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---
title: "T009: Cospas-Sarsat Geolut Performance Specification And Design Guidelines C"
description: "Official Cospas-Sarsat T-series document T009"
sidebar:
badge:
text: "T"
variant: "note"
# Extended Cospas-Sarsat metadata
documentId: "T009"
series: "T"
seriesName: "Technical"
documentType: "specification"
isLatest: true
issue: 2
revision: 6
documentDate: "October 2025"
originalTitle: "Cospas-Sarsat"
---
> **📋 Document Information**
>
> **Series:** T-Series (Technical)
> **Version:** Issue 2 - Revision 6
> **Date:** October 2025
> **Source:** [Cospas-Sarsat Official Documents](https://www.cospas-sarsat.int/en/documents-pro/system-documents)
---
# T009 - T009-OCT-23-2025.pdf
**Pages:** 25
---
COSPAS-SARSAT
GEOLUT
PERFORMANCE SPECIFICATION
AND DESIGN GUIDELINES
C/S T.009
Issue 2 – Revision 6
***Specifications related to C/S T.018 beacons are preliminary and would need further development
COSPAS-SARSAT GEOLUT
PERFORMANCE SPECIFICATION AND DESIGN GUIDELINES
History
Issue
Revision
Date
Comments
Approved (CSC-21)
Approved (CSC-23)
Approved (CSC-29)
Approved (CSC-33)
Approved (CSC-35)
Approved (CSC-37)
Approved (CSC-41)
Approved (CSC-43)
Approved (CSC-49)
Approved (CSC-53)
Approved (CSC-59)
Approved (CSC-61)
Approved (CSC-62)
Approved (CSC-64)
Approved (CSC-67)
Approved (CSC-71)
Approved (CSC-73)
TABLE OF CONTENTS
Page
Contents
1.
INTRODUCTION................................................................................................. 1-1
1.1
Overview ............................................................................................................. 1-1
1.2
Scope .................................................................................................................... 1-1
1.3
Document Organisation ..................................................................................... 1-1
1.4
Reference Documents ......................................................................................... 1-1
2.
COSPAS-SARSAT GEOLUT DESCRIPTION ................................................. 2-1
3.
OPERATIONAL REQUIREMENTS ................................................................. 3-1
3.1
GEOLUT Data Availability............................................................................... 3-1
3.2
Data Requirements ............................................................................................. 3-1
3.3
Satellite Tracking Capability ............................................................................ 3-1
3.4
Satellite Visibility ................................................................................................ 3-2
3.5
Status and Alarm ................................................................................................ 3-2
3.6
RF Radiation and Emissions ............................................................................. 3-2
3.7
Interference ......................................................................................................... 3-2
3.8
Data Archiving .................................................................................................... 3-2
3.9
Cospas-Sarsat Quality Management System (QMS) Continuous
Monitoring and Objective Assessment....................................................... 3-3
4.
FUNCTIONAL AND PROCESSING REQUIREMENTS ............................... 4-1
4.1
Functional 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 MCC Interface .......................................................................................... 4-1
4.2
Processing Requirements ................................................................................... 4-1
4.2.1 General Processing Requirements ............................................................ 4-1
4.2.2 406 MHz Beacon Message Recovery ...................................................... 4-2
4.2.3 Bit Verification ......................................................................................... 4-2
4.2.4 Beacon Message Validation ..................................................................... 4-4
4.2.5 Beacon Message Processing ..................................................................... 4-5
4.2.6 Redundant Alert Data ............................................................................... 4-6
4.2.7 Updated Location Data ............................................................................. 4-6
4.2.8 Bit-Shifted Beacon Messages ................................................................... 4-6
4.2.9 Special National Processing Requirements .............................................. 4-7
5.
