gr-mcp-docs/reference/cospas-sarsat/t-series/t019.md

---
title: "T019: C/S T.019 - Issue 2 Rev.10"
description: "Official Cospas-Sarsat T-series document T019"
sidebar:
  badge:
    text: "T"
    variant: "note"
# Extended Cospas-Sarsat metadata
documentId: "T019"
series: "T"
seriesName: "Technical"
documentType: "specification"
isLatest: true
issue: 2
revision: 10
documentDate: "October 2025"
originalTitle: "C/S T.019 - Issue 2 Rev.10"
---

> **📋 Document Information**
>
> **Series:** T-Series (Technical)
> **Version:** Issue 2 - Revision 10
> **Date:** October 2025
> **Source:** [Cospas-Sarsat Official Documents](https://www.cospas-sarsat.int/en/documents-pro/system-documents)

---

COSPAS-SARSAT MEOLUT PERFORMANCE
SPECIFICATION AND DESIGN GUIDELINES
C/S T.019
Issue 2 - Revision 10

NOTES
This specification and design guidelines document contains specification values related to
C/S T.018 beacons that are in square brackets [ ], representing information that is to be
confirmed or further defined. These C/S T.018-related specifications are provided for awareness
and are subject to change.
This document includes specifications for location accuracy of slow-moving medium speed and
fast-moving beacons with values that are to be determined. The finalization of these
specifications is ongoing.

![Image 1 from page 1](/images/cospas-sarsat/T-series/T019/T019_page_1_img_1.png)


COSPAS-SARSAT MEOLUT PERFORMANCE
SPECIFICATION AND DESIGN GUIDELINES
HISTORY
Issue
Revision
Date
Comments


Approved by the Cospas-Sarsat Council (CSC-55)


Approved by the Cospas-Sarsat Council (CSC-57)


Approved by the Cospas-Sarsat Council (CSC-58)


Approved by the Cospas-Sarsat Council (CSC-59)


Approved by the Cospas-Sarsat Council (CSC-60)


Approved by the Cospas-Sarsat Council (CSC-61)


Approved by the Cospas-Sarsat Council (CSC-62)


Approved by the Cospas-Sarsat Council (CSC-64)


Approved by the Cospas-Sarsat Council (CSC-66)


Approved by the Cospas-Sarsat Council (CSC-67)


Approved by the Cospas-Sarsat Council (CSC-69)


Approved by the Cospas-Sarsat Council (CSC-71)


Approved by the Cospas-Sarsat Council (CSC-73)


TABLE OF CONTENTS
Page
History ..................................................................................................................................................... i
Table of Contents ................................................................................................................................... ii
List of Figures ....................................................................................................................................... iv
List of Tables ......................................................................................................................................... v
1.
Introduction .......................................................................................................................... 1-1
1.1
Overview .................................................................................................................... 1-1
1.2
Scope .......................................................................................................................... 1-1
1.3
Document Organization ............................................................................................. 1-1
1.4
Reference Documents................................................................................................. 1-2
2.
Cospas-Sarsat MEOLUT Description .................................................................................. 2-1
3.
Operational Requirements .................................................................................................... 3-1
3.1
MEOLUT Data Availability ....................................................................................... 3-1
3.2
Data Requirements ..................................................................................................... 3-1
3.3
Data Channels ............................................................................................................ 3-2
3.3.1
Satellite Data Channels .................................................................................. 3-2
3.3.2
MEOLUT Data Exchange ............................................................................. 3-2
3.4
Satellite Tracking and Visibility ................................................................................. 3-2
3.5
Status and Alarm ........................................................................................................ 3-3
3.6
RF Radiation and Emissions ...................................................................................... 3-3
3.7
Data Archiving ........................................................................................................... 3-3
3.8
Cospas-Sarsat Quality Management System (QMS) Continuous Monitoring and
Objective Assessment................................................................................................. 3-3
4.
Functional and Processing Requirements ............................................................................ 4-1
4.1
Summary of Requirements ......................................................................................... 4-1
4.1.1
Antenna and RF Subsystem ........................................................................... 4-1
4.1.2
Time and Frequency Reference Subsystem ................................................... 4-1
4.1.3
Satellite Tracking Subsystem ......................................................................... 4-2
4.1.4
MCC Interface ............................................................................................... 4-2
4.2
Processing 406 MHz Beacon Message Data .............................................................. 4-2
4.2.1
General Processing Requirements ................................................................. 4-2
4.2.2
Beacon Message Recovery ............................................................................ 4-3
4.2.3
Bit Verification .............................................................................................. 4-3


4.2.4
Beacon Message Validation ........................................................................... 4-4
4.2.5
Multiple Invalid Beacon Message Processing ............................................... 4-5
4.2.6
Beacon Message Association ......................................................................... 4-6
4.2.7
Multiple Valid C/S T.001 Message Processing ............................................. 4-7
4.2.8
MEOLUT Data Exchange ............................................................................. 4-7
4.2.9
Time and Frequency Requirements ............................................................... 4-7
4.2.10 Independent Location Processing .................................................................. 4-8
4.2.11 Transmitting Data to the MCC ...................................................................... 4-8
5.
Performance Requirements .................................................................................................. 5-1
5.1
RF Signal Margin ....................................................................................................... 5-1
5.2
Sensitivity ................................................................................................................... 5-1
5.2.1
C/S T.001 Sensitivity ..................................................................................... 5-1
5.2.2
C/S T.018 Sensitivity ..................................................................................... 5-2
5.3
Beacon Detection Probability ..................................................................................... 5-2
5.3.1
C/S T.001 Beacon Detection Probability ....................................................... 5-2
5.3.2
C/S T.018 Beacon Detection Probability ....................................................... 5-2
5.4
Probability of FDOA/TDOA Location ....................................................................... 5-2
5.4.1
Single-Burst Probability of Location ............................................................. 5-2
5.4.2
Multi-Burst Probability of Location .............................................................. 5-3
5.5
Capacity ...................................................................................................................... 5-3
5.6
Location Accuracy ..................................................................................................... 5-3
5.6.1
C/S T.001 Location Accuracy for Nearly-Static Beacons ............................. 5-3
5.6.2
C/S T.018 Location Accuracy for Nearly-Static Beacons ............................. 5-4
5.6.3
C/S T.001 Location Accuracy for Slow-Moving Beacons (Low Speed) ...... 5-4
5.6.4
C/S T.018 Location Accuracy for Slow-Moving Beacons (Low Speed) ...... 5-5
5.6.5
C/S T.001 Location Accuracy for Slow-Moving Beacons (Medium Speed) 5-5
5.6.6
C/S T.018 Location Accuracy for Slow-Moving Beacons (Medium Speed) 5-6
5.6.7
C/S T.001 Location Accuracy for Fast-Moving Beacons .............................. 5-6
5.6.8
C/S T.018 Location Accuracy for Fast-Moving Beacons .............................. 5-6
5.7
Processing Frequency ................................................................................................. 5-7
5.7.1
Processing Bandwidth .................................................................................... 5-7
5.7.2
Acquisition Frequency Range ........................................................................ 5-7
5.8
MEOLUT Data Exchange .......................................................................................... 5-7
5.8.1
TOA/FOA Measurement Accuracy ............................................................... 5-7
5.8.2
External Data Processing ............................................................................... 5-8
5.9
Processing Combined with non-MEOSAR Satellites (Optional Capability) ............. 5-8
5.10 Expected Horizontal Error / Quality Factor ............................................................... 5-8


5.11 Processing Anomaly Rate ........................................................................................ 5-10
LIST OF ANNEXES
ANNEX A Design Guidelines for Determining the Link Power Budget for MEOSAR Systems .... A-1
ANNEX B Beacon Message Processing Information ........................................................................ B-1
ANNEX C MEOLUT Network Architecture .................................................................................... C-1
ANNEX D MEOLUT Coverage Area ............................................................................................... D-1
ANNEX E Optional Processing of Interference using the 406 MHz Repeater Band ........................ E-1
ANNEX F JDOP Definition .............................................................................................................. F-1
LIST OF FIGURES
Figure 2.1: Functional Block Diagram of a Typical Cospas-Sarsat MEOLUT System ..................... 2-2
Figure C.1: Primary Topology for a MEOLUT Network: a Partial Mesh ......................................... C-1
Figure C.2: Optional Node Forwarding Topology ............................................................................. C-2
Figure C.3: Optional Central Data Server Topology ......................................................................... C-3


LIST OF TABLES
Table 3.1: Standard Formats for MEOLUT to MCC Data Exchange ................................................ 3-1
Table 4.1: Fixed Bits of Beacon Protocols ......................................................................................... 4-6
Table 5.1: Quality Factor .................................................................................................................... 5-9
Table A.1: Example of Downlink Power Budget Parameters for MEOSAR .................................... A-5
Table A.2: Example of Uplink Power Budget Parameters for MEOSAR ......................................... A-6
Table B.1: Short Messages Validation ............................................................................................... B-1
Table B.2: Orbitography Beacons Specific Case ............................................................................... B-1
Table B.3: Long Messages Validation ............................................................................................... B-2

1-1

1.
INTRODUCTION
1.1
Overview
The purpose of the Cospas-Sarsat System is to provide distress alert and location data for search and
rescue (SAR), using spacecraft and ground facilities to detect and locate the signals of Cospas-Sarsat
distress radiobeacons operating on 406 MHz. An earth receiving station that tracks medium earth
orbiting (MEO) satellites in the Cospas-Sarsat System (the Cospas-Sarsat MEOSAR system) is called
a MEOSAR Local User Terminal (MEOLUT). The MEOLUT transmits alert and location data to its
associated Cospas-Sarsat Mission Control Centre (MCC) for subsequent distribution to SAR
authorities.
For acceptance as part of the Cospas-Sarsat System, a MEOLUT shall be commissioned as defined in
document C/S T.020, Cospas-Sarsat MEOLUT Commissioning Standard, to verify compliance of its
performance with this specification.
1.2
Scope
This specification describes the minimal operational capabilities and performance requirements of a
Cospas-Sarsat MEOLUT. The specifications in this document apply to data transmitted by a MEOLUT
for distribution in the Cospas-Sarsat MCC network, and to data exchanged between Cospas-Sarsat
MEOLUTs.
1.3
Document Organization
A brief description of a MEOLUT is provided in section 2. Operational requirements are provided in
section 3, section 4 defines the functional and processing requirements, and section 5 contains specific
performance requirements for a MEOLUT.
The Annexes to this document contain information about the MEOSAR Link Budget, the Beacon
Message Processing, the MEOLUT Network Architecture, and MEOLUT Coverage Area.

