IS-GPS-800A - US Coast Guard Navigation Center

conditions with 1 -1e-5 per hour probability. When the integrity status flag is ‘on’, 5.73 times URA boundsinstantaneous URE under all conditions with 1-1e-8 per hour probability.Note #1: URA applies over the curve fit interval that is applicable to the NAV data from which the URA is read, forthe worst-case location within the intersection of the satellite signal and the terrestrial service volume.Note #2: The URA for a particular signal may be represented by a single parameter in the NAV data or by more thanone parameter representing components of the total URA. Specific URA parameters and formulae for calculating thetotal URA for a signal are defined in the applicable Space Segment to Navigation User Segment ICD’s.6.2.1.1 Integrity Assured URAWhen the integrity assurance monitoring is available, as indicated by the “integrity status flag” being set to “1”, theURA value is chosen such that the probability of the “actual” URE exceeding a threshold is met (see section3.5.3.10 for probability values). The URA value is conveyed to the user in the form of a URA index value. TheURA index represents a range of values; for integrity assurance applications, it is prudent to use the RSS of thelargest URA index values in the URA index range.6.2.1.2 User Differential Range AccuracyUser Differential Range Accuracy (UDRA) is a statistical indicator of the GPS ranging accuracy obtainable with aspecific signal and SV after the application of the associated differential corrections (DC parameters).6.2.2 GPS Week NumberThe GPS week numbering system is established with week number zero (0) being defined as that week whichstarted with the X1 epoch occurring at midnight UTC(USNO) on the night of January 5, 1980/ morning of January6, 1980. The GPS week number continuously increments by one (1) at each end/start of week epoch without everresetting to zero. Users must recognize that the week number information contained in the navigation message maynot necessarily reflect the current full GPS week number (see paragraph 3.5.3.1).6.2.3 Legendre SequenceThe Legendre sequence L(t) of length 10223, defined in Section 3.2.2.1.1, is given in Table 6.2-1.6.2.4 LDPC SubmatricesThis section defines the coordinates of elements with value “1” in each of the submatrices specified in Section 3.2.3.4.Tables 6.2-2, 6.2-3, 6.2-4, 6.2-5, 6.2-6, and 6.2-7 define the coordinates of elements with value “1” in each of thesubmatrices A, B, C, D, E, and T, respectively, for Subframe 2. Tables 6.2-8, 6.2-9, 6.2-10, 6.2-11, 6.2-12, and 6.2-13define the coordinates of elements with value “1” in each of the submatrices A, B, C, D, E, and T, respectively, forSubframe 3.Due to large amount of information provided in some of the submatrix tables, supplemental information is provided inTables 6.2-14, 6.2-15, 6.2-16, and 6.2-17. The supplemental information tables provide the number of 1’s in each rowand column of submatrices A and T for subframes 2 and 3.69 IS-GPS-800A8 June 2010