricultural machines get more and more often integrated in telema-tics systems. So a wireless exchange of information with a central database or other machines that are involved in the actual working process is enabled. To reduce the amount of data that has to be transferred, suitable compression methods had to be developed because especially in rural areas, where the operation of agricultural

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... s usually takes place, the infrastructure for wireless communication is often not that powerful and still very expensive as well. The compression results that can be achieved with the developed algorithms show that in most cases savings from more than 90 % can be realised without loosing signifi cant information from the original data. Abstract Landtechnik 64 (2009), no. 1, pp. 40-42, 3 fi gures , 1 reference A t the Institute of Agricultural Machinery and Fluid Power of the Technical University of Braunschweig (ILF), current research is addressing the development of a data management system for remote service in mobile machines. These studies are being carried out as part of a so-called collaborative research project with the fi nancial support of the Federal Ministry of Education and Research and the participation of the companies Claas, Grimme, and Eck*cellent IT as industrial partners. Goals An internet connection allows different mobile machines (e.g. agricultural machinery) to exchange data with a central back-end server. This back-end server can be accessed via internet by different persons involved (e.g. the machine operator, the maintainer, or the manufacturer). Hence, this is a telematics system characterized by the networking of several computers with the aid of a communication system, which combines them into one computer system. As part of this data management system, methods are being developed at the ILF which allow the quantity of data on the machine to be reduced before communication without losing important information. This is necessary because the mobile use of the machines requires communication via wireless media (generally mobile communication networks), which sometimes have rather small useable bandwidths (at least in rural regions) and are still relatively expensive. Fundamentals of data compression Data compression is defi ned as a modifi cation of the digital form of representation of a given quantity of data with the objective of reducing the required storage space and/or increasing transmission speed. The data compression rate is defi ned as the quotient of the quantity of the original and the compressed data [1]. Thus, the data compression rate increases as the quantity of data is compressed more and more. If the quantity of data grows during compression because an unsuitable compression method has been chosen, data compression rates may even be smaller than one. The saved quantity of data is often termed compression gain. If the size of this data quantity saved by means of compression is correlated with the original data quantity and multiplied by 100, the result shows the savings in the form of a percentage value. In principle, two different kinds of data compression can be distinguished, namely lossless and lossy compression. The characteristic of lossless methods of data compression is that all information of the original data can be perfectly reconstructed from the compression results. This means that