1-2

1.4
Reference Documents
- END OF SECTION 1 -
Reference
Title
C/S T.001
Specification for Cospas-Sarsat 406 MHz Distress Beacons
C/S T.015
Cospas-Sarsat Specification and Type Approval Standard for 406 MHz Ship Security
Alert (SSAS) Beacons
C/S T.016
Description of the Cospas-Sarsat MEOSAR Space Segment
C/S T.017
Cospas-Sarsat MEOSAR Space Segment Commissioning Standard
C/S T.018
Specification for Second Generation Cospas-Sarsat 406 MHz Distress Beacons
C/S T.020
Cospas-Sarsat MEOLUT Commissioning Standard
C/S A.001
Cospas-Sarsat Data Distribution Plan
C/S A.002
Cospas-Sarsat MCC Standard Interface Description
C/S A.003
Cospas-Sarsat Monitoring and Reporting
C/S A.005
Cospas-Sarsat Mission Control Centre (MCC) Performance Specification and Design
Guidelines

2-1

2.
COSPAS-SARSAT MEOLUT DESCRIPTION
The MEOLUT is a ground receiving station in the Cospas-Sarsat MEOSAR system that detects,
characterizes and locates emergency beacons, and forwards the appropriate information to an MCC.
The MEOLUT receives and processes beacon signals received through downlinks from BDS, Galileo,
GPS and GLONASS MEOSAR satellites to obtain beacon data. The MEOLUT uses this beacon data
to meet all the operational, functional, processing, and performance requirements contained in this
document.
The MEOLUT measures the received frequency and time of the beacon burst and calculates the uplink
frequency of arrival (FOA) and time of arrival (TOA) of detected beacon bursts at the satellite for each
satellite channel. The MEOLUT then uses uplink TOA and FOA data to calculate an unambiguous
location for the beacon if the message is received from at least three MEOSAR satellites for a given
burst. This method of beacon location will be referred to in this document as Frequency Difference
of Arrival/Time Difference of Arrival (FDOA/TDOA) location. The MEOLUT can improve the
location accuracy of the beacon over the first burst by combining data from subsequent bursts as it
is received.
A MEOLUT consists of at least the following basic components and appropriate interfaces:
a) antenna(s) and radio frequency subsystems,
b) one or more processor(s),
c) a time and/or frequency reference subsystem,
d) a satellite tracking subsystem, and
e) an MCC interface.
Figure 2.1 contains a functional block diagram of a typical MEOLUT system.
The MEOLUT shall meet the operational, functional, processing, and performance requirements
contained in this document without relying upon TOA/FOA data received from other MEOLUTs. In
addition, the MEOLUT shall be capable of exchanging data with other MEOLUTs, according to
specifications in Annex C.  Sharing of MEOSAR TOA/FOA data is optional, determined by national
requirements and arranged on a bilateral basis between MEOLUT operators. The intent of MEOLUT
data exchange is to enhance the Cospas-Sarsat System performance and support redundancy within the
Cospas-Sarsat Ground Segment.
The SAR instruments on Cospas-Sarsat MEOSAR satellites receive up-link signals from distress
beacons, test beacons and system beacons such as orbitography beacons. These up-link signals, along
with unwanted interfering signals, are frequency translated and retransmitted to the ground upon a
downlink carrier for reception by a MEOLUT. Cospas-Sarsat MEOLUTs may also process the
downlinks to characterize and locate interferers.

2-2

Figure 2.1: Functional Block Diagram of a Typical Cospas-Sarsat MEOLUT System
The operational, functional and performance requirements for these processing channels are described
in the following sections of this document. They are intended to ensure that:
a) the MEOLUT is available and capable of receiving and processing:
i.
signals from C/S T.001- and C/S T.018-compliant beacons that are received through
MEOSAR satellite downlinks; and
ii.
406 MHz beacon data from other MEOLUTs, if MEOLUT data exchange processing
is implemented,
b) the MEOLUT provides timely reliable alerts and accurate position data by:
i.
detecting valid and invalid 406 MHz beacon messages and processing them in
accordance with this specification;
ii.
verifying whenever possible that the beacon identification and encoded position
information are valid;
iii.
properly selecting the data points used to calculate beacon locations;
iv.
providing updated position information to the MCC, as appropriate;
v.
validating calculated beacon locations; and
vi.
maintaining an accurate time reference.
- END OF SECTION 2 –
Antennas
RF subsystems
Reception
Processing
Antenna management
MEOLUT management
Networked
MEOLUT(s)
MCC
MEOLUT
satellite channels
antenna
command/control

3-1

3.
OPERATIONAL REQUIREMENTS
The basic operational objective of a MEOLUT is to process data from as many satellites as possible
and to send the resultant alert data to its associated MCC, according to the specifications contained in
this document. Once a MEOLUT has been commissioned and connected to the Cospas-Sarsat network
through an MCC, it shall continue to meet the specifications of this document.
3.1
MEOLUT Data Availability
A MEOLUT commissioned for operation within the Cospas-Sarsat System shall provide data to the
associated MCC twenty-four (24) hours a day, seven (7) days a week with less than five (5) percent
downtime calculated over a year.
A MEOLUT should be designed to maximise data availability (including beacon detections, alerts and
location solutions, and data to be exchanged among MEOLUTs) in the event that not all MEOLUT
performance requirements are being met.
3.2
Data Requirements
The MEOLUT shall provide all data necessary for the MCC to distribute relevant alert data to the
appropriate authorized destination(s), according to document C/S A.002, Cospas-Sarsat MCC Standard
Interface Description.
The MEOLUT shall be capable of sending data to the MCC in the SIT message formats identified in
Table 3.1, as specified in document C/S A.002.
SIT
Number
Required Usage

First Generation Beacon (FGB) solution without DOA location

FGB solution with DOA location

Second Generation Beacon (SGB) solution without DOA location

SGB solution with DOA location

MEOLUT status, warning and alarm messages
Table 3.1: Standard Formats for MEOLUT to MCC Data Exchange

3-2

MEOLUTs may send data to the MCC in alternative formats (i.e., formats not described in Table 3.1)
based on national requirements, provided that the MEOLUT can be configured to send data to the
MCC in the standard format identified in Table 3.1.
Optionally, the MEOLUT may provide 406 MHz beacon data to other MEOLUTs according to the
specifications contained in Annex C.
3.3
Data Channels
3.3.1
Satellite Data Channels
The MEOLUT shall receive and process beacon signals received through downlinks from MEOSAR
satellites to obtain beacon data. The MEOLUT shall use this beacon data to meet all the operational,
functional, processing, and performance requirements contained in this document. The MEOLUT shall
be able to process beacon messages relayed from any combination of commissioned BDS, Galileo,
Glonass and GPS III L-band MEOSAR satellites as described in documents C/S T.016 and C/S T.017.
Optionally, the MEOLUT can also process beacon messages relayed by commissioned S-band
MEOSAR satellites1.
The MEOLUT may also receive and process beacon signals received through downlinks from non-
MEOSAR, Cospas-Sarsat commissioned satellites to obtain beacon data. However, the MEOLUT shall
meet all the operational, functional, processing, and performance requirements contained in this
document without relying upon TOA/FOA data from non-MEOSAR satellites.
3.3.2
MEOLUT Data Exchange
Optionally, the MEOLUT may exchange data with other MEOLUTs, according to the specifications
contained in Annex C, to enhance system performance and support redundancy of the Cospas-Sarsat
Ground System. However, this beacon data cannot be relied upon to meet the operational, functional,
processing, and performance requirements contained in this document.
3.4
Satellite Tracking and Visibility
The MEOLUT shall be capable of simultaneously tracking as many visible MEOSAR satellites as the
MEOLUT has antenna beams.
The MEOLUT should be located to give the widest possible horizon because it is desirable to be able
to track satellites down to the horizontal plane for all azimuth angles. The MEOLUT shall be capable
of continuously receiving and processing all satellite data for all portions of a satellite pass above its
1 The DASS S-band constellation’s data may be used operationally. The USA will commission DASS satellites in
order to document their performance and support their use as needed. The capability to use the DASS S-band satellites
is not required but the SAR payloads are available for continued support of the MEOSAR system development,
operations and interference monitoring, as long as they remain in operation.

3-3

minimum declared elevation angle, except where prevented by local obstructions, without any data
degradation or loss.
3.5
Status and Alarm
The MEOLUT shall provide all data necessary for the MCC to identify degradation of its operational
capability in accordance with the specifications described in this document at a minimum.
3.6
RF Radiation and Emissions
The MEOLUT shall not radiate or emit any radio frequency (RF) signals that will interfere with the
functioning of the Cospas-Sarsat System.
3.7
Data Archiving
At a minimum, the MEOLUT shall store the following data for a period of at least 90 days:
a) the 36 hexadecimal character representation of each C/S T.001 beacon message or the
63 hexadecimal character representation of each C/S T.018 beacon message;
b) the frequency and time measurement of each beacon burst;
c) the C/N0 ratio for each beacon burst on each satellite channel;
d) the beacon locations and related solution data calculated by the MEOLUT;
e) the solution data for all 406 MHz interferers detected;
f) the log files that capture the status of the MEOLUT during the time period; and
g) the satellite orbit vectors for each satellite data channel and each beacon transmission.
3.8
Cospas-Sarsat Quality Management System (QMS) Continuous Monitoring and
Objective Assessment
The MEOLUT shall support requirements provided in document C/S A.003.
- END OF SECTION 3 -

4-1

4.
FUNCTIONAL AND PROCESSING REQUIREMENTS
4.1
Summary of Requirements
The basic functional and processing requirements for the MEOLUT are to:
a) maintain and update satellite ephemeris;
b) acquire, track and receive the downlink signal from Cospas-Sarsat MEOSAR satellites;
c) maintain and update the required time and frequency references;
d) demodulate the satellite data channels;
e) process satellite data channels as described in section 4.2;
f) calculate beacon positions whenever enough reliable data is available;
g) optionally use network data from other MEOLUTs to enhance the computed beacon position
estimate;
h) maintain and update a database of relevant information pertaining to each detected beacon and
associated location processing;
i) provide interfaces for command and data access both locally and remotely; and
j) provide the resultant data to the associated MCC, as necessary, to support the requirements of
document C/S A.002, Cospas-Sarsat MCCs Standard Interface Description.
4.1.1
Antenna and RF Subsystem
The MEOLUT shall have antenna beams and RF subsystems that are able to acquire, track and receive
the downlink signal from any Cospas-Sarsat BDS, Galileo, Glonass and GPS III L-band MEOSAR
satellite as described in document C/S T.016. Optionally, this may also include use of satellites with
S-band downlink2.
4.1.2
Time and Frequency Reference Subsystem
The MEOLUT shall maintain system time and frequency references with sufficient accuracy to ensure
that the beacon location accuracy specifications are met.
2 The DASS S-band constellation’s data may be used operationally. The USA will commission DASS satellites in
order to document their performance and support their use as needed. The capability to use the DASS S-band satellites
is not required but the SAR payloads are available for continued support of the MEOSAR system development,
operations and interference monitoring, as long as they remain in operation.

4-2

4.1.3
Satellite Tracking Subsystem
The MEOLUT shall maintain accurate satellite orbital elements and tracking schedules for all MEOSAR
satellites. In addition, the MEOLUT shall have the capability to implement MCC provided orbital
elements. The MEOLUT may receive orbital elements from the MEOLUT operator or the GNSS
satellites hosting the MEOSAR payloads.
The MEOLUT shall be capable of generating its own satellite pass tracking schedule but may also be
capable of accepting a satellite pass tracking schedule from an external source, such as its host MCC, and
be configurable to follow either satellite pass tracking schedule.
The MEOLUT shall be able to generate a tracking schedule based on configuration at the MEOLUT.
The tracking schedule algorithm should be configurable locally or remotely.
The MEOLUT shall be able to optimize its tracking schedule to maximize performance over its derived
coverage area.
The MEOLUT may modify its satellite tracking schedule to account for a satellite experiencing an
abnormal status (e.g., during a manoeuvre, SAR transponder off) using external information (e.g., SIT
messages, NANU/NAGU messages, health status broadcast in navigation messages).
4.1.4
MCC Interface
The MEOLUT must provide timely information of the level of quality and detail required by documents
C/S A.002 and C/S A.005.
4.2
Processing 406 MHz Beacon Message Data
4.2.1
General Processing Requirements
The MEOLUT shall process 406 MHz beacon message data based on the formats described in document
C/S T.001 (Specification for Cospas-Sarsat 406 MHz Distress Beacons) and in document C/S T.018
(Specification for Second Generation Cospas-Sarsat 406 MHz Distress Beacons). The processing
consists of the following sequence (portion of which are illustrated in Annex B):
a) message recovery;
b) bit verification;
c) message validation;
d) message association;
e) FDOA/TDOA location processing; and
f) transmission of resultant alert data to the MCC.
These processing requirements apply to all satellite data channels. If implemented, MEOLUT data
exchange channels will meet the requirements specified in section 4.2.8.