PERFORMANCE REQUIREMENTS ............................................................... 5-1
5.1
Processing Performance .................................................................................... 5-1
5.1.1 C/S T.001 Beacons ................................................................................... 5-1
5.1.2 C/S T.018 Beacons ................................................................................... 5-2
5.2
Frequency Measurement ................................................................................... 5-2
5.3
Capacity ............................................................................................................... 5-2
5.4
Processing Anomaly Rate .................................................................................. 5-2
5.5
Downlink Fading ................................................................................................ 5-3
5.6
Processing Frequency ........................................................................................ 5-3
5.6.5 Processing Bandwidth .............................................................................. 5-3
5.6.6 Acquisition Frequency Range .................................................................. 5-3
LIST OF FIGURES
Figure 2.1: A Typical Cospas-Sarsat GEOLUT Functional Block Diagram............................... 2-1
LIST OF ANNEXES
GEOSAR SPACE SYSTEM PERFORMANCE PARAMETERS AND
DOWNLINK BUDGET .................................................................................... A-1
A.1 Introduction ....................................................................................................... A-1
A.2 Explanation of the downlink budget................................................................ A-1
A.3 Calculations ........................................................................................................ A-1
A.4 Summary ............................................................................................................ A-2
1-1
1.
INTRODUCTION
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 in the Cospas-
Sarsat System which receives and processes 406 MHz signals relayed by a geostationary satellite
is called a GEOSAR Local User Terminal (GEOLUT). The GEOLUT transmits alert and location
data to the associated Cospas-Sarsat Mission Control Centre (MCC) for subsequent distribution to
SAR authorities.
For acceptance as part of the Cospas-Sarsat System, a GEOLUT shall be commissioned as defined
in the document C/S T.010, Cospas-Sarsat GEOLUT Commissioning Standard, to verify
compliance of its performance with this specification.
This specification describes the minimum operational capabilities and performance requirements
of a Cospas-Sarsat GEOLUT. The specifications in this document apply to data transmitted by a
GEOLUT for distribution in the Cospas-Sarsat MCC network.
A brief description of a GEOLUT is provided in section 2. Section 3 defines basic GEOLUT
operational requirements, functional and processing requirements are provided in section 4, and
section 5 contains specific performance requirements for a GEOLUT.
The annex to this document contains reference information for GEOLUT operators and designers.
The latest version of the following documents contain useful information describing the signals to
be received by a GEOLUT (references a, d and f), and defining how a GEOLUT is integrated into
the Cospas-Sarsat System:
C/S T.001, Specification For Cospas-Sarsat 406 MHz Distress Beacons;
C/S T.002, Cospas-Sarsat LEOLUT Performance Specification and Design
Guidelines;
C/S T.005, Cospas-Sarsat LEOLUT Commissioning Standard;
1-2
C/S T.006, Cospas-Sarsat Orbitography Network Specification;
C/S T.010, Cospas-Sarsat GEOLUT Commissioning Standard;
C/S T.011, Description of the 406 MHz Payloads Used in the Cospas-Sarsat
GEOSAR System;
C/S A.001, Cospas-Sarsat Data Distribution Plan (DDP);
C/S A.002, Cospas-Sarsat Mission Control Centres Standard Interface
Description (SID);
C/S A.005, Cospas-Sarsat Mission Control Centre Performance Specification and
Design Guidelines; and
***C/S T.018, Specification for Second-Generation Cospas-Sarsat 406-MHz
Distress Beacons.
- END OF SECTION 1 -
2-1
2.
COSPAS-SARSAT GEOLUT DESCRIPTION
A GEOLUT is a ground receiving station in the Cospas-Sarsat System that detects, processes, and
recovers the coded transmissions of 406 MHz emergency beacons, and relays the appropriate
information to an MCC. It processes this data which has been modulated onto a single downlink
carrier by a Geostationary Search And Rescue (GEOSAR) satellite. The technical parameters of
the various GEOSAR satellites are described in detail in document C/S T.011 (description of
GEOSAR payloads).
A GEOLUT is defined in this document as a function. It may be implemented in many ways, such
as sharing equipment or software with a LEOLUT, MEOLUT or an MCC. However, an
implementation based on sharing equipment or software must meet the data availability
requirements specified in this document.
A GEOLUT consists of at least the following basic components and interfaces:
an antenna and radio frequency subsystem;
a processor;
a time and/or frequency reference subsystem; and
an MCC interface.
A typical Cospas-Sarsat GEOLUT functional block diagram is shown in Figure 2.1.
