Repeats every 125 minutes eecs 455 univ of michigan

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Unformatted text preview: gan) Fall 2012 October 16, 2012 25 / 62 Lecture Notes 12 GPS Data Cold Start. A GPS receiver without information in memory that requires it to find the satellites. Must search for satellite signal. More than 30 seconds. Warm Start. A GPS receiver with almanac data, old ephemeris data and approximate position in memory that allows it rapidly find the necessary satellites. About 35-40 seconds. Hot Start. A GPS receiver without ephemeris data and approximate position. Takes 5-10 seconds to collect valid time satellites. EECS 455 (Univ. of Michigan) Fall 2012 October 16, 2012 26 / 62 Lecture Notes 12 GPS Data 1 Subframe=10 Words=300 bits=6 seconds Subframe TLM 1 HOW Clock Correction Data 2 TLM HOW Ephemeris Data 3 TLM HOW Ephemeris Data 4 TLM HOW Almanac, Ionohsphere, UTC Data 5 TLM HOW Almanac Data 1 Frame 30 Seconds 1500 bits = Preamble EECS 455 (Univ. of Michigan) Fall 2012 October 16, 2012 27 / 62 Lecture Notes 12 GPS Telemetry Word 1 Word=30 bits=.6 seconds Preamble 10001011 EECS 455 (Univ. of Michigan) TLM Message 14 bits Fall 2012 RR Parity 6 bits October 16, 2012 28 / 62 Lecture Notes 12 GPS Handover Word 1 Word=30 bits=.6 seconds Subframe F1F2 R1 R2 ID 3 bits TOW Count (Tuncated) 17 bits EECS 455 (Univ. of Michigan) Fall 2012 Parity 00 October 16, 2012 29 / 62 Lecture Notes 12 GPS Handover Word Flags F1 and F2 are for synchronization, anti-spoofing and momentum flags. The last two parity bits are forced to zero by choosing R1 and R2 appropriately. Parity is determined by using an extended Hamming code with 24 information bits and 6 parity check bits. Time of week (TOW) should increment by 1 each subframe (this can be used as a check that synchronization is achieved). EECS 455 (Univ. of Michigan) Fall 2012 October 16, 2012 30 / 62 Lecture Notes 12 GPS Data Subframe 1: Clock Correction and Space Vehicle Accuracy Clock correction for the satellite as uploaded from the GPS control segment Delay correction term for L1 and L2 bands Space vehicle-user range accuracy index Subframe 2 and 3: Ephemeris Parameters Satellite position vs. time Fit interval for ephemeris data Subframe 4 and 5: Almanac Data, Space Vehicle Health Data, Ionoshpere M...
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This note was uploaded on 02/12/2014 for the course EECS 455 taught by Professor Stark during the Fall '08 term at University of Michigan.

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