4-3

4.2.2
Beacon Message Recovery
The MEOLUT shall process all normal mode beacon messages and transmit them to the MCC based on
specifications in this document. Beacon messages that are not in normal mode shall not be processed
operationally. The following apply:
a) Normal mode C/S T.001 beacon messages have a perfect match of bits 16 to 24 with the 9-bit
frame synchronization pattern described in document C/S T.001;
b) Normal mode C/S T.018 beacon messages have a normal mode Pseudo Random Noise (PRN)
sequence as described in document C/S T.018; and
c) Normal mode C/S T.018 beacon messages overlapping in time for at least four (4) separate
messages.
The MEOLUT may include the capability to integrate different messages, received from the same
transmission through different satellite channels, to determine the contents of the beacon message (cross-
channel integration of the same beacon burst).
Successive bursts of the same transmitting C/S T.001 beacon may also be integrated until a valid message
is produced. However, C/S T.001 ELT(DT) messages that have been recovered by integration of
successive beacon bursts shall not be forwarded to the associated MCC. For C/S T.018 beacons,
successive bursts of the same transmitting beacon shall not be integrated.
The MEOLUT shall be capable of recording “self-test” mode beacon messages, however, such data shall
not be used in the processing of operational distress alerts.
a) Self-test mode C/S T.001 beacon messages have an inverted frame synchronization pattern; and
b) Self-test mode C/S T.018 beacon messages have a self-test mode Pseudo Random Noise
sequence as described in document C/S T.018.
The MEOLUT shall be capable of sending alert solutions from both C/S T.001 and C/S T.018 "self-test"
mode beacon message(s) for designated QMS reference beacons to the MCC, based on procedures
specified in sections 4.2.11 and 3.8 for operational alert solutions. This capability shall be configurable
by reference beacon.
“Self-test” mode beacon messages may be forwarded to the MCC for other uses, such as the verification
of beacon registration, system test support or message traffic analysis.  If this capability is provided, the
transmission of “self-test” mode beacon messages shall be configurable.
4.2.3
Bit Verification
4.2.3.1 C/S T.001 Beacon Bit Verification
The MEOLUT shall detect and correct bit errors in the 406 MHz beacon messages received through the
satellite data channels, as follows.
1)
The digital message transmitted by 406 MHz beacons includes a 21-bit BCH error correcting code,
and, in the long message format, an additional 12-bit BCH error correcting code (except for the

4-4

orbitography protocol as noted below). The MEOLUT shall use these BCH codes to verify and
correct as necessary the received data. All beacon messages include the following fields:
a)
first protected data field (PDF-1, bits 25 to 85) which contains the beacon identification
and can include position data; and
b)
first BCH error correcting field (BCH-1, bits 86 to 106) which contains the 21-bit BCH
error correcting code that protects the 82 bits of PDF-1 and BCH-1.
The 82 bits of PDF-1 and BCH-1 are also referred to as the first protected field.
2)
The long message format may also include:
a)
the second protected data field (PDF-2, bits 107 to 132) which contains position and
supplementary data; and
b)
the second BCH error correcting field (BCH-2, bits 133 to 144) which contains the 12-bit
BCH error correcting code that protects the 38 bits of PDF-2 and BCH-2.
The 38 bits of PDF-2 and BCH-2 are also referred to as the second protected field.
3)
The MEOLUT shall use BCH-1 to correct all messages that have a maximum of three bit errors in
the first protected field, and detect the existence of more than three (3) errors with a probability of
95%. The MEOLUT shall use BCH-2 to correct any messages that have one bit error in the second
protected field of the long message format and to detect the existence of two or more bit errors.
When the MEOLUT determines there are two or more bit errors in the second protected field, bits
113 to 144 shall all be replaced with “1”.  For short format beacon messages, the MEOLUT shall
set bits 113 to 144 to all “0” values.
4)
The MEOLUT shall process the orbitography protocol beacon messages with the short message
portion (bits 25-106) error corrected by BCH-1; the data in bits 107 to 144 is sent without error
detection and correction.
4.2.3.2 C/S T.018 Beacon Bit Verification
The digital message transmitted by 406 MHz beacons includes a 48-bit BCH error correcting code.
The MEOLUT shall use the BCH code to verify and correct as necessary the received data.
4.2.4
Beacon Message Validation
4.2.4.1 C/S T.001 Message Validation
•
A 406 MHz first generation beacon message produced by a MEOLUT is valid when:
−
the first protected field (PDF-1 + BCH-1) has 2 or less corrected bit errors and the fixed bits
of Standard and National location protocols that start at bit 107 contain no errors; or
−
the first protected field (PDF-1 + BCH-1) has 3 corrected bit errors and is confirmed by an
identical match with another valid message3 from the same beacon ID detected from the
3 i.e., that has 2 or fewer corrected bit error in its first protected fields

4-5

same transmitted burst through another channel or bursts within ± 5 minutes, and the fixed
bits of Standard and National location protocols that start at bit 107 contain no errors.
•
A 406 MHz first generation beacon message produced by a MEOLUT is complete when it consists
of:
−
the first protected field (PDF-1+BCH-1) of a valid short message; or
−
the first and second protected fields (PDF-1+BCH-1+PDF-2+BCH-2) of a valid long
message where the second protected field contains less than 2 corrected bit errors.
Bits 113 to 144 of the second protected field of a valid long message shall all be set to “1” if this field
contains two or more bit errors. The message is then declared incomplete.
If a long message is valid but not complete, for any protocol other than the orbitography protocol, bits
113 to 144 of the second protected field shall all be set to “1” by the MEOLUT.
4.2.4.2 C/S T.018 Message Validation
A 406 MHz second generation beacon message produced by a MEOLUT is valid when:
•
the message has 4 or fewer corrected bit errors; or
•
the message has 5 or 6 corrected bit errors and is confirmed by an identical match with another
message with 6 or fewer corrected bits detected from the same transmitted burst through another
channel or from another burst within ± 5 minutes.
4.2.4.3 Message Confirmation
A confirmed beacon message may be a confirmed valid message or a confirmed complete message. The
message confirmation process requires that two independent burst processing results produce identical
valid or complete messages.
The confirmation can be obtained from successive transmitted burst processing or, in the case of multi-
channel MEOLUT processing, from the result of the processing of the same transmitted burst via two or
more satellites provided each received burst is processed independently to produce a beacon message
and both messages produced are identical.
4.2.5
Multiple Invalid Beacon Message Processing
4.2.5.1 Multiple Invalid C/S T.001 Beacon Message Processing
When three or more invalid beacon messages from the same burst have matching bits from bit 25 to
bit 106 (before bit correction in PDF1+BCH1), the MEOLUT shall calculate a FDOA/TDOA 2D or
3D location, and send it to the MCC containing the bits 25 to 106 of the 36 hexadecimal message
without any bit correction and with bits 107 to 144 set to “1”.

4-6

4.2.5.2 Multiple Invalid C/S T.018 Beacon Message Processing
When three or more invalid beacon messages from the same burst have matching bits from bit 1 to
bit 202 (before bit correction), the MEOLUT shall calculate a FDOA/TDOA 2D or 3D location, and
send it to the MCC without any bit correction in the beacon message.
4.2.6
Beacon Message Association
Beacon messages shall only be treated as being from the “same burst” when the associated times are
within 2.5 seconds. If the associated times for two beacon messages exceeds this threshold, then the
messages should be treated as being from separate bursts.
In order to provide updated beacon messages and to generate TDOA/FDOA locations, it is necessary to
associate 406 MHz beacon messages received from different satellites and at different times for the
“same” beacon. This section specifies the rules for associating independent packets for the same beacon.
4.2.6.1 C/S T.001 Message Association
Two 406 MHz beacon messages are associated (i.e., treated as being from the same beacon) when the
fixed bits of the first protected field (PDF-1 + BCH-1) of the two beacon messages are identical. Since
the encoded position data in 406 MHz beacon messages using location protocols may change over time
(in accordance with document C/S T.001), only fixed bits in a beacon message can be used for matching.
Beacon messages shall be matched based on the fixed bits in accordance with Protocol type, as follows:
Table 4.1: Fixed Bits of Beacon Protocols
Protocol
Fixed Bits
User and User-Location
25 to 85 (61 bits)
Standard Location
25 to 64 (40 bits)
National Location
25 to 58 (34 bits)
RLS Location
25 to 66 (42 bits)
ELT(DT)
25 to 66 (42 bits)
Undefined
25 to 106 (82 bits)
If a beacon message is not valid, then its Protocol is “undefined” and matching shall be based on bits
25 to 106, as specified above.
In addition, two beacon messages are associated when the first protected field (PDF-1 + BCH-1) of
one beacon message has 3 corrected bit errors and its PDF-1 is identical to the PDF-1 of a valid beacon
message that was received by a MEOLUT from the same transmitted burst through another channel or
bursts within ± 5 minutes. In this case, the MEOLUT shall use the valid beacon message in subsequent
processing.

4-7

4.2.6.2 C/S T.018 Message Association
Two 406 MHz beacon messages are associated when the fixed bits of the two beacon messages are
identical. Since the encoded position data in 406 MHz beacon messages may change over time (in
accordance with document C/S T.018), only fixed bits in a beacon message can be used for matching.
Beacon messages shall be matched based on the 23 Hex ID as defined in section 3 of document
C/S T.018.
When multiple beacon messages are associated with each other, the solution to be sent by the
MEOLUT to the MCC shall:
a) use the beacon message with the most recent detect time, if all associated beacon messages are
invalid, or
b) use the valid beacon message with the most recent detect time.
4.2.7
Multiple Valid C/S T.001 Message Processing
After Beacon Message Validation and the Message Association, the MEOLUT could have several
copies of the same beacon message, all belonging to the “Same Beacon Burst”, and received and
processed through the different MEOLUT data channels.
To ensure that the most complete information is forwarded to SAR services, the following principles
shall apply to the selection of the 406 MHz valid FGB Message to be sent to the MCC when multiple
valid transponded beacon messages have been processed for the “Same Beacon Burst” (SBB):
a) If there is only one complete message the MEOLUT shall include that beacon message in the
alert transmitted to the MCC.
b) If there is more than one complete beacon message of the SBB that matches with another
complete message from the SBB, the MEOLUT shall include that beacon message in the alert
transmitted to the MCC.
c) If no complete message matches another, the MEOLUT shall select the beacon message with
zero corrected errors in the PDF-2, if available. If the number of corrected errors in PDF-2 is
the same, the MEOLUT shall select the beacon message with the highest C/N0.
d) If neither (a), (b) or (c) above are satisfied, the MEOLUT shall include in the alert transmitted
to the MCC a valid message, with bits 113 to 144 all set to “1” in the case of a long message
format.
4.2.8
MEOLUT Data Exchange
If implemented, the MEOLUT shall provide data to, and retrieve data from other MEOLUTs according
to the MEOLUT data exchange specifications contained in Annex C.
4.2.9
Time and Frequency Requirements
The MEOLUT shall measure the time and frequency to the accuracy required to satisfy the location
accuracy requirements specified in section 5.