Figure 2.1: A Typical Cospas-Sarsat GEOLUT Functional Block Diagram
406 MHz BEACON MESSAGES
COMMANDS
RECEIVER
PROCESSOR
COMMUNICATIONS
INTERFACE
TIME
AND
FREQUENCY
STANDARD
2-2
The SAR instruments on Cospas-Sarsat GEOSAR satellites receive uplink signals from 406 MHz
distress beacons, test beacons and system beacons such as orbitography beacons. These uplink
signals, along with unwanted interfering signals, are relayed by the GEOSAR satellite for reception
by a GEOLUT.
A Cospas-Sarsat GEOLUT shall process the GEOSAR downlink signal to produce 406 MHz
GEOSAR alerts, including the associated location data when available in the beacon message, and
forward this information to the associated MCC for further action.
The operational, functional and performance specifications of this document must be met to ensure
that:
the GEOLUT is available and capable to receive and process beacons signals in
the GEOSAR downlink signal; and
the GEOLUT provides reliable alerts and accurate position data by:
i) detecting invalid 406 MHz beacon messages and processing them in
accordance with this specification,
ii) verifying whenever possible that data formats are correct and encoded data is
valid, including the beacon identification and encoded position information,
and
iii) providing updated position information to the MCC, as appropriate.
A GEOLUT may be used to supply data from a geostationary satellite to improve the quality of the
solution data for 406 MHz beacons which are detected and located by a LEOLUT.
- END OF SECTION 2 -
3-1
3.
OPERATIONAL REQUIREMENTS
The basic operational objective of a GEOLUT is to receive and process data from a selected
GEOSAR satellite and to send the resulting 406 MHz beacon messages to the associated MCC,
according to the functional and performance specifications contained in this document. Once the
GEOLUT has been commissioned and connected to the Cospas-Sarsat network through an MCC,
it shall continue to meet the operational, functional and performance specifications of this
document.
A GEOLUT 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 percent
(5%) downtime calculated over a year. Outages of the GEOSAR satellite to GEOLUT downlink
signal due to propagation effects shall be included in the computation of the GEOLUT's
availability. However, outages of the GEOSAR satellite itself and seasonal outages due to
increased noise levels when the GEOSAR satellite transits the sun shall be excluded from the
calculation.
The GEOLUT shall provide all data necessary for the MCC to distribute relevant beacon alert data
to the appropriate destination(s), according to the documents C/S A.001 (DDP) and C/S A.002
(SID).
The GEOLUT shall be capable of continuously receiving the downlink signal from at least one
GEOSAR satellite of the type described in document C/S T.011, Description of the 406 MHz
Payloads Used in the Cospas-Sarsat GEOSAR System. The GEOLUT shall be capable of detecting
and processing beacon signals in the entire uplink bandwidth that is used by the selected GEOSAR
satellite for operational 406 MHz beacons. The GEOLUT shall be capable of operating without
degradation in all operational modes of the selected GEOSAR satellite.
The GEOLUT shall be capable of processing all data from a GEOSAR satellite without significant
degradation or loss due to relative satellite motion caused by orbit eccentricity and inclination.
3-2
It is recommended that GEOLUTs operate with GEOSAR satellites that have elevation angles at
least 5 degrees above the local horizon. If the GEOLUT must operate at an elevation angle lower
than 5 degrees, the GEOLUT should be equipped with a receive antenna with appropriate gain and
beamwidth to avoid the unnecessary introduction of background noise into the GEOLUT’s
receiver system.
The GEOLUT shall provide the MCC with sufficient status and alarm information to permit the
MCC to determine the degradation of its operational capabilities.
The GEOLUT shall not emit or radiate any Radio Frequency (RF) signals which will interfere with
the proper functioning of the Cospas-Sarsat System or other authorized users of the
electromagnetic spectrum.
The GEOLUT should be designed to operate with minimal degradation or loss of data in the
presence of interference in the beacon to GEOSAR uplink signal, the GEOSAR to GEOLUT
downlink signal, and in the local GEOLUT's site environment.
