MSC.1/Circ.1575
16 June 2017
GUIDELINES
FOR SHIPBORNE POSITION, NAVIGATION AND TIMING (PNT) DATA PROCESSING
1 The Maritime
Safety Committee, at its ninety-fifth session (3 to 12 June 2015), adopted
resolution MSC.401(95)
on Performance standards for multi-system shipborne radio navigation
receivers and recognized the need to develop associated guidelines.
2 The Maritime
Safety Committee, at its ninety-eighth session (7 to 16 June 2017), approved
the Guidelines for shipborne position, navigation and timing (PNT) data
processing to the Performance standards for multi-system shipborne radio
navigation receivers, developed by the Sub-Committee on Navigation,
Communications and Search and Rescue at its fourth session (6 to 10 March
2017), as set out in the annex.
3 Member States are
invited to bring these Guidelines to the attention of the appropriate national
authorities and all other parties concerned.
ANNEX
GUIDELINES FOR SHIPBORNE POSITION, NAVIGATION AND TIMING (PNT)
DATA PROCESSING
Purpose
1 The purpose of
these Guidelines is to enhance the safety and efficiency of navigation by
improved provision of position, navigation and timing (PNT) data to bridge
teams (including pilots) and shipboard applications (e.g. AIS, ECDIS, etc.).
2 The shipborne
provision of resilient PNT data and associated integrity (I) and status data
(S) is realized through the combined use of onboard hardware (HW) and software
(SW) components. The shipborne PNT Data Processing (PNT-DP) is the core
repository for principles and functions used for the provision of reliable and
resilient PNT data.
3 The PNT-DP
specified within these Guidelines is defined as a set of functions
facilitating:
.1 multiple sources of
data provided by PNT-relevant sensors and services (e.g. GNSS receiver, DGNSS
corrections) and further onboard sensors and systems (e.g. radar, gyro, speed
and distance measuring equipment (SDME), echo-sounder providing real-time data)
to exploit existing redundancy in the PNT-relevant input data; and
.2 multi-system and
multi-sensor-based techniques for enhanced provision of PNT data.
4 These Guidelines
aim to establish a modular framework for further enhancement of shipborne PNT
data provision by supporting:
.1 consolidation and
standardization of requirements on shipborne PNT data provision considering the
diversity of ship types, nautical tasks, nautical applications, and the
changing complexity of situations up to customized levels of support;
.2 the identification
of dependencies between PNT-relevant data sources (sensors and services),
applicable PNT data processing techniques (methods and thresholds) and
achievable performance levels of provided PNT data (accuracy, integrity,
continuity and availability);
.3 harmonization and
improvement of onboard PNT data processing based on a modular approach to
facilitate changing performance requirements in relation to nautical tasks,
variety of ship types, nautical applications, and under consideration of user
needs (SN.1/Circ.274);
.4 the consequent and
coordinated introduction of data and system integrity as a smart means to
protect PNT data generation against disturbances, errors, and malfunctions
(safety) as well as intrusions by malicious actors; and
.5 standardization of
PNT output data including integrity and status data.
Scope
5 These Guidelines
define principles and functions for onboard PNT data processing, taking into
account the scalability of PNT-DP.
6 These Guidelines
provide recommendations on how to handle differences regarding installed
equipment, current system in use, feasibility of tasks and related functions,
performance of data sources as well as usability in specific regions and
situations.
7 A structured
approach for the stepwise introduction of integrity is developed to achieve
resilient PNT data provision in relation to the application grades and
supported performance levels.
8 These Guidelines
aim to achieve standardized and integrity tested PNT output data to enhance
user awareness regarding achieved performance level.
Structure of Guidelines
9 These Guidelines
have a modular structure, starting with a general section which introduces the
purpose, scope and application of the Guidelines. The general section also
explains the high-level architecture of PNT-DP and how the PNT-DP can be
integrated into onboard navigation systems, e.g. INS1, ECDIS2
and RADAR3.
