GPS tracking device for cars – Intelligent Vehicle Technologies
The navigation message
The navigation message broadcast by every GPS satellite contains a variety of information used by each tracking platform to calculate a PVT solution. The information in this message includes time of signal transmission, clock correction and ephemeris data for the specific SV, and an extensive amount of almanac and additional status and health information on all of the satellites in the GPS.
Each SV repeatedly broadcasts a navigation message that is 12.5 minutes in length,and consists of 25 1500-bit data frames transmitted at 50 bits per second. A single data frame is composed of five 300-bit subframes, each containing different status or data information for the receiver, preceded by two 30-bit words with SV-specific telemetry and handover information. The first three subframes, containing clock correction and ephemeris data relevant to the specific SV, are refreshed as necessary for each data frame transmitted during the navigation message broadcast. The almanac and other data transmitted in the final two subframes are longer data segments, relevant to the entire GPS magnetic tracker, requiring the full 25 data frames to be broadcast completely. Below is a brief description of the contents of each subframe. For an illustration of the complete Navigation Message.
Clock correction subframe
The clock correction subframe, the first subframe transmitted in the navigation message data frame, contains the GPS week number, accuracy and health information specific to the transmitting SV, and various clock correction parameters relating to overall system time, such as clock offset and drift.
SV ephemeris subframes
The second and third subframes of the navigation message contain ephemeris data. This data provides the GPS with precise orbit information and correction parameters about the transmitting SV that the receiver uses accurately to calculate the satellite’s current position in space. This information, in turn, is used with the clock information to calculate the range to the SV. Included in the ephemeris subframes are telemetry parameters specific to the transmitting SV, such as correction factors to the radius of orbit, angle of inclination, and argument of latitude, as well as the square root of the semi-major axis of rotation, the eccentricity of the orbit of the SV, and the reference time that the ephemeris data was uploaded to the SV.
Almanac and support data subframes
Subframes four and five of the navigation message data frame contain comprehensive almanac data for the entire GPS constellation, along with delay parameters that the receivers use for approximating phase delay of the transmitted signal through the ionosphere, and correction factors to correlate GPS and Universal Time Coordinated (UTC). The almanac data contains orbit and health information on all of the satellites in the GPS constellation. GPS use this information to speed up the acquisition of SV signal transmissions. The almanac data in subframe four contains health and status information on the operational satellites numbered 25 through 32, along with ionospheric and UTC data. The almanac data in subframe five contains health and status information on the operational satellites in the GPS numbered 1 through 24. For a more detailed description of the information contained in the Navigation Message, refer to the ICD-GPS-200c specification, which is available from the US Coast Guard Navigation Center.
More GPS tracking solutions at http://www.jimilab.com/ .
The navigation message broadcast by every GPS satellite contains a variety of information used by each tracking platform to calculate a PVT solution. The information in this message includes time of signal transmission, clock correction and ephemeris data for the specific SV, and an extensive amount of almanac and additional status and health information on all of the satellites in the GPS.
Each SV repeatedly broadcasts a navigation message that is 12.5 minutes in length,and consists of 25 1500-bit data frames transmitted at 50 bits per second. A single data frame is composed of five 300-bit subframes, each containing different status or data information for the receiver, preceded by two 30-bit words with SV-specific telemetry and handover information. The first three subframes, containing clock correction and ephemeris data relevant to the specific SV, are refreshed as necessary for each data frame transmitted during the navigation message broadcast. The almanac and other data transmitted in the final two subframes are longer data segments, relevant to the entire GPS magnetic tracker, requiring the full 25 data frames to be broadcast completely. Below is a brief description of the contents of each subframe. For an illustration of the complete Navigation Message.
Clock correction subframe
The clock correction subframe, the first subframe transmitted in the navigation message data frame, contains the GPS week number, accuracy and health information specific to the transmitting SV, and various clock correction parameters relating to overall system time, such as clock offset and drift.
SV ephemeris subframes
The second and third subframes of the navigation message contain ephemeris data. This data provides the GPS with precise orbit information and correction parameters about the transmitting SV that the receiver uses accurately to calculate the satellite’s current position in space. This information, in turn, is used with the clock information to calculate the range to the SV. Included in the ephemeris subframes are telemetry parameters specific to the transmitting SV, such as correction factors to the radius of orbit, angle of inclination, and argument of latitude, as well as the square root of the semi-major axis of rotation, the eccentricity of the orbit of the SV, and the reference time that the ephemeris data was uploaded to the SV.
Almanac and support data subframes
Subframes four and five of the navigation message data frame contain comprehensive almanac data for the entire GPS constellation, along with delay parameters that the receivers use for approximating phase delay of the transmitted signal through the ionosphere, and correction factors to correlate GPS and Universal Time Coordinated (UTC). The almanac data contains orbit and health information on all of the satellites in the GPS constellation. GPS use this information to speed up the acquisition of SV signal transmissions. The almanac data in subframe four contains health and status information on the operational satellites numbered 25 through 32, along with ionospheric and UTC data. The almanac data in subframe five contains health and status information on the operational satellites in the GPS numbered 1 through 24. For a more detailed description of the information contained in the Navigation Message, refer to the ICD-GPS-200c specification, which is available from the US Coast Guard Navigation Center.
More GPS tracking solutions at http://www.jimilab.com/ .
Comments
Post a Comment