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

transmitted by the SVs will degrade over time.3.5.4.3.5.1 Reduced Almanac PacketThe following shall apply when interpreting the data provided in each packet of reduced almanac (see Figure 3.5-9).3.5.4.3.5.1.1 Reduced AlmanacThe reduced almanac data is provided in bits 9 through 30 of each packet. The data from a packet along with thereference values (see Table 3.5-6) provide ephemeris with further reduced precision. The user algorithm isessentially the same as the user algorithm employed for computing the ephemeris from the parameters in subframe 2(see Section 3.5.3.6.1 and Table 3.5-2). Other parameters appearing in the equations of Table 3.5-2, but notprovided by the reduced almanac with the reference values, are set to zero for SV position determination.33 BITS1 9 17 24 31 32 33PRN a A 0 08 BITS8 BITS7 BITS7 BITSL1 HEALTHL2 HEALTH* See Figures 3.5-4 for complete bit allocation in the message.L5 HEALTHFigure 3.5-9. Reduced Almanac Packet Content58 IS-GPS-800A8 June 2010