ACP-WG-F/16 & NSP SSG IP08
INTERNATIONAL CIVIL AVIATION ORGANIZATION
Combined Meeting of
AERONAUTICAL COMMUNICATION PANEL WORKING GROUP F (WG-F/16)
and
Navigation Systems Panel Spectrum-Sub-group (SSG)
(Montreal, 11 – 15December 2006)
Agenda Item 2: Review of the output of the last ICAO NSP SSG meeting
FINAL REPORT
OF THE
ICAO NSP SPECTRUM SUB-GROUP (SSG) MEETING
10th to 13th October 2006, ICAO Headquarters, Montreal
Prepared / Presented by: Felix Butsch, rapporteur of the ICAO NSP Spectrum Sub-group
SummaryThis information paper presents the final report of the ICAO NSP Spectrum Sub-group 10th to 13th October 2006, ICAO Headquarters, Montreal.It was published as attachment F of the final report of the ICAO Navigation Systems Panel of the Working Group of the Whole Meeting Montreal, Canada, 10 – 20 October, 2006.
I. Introduction
The meeting of the GNSSP Spectrum Sub-group (SSG) was held at ICAO Headquarters, Montreal from 10th to 13th October 2006. Mr. Felix Butsch, the rapporteur of the Spectrum Sub-group, chaired the meeting. The spectrum sub-group expressed its appreciation to the ICAO secretariat for hosting the meeting. Working and information papers are listed in attachment A. Attachment B contains a list of action items and actionees. Attachment C provides a list of participants.
The agenda for the meeting was as follows:
Agenda Item 6: Spectrum
6 a):Future use of the band 960 to 1215 MHz
6 b):Future use of the band 5030 to 5150 MHz
6 c):Protection requirements for the Microwave Landing System (MLS)
6 d):Update of guidance material on VOR and DME service volumes
6 e): Updating of SARPs for terrestrial radio navigation aids
6 f):Characterization of new GNSS signals
6 g):Navigation data links in the band 108 to 117.975 MHz
6 h):Guidelines for the safe use of GNSS re-radiators in aviation
6 i):Preparation of World Radio Conference 2007
6 j):Other issues
Note: Agenda item 6 i) ‘Preparation of World Radio Conference 2007’ has been added to the agenda at the meeting.
II. Results of the Discussions
Agenda Item 6 a): Future use of the band 960 to 1215 MHz
Note: The intended purpose of this agenda item was to cover World Radio Conference (WRC) related issues of the use of the band 960 to 1215 MHz. However, since some input documents on this subject address the future use of various bands, the new agenda item 6 i) was formed, to cover all WRC related issues.
Agenda Item 6 b): Future use of the band 5030 to 5150 MHz
Note: The intended purpose of this agenda item was to cover World Radio Conference (WRC) related issues of the use of the band 5030 to 5150 MHz. However, since some input documents on this subject address the future use of various bands, the new agenda item 6 i) was formed, to cover all WRC related issues.
Agenda Item 6 c): Protection requirements for the Microwave Landing System (MLS)
WP33, “To explain, why noise was not taken into account for the derivation of the values in the table in Appendix C of ICAO, NSP May06 WG1&2/WP6”,
6cX) At the end of the meeting further information was provided by the member of the group, who submitted WP33. In the light of this information that member withdrew WP33. The meeting agreed that the contents of WP33 shall not be further considered. Therefore, action SSG9/13 is still open. A WP on the same issue to be submitted to the next meeting was announced. The above-mentioned member expressed the view that based on the new information (not available at this SSG meeting) will likely lead to an aggregated interference threshold of 120 dBm (compared with the existing –130 dBm).
Note: Sections 6c1) to 6c5) have been deleted from the report, since WP33 was withdrawn at the end of the meeting.
WP 20-rev1, “MLS Interference issues”,
6c6) The group noted, the main goal of WP20 to develop in-band interference susceptibility limits for MLS to be used in the definition of planning criteria needed to sharing of the MLS band with other services operating in part of the MLS band or in the adjacent bands (e.g. aeronautical mobile telemetry and ground AM(R)S applications). WP20 presents an approach, which differs from the approach pursued to date by ICAO, which specifies in its recently updated guidance material (Att. G of Annex 10) a pure Signal-to-Interference (S/I) threshold. By assuming that a Signal-to-Noise-plus-Interference ratio, S/(N+I) threshold would be compatible with the allowable Control Motion Noise Error (CMN) as long as the stipulated 95 % probability limit is not exceeded. With this assumption, WP20 comes to the conclusion, that anI/N ratio of -14 dB would be suitable. This would result in an aggregate interference threshold of I = -120 dBm. Compared with the currently applicable value of –130 dBm, this would mean, that the allowable in-band MLS external interference limit could be relaxed by 10 dB.
6c7) Various members of the group pointed out, that due to sampling and usage of sliding window methodology (guidance material Figure G-12, MLS measurement methodology), the assumption of Gaussian distribution for the CMN errors to determine the -14 dB is not acceptable for test validation and that a sliding window in time as indicated by the GM fig. G-12 should be used. The group agreed that those bench tests need to be carried out before the SSG can conclude on any relaxation of the aggregate interference threshold of MLS.