4-8

4.2.10
Independent Location Processing
The MEOLUT shall calculate the uplink FOA and TOA of each beacon burst received. When the same
burst is received from the same beacon through three or more satellites, the MEOLUT shall use these
calculations to produce FDOA/TDOA 2D or 3D locations. It is noted that, due to environmental
conditions in which a beacon was activated (e.g., being afloat, bobbing on the waves, mounted on a
raft and adrift, or on a sailing ship working in a seaway), received signal frequency may change
significantly during the burst due to additional Doppler shift in comparison to assuming no beacon
motion during the burst and not expecting additional errors in the frequency measurements. This may
translate into additional error in the FOA calculation, and subsequently impact the location accuracy
and error estimation. The MEOLUT is expected to include means to minimize such an impact on the
MEOLUT’s ability to meet location performance requirements.
The MEOLUT shall not produce a located solution if the location is outside the footprint of any satellite
(as done by MCCs according to Appendix B.2 of document C/S A.002) for which data was used to
compute the location at the time of the associated burst data.
The MEOLUT should be capable of identifying and filtering beacon messages with low quality
measurements that degrade location accuracy (e.g., by filtering of harmonic signals). The MEOLUT
should use all available FOA/TOA data to calculate FDOA/TDOA locations, except when the
FOA/TOA data is identified as low quality.
The MEOLUT should be capable of identifying and filtering from the location process beacon
messages received through satellites experiencing an abnormal status (e.g., satellite manoeuvres).
4.2.11
Transmitting Data to the MCC
The latency between the latest beacon message detect time associated with a solution and the
availability of that solution for delivery to the MCC shall be less than 3 minutes.
Upon initial detection and processing of a beacon message for a given 406 MHz beacon:
a) if an independent location is available, the MEOLUT shall send an alert with the independent
location to the associated MCC immediately;
b) if an independent location is not available but the beacon message is valid, the MEOLUT shall
send an alert solution without independent location to the associated MCC as soon as the
beacon message is confirmed (with an indication that the beacon message is confirmed), or
after 3 minutes if the beacon message remains unconfirmed; and
c) for a beacon identified as an ELT(DT), the MEOLUT shall send an alert with the encoded
location to the associated MCC as soon as the message is valid (i.e., no need for message
confirmation).
After the initial alert has been sent by the MEOLUT to the associated MCC for a given beacon, the
MEOLUT shall:
•
apply the rules in section 4.2.7 for determining the selected beacon message for the burst with the
most recent detect time,

4-9

•
send a new alert solution (i.e., an alert with data not previously sent) to the associated MCC
immediately if any of the following conditions is met:
a)
an independent location is first available;
b)
a better quality independent location than all previously sent for that beacon is available;
c)
the content of the PDF-1 or PDF-2 fields for C/S T.001 beacon message, or the content of the
main or rotating fields of the C/S T.018 beacon message, has changed compared to the
previous distributed message;
d)
a confirmed beacon message is available for the first time;
e)
five (5) minutes has transpired with no other alert being sent and data has been received since
the previous alert was sent, then the MEOLUT shall send a single new alert to the associated
MCC:
•
if an independent location with a detect time in the last (5) minutes is available: the
MEOLUT shall send the alert corresponding to the burst with the independent location
with the most recent detect time,
•
otherwise, if a valid message with a detect time in the last (5) minutes is available: the
MEOLUT shall send the alert (with no independent location) corresponding to the burst
with that valid message;
f)
for ELT(DT)s, a new valid message per transmitted burst is available; or
g)
a first or a new cancellation message is available.
The MEOLUT shall not send more than three alert solutions with the same latest detect time.
The MEOLUT shall not send duplicated alerts to the associated MCC (duplicated alerts are solutions
with exactly the same content).
If the detect time of a new alert is more than 10 minutes after the most recent detect time processed by
the MEOLUT for the same beacon identification, then:
a) the new alert shall be treated as a new beacon activation; and
b) all alerts with a detect time not after the most recent detect time in an alert distributed to the
MCC for the previous beacon activation shall not be used in MEOLUT processing of the new
beacon activation.
MEOLUTs may reset the beacon activation status prior to the expiration of this time threshold based
on other criteria. The MEOLUT shall not combine data from cancellation messages with data from
alert (i.e., non-cancellation) messages.
The MEOLUT shall have the capability of suppressing all orbitography and calibration beacon
messages and passing them to the MCC only on request.
The MEOLUT shall transmit all the necessary data to enable the associated MCC to satisfy the
requirements of documents C/S A.002 and C/S A.005.

4-10

The MEOLUT shall transmit data to its associated MCC as required by the QMS continuous
monitoring and objective assessment process described in document C/S A.003.
The MEOLUT shall not transmit any C/S T.001 ELT(DT) message data processed by integration of
successive beacon bursts to its associated MCC.
The MEOLUT may filter or send additional alerts to the MCC as defined by national administrations.
- END OF SECTION 4 -

5-1

5.
PERFORMANCE REQUIREMENTS
The performance requirements defined in the following sections establish measurable performance
criteria that a MEOLUT must meet before it can be integrated into the Cospas-Sarsat System and be
commissioned by the Cospas-Sarsat Council. This specification applies to C/S T.001 and C/S T.018
compliant beacons using the MEOSAR space segment as defined in document C/S T.016.
The Minimum Performance Area (MPA) of the MEOLUT is defined as the minimum area over which
the MEOLUT can expect to receive sufficient data to meet all of the performance requirements of this
MEOLUT Specification and Design Guidelines. The Minimum Performance Area is an area equivalent
to the area of a circle with a radius of at least 1,000 km from a reference location (e.g., the geographical
centre of associated antenna(s)).
MEOLUT performance is expected to extend over a coverage area beyond the Minimum Performance
Area. The actual coverage area is derived using performance analysis, simulation, or both. It shall
indicate the coverage for the following beacon types: FGB, FGB ELT(DT), SGB and SGB ELT(DT).
It may not necessarily be of a circular shape.
The national Administration, in consultations with the MEOLUT manufacturer, shall declare what area
within derived coverage area will be recognized by the Cospas-Sarsat Council as an area where all the
performance requirements of a MEOLUT are guaranteed to be met (e.g., a radius of a circle around the
MEOLUT or around a point between several networked MEOLUTs) for the beacon types FGB, FGB
ELT(DT), SGB and SGB ELT(DT).
Every such declaration is referred to as the MEOLUT Declared Coverage Area (DCA) for a particular
beacon type (FGB, FGB ELT(DT), SGB or SGB ELT(DT)). The DCA is identified in the
commissioning report and must by its definition be larger than the Minimum Performance Area. DCA
size is usually slightly more conservative than the size of a derived coverage area.
Refer to Annex D for a discussion of the MEOLUT coverage area and the factors that affect it.
5.1
RF Signal Margin
The MEOLUT shall be designed to maintain a positive link margin from MEOSAR satellites (refer to
the MEOSAR link budget contained in Annex A).
5.2
Sensitivity
The signal sensitivity threshold is the C/N0 level at which the MEOLUT will produce valid messages
for at least 90% of individual beacon messages, where C/N0 is the ratio of the unmodulated carrier
power to noise power density in dB-Hz.
5.2.1
C/S T.001 Sensitivity
The MEOLUT signal sensitivity shall be better than 34.8 dB-Hz.

5-2

5.2.2
C/S T.018 Sensitivity
The MEOLUT signal sensitivity shall be better than 30.55 dB-Hz.
5.3
Beacon Detection Probability
5.3.1
C/S T.001 Beacon Detection Probability
The probability of detecting the transmission of a 406 MHz beacon and recovering a valid beacon
message at the MEOLUT, within 10 minutes from the first beacon message transmission shall be a
minimum of 99%.
The probability of detecting the transmission of a C/S T.001 ELT(DT) beacon and recovering a
complete beacon message at the MEOLUT, within any one-minute period, shall be a minimum of 99%.
5.3.2
C/S T.018 Beacon Detection Probability
The probability of detecting a single-burst transmission and recovering a valid beacon message at the
MEOLUT for each of the beacon messages that partially overlap each other in time in four (4) separate
messages, shall be a minimum of 95%.
The probability of detecting the transmission of a 406 MHz beacon and recovering a valid beacon
message at the MEOLUT, within 30 seconds from the first beacon message transmission shall be a
minimum of 99.9%.
The probability of detecting the transmission of a C/S T.018 ELT(DT) beacon and recovering a valid
beacon message at the MEOLUT, within any one-minute period, shall be a minimum of 99%.
5.4
Probability of FDOA/TDOA Location
5.4.1
Single-Burst Probability of Location
5.4.1.1 C/S T.001 Beacon
The probability of obtaining a 2D location (latitude/longitude), independently of any encoded position
data at the MEOLUT in the 406 MHz beacon message, using a single-burst transmission (i.e., the
transmission of only one burst) shall be at least 90%.
5.4.1.2 C/S T.018 Beacon
The probability of obtaining a 2D location (latitude/longitude), independently of any encoded position
data at the MEOLUT in the 406 MHz beacon message, using a single-burst transmission (i.e., the
transmission of only one burst) shall be at least 95%.

5-3

5.4.2
Multi-Burst Probability of Location
5.4.2.1 C/S T.001 Beacon
The probability of obtaining a 2D location (Latitude/Longitude), independently of any encoded
position data at the MEOLUT in the 406 MHz beacon message, within 10 minutes from the first beacon
message transmission, shall be at least 98%.
5.4.2.2 C/S T.018 Beacon
The probability of obtaining a 2D location (latitude/longitude), independently of any encoded position
data at the MEOLUT in the 406 MHz beacon message, within 30 seconds from the first beacon
message transmission, shall be at least 98%.
The probability of obtaining a 2D location (latitude/longitude), independently of any encoded position
data at the MEOLUT in the 406 MHz beacon message, within 5 minutes from the first beacon message
transmission, shall be at least 98%.
The probability of obtaining a 2D location (latitude/longitude), independently of any encoded position
data at the MEOLUT in the 406 MHz beacon message, within 30 minutes from the first beacon
message transmission, shall be at least 98%.
5.5
Capacity
The MEOLUT must be able to detect and process a total of at least 100 simultaneously active beacons:
either fully C/S T.001 beacons, fully C/S T.018 beacons, or any combination thereof.
It is recognized that 406 MHz beacon transmissions can be expected to overlap in both time and
frequency. The MEOLUT's ability to handle beacon transmissions that partially overlap in time will
impact the upper limit of the MEOSAR system capacity.
5.6
Location Accuracy
The location accuracy specifications are defined for three categories of beacons:
•
nearly-static beacons, whose actual speed is between 0 and 0.5 m/s,
•
slow-moving beacons (low speed), whose actual speed is between 0.5 and 5 m/s,
•
slow-moving beacons (medium speed), whose actual speed is between 5 and 10 m/s,
•
fast-moving beacons, whose actual speed is above 10 m/s.
5.6.1
C/S T.001 Location Accuracy for Nearly-Static Beacons
Independent locations, using a single-burst transmission, shall meet the following accuracy
requirement:
M/N shall be greater than or equal to 0.90 where:
M = number of locations within 5 km
N = number of locations.

