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ACP/1-WP/28
/
International Civil Aviation Organization
WORKING PAPER / ACP/1-WP/28
9/5/07
English only

AERONAUTICAL COMMUNICATIONS PANEL (ACP)

FIRST MEETING

Montréal, 10 to 18 May 2007

Agenda Item / 1: / Review of the progress on the future communication study

PERFORMANCE OF AERONAUTICAL COMMUNICATION SYSTEMS

(Presented by the Secretary)

SUMMARY
This paper identifies the need for a general review on performance-related provisions for communication systems as contained in Annex 10, Volume III.
Action by the ACP is in paragraph 5.

1.INTRODUCTION

1.1With the increasing emphasis being placed by the Organization on the performance of the air navigation system as a whole, which is evident from the effort spent on the development of required communication performance (RCP), required surveillance performance (RSP) and required navigation performance (RNP), there is a need for a general review of performance in various aeronautical communication systems.

2.background

2.1The Secretariat highlighted the issue of inconsistency in existing integrity-related provisions of Annex 10 — Aeronautical Telecommunicationsat the eighth meeting of the Aeronautical Mobile Communications Panel (AMCP/8)by presenting a working paper entitled “Integrity considerations in end-to-end communication performance requirements”. A copy of the subject working paper is provided in the appendix for ease of reference.

2.2Although the correctness of the material contained in the paper was not disputed, no proposal was eventually formulated to undertake the work as proposed in the working paper (AMCP/8 Report, Agenda Item 7, Paragraph 7.4 refers).

2.3Many examples can be given to show the degree of inconsistency between various chapters of Annex 10 which have been developed by different groups at different times. For example, the term “transit delay” refers to 95 percentile in the ATN SARPs but has the meaning of “mean” in HFDL SARPs (the term “transfer delay” is used in the latter for 95 percentile).

2.4Since AMP/8, further developments in ICAO, some of which are mentioned below, have provided additional support to the notion of performance-oriented standardization:

a)the 35th Session of the Assembly held in 2004 reiterated the Resolutions adopted at previous sessions which placed emphasis on the development of performance-based ICAO provisions (Resolutions A35-14 Appendix A and A35-15 Appendix B refer);

b)ALLPIRG/5 meeting in 2006 adopted a conclusion calling for ICAO to develop provisions governing the end-to-end performance of digital communication systems (in the context of ground-ground communications) irrespective of the technologies and protocols used therein (ALLPIRG/5 Report, Conclusion 5/17 refers);

c)new SARPs relating to required communication performance (RCP) have been developed and adopted by the Council for inclusion in Annexes 6 and 11 with the applicability date of 22 November 2007. Associated guidance material is to be published in the form of a manual; and

d)the Worldwide Symposium on Performance of the Air Navigation System was held at the ICAO Headquarters from 26 to 30 March 2007. The symposium findings which will be presented to the next Session of the Assembly later this year, support the notion of collaborating on the establishment (& monitoring) of performance indicators.

In summary, the trend to concentrate on performance has considerably gained pace during the past couple of years.

3.rcp provisions

3.1
As stated earlier, new provisions have been developed for the definition of RCP values as well as for their operational use. The table below (extracted from the draft RCP manual) shows the recommended RCP values for air-ground communications:

3.2As the subject manual is being published as an ICAO document, it is prudent to ensure a logical relationship between the figures contained therein and those shown for various standardized systems in Annex 10. For example, while SARPs for most air-ground data links and subnetworks do contain figures for “integrity” and “transit/transfer time” (presumably closely related to “transaction time”), they do not address continuity an availability. Moreover, the relationship between an absolute “probability” and “probability per flight hour” as to a typical air-ground communication system has not been explained anywhere in ICAO documentation.

4.conclusion

4.1Performance-related provisions for aeronautical communication systems and services have been developed by different groups and at different times. As a result, they lack uniformity and consistency. Moreover, there are no formal performance requirements for ground communication systems supporting aeronautical fixed service and other emerging applications.

5.ACTION BY THE ACP

5.1The ACP is invited to:

a)note the recent developments in ICAO towards a performancebased air navigation system;

b)recognize the need to review, update and align existing performance-related provisions for aeronautical communication systems taking into account relevant RCP provisions; and

c)agree to include the necessary work in the proposed future work programme of the panel.

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A-1 / ACP/1-WP/28
Appendix
ACP/1-WP/28
Appendix

APPENDIX

AMCP/8-WP/38

6/1/03

AERONAUTICAL MOBILE COMMUNICATIONS PANEL (AMCP)

EIGHTH MEETING

Montreal, 4 to 13 February 2003

Agenda Item / 7: / Future work

INTEGRITY CONSIDERATIONS IN ENDTOEND COMMUNICATION PERFORMANCE REQUIREMENTS

(Presented by the Secretary)

SUMMARY
This paper identifies the need for development of generic end-to-end performance requirements relating to aeronautical communications for inclusion in Annex10, VolumeIII, PartI, Chapter2 (General) and discusses refinement of the existing integrity-related provisions in Annex10.
Action by the AMCP is in paragraph4.