_________________
1 Equipment
according to MSC.252(83).
2 Equipment
according to MSC.232(82).
3 Equipment according to MSC.92(79).
10 More detailed
guidance on the PNT-DP is given as follows:
• Module A – data input: sensors, services,
and sources;
• Module B – functional aspects;
• Module C – operational aspects;
• Module D – interfaces; and
• Module E –
documentation.
11 In addition, these
Guidelines have three appendices listing definitions, abbreviations and
expected operational and technical requirements on PNT/I data output.
Application of Guidelines
12 These Guidelines
provide prerequisites for harmonized provision of PNT and associated integrity
data.
13 These Guidelines
are recommended for equipment manufacturers, shipyards, ship owners and
managers responsible for onboard equipment and systems used for PNT data
provision.
Definitions
14 Definitions used in
the context of PNT, WWRNS and GNSS are detailed in appendix A.
Architecture
15 Generally, a
shipborne PNT-DP is made up of three functional blocks:
.1 Pre-processing;
.2 Main processing; and
.3 Post-processing.
16 The pre-processing
function extracts, evaluates, selects and synchronizes input (sensor and
service) data (including the associated integrity data) to preselect the applicable
techniques to determine PNT and integrity output data.
17 The architecture of
the PNT-DP is shown in figure 1.
Figure 1: Architecture of
PNT-DP
18 The main processing
function generates the PNT output data and associated integrity and status
data.
19 The post-processing
function generates the output messages by coding the PNT output data (PNT,
integrity, and status data) into specified data protocols.
Integration
20 The PNT-DP can be
integrated as software into ships' navigation systems such as INS, ECDIS or
RADAR as shown in figure 2.
Figure 2: PNT-DP integrated
as software into INS, ECDIS, or RADAR
21 The Multi-system
Shipborne Radionavigation Receiver (MSR) is appropriate to facilitate the
combined use of WWRNS to improve the provision of position, velocity and time
(PVT) data and related integrity data. The application of enhanced processing
techniques can be realized by the MSR (figure 3) itself or by PNT-DP as part of
INS (figure 2).
Figure 3: PVT-DP integrated as software into MSR
Module A – Data input:
Sensors, services and sources
22 Different PNT data
processing functions need comprehensive input data to keep the PNT-DP running
as specified in this document. These Guidelines define how the shipborne PNT-DP
should provide output data by processing input data (from sensors and/or
services and/or sources) while availability and performance of input data may
vary temporally and spatially (see figure 4).
Figure
4: Sensors, services, and sources
23 The desired level
of PNT data output depends on currently available inputs that may independently
vary over a short or long period of time. These Guidelines aim to specify the
demand on needed types of services, sensors, and sources for predefined
performance levels of PNT/I data (module B).
24 These Guidelines
specify PNT-DP's real-time adjustments of the used data processing functions
(module B and C) to applicable methods taking into account the available input
data.
25 The PNT-DP
processes data from type-approved sensors and recognized services.
26 In a minimum
configuration, PNT-DP uses the minimum number and type of sensors as defined in
SOLAS (depending on the ship type). The manufacturer may add inputs and outputs
to achieve better performance or more information (e.g. with integrity
indication) at output of PNT-DP to support additional nautical functions and
tasks that require better performance or more information (e.g. with integrity
indication).
27 The necessary
sensor, service, and source layout is determined by the necessary performance
of PNT data provision and integrity evaluation for the subsequent nautical
functions and tasks.
A.1 Types of services
for positioning
28 Services are
classified by grade/type as follows:
.1 Radionavigation
services provide navigation signals and data which enable the determination
of ships' position, velocity and time.
.2 Augmentation
services are other services that provide additional correction and/or
integrity data to enable improvement of radionavigation-based determination of
ships position, velocity and time.
29 Services are
classified regarding its geographical coverage:
.1 Global services
are characterized by their worldwide coverage. They may have limitations
regarding usability for different phases of navigation due to signal
disturbances reducing the availability or performance of transmitted signals
and/or provided data.