5-4

An independent location provided within 10 minutes from the first beacon message transmission shall
meet the following accuracy requirement:
M/N shall be greater than or equal to 0.95 where:
M = number of locations within 5 km
N = number of locations.
M/N shall be greater than or equal to 0.98 where:
M = number of locations within 10 km
N = number of locations.
5.6.2
C/S T.018 Location Accuracy for Nearly-Static Beacons
Independent locations, using a single-burst transmission, shall meet the following accuracy
requirement:
M/N shall be greater than or equal to 0.95 where:
M = number of locations within 5 km
N = number of locations.
An independent location provided within 30 seconds from the first beacon message transmission shall
meet the following accuracy requirement:
M/N shall be greater than or equal to 0.97 where:
M = number of locations within 5 km
N = number of locations.
An independent location provided within 5 minutes from the first beacon message transmission shall
meet the following accuracy requirement:
M/N shall be greater than or equal to 0.97 where:
M = number of locations within 1 km
N = number of locations.
An independent location provided after 30 minutes from the first beacon message transmission shall
meet the following accuracy requirement:
M/N shall be greater than or equal to 0.97 where:
M = number of locations within 100 meters
N = number of locations.
5.6.3
C/S T.001 Location Accuracy for Slow-Moving Beacons (Low Speed)
Independent locations, using a single-burst transmission, shall meet the following accuracy
requirement for slow-moving beacons:
M/N shall be greater than or equal to 0.70 where:
M = number of locations within 10 km
N = number of locations.
M/N shall be greater than or equal to 0.95 where:
M = number of locations within 20 km
N = number of locations.
An independent location provided within 10 minutes from the first beacon message transmission, shall
meet the following accuracy requirement:

5-5

M/N shall be greater than or equal to 0.75 where:
M = number of locations within 5 km
N = number of locations.
M/N shall be greater than or equal to 0.95 where:
M = number of locations within 7 km
N = number of locations.
5.6.4
C/S T.018 Location Accuracy for Slow-Moving Beacons (Low Speed)
Independent locations, using a single-burst transmission, shall meet the following accuracy
requirement for slow-moving beacons:
M/N shall be greater than or equal to 0.95 where:
M = number of locations within 5 km
N = number of locations.
An independent location provided within 30 seconds from the first beacon message transmission shall
meet the following accuracy requirement:
M/N shall be greater than or equal to 0.97 where:
M = number of locations within 5 km
N = number of locations.
An independent location provided within 5 minutes from the first beacon message transmission shall
meet the following accuracy requirement:
M/N shall be greater than or equal to 0.97 where:
M = number of locations within 1 km
N = number of locations.
5.6.5
C/S T.001 Location Accuracy for Slow-Moving Beacons (Medium Speed)
Independent locations, using a single-burst transmission, shall meet the following accuracy
requirement for slow-moving beacons:
M/N shall be greater than or equal to [0.70] where:
M = number of locations within 10 km
N = number of locations.
M/N shall be greater than or equal to [0.95] where:
M = number of locations within 20 km
N = number of locations.
An independent location provided within 10 minutes from the first beacon message transmission, shall
meet the following accuracy requirement:
M/N shall be greater than or equal to [0.75] where:
M = number of locations within 5 km
N = number of locations.
M/N shall be greater than or equal to [0.95] where:
M = number of locations within 7 km
N = number of locations.

5-6

5.6.6
C/S T.018 Location Accuracy for Slow-Moving Beacons (Medium Speed)
Independent locations, using a single-burst transmission, shall meet the following accuracy
requirement for slow-moving beacons:
M/N shall be greater than or equal to 0.95 where:
M = number of locations within 5 km
N = number of locations.
An independent location provided within 30 seconds from the first beacon message transmission shall
meet the following accuracy requirement:
M/N shall be greater than or equal to 0.97 where:
M = number of locations within 5 km
N = number of locations.
An independent location provided within 5 minutes from the first beacon message transmission shall
meet the following accuracy requirement:
M/N shall be greater than or equal to 0.97 where:
M = number of locations within 1 km
N = number of locations.
5.6.7
C/S T.001 Location Accuracy for Fast-Moving Beacons
Independent locations, using a single-burst transmission, shall meet the following accuracy
requirement:
M/N shall be greater than or equal to 0.90 where:
M = number of locations within TBD km
N = number of locations.
An independent location provided within 10 minutes from the first beacon message transmission, shall
meet the following accuracy requirement:
M/N shall be greater than or equal to 0.95 where:
M = number of locations within TBD km
N = number of locations.
M/N shall be greater than or equal to 0.98 where:
M = number of locations within TBD km
N = number of locations.
5.6.8
C/S T.018 Location Accuracy for Fast-Moving Beacons
Independent locations, using a single-burst transmission, shall meet the following accuracy
requirement:
M/N shall be greater than or equal to 0.95 where:
M = number of locations within TBD km
N = number of locations.
An independent location provided within 30 seconds from the first beacon message transmission shall
meet the following accuracy requirement:
M/N shall be greater than or equal to 0.97 where:
M = number of locations within TBD km

5-7

N = number of locations.
An independent location provided within 5 minutes from the first beacon message transmission shall
meet the following accuracy requirement:
M/N shall be greater than or equal to 0.97 where:
M = number of locations within TBD km
N = number of locations.
5.7
Processing Frequency
5.7.1
Processing Bandwidth
At a minimum, the MEOLUT shall be capable of processing the signals of the 406 MHz beacons
defined in documents C/S T.001 and C/S T.018. Processing the 406.006 MHz to 406.094 MHz
bandwidth (i.e., 88 kHz) is required.
5.7.2
Acquisition Frequency Range4
Regarding C/S T.001 beacons, the MEOLUT shall be capable of processing transmitted beacon signals
with a deviation from the beacon center frequency of ± 5.45 kHz.
Regarding C/S T.018 beacons, the MEOLUT shall be capable of processing beacon signals with a
center frequency on the range 406.05 MHz ± 1.65 kHz.
5.8
MEOLUT Data Exchange
5.8.1
TOA/FOA Measurement Accuracy
This specification applies to data obtained from a beacon that is visible to a satellite being tracked by
the MEOLUT.
It is expected that TOA and FOA measurements accuracy quoted below will also allow the MEOLUT
to meet its expected location accuracy requirement.
5.8.1.1 C/S T.001 TOA/FOA Measurement Accuracy
If the MEOLUT provides data for use by other MEOLUTS, the accuracy of the TOA and FOA data
shall be as follows:
•
The TOA measurement accuracy for beacon transmissions received with a C/N0 between
34.8 dB-Hz and 37.8 dB-Hz shall be better than the standard deviation of 25 microseconds.
4 The frequency range is the combination of the maximum beacon frequency offset allowed and the motion of a beacon
moving at 1,200 km/h.

5-8

The bias of the mean of the measurement errors from the actual TOA of the beacon
transmission shall be less than 2.5 microseconds,
•
The FOA measurement accuracy for beacon transmissions received with a C/N0 between
34.8 dB-Hz and 37.8 dB-Hz shall be better than the standard deviation of 0.20 Hz. The bias
of the mean of the measurement errors from the actual FOA of the beacon transmission shall
be less than 0.02 Hz.
5.8.1.2 C/S T.018 TOA/FOA Measurement Accuracy
If the MEOLUT provides data for use by other MEOLUTS, the accuracy of the TOA and FOA data
shall be as follows:
•
The TOA measurement accuracy for beacon transmissions received with a C/N0 between
[30.55] dB-Hz and [33.55] dB-Hz shall be better than the standard deviation of
[1] microseconds. The bias of the mean of the measurement errors from the actual TOA of
the beacon transmission shall be less than [0.2] microseconds,
•
The FOA measurement accuracy for beacon transmissions received with a C/N0 between
[30.55] dB-Hz and [33.55] dB-Hz shall be better than the standard deviation of [0.20] Hz.
The bias of the mean of the measurement errors from the actual FOA of the beacon
transmission shall be less than [0.02] Hz.
5.8.2
External Data Processing
The MEOLUT may process 406 MHz beacon data retrieved from other commissioned MEOLUTs,
according to the specifications contained in Annex C, to enhance system performance and support
redundancy of the Cospas-Sarsat Ground System. However, this beacon data cannot be relied upon to
meet the operational, functional, processing, and performance requirements contained in this
document.  Furthermore, the performance of the MEOLUT shall still be compliant with the
performance requirements of sections 5 and 4.2.11, despite the processing of data retrieved from other
commissioned MEOLUTs.
5.9
Processing Combined with non-MEOSAR Satellites (Optional Capability)
If the MEOLUT does use data from non-MEOSAR satellites as described in section 3.3.1, the
MEOLUT shall meet all the operational, functional, processing, and performance requirements
contained in this document without relying upon TOA/FOA data from non-MEOSAR satellites and
the MEOLUT’s capability to meet the performance requirements contained in this document shall not
be impaired.
5.10
Expected Horizontal Error / Quality Factor
The MEOLUT shall produce an Expected Horizontal Error for every independent location, whether
the location calculated is situated inside or outside the DCA. The Expected Horizontal Error is the
radius of the circle that is centred on the estimated location and contains the true location with a
probability of 95  2 %.

5-9

In addition, the EHE shall:
•
be larger than 10 times the location error with a probability of less than 15%,
•
be smaller than the location error divided by 2 with a probability of less than 1%.
The MEOLUT shall produce a Quality Factor (QF) derived from the Expected Horizontal Error as per
Table 2, which also provides the mapping with a Confidence Factor (CF) for information.
Table 5.1: Quality Factor
Quality
Factor (QF)
Expected Horizontal Error
Confidence
Factor (CF)
CF Radius

xx ≤ 0.05 NM

1 NM

0.05 NM < xx ≤ 0.1 NM

0.1 NM < xx ≤ 0.25 NM

0.25 NM < xx ≤ 0.5 NM

0.5 NM < xx ≤ 1 NM

1 NM < xx ≤ 2.7 NM

5 NM

2.7 NM < xx ≤ 5 NM

5 NM < xx ≤ 10 NM

20 NM

10 NM < xx ≤ 20 NM

20 NM < xx ≤ 50 NM

50 NM

xx > 50 NM

> 50 NM
As an example, the Expected Horizontal Error can be calculated from the horizontal JDOP model. A
JDOP definition is provided at Annex F or can also be derived from the general formula presented
below:
𝐽𝐷𝑂𝑃= √𝑇𝑟(𝐺(1,1) + 𝐺(2,2))
With the matrix G defined as:
𝐺= 𝑀𝑇. (𝐻𝑇. 𝑅−1. 𝐻)−1. 𝑀
With:
•
M: transformation matrix between the ECEF global frame and the ENU (East North Up)
local frame,
•
H: the matrix of partial derivatives of the measurement equations with respect to the position
coordinates in ECEF coordinate system.
•
R: the weighting matrix normalized with 𝜎𝑇𝑂𝐴, 𝑅=
[


…
…
…


⋱
⋱
⋱
⋮
⋮
⋱
⋱
⋱
⋱
⋮
⋮
⋱
⋱
⋱
⋱
⋮
⋮
⋱
⋱
⋱
𝜎𝐹𝑂𝐴
𝜎𝑇𝑂𝐴


…
…
…

𝜎𝐹𝑂𝐴
𝜎𝑇𝑂𝐴]
Finally, the Expected Horizontal Error with a 95% probability can be defined by:

5-10

𝐸𝑥𝑝𝑒𝑐𝑡𝑒𝑑 𝐻𝑜𝑟𝑖𝑧𝑜𝑛𝑡𝑎𝑙 𝐸𝑟𝑟𝑜𝑟= 2 × 𝐽𝐷𝑂𝑃× 𝜎𝑇𝑂𝐴
With 𝜎𝑇𝑂𝐴 expressed in NM.
5.11
Processing Anomaly Rate
A processing anomaly is an alert message produced by the MEOLUT, which should not have been
generated, or which provided incorrect information. The ratio of MEOLUT processing anomalies to
actual alerts shall not exceed 1 x 10-4.
- END OF SECTION 5 -

A-1

ANNEX A
DESIGN GUIDELINES FOR DETERMINING THE LINK POWER BUDGET
FOR MEOSAR SYSTEMS
A.1
Introduction
Administrations intending to acquire a Local User Terminal (LUT) to be used in the Cospas-Sarsat
MEOSAR system should ensure that the station's antenna and RF subsystems will meet the Cospas-
Sarsat performance standards defined in documents C/S T.019 (MEOLUT Performance Specification
and Design Guidelines) and C/S T.020 (MEOLUT Commissioning Standard).  MEOLUTs will need
to be able to receive the downlink signal from any Cospas-Sarsat MEOSAR satellite as described in
document C/S T.016 (Description of the 406 MHz Payload Used in the Cospas-Sarsat MEOSAR
System). As such, a link budget analysis is necessary. In this annex an uplink and downlink budget are
provided. This annex provides guidance for making these calculations for all MEOSAR satellites.
A.2
Explanation of the Uplink Budget
When doing a link budget of a satellite communication system, one needs to ensure that the signal
originating from the ground can reach and be relayed by the satellite. For beacons, the accepted antenna
designs and beacon specifications as per document C/S T.001 should be used in this calculation. As
well, the provided receiver properties as per document C/S T.016 should be used at the satellite receive
side. Administrations should consider the following when calculating a 406 MHz beacon signal up link
budget:
propagation (free space) loss
=
ionoshperic fading loss
=
rain fall / atmospheric attenuation
=
antenna polarization mismatch
=
beacon antenna pointing loss or view angle
=
other localised losses such as ground plane or movement in water
=
TOTAL LOSSES (Lo)
=
A nominal example uplink budget is provided in Table A-2. As with any link budget, factors such as
time of day, time of year the beacon is activated and solar cycles will vary the final values of the link
budget calculations by 1 or 2 dB. Worse, nominal, and best-case link budget analysis should also be
performed considering the large variation in fading loss and antenna gain ranges.
The uplink budget is used in the calculation of the overall system (C/N0) which is the actual energy the
MEOLUT will detect and use to process the messages. If the actual overall C/N0 is larger than the
required C/N0, which is derived from the Eb/No requirements, then there is a positive link margin,
which gives a very good probability for a beacon signal to be properly decoded.