The GEOLUT shall maintain access to the data elements listed below for a period of at least
three months:
the hexadecimal character representation of each 406 MHz beacon burst received;
the frequency and time measurement of each 406 MHz beacon burst received;
the C/No ratio for each 406 MHz beacon burst received;
the hexadecimal character representation of all valid and confirmed (or valid,
regardless of confirmation, for an ELT(DT) message) 406 MHz beacon alerts
provided to the MCC;
the frequency, date/time, C/No ratio, and number of independent integrations for
all valid and confirmed (or valid, regardless of confirmation, for an ELT(DT)
message) 406 MHz beacon alerts provided to the MCC;
3-3
the data from an ELT-DT beacon message*
power spectrum data for 406 MHz interferers detected by the GEOLUT; and
the log files that capture the status of the GEOLUT.
The GEOLUT shall transmit solution data to its associated MCC as required by the QMS
continuous monitoring and objective assessment process described in section 2 of C/S A.003.
- END OF SECTION 3 -
* Noting that the alert message decoded using integration shall not be forwarded to the MCC as stated in section 4.2.2.
4-1
4.
FUNCTIONAL AND PROCESSING REQUIREMENTS
The basic functional and processing requirements of a GEOLUT are to:
acquire and receive the downlink signal from the selected GEOSAR satellite(s);
maintain time and frequency references;
process and recover 406 MHz beacon messages; and
provide the appropriate data to the associated MCC to enable the MCC to satisfy
the requirements of document C/S A.002 (SID).
4.1.1
Antenna and RF Subsystem
The GEOLUT's antenna and RF subsystem shall be able to acquire and continuously receive
the downlink signal from the GEOSAR satellite(s) with which the GEOLUT is required to
operate. GEOLUTs operating with GEOSAR satellites that have 1544.5 MHz downlink
frequencies should use right hand circular polarisation (RHCP) receive antennas to reduce the
potential for interference from LEOSAR satellite downlink signals. However, linearly
polarised antennas are acceptable for satellites that have linearly polarised downlinks.
4.1.2
Time and Frequency Reference Subsystem
The GEOLUT system time shall be maintained to within ten (10) milliseconds of universal
co-ordinated time (UTC). Additionally, it is recommended that the frequency reference for all
applicable local oscillators should have a stability of five parts in ten raised to the power of
nine, over fifteen minutes.
4.1.3
MCC Interface
The GEOLUT must provide timely information of the level of quality and detail specified in
the documents C/S A.002 (SID) and C/S A.005 (MCC specification).
4.2.1
General Processing Requirements
The GEOLUT shall process 406 MHz beacon messages as described in this section. The
GEOLUT shall process all available information and provide, as appropriate, encoded
position data or unlocated alerts. The processing consists of the following sequence: message
4-2
recovery, bit verification, message validation, message processing and transmission of
resultant alert data to the associated MCC.
4.2.2
406 MHz Beacon Message Recovery
4.2.2.1 C/S T.001 Beacons
The GEOLUT must recover 406 MHz digital bursts relayed by the selected GEOSAR
satellite. Successive bursts of the same transmitting beacon can be integrated until a valid
message is produced. A valid (or complete) ELT-DT distress alert message that had to be
integrated to be decoded shall not be forwarded to the associated MCC for processing.
The GEOLUT shall process and transmit to the associated MCC only beacon messages
that achieve a perfect match of bits 16 to 24 with the 9 bit frame synchronisation pattern
described in the document C/S T.001 (Beacon Specification).
If a valid message (section 4.2.4 refers) cannot be produced by the GEOLUT within
twenty (20) minutes from the time of reception of the first burst of the current integration
process, the GEOLUT integration process must be halted, reset, and restarted for that
particular beacon message.
The GEOLUT may also record for off-line processing “self-test” mode beacon messages
that have an inverted frame synchronisation pattern. However, such data shall not be used
in the processing of operational alerts.
4.2.2.2 ***C/S T.018 Beacons
The GEOLUT must recover 406 MHz digital bursts relayed by the selected GEOSAR
satellite. Successive bursts of the same transmitting beacon shall not be integrated.
The GEOLUT shall process and transmit to the associated MCC only beacon messages
that achieve a perfect match of bit frame synchronisation pattern described in the
document C/S T.018 (Beacon Specification).
The GEOLUT may also record for off-line processing “self-test” mode beacon messages
that have a “self-test” PRN sequence. However, such data shall not be used in the
processing of operational alerts.