.2 Regional services
(and maybe local services) are only available in dedicated service areas. They
may be used to improve the performance of ships' navigational data in terms of
accuracy, integrity, continuity and availability even in demanding operations
when, for example, higher accuracy and integrity level is required during coast
and port navigation.
A.2 Types of sensors
and sources
30 The type-approved
sensors and data sources are distinguished into the following categories:
.1 Service-dependent
sensors rely on any service from outside the ship provided by human effort.
They cannot be used on board without at least a satellite-based or terrestrial
communication link to the service provider (shown in figure 4, mainly used to
provide data of ships position, velocity and time).
.2 Shipborne sensors
and sources:
.1 Primary sensors
use a physical principle, e.g. earth rotation or water characteristics and are
independent of any human applied service provision (shown in figure 4, mainly
used to provide data of ships attitude and movement);
.2 Secondary sensors
and sources may be used to provide additional data for the verification of PNT
data (see figure 4), e.g. water depth at known position from an ENC, line of
position, or directions and distances provided by onboard RADAR.
31 The above described
sensors are considered to be usable worldwide and free of any rebilling user
charge.
A.3 Additional input
data
32 In addition to
sensors, services and sources listed in A.1 and A.2 further PNT-relevant data
may be used for shipborne PNT data provision to increase redundancy or to
evaluate plausibility and consistency of data input (ship sensed position, e.g.
by position reference systems). Such data may be provided via AIS or VHF Data
Exchange System (VDES), see figure 4.
A.4 Requirements on
input data
All sensors, services and data sources used as input for the
shipborne PNT-DP should comply with the relevant IMO performance standards.
Module
B – Functional aspects
B.1 General
B.1.1 Objective
33 The overarching
objective of the shipborne PNT-DP is the resilient provision of PNT data
including associated integrity and status data.
34 In this context
resilience is:
.1 the ability to
detect and compensate against relevant failures and malfunctions in data
acquisition and processing to meet the specified performance requirements on
PNT data for accuracy and integrity with respect to continuity and availability
under nominal conditions; and
.2 the ability to
detect, mitigate and compensate malfunctions and failures based on supported
redundancy in data acquisition and processing to avoid loss or degradation in
functionality of PNT-DP.
B.1.2 Functional
Architecture
35 The architecture of
PNT-DP is shown in figure 1. Depicting the principal functions: pre-processing,
main processing, and post-processing.
36 The pre-processing
of input data:
.1 conducts:
.1 analysing of their
current availability in relation to their usability for ongoing PNT data
processing and selection;
.2 timely and spatial
synchronization of input data within the consistent common reference system
(CCRS); and
.3 determining the
feasibility of functions in relation to supported methods taking into account
the current performance of data input; and;
.2 provides evaluated,
selected and synchronized data for the main processing.
37 The main
processing:
.1 conducts:
.1 determination of PNT
data;
.2 determination of
associated integrity and status data in relation to integrity of sensors and
services, functional capability of onboard data processing, and estimated integrity
of PNT output data; and
.3 selection of PNT
output data including integrity and status data and;
.2 provides the selected PNT output data to post-processing.
38 The
post-processing:
.1 conducts:
.1 checking the
completeness of PNT output data in relation to supported composition of
messages; and
.2 the generation of
output data streams in the designated message-coding; and
.2 provides the
selected PNT data output.
39 The functional
architecture of the shipborne PNT-DP supports the use of numerous processing
channels operated in parallel:
.1 to enable the
application of different processing methods for PNT data generation in relation
to intended accuracy and integrity levels;
.2 to improve
continuity and availability in PNT data processing and provision by redundant
system layout and/or implemented fall-back option; and
.3 to enable reliable
detection, mitigation and compensation of failures and malfunctions in data
input and processing.
40 The functional
architecture of the shipborne PNT-DP is based on a modular structure to support
the adaption of shipborne data processing to:
.1 different
performance requirements on PNT output data in relation to navigational
situation and nautical tasks in their spatial and temporal context;
.2 differences in data
input of PNT-DP depending on carriage requirements, equipment levels, or both;
and
.3 occurring changes of
available/usable sensors, services, and other data sources during
operation.