A-2

It should be noted that, at various times during a satellite pass, transient signal activity in the uplink
channels, including interference from all ground sources such as radars, can cause the satellite repeaters
to supress their gain (so the receive Low Noise Amplifier is not saturated) up to 30 dB for periods of
10s to 100s of milliseconds. This in turn may increase bit errors within the message and/or deteriorate
beacon signal detection rates as received at the ground station.
A.3
Explanation of the Downlink Budget Calculation
In contrast with LEOSAR, the MEOSAR repeaters do not perform any type of decoding or baseband
manipulation of the received signals. It simply receives all signals within the individual constellation
satellites passband (approximately 90 kHz, see details for each constellation in document C/S T.016).
It then down converts and conditions the signal to reduce intermodulation products, and then finally
up converts to a downlink signal (centre frequencies for each constellation are provided in document
C/S T.016) for transmission back to the Earth. Therefore the onus of demodulation falls on the
MEOLUT to demodulate what is a very close approximation, as repeated by the MEOSAR satellite,
of the original beacon signal as described in document C/S T.001, and as analysed in section A.2.
The Cospas-Sarsat signal is designed to provide reliable performance if the "bit error rate" (BER)
received at the MEOLUT is better than 5x10-5. To ensure reliable reception of the downlink signal, an
analysis should be made on the antenna and RF subsystems and the probable "bit error rate" computed.
Such an analysis should include:
•
the satellite transmit parameters (EIRP, antenna gain, etc.),
•
power sharing losses,
•
the geometry between the moving satellite and the MEOLUT, the MEOLUT location, local
environment (e.g., site conditions, meteorological and ionospheric effects, noise and
interference sources, etc.),
•
the MEOLUT receive and processing characteristics (e.g., antenna, radome, RF system,
receiver, bit synchronizer, modem implementation and data modulation losses, etc.).
Administrations should also consider the following atmospheric and design dependent losses and
determine appropriate values for their MEOLUT design and specific site location.
propagation (free space) loss
=
atmospheric absorption
=
ionospheric fading loss
=
excess rain fall attenuation
=
antenna polarization mismatch
=
terminal antenna pointing loss
=
other localised losses at the ground station
=
TOTAL LOSSES (Lo)
=

A-3

A.4
Calculations
Table A.1 is a detailed downlink budget analysis for a nominal case that looks at the energy-per-bit-
to-noise-density ratio (Eb/N0) of an individual beacon message (i.e., the primary factor governing the
BER of the data) received by the MEOLUT via the satellite. It also provides indicative values for some
of the parameters described in sections A.3 for calculating the system link power budget and link
margin. Worse, nominal, and best-case link budget analysis should also be performed by
administrations, considering the large variation in fading and polarisation mismatch losses.
Eb/N0 can be calculated using the following equation5:
(Eb/N0)c = (EIRP) - (FSL) - (Lf + Lo) + (G/T) - (k) - (r) + (CG) dB
where:
EIRP  Equivalent Isotropic Radiated Power
FSL
Free Space Loss
Lf:
Fading and other ionospheric losses
Lo:
Other LUT local losses (atmospheric/weather/noise), including modem, modulation
processing implementation and modulation index losses
k:
Boltzmann constant
r:
data rate of message
CG:
Coding gain at LUT.
Theoretically, a value of (Eb/N0)th = 8.8 dB is necessary to achieve the required BER value of 5x10-5
in for a BPSK type signal\*.
Solving the initial equation using values from Table A.1 shows that the difference between the
calculated value (Eb/N0)c and the theoretically required value (Eb/N0)th is the link margin:
Link Margin = (Eb/N0)c - (Eb/N0)th = G/T – Lo + XG
where XG is the individual constellation difference value, which is different mostly due to path loss
difference of different orbits, and repeater design.

For coherent detection of a biphase-phase-shift-keyed (BPSK) signal in a Gaussian noise channel, as
defined in communications textbooks, such as Spilker, J.J., "Digital Communications by Satellite",
Prentice-Hall Inc., New Jersey, USA, 1977, pp 31-32, (ISBN 0-13-214155-8), and Roger L.
Freeman, “Telecommunication Transmission Handbook” "Principles of Coherent Communication",
A Wiley Interscience Publication, New York, USA, 1991, pp. 430 and 434 (ISBN0-471-51816-6).

A-4

However, to meet this link margin, one needs to calculate the overall carrier to noise ratio of the entire
system from end to end ((C/N0)sys) since the MEOSAR satellites are analogue repeaters. As such6:
(C/N0)sys= 1/ [(C/N0)up-1 + (C/N0)dn-1 + (C/N0)im-1] (dB.Hz) where:
(C/N0)up  : uplink carrier to noise ratio
(C/N0)dn  : downlink carrier to noise ratio
(C/N0)im : intermodulation products carrier to noise ratio (or IM noise).
If the (C/No)sys is greater than the required C/N0, which is derived from the calculated Eb/N0 and the
data rate of the beacon signal, then the link margin is positive and the beacon message can be decoded
with a high percentage of availability. This percentage of availability can range from 99 to 99.99%
depending on the atmospheric, excess rain, and other local attenuation values (antenna elevation)
chosen. Such values can be found in tabular format in various satellite and telecommunications
textbooks7.
A.5
Summary
From sections A.2 to A.4, administrations have two parameters that they can modify to ensure they
can achieve a positive link margin: the LUT G/T (Antenna gain) and the local losses at the LUT (Lo).
Administrations should ensure that their MEOLUT antenna G/T values, when combined with the other
losses, will provide a positive value link margin.  The excel sheets allow for such analysis for various
values of losses that could be locally seen for all three MEOSAR constellations.
6  Roger L. Freeman, “Telecommunication Transmission Handbook” "Principles of Coherent
Communication", A Wiley Interscience Publication, New York, USA, 1991, sections 6.4.8 (pp. 383-388)
and 6.8 (pp. 441-443) (ISBN0-471-51816-6).
7  Roger L. Freeman, “Telecommunication Transmission Handbook” "Principles of Coherent
Communication", A Wiley Interscience Publication, New York, USA, 1991, pp. 494-537 (ISBN0-471-
51816-6).

A-5

Table A.1: Example of Downlink Power Budget Parameters for MEOSAR
Parameter
Units
Galileo
Glonass
GPS
GPS /DASS
Source
Nominal
Carrier frequency
(MHz)
1544.1
1544.9
1544.9
2226.3
C/S T.016
Polarization (circular)
(n/a)
LHCP
LHCP
RHCP
LHCP
C/S T.016
Minimum elevation angle
(degrees)


C/S T.019
Satellite altitude
(km)


C/S T.016
Satellite transmit EIRP
(dBW)
17.0
17.0
17.0
7.5
C/S T.016 / C/S T.017
Power sharing loss****
(dB)


C/S R.012
Beacon satellite EIRP\*
(dBW)
7.0
7.0
7.0
-2.5
Slant range (SR)@ 5 degrees
(km)


from geometry
Free-space path loss (FSL) @ SR
(dB)
185.4
183.9
184.3
187.4
standard formula
Fading loss (Lf)
(dB)
2.5
2.5
2.5
2.5
between -20 dB, and -0.5 dB
Other local to/and LUT losses (Lo)**
(dB)
Lo**
Lo**
Lo**
Lo**
LUT design/site dependent
Antenna (G/T)***
(dBK-1)
G/T
G/T
G/T
G/T
LUT design dependent
Boltzmann constant (k)
(dBWK-1Hz-1)
-228.6
-228.6
-228.6
-228.6
physical constant
Data rate factor @ 400bps (r) (BPSK)
(dBHz)
29.0
29.0
29.0
29.0
C/S T.001 (800 Hz equivalent)
Coding gain (CG)
(dB)
2.0
2.0
2.0
2.0
BPSK BCH C/S T.001
Calculated (Eb/N0)c
(dB)
G/T-Lo+ 23.7
G/T-Lo+ 25.2
G/T-Lo+ 24.8  G/T-Lo+ 12.2
from above parameters
Desired maximum Bit Error Rate
(BER)
5x10-5
5x10-5
5x10-5
5x10-5
BPSK Signal
Theoretical (Eb/N0)th
(dB)
8.8
8.8
8.8
8.8
for desired maximum BER
Link margin
(dB)
G/T-Lo+ 14.9
G/T-Lo+ 16.4
G/T-Lo+ 16.0  G/T-Lo+ 3.4
see text in section A.3
------------------
\*
Equivalent Isotropic Radiated Power per beacon signal, must include antenna gain and power sharing loss
**
See factors in previous list (page A-3)
***
Antenna Gain-to-Noise Temperature Ratio, to include radome, if applicable, and cable losses
****
Power sharing loss assuming 8 total signals + 1 dB for noise.

A-6

Table A.2: Example of Uplink Power Budget Parameters for MEOSAR
Parameter
Units
Galileo
Glonass
GPS
GPS /DASS
Source
Nominal
Beacon signal frequency
(MHz)
406.034
406.034
406.034
406.034
C/S T.001/T.012
Polarization
(n/a)
Linear
Linear
Linear
Linear
C/S T.001
Antenna pattern view angle\*
(degrees)
5 - 60
5 - 60
5 - 60
5 - 60
C/S T.001
Satellite altitude
(km)


C/S T.016
Beacon transmit power
(dBW)


C/S T.001
Antenna gain\*
(dBi)


C/S T.001
Beacon EIRP\*
(dBW)
9.0
9.0
9.0
9.0
Slant range (SR)@ 5 degrees
(km)


from geometry
Free-space path loss (FSL) @ SR
(dB)
-173.7
-172.3
-172.9
-172.9
standard formula at 406 MHz
Polarization loss (Pol)
(dB)


linear to circular mismatch
Fading loss (Lf)
(dB)
-2.5
-2.5
-2.5
-2.5
between -20 dB, and -0.5 dB
Satellite receive antenna (G/T)**
(dBK-1)
-12.7
-16.3
- 14.6
-21.5
C/S T.016 or estimated value
Boltzmann constant (k)
(dBWK-1Hz-1)
-228.6
-228.6
-228.6
-228.6
physical constant
Calculated (C/N0)c***
(dB.Hz)
45.7
43.5
44.6
37.7
------------------
\*
Equivalent Isotropic Radiated Power per beacon, must include antenna gain from above column. Gain can vary from +4 to -10 dBi depending on view angle and ground plane (i.e antenna
pattern)
**
Measured Antenna Gain-to-Noise Temperature Ratio to include any waveguide/cable/connector losses and effective thermal noise. If the G/T is estimated by antenna gain over global
earth temperature, then Noise Figure value should be added as part of link budget calculation.
***
C/N0= Beacon EIRP+FSL+Pol+Lf+G/T-k
END OF ANNEX A-

B-1

ANNEX B
BEACON MESSAGE PROCESSING INFORMATION
B.1
Beacon Message Validation
The Beacon Message Validation process is presented in the following tables B.1, B.2 and B.3.
Number of Bit Errors
Number of detected messages for same Beacon Event
(PDF-1
+BCH-1)
(PDF-2
+BCH-2)

 2
 2
NA
Message is complete (valid short
message) but unconfirmed. Set
bits 113 to 144 all to “0”
Message is complete and confirmed. Set bits 113 to 144 all to “0”.