4.2.3
Bit Verification
The GEOLUT shall detect and correct as follows, bit errors in the 406 MHz beacon messages.
The processing is specific to each beacon specification (C/S T.001 or ***C/S T.018).
4-3
4.2.3.1 C/S T.001 Beacons
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 as noted below). The GEOLUT shall use these BCH codes to
verify and correct as necessary the received 406 MHz beacon messages. All beacon
messages include the following fields:
-
first protected data field (PDF-1, bits 25 to 85) which contains the beacon
identification and can include position data; and
-
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.
The long message format also includes:
-
the second protected data field (PDF-2, bits 107 to 132) which contains position
and supplementary data; and
-
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.
The GEOLUT 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 GEOLUT 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 GEOLUT determines there are 2 or
more bit errors in the second protected field, bits 113 to 144 shall all be replaced with
“1”. The GEOLUT shall set bits 113 to 144 all to “0” for short format beacon messages.
The GEOLUT shall have the capability to suppress all orbitography and calibration
beacon messages, and pass them to the MCC only on request. The long version of the
orbitography protocol (bits 37-39 = “000”) messages are processed differently from other
protocol messages in respect to verification of bits 107 to 144 and are not subject to
message validation defined in 4.2.4. While the short message portion (bits 25-106) is error
corrected by BCH-1, there is no error correction and detection applicable to bits 107 to
144. The GEOLUT shall send the uncorrected data in bits 107 to 144 to the associated
MCC.
As defined in document C/S T.001, Specification for Cospas-Sarsat 406 MHz Distress
Beacons specific messages contain fixed bit sequences:
• Standard location protocol beacon messages contain “1101” in bits 107-110
• National location protocol beacon messages contain “110” in bits 107-109.
4-4
The other beacon messages do not contain any fixed data in bits 107-1102 .
These fixed bits, which immediately follow BCH-1, are used to identify a beacon message
that is corrupted due to bit-shift errors, in case the bit-shifted beacon message passes
BCH-1 error detection. After using the BCH-1 and BCH-2 to correct bit errors in the
406 MHz beacon message (as defined above), the GEOLUT shall verify the fixed bits
that begin in bit 107 for location protocol beacons (as described above).
4.2.3.2 ***C/S T.018 Beacons
The digital message transmitted by C/S T.018 406 MHz beacons includes a single 48-bit
BCH error correcting code, and correct as necessary the received 406 MHz beacon
messages.
The GEOLUT shall use the BCH to correct all messages including the frame
synchronization pattern that have a maximum of six (6) bit errors, and detect the existence
of more than six (6) errors.
The GEOLUT shall have the capability to suppress any calibration and reference beacon
messages, and pass them to the MCC only on request.
4.2.4
Beacon Message Validation
4.2.4.1 C/S T.001 Beacons
A 406 MHz beacon message is valid when the first protected field (PDF-1 + BCH-1) has
2 or less corrected bit errors and the fixed bits that start in bit 107 contain no errors.
A complete message 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 no errors or
1 corrected bit error.
Bits 113 to 144 of the second protected field of a valid long message shall all be set to
“1” if this field contains 2 or more bit errors.
4.2.4.2 ***C/S T.018 Beacons
A 406 MHz beacon message is valid when the BCH has detected 6 or less corrected bit
errors.
2 Note that beacon cancellation protocol message has fixed bits in this range as well however these bits shall not be
used in the context of the identification of a beacon message that is corrupted due to bit-shift errors
4-5
4.2.5
Beacon Message Processing
406 MHz alert data recovered by the GEOLUT, but not including ELT(DT) data acquired
through integration of successive bursts, shall be transmitted to the associated MCC for
distribution to appropriate destination(s), as provided for in the document C/S A.001 (DDP).
The GEOLUT shall confirm the validity of GEOSAR alert data whenever possible, and
process beacon messages in accordance with the principles described below.
4.2.5.1 Confirmed C/S T.001 Beacon Messages
The GEOLUT shall transmit to the MCC complete messages confirmed in accordance
with the following rules:
the first protected field (PDF-1 + BCH-1) of a valid message is confirmed when
the first protected data field (PDF-1) matches with the first protected data field of
the second message obtained as a result of an independent integration process; and
the second protected field (PDF-2 + BCH-2) of a complete message is confirmed
when the second protected data field (PDF-2) matches with the second protected
data field of the second message obtained as a result of an independent integration
process.