B.1.3 Requirements4
_____________________
4 Approaches for
resilient provision of PNT data can only be discussed in relation to specific
requirements, e.g. accuracy. A sufficient scaling of requirements is considered
as an appropriate way to facilitate the diversity of PNT-DP implementations.
41 The requirements on data output of PNT-DP
are specified by:
.1 the application
grade of PNT-DP defining the amount and types of output data; and
.2 the supported
performance level of provided PNT data regarding accuracy and integrity.
Figure
5: Application Grades of PNT-DP (*provided with improved accuracy)
42 The following
application grades of a PNT-DP (see figure 5) are used to define different
requirements on the amount and types of PNT data output:
.1 Grade I supports the
description of position and movement of a single onboard point (e.g. antenna
location of a single GNSS receiver);
.2 Grade II ensures
that horizontal attitude and movement of ship's hull are unambiguously
described;
.3 Grade III provides
additional information for vertical position of a single onboard point and
depth; and
.4 Grade IV is prepared
for the extended need on PNT data e.g. to monitor or control ship's position
and movement in three-dimensional space.
43 Depending on the
supported application grade of an onboard PNT-DP, the following PNT data is
provided:
.1 Grade I: horizontal
position (latitude, longitude), SOG, COG, and time;
.2 Grade II: heading,
rate of turn, STW and CTW in addition to Grade I5;
.3 Grade III: altitude,
and depth in addition to Grade II; and
.4 Grade IV: heave,
pitch, and roll (and may be surge, sway, and yaw with higher performance) in
addition to Grade III.
_____________________
5 A sufficient provision
of Grade II PNT data enables the determination of surge, sway and yaw.
44 Performance
requirements on each set of PNT output data are described in terms of accuracy
and integrity, whereby several levels are specified to address the diversity of
operational as well as technical requirements (see figure 6).
Figure
6: Generic performance level for each PNT output data in relation to accuracy
and integrity
45 Numbers and
thresholds of operational performance levels per PNT data type should be
compliant with existing performance standards and resolutions, e.g. A.1046(27), for
horizontal positioning results into two operational accuracy levels: A (better
than 100 m) and B (better than 10 m) to 95% confidence; A.915(22) specifies the future need for two
additional operational accuracy levels: C (better than 1 m) and D (better than
0.1 m).
46 In addition, the
introduction of technical performance levels (A.1, A.2, B.1, B.2, …) enables a
graduated specification of task- and application-related requirements on PNT
data. Furthermore, it prepares a need-driven evaluation and indication of
accuracy.
47 Integrity data per
each individual PNT output data should be provided to indicate the further
usability of data. The value of included integrity information depends on
applied principles of integrity evaluation in relation to a dedicated accuracy
level:
.1 None: Unavailable
integrity evaluation;
.2 Low: Integrity
evaluation based on plausibility and consistency checks of data provided by
single sensors, systems, services, or sources;
.3 Medium: Integrity
evaluation based on consistency checks of data provided by different sensors,
systems, services, and sources with uncorrelated error parts6 as far
as possible; and
.4 High: Integrity
evaluation based on estimated accuracy (protection level).
_____________________
6 See definition of
correlation and uncorrelated error parts in appendix A.
48 As a result of
preceding paragraphs, the performance of an individual PNT output data (requirement
as well as result of evaluation) should be defined by specified accuracy and
integrity levels.
49 Accuracy and
integrity levels should be defined for all PNT data of the supported
application grade or a combination of them (see figure 7) to ensure that the
requirements on data output of a PNT-DP are comprehensively specified.
Figure
7: Composition of requirements on PNT/I output data (application grade II as
example)
50 Figure 8
illustrates the interdependencies between application grade and supported
performance levels in relation to current and future nautical tasks and
applications (exemplified).