NA
Identified as invalid
From the same transmitted burst through another channel or bursts
within ± 5 minutes
A message is invalid, but its confirmation with a valid message
(BCH<3) changes it into a valid message (PDF-1 confirmed). Set
bits 113 to 144 all to “0”.
≥ 3
NA
Identified as invalid
From the same transmitted burst
After 3 identical invalid messages (PDF1+BCH1)
Calculate a FDOA/TDOA 2D or 3D location and send it
immediately to the MCC containing the invalid message (e.g.,
miscoded beacon) with bits 107 to 144 set all to “1”.
Table B.1: Short Messages Validation
Number of Bit Errors
Number of detected messages for same Beacon Event
(PDF-1
+BCH-1)
(PDF-2
+BCH-2)

 2
 2
NA
No correction
is done on bits
107 to 144.
Message is valid
Message is valid and confirmed.

NA
No correction
is done on bits
107 to 144.
Identified as invalid
Message is invalid, but its confirmation changes it into a valid
message (PDF-1 confirmed).
> 3
NA
Identified as invalid
Identified as invalid
Table B.2: Orbitography Beacons Specific Case

B-2

Number of Bit Errors
Number of detected messages for same Beacon Event
(PDF-1
+BCH-1)(\*)
(PDF-2
+BCH-2)

 2
 2
 1
Message is complete but
unconfirmed
Message is complete and confirmed.
 2
Message is valid but incomplete
and unconfirmed. Set bits 113 to
144 all to “1”
Message is confirmed but incomplete.
Set bits 113 to 144 all to “1”.

 1
Identified as invalid
From the same transmitted burst through another channel or
bursts within ± 5 minutes
Message was invalid, but its confirmation changes it into a valid
message (PDF-1 confirmed).
 2
Identified as invalid
From the same transmitted burst through another channel or
bursts within ± 5 minutes
Message is invalid, but its confirmation changes it into a valid
message (PDF-1 confirmed).
Message is confirmed but incomplete.
Set bits 113 to 144 all to “1”.
≥ 3
NA
Identified as invalid
From the same transmitted burst
After 3 identical invalid messages (PDF1+BCH1).
Calculate a FDOA/TDOA 2D or 3D location and send
immediately to the MCC containing the invalid message (e.g.,
miscoded beacon) with bits 107 to 144 set all to “1”.
Table B.3: Long Messages Validation
(\*) and no errors in fixed bits starting at bit 107 for Standard and National Location protocols. Otherwise the message
shall be processed as if it had more than 3 errors in (PDF-1 + BCH-1).
- END OF ANNEX B -

C-1

ANNEX C
MEOLUT NETWORK ARCHITECTURE
This Annex illustrates the architectural concept for MEOLUT networking for the exchange of
TOA/FOA data packets.
C.1
MEOLUT Network Topology
Network topology refers to the physical connectivity between MEOLUT sites: examples include mesh,
star and ring configurations. The primary approach for exchanging data is a partial mesh topology,
involving point-to-point connections between MEOLUTs, as necessary to provide connections to
neighbouring MEOLUTs. Two optional approaches are also described.
C.1.1
Primary Partial Mesh Topology
The primary approach for exchanging data is a partial mesh topology, involving point-to-point
connections between MEOLUTs, as necessary to provide connections to neighbouring MEOLUTs.
Each MEOLUT providing TOA/FOA data using this approach will only provide its own local data to
the receiving MEOLUT. This topology is illustrated in Figure C.1.
Figure C.1: Primary Topology for a MEOLUT Network: a Partial Mesh

![Image 1 from page 42](/images/cospas-sarsat/T-series/T019/T019_page_42_img_1.png)

C-2

C.1.2
Optional Data Forwarding Topology
As an option, some MEOLUT providers may want to share measurement data with all participating
MEOLUTs while limiting the number of point-to-point connections. An example of this is a node
forwarding methodology, in which the forwarding of data received from other MEOLUTs requires the
preliminary step of the concatenation of the local MEOLUT data with all data coming from other
MEOLUTs. Forwarded MEOLUT TOA/FOA data shall not be modified by the transit nodes. This
topology is illustrated in Figure C.2.
Figure C.2: Optional Node Forwarding Topology
C.1.3
Optional Central Data Server Node Topology
An optional MEOLUT Central Data Server could be implemented within the primary partial mesh
topology of the MEOLUT network. MEOLUTs could store their data on the Central Data Server.
MEOLUTs could then obtain data from the central data server as desired, as illustrated in Figure C.3.
MCC
MEOLUT
Location Data
MCC
MEOLUT
Location Data
MCC
MEOLUT
Location Data
MCC
MEOLUT
Location Data

![Image 1 from page 43](/images/cospas-sarsat/T-series/T019/T019_page_43_img_1.png)

![Image 2 from page 43](/images/cospas-sarsat/T-series/T019/T019_page_43_img_2.png)

![Image 3 from page 43](/images/cospas-sarsat/T-series/T019/T019_page_43_img_3.png)

![Image 4 from page 43](/images/cospas-sarsat/T-series/T019/T019_page_43_img_4.png)

![Image 5 from page 43](/images/cospas-sarsat/T-series/T019/T019_page_43_img_5.png)

![Image 6 from page 43](/images/cospas-sarsat/T-series/T019/T019_page_43_img_6.png)

![Image 7 from page 43](/images/cospas-sarsat/T-series/T019/T019_page_43_img_7.png)

![Image 8 from page 43](/images/cospas-sarsat/T-series/T019/T019_page_43_img_8.png)

![Image 9 from page 43](/images/cospas-sarsat/T-series/T019/T019_page_43_img_9.png)

![Image 10 from page 43](/images/cospas-sarsat/T-series/T019/T019_page_43_img_10.png)

![Image 11 from page 43](/images/cospas-sarsat/T-series/T019/T019_page_43_img_11.png)

![Image 12 from page 43](/images/cospas-sarsat/T-series/T019/T019_page_43_img_12.png)

C-3

Figure C.3: Optional Central Data Server Topology
C.2
MEOLUT TOA/FOA Data Exchange
Sharing of MEOSAR TOA/FOA data is optional, determined by national requirements and arranged
on a bilateral basis between MEOLUT operators. All TOA/FOA data shall include data content and be
transferred in the data format specified in document C/S [A.002]. Data transfer shall use a secure form
of FTP as per the specifications found in document C/S [A.002]. Using shared data for location
processing is optional.
The following conventions shall apply to all TOA/FOA data shared between MEOLUTs:
•
The exchanged files shall be limited to a maximum number of [2000] TOA/FOA data records
(number to be implemented as a configurable value to allow possible future adjustments),
•
Beyond the maximum number of records, the older records (based on TOA) shall be removed
from the TOA/FOA data file to be exchanged,
•
TOA/FOA data files shall be pushed every [60] seconds (periodicity to be implemented as a
configurable value to allow possible future adjustment) by the MEOLUT to all linked
MEOLUTs. No accurate time synchronization shall be required,
•
Any possible duplicated TOA/FOA data records shall be removed, and not inserted into the
exchange file.
- END OF ANNEX C -
Central
Data
Server
MCC
MEOLUT
Location Data
MCC
MEOLUT
Location Data
MCC
MEOLUT
Location Data
MCC
MEOLUT
Location Data

![Image 1 from page 44](/images/cospas-sarsat/T-series/T019/T019_page_44_img_1.png)

![Image 2 from page 44](/images/cospas-sarsat/T-series/T019/T019_page_44_img_2.png)

![Image 3 from page 44](/images/cospas-sarsat/T-series/T019/T019_page_44_img_3.png)

![Image 4 from page 44](/images/cospas-sarsat/T-series/T019/T019_page_44_img_4.png)

![Image 5 from page 44](/images/cospas-sarsat/T-series/T019/T019_page_44_img_5.png)

![Image 6 from page 44](/images/cospas-sarsat/T-series/T019/T019_page_44_img_6.png)

![Image 7 from page 44](/images/cospas-sarsat/T-series/T019/T019_page_44_img_7.png)

![Image 8 from page 44](/images/cospas-sarsat/T-series/T019/T019_page_44_img_8.png)

![Image 9 from page 44](/images/cospas-sarsat/T-series/T019/T019_page_44_img_9.png)

![Image 10 from page 44](/images/cospas-sarsat/T-series/T019/T019_page_44_img_10.png)

![Image 11 from page 44](/images/cospas-sarsat/T-series/T019/T019_page_44_img_11.png)

D-1

ANNEX D
MEOLUT COVERAGE AREA
The coverage area of a stand-alone MEOLUT shall, at a minimum, be derived from the executed
MEOLUT satellite pass tracking. Each possible beacon location within the MEOLUT coverage area
shall meet the following geometrical beacon-satellite-MEOLUT conditions, with the following
assumptions:
•
a minimum MEOLUT-to-satellite elevation angle of 5 degrees,
•
beacon-to-satellite elevation angle between 5 and 60 degrees (portion of antenna radiation
pattern that is specified in document C/S T.001) unless the national administration
demonstrates performance above 60 degrees measured from operational beacons,
•
a minimum of three satellites in beacon-MEOLUT mutual visibility (i.e., within the above
elevation conditions).
- END OF ANNEX D –

E-1

ANNEX E
OPTIONAL PROCESSING OF INTERFERENCE
USING THE 406 MHZ REPEATER BAND
E.1
Introduction
This annex describes how the 406 MHz repeater system aboard some of the Cospas-Sarsat MEOSAR
satellites can be used by MEOLUTs to perform interference monitoring of the 406 MHz band.
E.2
Functional Description
To detect and locate interfering signals in the 406 MHz band (i.e., non-beacon signals), the approach
needed is different than for beacon signals because interferers do not transmit in the same format as a
beacon signal. Interferers generally transmit continuous signals for several seconds, minutes, or even
hours, compared to the one-half second burst of a beacon signal. Still, locating the source of such
interfering signals may be done for example by using DOA methodology if suspected signals are
correlated over multiple satellite data channels, or by processing the Doppler curves generated by the
tracked MEOSAR satellites with respect to the interferer, possibly combined with a triangulation
methodology. No message can be extracted from an interfering signal as its modulation and format is
not compatible with a 406 MHz beacon signal.
E.3
Operational Recommendations
406 MHz interference monitoring is encouraged for all MEOLUTs on a best effort basis. As much data
as possible should be collected and recorded.
When a new 406 MHz interferer is identified, the MEOLUT/MCC operator is encouraged to inform
the appropriate Search and Rescue authorities in the area of the interferer (i.e., locations and times), to
periodically report such interference to the ITU, using national procedures, and to the Secretariat.
Detailed instructions for interference reporting are included in Cospas-Sarsat document C/S A.003.
E.4
Performance Specification
E.4.1
Processing Performance
Additional processing of the 406 MHz repeater band for interference monitoring shall not affect the
compliance of the MEOLUT to the requirements defined in this document.
E.4.2
Location Accuracy
The objective is to achieve a location accuracy of interfering emitters better than 20 km. The location
accuracy however depends on the nature of the interfering signal.
- END OF ANNEX E -

F-1

ANNEX F
JDOP DEFINITION
F.1
JDOP Implementation Algorithm
JDOP definition
JDOP is defined as the Horizontal Dilution of Precision using DOA observations assuming
uncorrelated observations with identical standards deviations per observation type:
σTOA = 25 μs
for all TOA observations, and
σTOA = 0.25 Hz
for all FOA observations.
The following algorithm shall be used:
Let there be N MEOSAR satellites visible simultaneously at the beacon location and the participating
MEOLUT(s) above an elevation angle of 5 degrees. Let these (ECEF) locations be denoted as:


b
b
b
z
y

,
,
and 

b
b
b
z
y




,
,
the approx. position and velocity of the alert beacon




z
y

,
,
and 



z
y




,
,
the approx. position and velocity of satellite i (i = 1,..,N).
The linearized observation equations can then be written as



















