1 INTRODUCTION
1.1 The Global Positioning System (GPS) and Global Navigation Satellite
System (GLONASS) are space-based positioning, velocity and time systems. The GPS
space segment will normally be composed of 24 satellites in six orbits. 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) < 6.
The GLONASS space segment will normally be composed of 24 satellites placed in 3
orbital planes with 8 satellites in each plane. 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 PDOP < 6.
1.2 A combined receiver, when compared to either the GPS or GLONASS
receiver, offers improved availability, integrity, accuracy and resistance to
interference; increased ease of installation, and the ability to operate in the
differential GPS mode (DGPS), differential GLONASS mode (DGLONASS) and combined DGPS
and DGLONASS mode, when available.
1.3 Receiver equipment capable of combining individual satellite
measurements from GPS and GLONASS constellations to form a single solution is
intended for navigational purposes on ships with maximum speeds not exceeding 70
knots. Such equipment should, in addition to the general requirements contained in
resolution A.694(17)footnote, comply with the following minimum performance
requirements.
1.4 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 COMBINED GPS/GLONASS RECEIVER EQUIPMENT
2.1 The words "combined GPS/GLONASS receiver equipment" as used in these
performance standards include all the components and units necessary for the system
to properly perform its intended functions. The equipment should include the
following minimum facilities:
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.1 antenna capable of receiving both GPS and GLONASS
signals;
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.2 combined GPS/GLONASS receiver and processor;
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.3 means of accessing the computed latitude/longitude
position;
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.4 data control and interface; and
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.5 position display.
2.2 The antenna design should be suitable for fitting at a position on
the ship which ensures a clear view of the satellite constellations.
3 PERFORMANCE STANDARDS FOR COMBINED GPS/GLONASS RECEIVER
EQUIPMENT
3.1 The combined GPS/GLONASS receiver equipment should:
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.1.1 be capable of receiving and processing the Standard
Positioning Service (SPS) signals of the GPS as modified by Selective
Availability (SA) and range code signals in GLONASS and provide position
information in latitude and longitude World Geodetic System (WGS) 84
co-ordinates in degrees, minutes and thousandths of minutes. Means may be
provided to transform the computed position into data compatible with the
datum of the navigational chart in use. Where this facility exists, the
display and any data output should indicate that the co-ordinate
conversation is being performed and should identify the co-ordinate system
in which the position is expressed;
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.1.2 operate on the L1 frequency signal and C/A code in GPS and
L1 frequency signal and range code in GLONASS;
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.1.3 be provided with at least one output from which position
information can be supplied to other equipment. The output of position
information should be in accordance with the relevant international
standards;footnote
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.1.4 have static accuracy such that the position of the antenna
is determined to within 35 m (95%) in non-differential mode and 10 m (95%)
in differential mode with horizontal dilution of precision (HDOP) ≤ 4 or
position dilution of precision (PDOP) ≤ 6;
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.1.5 have dynamic accuracy such that the position of the ship is
determined to within 35 m (95%) in non-differential mode and 10 m (95%) in
differential mode with HDOP ≤ 4 or PDOP ≤ 6 under the conditions of sea
states and ship's motion likely to be experienced in shipsfootnote;
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.1.6 be capable of selecting automatically the appropriate
satellite transmitted signals for determination of the ship's position with
the required accuracy and update rate;
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.1.7 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;
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.1.8 be capable of acquiring position to the required accuracy,
within 30 min, when there is no valid almanac data;
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.1.9 be capable of acquiring position to the required accuracy,
within 5 min, when there is valid almanac data;
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.1.10 be capable of re-acquiring position to the required
accuracy, within 5 min, when all GPS and GLONASS signals are interrupted for
a period of at least 24 h, but there is no loss of power;
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.1.11 be capable of re-acquiring position to the required
accuracy, within 2 min, when subjected to a power interruption of 60 s;
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.1.12 be capable of re-acquiring an individual satellite signal
and utilizing it in the position solution within 10 s after being blocked
for 30 s;
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.1.13 generate and output to a display and digital interfacefootnote a new position solution at least once every 1
s;
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.1.14 have a minimum resolution of position, i.e. latitude and
longitude of 0.001 minutes;
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.1.15 generate 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
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.1.16 have the facilities to process DGPS and DGLONASS data fed
to it, in accordance with Recommendation ITU-R M.823 and the appropriate
RTCM standard; and
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.1.17 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 combined GPS/GLONASS 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 if the position
calculated is likely to be outside of the requirements of these performance
standards.
5.2 The combined GPS/GLONASS receiver equipment should provide as a
minimum:
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.1 an indication within 5 s if either:
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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;
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.2 a warning of loss of position;
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.3 DGPS and DGLONASS status indication of:
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.4 DGPS and DGLONASS integrity status and alarm; and
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.5 DGPS and DGLONASS text message display.