1.INTRODUCTION

1.1The Aeronautical Communications Panel (ACP) will be the one and only body of experts in ICAO which deals with all aspects of aeronautical communications. As the panel would no longer be concerned only with one or a number of sub-systems or specific technologies, it will be well placed to pay more attention to end-to-end system-level, functional and performance requirements (as stated in Assembly ResolutionA33-14, AppendixA).

1.2This paper identifies a need to develop end-to-end performance requirements for conducting air traffic services communications (ATSC) over a generic air-ground or ground-ground communication channel. In that context, the paper also suggests that current integrity requirements that are contained in Annex10 need further clarification and refinement.

2.discussion

2.1Communication, by nature, is an end-to-end function. The current activities in ICAO pertaining to the required communication performance (RCP) is a step towards concentrating on end-to-end requirements. This doesn’t negate the need to have adequate technical provisions for various subsystems that make the end-to-end communications possible. Rather, it implies that it should be possible for a system designer to establish the end-to-end performance parameters (e.g.transit time/residual error rate for data and audio delay for voice) that could be expected if a certain combination of air-ground and/or ground-ground links/subnetworks were employed to construct the communication system. In fact, the application of the “RCP concept” would require that communication systems be classified according to their “Integrity”, “Availability”, “Continuity” and “Communication process time”.

2.2One of the most important end-to-end performance parameters is “Integrity”. According to ATN SARPs (contained in Annex10, VolumeIII, PartI, Chapter3), “Data integrity” is defined as “The probability that data has not been altered or destroyed”. Some closely related terms like “Residual error probability” and “residual error rate (RER)” have also been defined in Manual of Technical Provisions for the Aeronautical Telecommunication Network (ATN) (Doc9705).

2.3The following is a listing of integrity-related provisions contained in Annex10, VolumeIII:

Subnetwork / Residual Error Rates (Probability of undetected errors)
AMSS / 10-6 (to aircraft) and 10-4 (from aircraft)
VDL Mode 2 / 10-4 ---Maximum corrected bit error rate
VDL Mode 3 / 10-3 ---Maximum uncorrected bit error rate
VDL Mode 4 / 10-4--- Maximum uncorrected bit error rate
HFDL / 10-6
SSR Mode S / Not specified
ATN End System / 10-8 (as per 3.4.28 in ATN SARPs)

Note. — (to 3.4.28).— It is assumed that ATN subnetworks will ensure data integrity consistent with this system level requirement.

2.4An examination of the above list reveals a few problems:

a)the terminology used in different subnetworks is not uniform, simple and user friendly;

b)the terms “maximum corrected/uncorrected bit error rate” have not been defined;

c)no such requirements have been specified for ground (fixed) subnetworks; and

d)it is not clear if all the listed subnetworks can ensure that their data integrity is in fact consistent with the ATN system-level requirement. Furthermore, there are no stated criteria for determining the said consistency.

2.5The problems identified in c) and d) above are of special concern. It is known that most subnetworks employ error detection/correction schemes to improve data integrity. It is also known that for any individual subnetwork, the RER can be measured (under nominal conditions) and compared to what has been specified in SARPs. However, a typical communication system comprises several different subnetworks of varying types (fixed/mobile or private/public). It would therefore be desirable to estimate or calculate the expected end-to-end RER using values given for the constituting individual subnetworks. The expected value can later be verified with actual measurements when the system has been implemented.

2.6Another point to consider is that a constituting subnetwork which has a high RER will prolong the end-to-end transit time of the messages due to re-transmission of corrupted packets. In other words, the transport mechanism of the end system may yield acceptable end-to-end RER but at the cost of unacceptable transit delay (as specified in Table3-1 of ATN SARPs).

2.7The existence of proper end-to-end performance requirements is also important from another perspective. Many States may decide to lease communication services from international aeronautical communication service providers. Those States, would not be engaging in detailed engineering and implementation work (due to various technical, operational or economical reasons) and thus, would not be concerned with details of specific subnetwork(s), but they do need clear ICAO provisions pertaining to “grade of service”. Such provisions, which also involve end-to-end performance requirements, would assist States in their dealings with service providers. In this regard, it is worth noting that the meeting of the AFI Planning and Implementation Regional Group (APIRG) will consider a draft conclusion (formulated by AFI ATN Task Force Meeting (29 to 31May 2002)) calling for the development of such material by ICAO.

3.conclusion

3.1Aeronautical safety communications can be conducted over a variety of standardized (or to be standardized) systems. There is therefore a need to have clear and concise ICAO provisions relating to end-to-end performance requirements that should be achieved regardless of the types/combination of various constituting subsystems. Such provisions could also serve as “acceptability criteria” for evaluating emerging or future systems.

3.2Chapter2 of Annex10, VolumeIII, PartI, which is designated as “general”and “to be developed” is a suitable placeholder for the subject performance requirements.

3.3There is a particular need to elaborate on and refine current provisions relating to “data integrity” in Annex10. Specially, some criteria are needed to determine if a subnetwork (or a number of connected subnetworks) with a given RER meets the overall end-to-end integrity requirements.

4.action by the meeting

4.1The AMCP is invited to agree that the following be included in the future work (to be progressed by the ACP):

a)development of generic end-to-end performance requirements relating to aeronautical communications for inclusion in Annex10, VolumeIII, PartI, Chapter2 (General); and

b)refinement of the existing integrity-related provisions in Annex10 as discussed in this paper.

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