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AERONAUTICAL COMMUNICATIONS PANEL (ACP)
29th MEETING OF WORKING GROUP F
Nairobi, Kenya, September 2013
Agenda Item 7: / Development of material for ITU-R meetingsITU Inputs Regarding FSS Performance
(Presented by Mike Biggs)
SUMMARYThe required communications performance levels that will enable unmanned aircraft systems (UAS) to operate safely and efficiently and in a manner compatible with the use of current non-segregated airspace are yet to be determined by ICAO. In parallel, the International Telecommunications Union (ITU) is developing a Report which contains, in part, availability performance for fixed satellite service (FSS) systems to help determine if those systems are suitable for UAS. Since the decision on suitability cannot be made until the requirements are completed, this paper suggests limiting the ITU responsibility to simply cataloguing the FSS performance.
ACTION
The paper proposes that the meeting endorse limiting ITU tasking to providing ICAO with FSS Fade Duration and Interfade Intervals using the methods described in ITU-R P.1623. Once ICAO has determined the performance requirements for UAS links it will then be able to use that material to assess the suitability of FSS for that function. The meeting is also encouraged to liaise this approach to ITU Working Party 5B.
1.0BACKGROUND
1.1The required communications performance levels that will enable UAS to operate safely and efficiently and in a manner compatible with the use of current non-segregated airspace are yet to be determined by ICAO. In their work so far ICAO has been considering, as a basis for the analysis, the work that they have previously completed for the required communication performance of the system that supports voice and data communications between the pilots and air traffic controllers defined in ICAO’s “Manual on Required Communication Performance (RCP). ICAO Document 9869”.
1.2The ICAO RCP Manual defines four parameters that can be used to characterize the required communications performance of any communications system (i.e., wired or wireless, terrestrial LOS or satellite). These four parameters are defined below.
- Availability: The probability that an operational communication transaction can be initiated when needed.
- Continuity: The probability that an operational communication transaction can be completed within the transaction time.
- Integrity: The probability of one or more undetected errors in a completed communication transaction.
- Transaction time: The maximum time for the completion of the operational communication transaction after which the initiator should revert to an alternative procedure.
1.3The key question that ICAO will have to answer is what RCP Type (a combination of Transaction Time, Integrity, Availability and Continuity) will be required for safe and efficient operation for each category of UAS, and in each class of airspace. After this determination ICAO will then be able to assess if unmanned aircraft system (UAS) control and non-payload communications (CNPC) links using applicable allocations (e.g., AM(R)S, AMS(R)S, AMSS or FSS) can provide this level of RCP under the conditions required.
2.0ITU ACTIVITIES
2.1From ITU’s perspective, analyses to date have resulted in levels of “ITU Availability” for various FSS link parameters and operating conditions (see Preliminary Draft New Report ITU-R M.[UAS-FSS]). However ITU Availability is not exactly the same as ICAO Availability. Additionally ITU does not explicitly address ICAO Transaction Time, Integrity or Continuity in their analysis.
2.2Various ITU documents define ITU Availability; typical of these is for example ITU-R S.579, which defines Availability for Hypothetical Reference Digital Paths as:
“ Availability = (100 – unavailability) %
where:
%
where the required time is defined as the period of time during which the user requires the digital path to be in a condition to perform a required function, and unavailable time is the cumulative time of digital path interruptions within the required time.”
3.0 DISCUSSION
3.1Statistically these ITU time-based definitions are equivalent to the per-attempt based definition for Availability used by ICAO, and both ITU and ICAO definitions include not only propagation related unavailability but also unavailability due to equipment malfunction. However these ITU definitions also include criteria for what constitutes an unavailable path. For example ITU-R S.579 defines the path to be unavailable if the digital signal is interrupted (i.e. alignment or timing is lost) or if the bit error ratio (BER), averaged over 1 s, exceeds 10−3. ICAO’s definition of Availability provides no such criteria.
3.2So ITU Availability can only be considered equal to ICAO Availability if the (unlikely) situation arises that the ICAO criteria that determine if a path is unavailable are the same as those used by ITU in its analysis of Availability. ICAO has not yet determined these parameters for CNPC links of any type.
3.3Additionally ITU does not explicitly consider ICAO Continuity in its analysis. However ITU-R P.1623 does provide the ability to calculate the fade durations that an FSS link will experience so using the analysis contained in ITU-R M.[UAS-FSS] ITU can provide this data to ICAO. Again ICAO has not yet determined the Transaction Time for CNPC information exchanges, so it is currently not possible to provide the time basis for any ICAO Continuity assessment by ITU.
4.0CONCLUSION AND RECOMMENDATION
4.1To resolve this situation it is proposed that, regarding the issue of availability provided in PDNR ITU-R M.[UAS-FSS], ITU tasking be limited to adding Fade Duration and Interfade Intervals using the methods described in ITU-R P.1623 to PDNR ITU-R M.[UAS-FSS]. Once ICAO has determined the RCP Type (levels of Availability, Continuity, Integrity and Transaction Time) required for CNPC links it will then be able to use the ITU Report to assess the suitability and/or necessary mitigations to allow the use of FSS for UAS CNPC links.
4.2The meeting is encouraged to endorse this way forward with regard to the development of ITU-R M.[UAS-FSS], and to liaise this approach to ITU Working Party 5B (the responsible group for PDNR ITU-R M.[UAS-FSS]). Elements for such a liaison statement are contained in Annex 1.
Annex 1: Elements for an ICAO Liaison to ITU-R Working Party 5B
The following text elements are provided as a basis for an ICAO liaison to WP5B on FSS performance characteristics.
The required communications performance (RCP) levels that will enable UAS to operate safely and efficiently and in a manner compatible with the use of current non-segregated airspace are yet to be determined by ICAO. The key question that ICAO will have to answer is what RCP Type (a combination of Transaction Time, Integrity, Availability and Continuity) will be required for safe and efficient operation for each category of UAS, and in each class of airspace. After this determination ICAO will then be able to assess if unmanned aircraft systems (UAS) command and non-payload communications (CNPC) links using applicable allocations can provide this level of RCP under the conditions required.
Working Party 5B, as the responsible group for World Radiocommunications Conference 2015 Agenda Item 1.5, is developing a Report which includes material dealing with “ITU Availability” for various FSS link parameters and operating conditions (see Preliminary Draft New Report (PDNR) ITU-R M.[UAS-FSS]). Questions have arisen as to how to determine if the documented FSS performance is suitable for UAS CNPC. As noted above however, performance requirements necessary to ensure suitability have yet to be developed by ICAO.
To resolve this situation it is proposed that, regarding the issue of availability provided in PDNR ITU-R M.[UAS-FSS], ITU tasking be limited to adding Fade Duration and Interfade Intervals using the methods described in ITU-R P.1623 to PDNR ITU-R M.[UAS-FSS]. Once ICAO has determined the RCP Type (levels of Availability, Continuity, Integrity and Transaction Time) required for CNPC links it will then be able to use the ITU Report to assess the suitability and/or necessary mitigations to allow the use of FSS for UAS CNPC links.
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