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
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
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
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
The last two parity bits are forced to zero by choosing R1 and R2
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
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,
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- Fall '08
- Global Positioning System, Univ. of Michigan