The GEOLUT shall also transmit to the MCC valid but incomplete long messages as soon
as the first protected field (PDF-1 + BCH-1) is confirmed as described above. In this case
bits 113 to 144 of the second protected fields shall all be set to “1”. If a complete long
message is subsequently obtained with the same PDF-1 data and confirmed as described
above, the confirmed complete message shall also be transmitted to the MCC.
In the case of ELT-DT beacons, all valid (including complete) distress messages and all
complete cancellation messages, both decoded without the use of integration, shall be
forwarded to the MCC, regardless of confirmation and the further processing pertaining
to unconfirmed message below does not apply. The GEOLUT shall send a complete
message without confirmation as soon as possible.
4.2.5.2 Unconfirmed C/S T.001 Short Message Format
If the confirmation of the first protected field of a valid short message is not achieved
within five (5) minutes from the time of its validation, this message shall be transmitted
to the MCC with the indication that it is unconfirmed.
If the confirmation of the first protected field of a valid short message is achieved after
the transmission of the unconfirmed message, the confirmed message shall also be sent
to the MCC.
4.2.5.3 Unconfirmed Long Message Format
If the confirmation of the first and second protected fields of a complete long message
format is not achieved within five (5) minutes from the time of its validation, this message
4-6
shall be transmitted to the MCC with bits 113 to 144 of the second protected field all set
to “1”, and with the indication that it is unconfirmed.
If the confirmation of the first and second protected fields, or the confirmation of the first
protected field only, are achieved after the transmission of an unconfirmed message, the
confirmed complete, or confirmed incomplete, message shall also be sent to the MCC.
Bits 113 to 144 of an incomplete message shall all be set to “1.
4.2.5.4 ***Confirmed C/S T.018 Beacon Messages
The GEOLUT shall transmit to the MCC valid messages confirmed as follows:
•
a valid message is confirmed when the 23 Hex Beacon ID matches a
second message obtained as a result of an independent integration process.
4.2.5.5 ***Unconfirmed C/S T.018 Beacon Messages
A valid message shall be sent to the MCC without delay while waiting for confirmation.
It shall be indicated that it has not been confirmed.
If the confirmation of a valid message is achieved after the transmission of the
unconfirmed message, the confirmed message shall also be sent to the MCC.
4.2.6
Redundant Alert Data
Except for the data collected as part of the QMS continuous monitoring and objective
assessment process, and except for ELT(DT) beacon messages, the GEOLUT shall suppress
redundant data as required by the MCC.
4.2.7
Updated Location Data
The GEOLUT shall provide to the MCC, in accordance with the rules set forth in 4.2.5, the
first location data acquired after the beacon has been turned on.
The GEOLUT shall then provide to the MCC only confirmed complete or confirmed
incomplete C/S T.001 beacon messages and only confirmed valid C/S T.018 beacon messages
containing location data updated in accordance with the applicable beacon specification
document.
Despite the above, in the case of ELT-DT beacons, the GEOLUT shall forward all valid
(including complete) messages to the MCC.
4.2.8
Bit-Shifted Beacon Messages
The GEOLUT shall not output to the MCC beacon messages which contain either complete
or partial bit-shifted versions of the transmitted beacon identification code caused by incorrect
bit synchronization by the GEOLUT to the beacon message’s bit and frame synchronization
pattern.
4-7
4.2.9
Special National Processing Requirements
In order to satisfy special national requirements, the associated MCC may request a GEOLUT
to transmit 406 MHz beacon alert messages which do not conform to the processing
requirements of section 4.2. However, operational alert data distributed internationally shall
always meet the requirements of section 4.2.
– END OF SECTION 4 –
5-1
5.
PERFORMANCE REQUIREMENTS
The performance requirements defined in the following paragraphs establish measurable quantities
that a GEOLUT must meet before it can be integrated into the Cospas-Sarsat System and
commissioned by the Cospas-Sarsat Council.