Figure 8: Illustration of interdependencies between application
grade, performance level, and nautical tasks / applications
B.2 Pre-processing
B.2.1 Objective
51 The pre-processing
prepares the input data for main processing and pre-evaluates the feasibility
of data processing methods supported by main processing under current
conditions.
B.2.2
Functional and methodical aspects
B.2.2.1 Evaluation of input data
52 Data streams
received from input data-providing entities should be time-stamped with the
time of reception using system time of the PNT-DP. The system time should be
synchronized with a common time base by using the input data of an appropriate
source, preferably UTC.
53 Incoming data
provided by sensors, systems and services should be evaluated with respect to:
.1 completeness and
correctness of transmission; and
.2 plausibility and
consistency of data content.
54 The evaluation of a
data stream received from an input data-providing entity should comprise the
following methods:
.1 The correctness of
transmitted input data should be checked with respect to the rules of the
protocol in use (completeness, parity, etc.). Incorrect data should be excluded
from further processing.
.2 It should be checked
if the expected data update rate, as needed for main processing, is met. If the
determined update rate implies a latency violation, the data should be marked
accordingly.
55 The evaluation of
data content should comprise the following methods:
.1 Parameters
describing the characteristics of the input data-providing entity should be
analysed to identify which following processing steps are applicable. Such
parameters include performance parameters, such as number and type of
measurements (e.g. GPS/DGPS); and status parameter, such as healthy/unhealthy.
.2 Data describing the
performance of input data should be analysed to identify the following
processing steps that are applicable. Such parameters include performance
parameters like UERE, HPL; and time of data validity, as available, with
respect to latency limitations.
.3 Plausibility and
consistency of data should be tested with respect to appropriate value ranges
and thresholds. Data failing those tests should be marked accordingly. Data of
former epochs may be used to detect dynamic value ranges and thresholds.
56 Input data provided
by sensors, systems, and services should be marked as invalid if the data
sources (e.g. sensors and services) have indicated that they are invalid.
57 Input data provided
by sensors, systems and services should be excluded from further PNT data
processing, if:
.1 data is indicated as
invalid;
.2 the identified
violation of latency, plausibility, or consistency
.1 is in an order which
is intolerable for the accuracy level intended in minimum by the PNT-DP; or
.2 cannot be managed by
the PNT-DP in a sufficient manner to avoid unintended degradations of PNT
output data.
B.2.2.2 Temporal/spatial adjustment of input data
58 Input data which
have passed the evaluation tests should be adjusted spatially and temporally
within a Consistent Common Reference System (CCRS), where required, to meet the
specified accuracy level.
59 The method for the
time synchronization should provide a common timescale referenced to the system
time of the PNT-DP, preferably given in UTC. The resolution of time
synchronization shall not degrade that of input data.
60 The timescale used
for time synchronization should also be used to trigger the complete data
processing: pre-processing, main processing, and post-processing. All
spatially-related information should use a CCRP. If CCRP transformation fails,
this should be indicated by corresponding status data.
B.2.2.3 Feasibility evaluation of main processing
61 The feasibility of
main processing should be assessed in relation to individual processing
channels and their requirements on data input.
62 A method performing
the feasibility evaluation in relation to an individual main processing channel
should include test procedures and thresholds reflecting its requirements on
data input.
63 The evaluation
results should be provided by internal status data to control the operation of
each supported processing channel.
64 The results of the
feasibility evaluation enable an early indication of performance degradation in
relation to supported performance levels.
B.2.3 Results of
pre-processing
65 Results of
pre-processing should comprise:
.1 input data indicated
as usable, time-stamped with a common time base, preferably UTC, and spatially
adjusted;
.2 metadata to describe
characteristics of usable input data;
.3 internal status data
describing the current status of pre-processing;
.4 internal status data
for controlling of main processing; and
.5 internal integrity
data as results of evaluation of input data utilized by main processing.
B.3 Main processing
B.3.1 Objective
66 The main processing
serves to improve PNT data provision by applying appropriate methods for
completion, refinement and/or integrity evaluation.
