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 3540 seconds.
Hot Start. A GPS receiver without ephemeris data and
approximate position. Takes 510 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, antispooﬁng 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 vehicleuser 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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 Fall '08
 Stark
 Global Positioning System, Univ. of Michigan

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