5.1.1
C/S T.001 Beacons
5.1.1.1 Beacon Message Processing
The GEOLUT shall be able to receive, detect, recover and provide to the associated MCC,
valid messages within 5 minutes of beacon activation with a probability of 0.95, provided that:
the beacon conforms to the coding, burst repetition and bit rate specifications detailed in
document C/S T.001;
the beacon signal was not interfered with by another emitter in the GEOSAR satellite
uplink field of view. For this particular requirement, interference is defined as any
emitter whose radiated energy occupies both the same time and frequency as the
individual bursts from the 406 MHz beacon; and
the beacon uplink signal is linearly polarised and has a transmit EIRP of:
• [32 dBm]* for GEOLUTs that operate with the MTG satellite,
• 32 dBm for GEOLUTs that operate with the MSG satellite,
• 29 dBm for GEOLUTs that operate with the GOES satellites,
• 31 dBm for GEOLUTs that operate with the INSAT satellite,
• 28.5 dBm for GEOLUTs that operate with the Electro-L satellite3, and
• 25.7 dBm for GEOLUTs that operate with the Louch satellites.
* To be confirmed during commissioning.
5.1.1.2 Beacon Message Processing for ELT(DT)s
For an ELT(DT) transmitting with an EIRP of 34 dBm, (and with the same criteria defined in
section 5.1.1 a) and b) above), the GEOLUT shall be able to receive, detect, recover and
provide to the associated MCC a complete ELT(DT) message within any one-minute period,
without message integration, with a probability of [TBD].
3 For Electro-L No. 2 (only) the beacon uplink transmit EIRP is 32 dBm. The EIRP of 28.5 dBm applies for other
Electro-L satellites.
5-2
5.1.2
C/S T.018 Beacons
The signal sensitivity threshold is the C/N0 level at which the GEOLUT 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.
The GEOLUT signal sensitivity shall be better than 30.55 dB-Hz.
Subject to the conditions described at section 5.1, and a beacon signal that completely conforms to
the specifications of document C/S T.001 or ***C/S T.018, the GEOLUT shall measure frequency
of beacon signals to an accuracy of 2 Hz4.
Due to the potential instability of the beacon frequency at the time of beacon activation, the
frequency measurement shall be based upon the most recent frequency data measured by the
GEOLUT.
C/S T.001 Beacons
The definition of capacity is provided in Cospas-Sarsat document C/S T.012 (406 MHz frequency
management plan). The GEOLUT shall support a capacity of 20 active beacons in each 406 MHz
channel.
***C/S T.018 Beacons
The GEOLUT shall support a capacity of 140 active C/S T.018 beacons.
The processing anomaly rate is the number of processing anomalies provided by the GEOLUT to
the MCC divided by the total number of valid messages produced by the LUT. The GEOLUT shall
include features, other than beacon message content validation, that reduce the processing anomaly
rate to a minimum. The ratio of GEOLUT generated false alerts caused by processing anomalies to
actual alerts shall not exceed 1 x 10-4.
4 For C/S T.018 beacons, no frequency accuracy requirement is defined.
5-3
The GEOLUT performance shall be maintained during periods of fading of the GEOSAR to
GEOLUT downlink channel as detailed in Annex A. The GEOLUT data availability specified in
paragraph 3.1 shall include the contribution of downlink outages. The design of the RF subsystem
shall be such that this overall availability is achieved considering the statistics of local rainfall and
other downlink propagation impairments.
5.6.5
Processing Bandwidth
At a minimum, the GEOLUT 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.
5.6.6
Acquisition Frequency Range5
Regarding C/S T.001 beacons, the GEOLUT shall be capable of processing transmitted beacon
signals with a deviation from the beacon centre frequency of ± 5.45 kHz.
Regarding C/S T.018 beacons, the GEOLUT shall be capable of processing beacon signals
with a centre frequency on the range 406.05 MHz ± 1.65 kHz.
– END OF SECTION 5
5 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.
