Annex - Revised Recommendation on Performance Standards for Shipborne Global Positioning System (GPS) Receiver Equipment
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Statutory Documents - IMO Publications and Documents - Resolutions - Maritime Safety Committee - Resolution MSC.112(73) - Adoption of the Revised Performance Standards for Shipborne Global Positioning System (GPS) Receiver Equipment - (Adopted on 1 December 2000) - Annex - Revised Recommendation on Performance Standards for Shipborne Global Positioning System (GPS) Receiver Equipment

Annex - Revised Recommendation on Performance Standards for Shipborne Global Positioning System (GPS) Receiver Equipment

 1 INTRODUCTION

1.1 The Global Positioning System (GPS) is a space-based positioning, velocity and time system that has three major segments: space, control and user. The GPS space segment will normally be composed of 24 satellites in six orbits. The satellites operate in circular 20,200 km orbits at an inclination angle of 55° with a 12-hour period. The spacing of satellites in orbit will be arranged so that a minimum of four satellites will be in view to users world-wide, with a position dilution of precision (PDOP) of = 6. Each satellite transmits on two "L" band frequencies, L1 (1575,42 MHz) and L2 (1227,6 MHz). L1 carries a precise (P) code and coarse/acquisition (C/A) code. L2 carries the P code. A navigation data message is superimposed on these codes. The same navigation data message is carried on both frequencies.

1.2 Receiver equipment for the GPS intended for navigational purposes on ships with maximum speeds not exceeding 70 knots should, in addition to the general requirements contained in resolution A.694(17)footnote, comply with the following minimum performance requirements.

1.3 These standards cover the basic requirements of position-fixing for navigation purposes only and do not cover other computational facilities which may be in the equipment.

2 GPS RECEIVER EQUIPMENT

2.1 The words "GPS receiver equipment" as used in these performance standards include all the components and units necessary for the system properly to perform its intended functions. The equipment should include the following minimum facilities:

  • .1 antenna capable of receiving GPS signals;

  • .2 GPS receiver and processor;

  • .3 means of accessing the computed latitude/longitude position;

  • .4 data control and interface; and

  • .5 position display and, if required, other forms of output.

2.2 The antenna design should be suitable for fitting at a position on the ship which ensures a clear view of the satellite constellation.

3 PERFORMANCE STANDARDS FOR GPS RECEIVER EQUIPMENT

  • The GPS receiver equipment should:

  • .1 be capable of receiving and processing the Standard Positioning Service (SPS) signals as modified by Selective Availability (SA) and provide position information in latitude and longitude World Geodetic System (WGS)-84 co-ordinates in degrees, minutes and thousandths of minutes and time of solution referenced to UTC (USNO). Means may be provided for transforming the computed position based upon WGS-84 into data compatible with the datum of the navigational chart in use. Where this facility exists, the display should indicate that co-ordinate conversion is being performed, and should identify the co-ordinate system in which the position is expressed;

  • .2 operate on the L1 signal and C/A code;

  • .3 be provided with at least one output from which position information can be supplied to other equipment. The output of position information based upon WGS-84 should be in accordance with international standards;footnote

  • .4 have static accuracy such that the position of the antenna is determined to within 100 m (95%) with horizontal dilution of precision(HDOP) = 4 (or PDOP = 6);

  • .5 have dynamic accuracy such that the position of the ship is determined to within 100m (95%) with HDOP = 4 (or PDOP = 6) under the conditions of sea states and ship's motion likely to be experienced in ships; footnote

  • .6 be capable of selecting automatically the appropriate satellite-transmitted signals for determining the ship's position with the required accuracy and update rate;

  • .7 be capable of acquiring satellite signals with input signals having carrier levels in the range of -130 dBm to -120 dBm. Once the satellite signals have been acquired, the equipment should continue to operate satisfactorily with satellite signals having carrier levels down to -133 dBm;

  • .8 be capable of acquiring position to the required accuracy, within 30 min, when there is no valid almanac data;

  • .9 be capable of acquiring position to the required accuracy, within 5 min, when there is valid almanac data;

  • .10 be capable of re-acquiring position to the required accuracy, within 5 min, when the GPS signals are interrupted for a period of at least 24 h but there is no loss of power;

  • .11 be capable of re-acquiring position to the required accuracy, within 2 min, when subjected to a power interruption of 60 s;

  • .12 generate and output to a display and digital interfacefootnote a new position solution at least once every 1 s;footnote

  • .13 have a minimum resolution of position, i.e. latitude and longitude, of 0.001 minutes;

  • .14 generate and output to the digital interfacefootnote course over the ground (COG), speed over the ground (SOG) and universal time co-ordinated (UTC). Such outputs should have a validity mark aligned with that on the position output. The accuracy requirement for COG and SOG should not be inferior to the relevant Performance Standards for Headingfootnote and SDME;footnote

  • .15 have the facilities to process differential GPS (DGPS) data fed to it in accordance with the standards of Recommendation ITU-R M.823 and the appropriate RTCM standard. When a GPS receiver is equipped with a differential receiver, performance standards for static and dynamic accuracies (paragraphs 3.4 and 3.5 above) should be 10 m (95%); and

  • .16 be capable of operating satisfactorily in typical interference conditions.

4 PROTECTION

Precautions should be taken to ensure that no permanent damage can result from an accidental short circuit or grounding of the antenna or any of its input or output connections or any of the GPS receiver equipment inputs or outputs for a duration of 5 min.

5 FAILURE WARNINGS AND STATUS INDICATIONS

5.1 The equipment should provide an indication of whether the position calculated is likely to be outside the requirements of these performance standards.

5.2 The GPS receiver equipment should provide as a minimum:

  • .1 an indication within 5 s if either:

  • .1.1 the specified HDOP has been exceeded; or

  • .1.2 a new position has not been calculated for more than 1 s.footnote

    • Under such conditions the last known position and the time of the last valid fix, with explicit indication of this state, so that no ambiguity can exist, should be output until normal operation is resumed;

  • .2 a warning of loss of position;

  • .3 differential GPS status indication of:

  • .3.1 the receipt of DGPS signals; and

  • .3.2 whether DGPS corrections are being applied to the indicated ship's position;

  • .4 DGPS integrity status and alarm; and

  • .5 DGPS text message display.

Parent topic: Resolution MSC.112(73) - Adoption of the Revised Performance Standards for Shipborne Global Positioning System (GPS) Receiver Equipment - (Adopted on 1 December 2000)
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