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In this paper, a novel preamble structure, including a synchronization field (S-field) and a cell-search field (C-field), is proposed for orthogonal-frequency-division-multiplexing-based cellular systems. An efficient algorithm for downlink synchronization and cell search using the preamble is also proposed. The synchronization and cell-search process includes the initial symbol-timing estimation using continuously or, at least, periodically transmitted downlink signal, the frame detection, the fine symbol-timing estimation, the frequency-offset estimation using the preamble S-field, and the cell identification using the preamble C-field. Performance of each synchronization and cell-search step is analyzed and verified by computer simulation. The overall performance of the synchronization and cell search is then analyzed in terms of the mean acquisition time. It is shown that the proposed preamble with the corresponding synchronization and cell-search algorithm can provide a very robust synchronization and cell-search capability, even in bad cellular environments. Index Terms--Cell search, cellular, orthogonal-frequency-division multiplexing (OFDM), preamble, synchronization.

AbstractThe shell nozzle diameter plays a crucial role in determining heat transfer efficiency and pressure characteristics in shell and tube heat exchangers. In this study, we have conducted a numerical simulation to explore the effects of varying shell nozzle diameters on heat transfer performance, flow behavior, and pressure drop within a shell and tube heat exchanger. Ranging from 10 to 110 mm, we assessed how altering the shell nozzle diameter affected heat transfer, flow patterns, and pressure drop. Employing the k-ω shear stress transport turbulence model, we compared numerical Nusselt numbers to experimental data, observing a correlation. As the shell nozzle diameter decreased, inlet velocity surged, generating a stronger vortex. Shrinking from 110 to 10 mm, this reduction amplified vorticity by an average of 169%, notably intensifying heat exchange by 35%. Evaluating the overall heat transfer coefficient against pressure drop, we used the thermal enhancement factor, reaching a peak of 4.39 at a 70 mm shell nozzle diameter. This exploration lays groundwork for optimizing shell nozzle diameters in these heat exchangers. [ABSTRACT FROM AUTHOR]