−
−
−
−
−
−
=

















=






z
y

z
y

H
H
R
R
ref

ref

ref

ref

ref

ref

FDOA
TDOA





















(1)
where
bi
b


bi
b


bi
b


z
z
R
y
y
R


R
−
=


=
−
=


=
−
=


=









bi
bi
bi
bi
bi
bi
bi
bi
b


bi
bi
bi
bi
bi
bi
bi
bi
b


bi
bi
bi
bi
bi
bi
bi
bi
b


z
z
z
y
y


z
z
R
y
z
z
y
y


y
y
R

z
z
y
y


R


















−
+
+
=


=
−
+
+
=


=
−
+
+
=


=



(2)
with the coordinate and velocity differences

F-2

(
)
(
)
(
)

b

bi

b

bi

b

bi
R
z
z
z
R
y
y
y
R


−
=
−
=
−
=
and
(
)
(
)
(
)

b

bi

b

bi

b

bi
R
z
z
z
R
y
y
y
R











−
=
−
=
−
=
(3)
with
(
)
(
)
(
)2


b

b

b


z
z
y
y


R
−
+
−
+
−
=
(4)
The subscript “ref” in equation (1) refers to the reference satellite, relative to which all DOA
observations are build.
If there are N pairs of DOA observations available, the left hand side is a [2N1] matrix, where
iR

is the [N1] sub-matrix with the linearized TDOA observations converted from seconds to meter, and
iR

is the [N1] sub-matrix with the linearized FDOA observations converted from Hz to m/s.
(
)
(
)
b
ref


ref


f
c
FOA
FOA
R
c
TOA
TOA
R
−
=

−
=


(5)
with fb, the beacon transmission frequency, and c the speed of light.
The matrix at the right contains the 3 beacon position unknowns, where the first two elements represent
the horizontal position and the third one the vertical position (e.g. Δx, Δy and Δz could point to the
East, North and zenith respectively).
For the DOP concept, all observations are assumed to be uncorrelated and have identical standards
deviations per observation type, i.e., σTDOA for all TDOA observations, and σFDOA for all FDOA
observations. The variance-covariance matrix of the linearized observations, CDOA, is then given by








=








=




=
I
I
I
I
C
C
C
FOA
TOA
FDOA
TDOA
FDOA
TDOA
DOA






(6)
And the variance-covariance matrix of the unknowns, G, is given by


−
−
−




+
=
FDOA
T
FDOA
FOA
TDOA
T
TDOA
TOA
H
H
H
H
G


(7)
In analogy to the HDOP concept in GNSS, the standard deviation of the estimated horizontal location
can be given as the trace of the matrix G:


G
G
HorzPos
+
=

(8)
In contrast to the DOP concept in GNSS, here the contribution of the beacon-satellite geometry cannot
be separated from the measurement accuracy as two different observation types have been used.
Therefore the auxiliary matrix G’ is defined by

F-3

'
−
−






+
=
=
FDOA
T
FDOA
FOA
TOA
TDOA
T
TDOA
TOA
H
H
H
H
G
G



(9)
and JDOP is then given as


'
'
G
G
JDOP
+
=
(10)
The expected standard deviation for the estimated horizontal location is given by
JDOP
TOA
HorzPos

=



.
(11)
Some closing remarks:
1. The definition of G’ in equation (9) contains a multiplication factor based on the variances of the
TOA and FOA measurements. These variances must be given in meter and meter/second
respectively. With the proposed values of 25 μsec and 0.25 Hz, the multiplication factor is thus
equal to
(
)
(
)


s

s

Hz

.0
μsec

=

=







=
−
b
b
FOA
TOA
f
f
c
c


taking fb = 406.05 MHz, the middle of the C/S frequency band.
2. The achievable JDOP is dependent not only on the beacon and satellite positions, but also on the
MEOLUT(s) position. Only satellites that are both visible at the beacon and MEOLUT(s) should
be taken into consideration for the JDOP computation.
3. JDOP is also dependent on the number of available antennas at the MEOLUT(s). Only satellites
that can actually be tracked should be taken into consideration. E.g., for a stand-alone MEOLUT
with four antennas, the maximum number of satellites can be four at most. If more satellites could
be tracked, i.e., if more satellites are visible both at the MEOLUT and beacon, the JDOP algorithm
should determine the minimum JDOP out of all potential combination of satellites. If the JDOP is
used to characterize an actual test situation, then of course only the satellites that are involved in
the test should be taken into consideration when computing JDOP.
4. Also, regarding the choice of the reference satellite with respect to which the DOA observations
are built, all satellites out of the N satellites should be evaluated as reference and the one giving
minimum JDOP should be chosen.
5. The minimum elevation angle of 5 degrees is in line with document C/S R.012, Annex N.

F-4

F.2
JDOP Compared to HDOP
Here JDOP and the classical HDOP are compared in an
example with 4 DASS satellites simultaneous observed
by an alert beacon and MEOLUT, both in Toulouse, see
the sky plot to the right.
The figure beneath shows the resulting values for the
classical HDOP and MEOSAR JDOP.
Towards 02:00, HDOP increases rapidly due to the near
alignment of all four satellites and the beacon in a single
plane. If only HDOP is considered, one could interpret
this an unfavourable time for a MEOSAR localization.
The JDOP however shows only a slight increase towards
the end of the evaluated epoch, indicating that a
localization is still feasible with a good accuracy.
The table below shows some values for the JDOP, which
is between 0.19 and 0.30 during this time span. The
expected standard deviation of the horizontal location
can be estimated as




km
6.

μs



=



=

=
JDOP
c
JDOP
JDOP
TOA
HorzPos


The location accuracy with a 95% confidence level is
equal to 2.4477 σHorzPos.
time
JDOP
σHorzPos
95%
00:00
0.275
2.9 km
7.1 km
01:00
0.187
2.0 km
4.9 km
02:00
0.303
3.2 km
7.9 km
F.3
Numerical Example for JDOP Computation
This attachment provides a numerical example for all steps in the JDOP computation. For this example,
the beacon-satellite constellation from section N.2 will be evaluated at epoch 01:00.
The approximate beacon position in ellipsoidal WGS-84 coordinates is given as:
φb [deg]
λb [deg]
hb [m]
43.55896
1.48373
144.0
Approximate beacon position in ECEF coordinates [m]:
xb
yb
zb
ẋb
ẏb
żb
4627932.896
119871.625
4372810.338
0.0
0.0
0.0

![Image 1 from page 50](/images/cospas-sarsat/T-series/T019/T019_page_50_img_1.png)

![Image 2 from page 50](/images/cospas-sarsat/T-series/T019/T019_page_50_img_2.png)

F-5

Satellite position in ECEF coordinates [m]:


yi
zi
ẋi
ẏi
żi

14473971.955
-7832995.284
20830145.566
131.653767
2646.645504
907.553640

9491732.521
-19294589.707
15760160.626
1821.654768
-757.320984
-2113.407054

10794083.534
19129385.521
15316333.557
-1703.556362
-849.593981
2271.346027

23929166.460
-10809572.853
3090142.279
-240.428338
388.774588
3207.984673
Satellite position relative to beacon position in ECEF coordinates [m]:

xi - xb
yi - yb
zi - zb
ẋi - ẋb
ẏi - ẏb
żi - żb

9846039.059
-7952866.909
16457335.228
131.653767
2646.645504
907.553640

4863799.625
-19414461.332
11387350.288
1821.654768
-757.320984
-2113.407054

6166150.638
19009513.896
10943523.219
-1703.556362
-849.593981
2271.346027

19301233.564
-10929444.478
-1282668.059
-240.428338
388.774588
3207.984673
Satellite position relative to beacon position in ECEF coordinates (normalized):

xbi
ybi
zbi
ẋbi
ẏbi
żbi

0.4742469545 -0.3830599176
0.7926884165
0.000006341271
0.000127479036
0.000043713472

0.2112202242 -0.8431118038
0.4945184559
0.000079109001
-0.000032888178
-0.000091778927

0.2706265010
0.8343095287
0.4803008509
-0.000074767472
-0.000037287874
0.000099687222

0.8687240104 -0.4919204157
-0.0577312604
-0.000010821374
0.000017498250
0.000144387316
Derivative of range R and range-rate Ṙ with respect to the beacon position in ECEF directions:

∂Ri/∂xb
∂Ri/∂yb
∂Ri/∂zb
∂Ṙi/∂xb
∂Ṙi/∂yb
∂Ṙi/∂zb

-0.4742469545
0.3830599176
-0.7926884165
-0.000011640325
-0.000123198871
-0.000052570669

-0.2112202242
0.8431118038
-0.4945184559
-0.000079309352
0.000033687904
0.000091309856

-0.2706265010
-0.8343095287
-0.4803008508
0.000073830068
0.000034397967
-0.000101350903

-0.8687240104
0.4919204157
0.0577312604
-0.000012064461
-0.000004539003
-0.000142866432
Derivative of range R and range-rate Ṙ with respect to the beacon position in local topocentric
directions {East, North, Zenith}:

αi=∂Ri/∂xb
βi=∂Ri/∂yb
γi=∂Ri/∂zb

=∂Ṙi/∂xb

=∂Ṙi/∂yb
i=∂Ṙi/∂zb

0.3952111986
-0.2545746564
-0.8826096831
-0.000122856161
-0.000027879262
-0.000046970680

0.8482982656
-0.2279009305
-0.4779657085
0.000035730173
0.000120201826
0.000006100303

-0.8270224462
-0.1467446168
-0.5426784416
0.000032474746
-0.000124918568
-0.000015711361

0.5142494235
0.6314961269
-0.5803104101
-0.000004225095
-0.000095138564
-0.000107274291
where the rotation matrix from ECEF to the local topocentric coordinate frame at the beacon position
is given by










=










−
−
−
=

0.68910065

0.01876382

0.72442267

0.72466563

0.01784293

0.68886961


0.99966471

0.02589307
-
sin
sin
cos
cos
cos
cos
sin
sin
cos
sin

cos
sin
b
b
b
b
b
b
b
b
b
b
b
b
R













F-6

Now the JDOP is computed for all choices of reference satellite. For ref = 1, the values are










=










−
−
−
−
−
−
−
−
−
=
=
=
=
=
=
=
=
=
=

0.30229927


0.33993124


0.40464397


.
.
.
.
-
.
.
H
ref
ref
ref
ref
ref
ref
ref
ref
ref
TDOA




























=










−
−
−
−
−
−
−
−
−
=
=
=
=
=
=
=
=
=
=


.
-
.
-
.
.
.
-
.
.
.
.
H
ref
ref
ref
ref
ref
ref
ref
ref
ref
FDOA














































=






+
=
−


'


.
.
-
.
-
.
-
.
.
.
-
.
.
H
H
H
H
G
FDOA
T
FDOA
FOA
TOA
TDOA
T
TDOA


with
(
)


s

Hz

.0
μsec

=

=







=
−
b
b
FOA
TOA
f
f
c
c


,


'
'


.
.
.
G
G
JDOPref
=
+
=
+
=
=
The computation of HTDOA, HTDOA, G’ and JDOP is repeated for ref=2, 3 and 4; this results in four
JDOP values, one for each choice of reference satellite:
ref = 1:
JDOPref=1 = 0.186747317
ref = 2:
JDOPref=2 = 0.220439416
ref = 3:
JDOPref=3 = 0.201995322
ref = 4:
JDOPref=4 = 0.237619737
The final JDOP value is then the minimum of these four values:
JDOP = min( JDOPref=i ) = 0.186747317
- END OF ANNEX F -
- END OF DOCUMENT -

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