ANNEXE TO
COSPAS-SARSAT
GEOLUT
PERFORMANCE SPECIFICATION
AND DESIGN GUIDELINES
A-1
GEOSAR SPACE SYSTEM PERFORMANCE PARAMETERS
AND DOWNLINK BUDGET
A.1
Introduction
Administrations intending to acquire a GEOLUT to be used in the Cospas-Sarsat System should
ensure that the station's antenna and RF subsystems will meet the Cospas-Sarsat performance
standards defined in documents C/S T.009 and C/S T.010. One way to determine this performance
is to calculate the downlink power budget for the applicable GEOSAR satellite that the GEOLUT
will track. This annex provides guidance for making these calculations. If the GEOLUT will be
capable of tracking different types of GEOSAR satellites, then these calculations should be
completed for each type of satellite used.
A.2
Explanation of the downlink budget
TBD Information for the completion of this section will need to be provided by the applicable
GEOSAR space segment providers. A separate description will be needed for each type of
GEOSAR satellite. This information could be placed either here or in document C/S T.011
(description of GEOSAR payloads).
A.3
Calculations
TBD Information for the completion of this section will need to be provided by the applicable
GEOSAR space segment providers. A separate description will be needed for each type of
GEOSAR satellite. This information could be placed either here or in document C/S T.011
(description of GEOSAR payloads).
A-2
GEOSAR Search and Rescue Repeater Link Budget - Nominal Link
GOES
MSG
INSAT**
MTG
Beacon EIRP (Linear Pol.)
7 dBW
7 dBW
4 dBW (RHCP)
7 dBW
Path Loss (5 Degree Elevation)
176.9 dB
176.9 dB
176.9 dB
176.9 dB
Polarization Loss
4.1 dB
5.0 dB
0.0 dB
(Rx RHCP)
5.0 dB
Spacecraft G/T
-18.5 dB/K
-19.5 dB/K
-19.0 dB/K
-15.5 dB/K
Boltzmann’s Constant
-228.6 dBW/kHz
-228.6 dBW/kHz
-228.6 dBW/kHz
-228.6 dBW/kHz
Uplink C/N0
36.1 dB-Hz
34.2 dB-Hz
36.7 dB-Hz
38.2 dB-Hz
Transmit EIRP
15 dBW
4 dBW
2.5 dBW*
Modulation Loss (1.0 Rad)
2.0 dB
NA
Power Sharing Loss (80 kHz BW)
13.1 dB
17 dB (including
modulation loss)
13.6 dB*
Transmit EIRP per Beacon
-0.1 dBW
-15.1 dBW
-13 dBW
-11.1 dBW
Path Loss (5 Degree Elevation)
188.5 dB
188.5 dB
196.9 dB
188.5 dB
Polarization Loss
0.3 dB
0.3 dB
0.0 dB
0.3 dB
Boltzmann’s Constant
-228.6 dBW/kHz
-228.6 dBW/kHz
-228.6 dBW/kHz
-228.6 dBW/kHz
Ground Station G/T
11 dB/K
14.5 dB/K
29.5 dB/K
15.5 dB/K
Downlink C/N0
50.7 dB-Hz
39.2 dB-Hz
48.2 dB-Hz
41.1 dB-Hz
Composite C/N0
36.0 dB-Hz
33.0 dB-Hz
36.4 dB-Hz
36.4 dB-Hz
* The nominal EIRP and the Power Sharing Loss are computed with FGM step 9 and assumed loading scenario is two beacons
operating at nominal levels (EIRP=37 dBm) and 3 additional beacons at EIRP 3 dB higher.
** As per the specifications of the INSAT-3D, INSAT-3DR, GSAT-17 and INSAT-3DS SAS&R payloads. The INSAT-3D
SAS&R payload uses a downlink frequency of 4.507 GHz. The INSAT-3DR, GSAT-17 and INSAT-3DS SAS&R payloads use a
downlink frequency of 4.5042 GHz.
A.4
Summary
Administrations should ensure that their GEOLUT antenna G/T value, when combined with the
other losses, will provide a positive value for the link margin.
- END OF ANNEX A -
- END OF DOCUMENT –
Cospas-Sarsat Secretariat
1250 René-Lévesque Blvd. West, Suite 4215, Montréal (Québec) H3B 4W8 Canada
Telephone: +1 514 500 7999
Fax: +1 514 500 7996
Email: mail@cospas-sarsat.int
Website: http://www.cospas-sarsat.int
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