B.3.2 Functional and
methodical aspects of PNT data generation
67 Within main
processing, the pre-evaluated input data (from sensors, systems and services,)
should be used to feed at least one data processing channel.
68 The feasibility
evaluation results of pre-processing (B.2.2.3), provided as internal status
data, should be used as a control parameter during main processing to
activate/deactivate individual processing channels.
69 Each processing
channel should be specified by the set of supported methods generating PNT
data, integrity data, and status data.
70 Each processing
channel should provide at least one, preferably several or all PNT data types
including associated integrity and status data.
71 Main processing
should, if available, combine single or multiple data processing channels, to
increase the performance of accuracy, integrity, continuity, availability, and
resilience of PNT data provision. Methods should be provided to manage changes
in data input, e.g. changes in availability of external service data.
72 The main processing
stage should generate status data on the mode and progress of data processing
for PNT data output.
B.3.2.1 Number and types of
processing channels
73 A single processing
channel should provide some or all intended PNT data and associated integrity
data (see channel 1 to 3 in figure 9).
74 The number of
processing channels operated in parallel should ensure at least the provision
of all PNT output data in the designated application grade and the supported
accuracy and integrity levels.
75 The methods
provided by an individual processing channel should at least ensure that the
intended PNT output data are provided with the intended accuracy and integrity
when the requirements on data input are met (nominal conditions).
Figure
9: Illustration of processing channels being operated parallel within main
processing
76 More than one
processing channel should be supported for the provision of one type of PNT
data and associated integrity data (see figure 9),
.1 if different
accuracy and integrity levels are supported by application of different methods
for data processing, or
.2 if an increase of
reliability and resilience is aimed by parallel processing of largely
independent input data with the same methods.
77 Parallel processing
channels should differ in used input data, or applied methods, or both. These
differences may result in measurable differences in PNT data output:
.1 The additional use
of augmentation data should improve the accuracy of PNT output data by
application of corrections, or should enhance the integrity evaluation with
independent evaluation results, or should serve both.
.2 If parallel
processing channels are equipped with the same methods and are fed with largely
independent input data, the results of those channels should cover the same
types/set of PNT data. The PNT data can be used alternatively for data output
due to its independence and should be used internally for integrity evaluation.
.3 Enhanced processing
channels should combine multiple types of input data to enable the application
of effective methods during data processing such as:
.1 self-correction
(e.g. dual-frequency GNSS signal processing to correct ionospheric path delays;
noise reduction by filtering);
.2 self-controlling
(e.g. detection and exclusion of outliers), self-evaluation (e.g. consistency
tests or estimation of protection level as overestimate of expected
inaccuracies); and/or
.3 self-management
(e.g. failure compensation by interpolation or extrapolation in a common model
of movement).
.4 The capability of
enhanced processing channels can be increased if redundancy in data input
enables the simultaneous and coordinated use of effective methods such as
self-correction, self-controlling, self-evaluation, and self-management.
78 The need for the
provision of reliable and resilient PNT data requires that at least a parallel
processing channel should be implemented as a fall-back solution for an
enhanced processing channel, which is more sensitive to availability of data
input (Fall-back may not be available after loss of sensitive input data).
79 Ultimately, the
number and types of parallel processing channels is determined by:
.1 the supported
application grade as well as supported accuracy and integrity levels of aimed
PNT data output;
.2 arranging of data
processing methods to single channels; and
.3 the aimed level of
reliability and resilience of PNT data specifying the residual need for
fall-back solutions per application grade and assigned accuracy and integrity
levels.
B.3.2.2 Methods to refine PNT data
80 An improvement to
accuracy for several or all PNT data types by a processing channel is achieved
if one, or a combination of the following methods, is applied:
.1 methods applying
augmentation data provided by recognized services and external sources (if
available and indicated as usable)
.1 to improve the
accuracy of data by error correction (e.g. GNSS range and range rate
corrections);