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The system availability index is defined as the probability that an Omega user can effectively utilize three or more Omega station signals with a properly functioning Omega receiving system at any location in the user's operating area (which may include the entire earth's surface) and at any time (hour/month/year). This index (denoted as PSA) has been developed to provide a probabilistic measure of system performance from the user's viewpoint and to provide a standard for evaluating the operational performance of the Omega system. The system availability model, used to compute PSA, is structured to address four system elements: (1) signal transmission reliability, (2) signal reception reliability, (3) signal coverage, and (4) regional priorities for Omega usage. Sample calculations and results are presented for assumed alternative station power level assignments to illustrate the numerical characteristics of PSA. Although the model is applied to the Omega system, the methodology presented in this paper is general and could be applied to other radionavigation systems. The development of the model/algorithm and the calculations performed to obtain the sample results were supported by the U.S. Coast Guard Omega Navigation System Center. |
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