Flimsy6, “Difference of opinions regarding the use of the MLS SARPS Att G. 2.6.1.2 formula between WP 33 and WP20 to derive SNR requirement as the result of incremental change in d”,
6c8) Flimsy6 was presented to the SSG to further explain details contained in WP20. The group noted the contents of this paper. It agreed however, that at this point in time it was not in the position to draw firm conclusions on the raised issues. The group encouraged re-submission of the material contained in Flimsy6 as an official working paper to its next meeting. [Post- meeting note: since WP 33 has been withdrawn (see 6cX), Flimsy 6 should no longer be considered]
Flimsy7, “Applying the ITU-R.S1342 RFI susceptibility limits to candidate ground AM(R)S, AMT and AS (Aeronautical Security) services/application in the MLS extension band 5091-50150 MHz”,
6c9) Concerns were expressed in Flimsy7, that a problem may arise to operate ground-AM(R)S (i.e. airport data links) in the MLS band, if –130 dBm is still considered as aggregate interference level. The group was of the view that a position on the issue of ‘aggregate’ versus ‘single entry’ susceptibility limits to protect MLS needs to be developed by SSG and presented to ITU.
6c10) Other members of the SSG pointed out, that the ground equipment AM(R)S antenna gain, and tilt would possibly mitigate the problem. Furthermore, the ICAO secretariat reminded the meeting, that ITU-R.S1342 only addresses trigger values for coordination between FSS feeder links vs. MLS. FSS mobile earth stations however are usually well apart from airports. Therefore, the application ground-AM(R)S in this band would still be possible.
6c11) One expert expressed the view, that according to one ITU footnote 5.443B the value of –124.5 dBW/m2 (–130 dBm for an isotropic antenna) is an aggregate limit per RNSS system, not an aggregate value for all systems.
6c12) Several experts expresses the view that –120 dBm is the appropriate value for an aggregate interference threshold. However, the meeting agreed, more evidence should be made available to confirm this value. At this point in time, with the given information, the group was not in the position to change its position, considering –130 dBm as an aggregated value.
WP4, “Methodology for the Development of D/U Criteria for MLS Frequency Planning”
6c13) The group noted, that this paper presents a method for the derivation of Desired-to-Undesired ratios (D/U) for the purpose of frequency coordination of MLS from required SNR values stipulated in ICAO Annex 10, for the strong signal region of the service volume (Region 1) and the rest of the service volume (Region 2). For this purpose, it is assumed that the receiver noise level is increased by a combination of co-channel interference noise and noise caused by extraneous interference.
It further assumes that allowable noise power caused by co-channel interference is 2.5 times the thermal noise and the allowable contribution of the extraneous interference is 0.5 times the thermal noise. With theses assumptions D/U ratios are derived for the Region 1 ((D/U)CO,1) and Region 2 ((D/U)CO,1).
6c14) The SSG agreed on the general concept of deriving D/U values for the purpose of frequency coordination from required minimum SNR values stipulated in ICAO Annex 10. However, members of the group emphasized that the term “Region” was misleading, since the two tables containing SNR values for a strong and a weak signal cases independently of the specific locations within the designated coverage area. . It was further pointed out, that there is only a need to take into account the SNR values in Table X2 of section 3.11.6.1.4 of ICAO Annex 10 dealing with the weak signal case. It was further mentioned during the discussion, that there is no need to take into account co-channel interference, since for the co-channel, first and second adjacent channel ICAO Annex 10 requires that MLS stations be separated by the radio horizon, plus a certain margin to cover beyond the horizon propagation. Moreover, it was pointed out that it can be safely assumed that noise cause by extraneous is sufficiently below the thermal noise level, and has therefore not to be taken into account. That means that for the derivation of the D/U, only contributions of interference of adjacent channels from the third onwards have to be taken into account.
6c15) During the discussion, it was further pointed out, that for this purpose it may be a problem that there is no emission mask standardized in the MLS SARPs. The group agreed that the MLS ad hoc group of ICAO EANPG should further refined the MLS coordination criteria based on the guidance of SSG mentioned above. If an emission mask for MLS would be developed in this context, the ICAO NSP CN&TSG in conjunction with SSG would be the right place to carry out the necessary drafting of a revision of the MLS SARPs. A member of the SSG emphasized that any emission mask for MLS developed by ICAO groups should be compatible with the generic emission masks in ITU-R.SM-329.
6c16) In this context it was also mentioned by a member of the SSG, that it would be desirable thatCN&TSG finalizes the draft of the Volume III, “Microwave Landing System” of ICAO DOC 8071. Inspection of the draft version of this document dating from Nov. 1989 gave the impression, that such a document could provide a valuable system documentation that is useful for the work of the SSG.
WP43, “AMT-MLS Coordination distance formula derivation”,
6c17) WP43, provides the derivation of the ‘bilateral coordination trigger distance’ between two ITU administrations concerned with the authorization of aeronautical mobile telemetry (AMT) operations in one country in case of interference risk potential to an MLS station in a neighboring country. The group noted that currently in the CPM text, the equation for the bilateral coordination trigger is based upon the –130 dBm single-entry interference threshold. No detailed discussion of this topic took place in the SSG.
WP42, “MLS external interference susceptibility test-plan”,
6c18) In WP42 a revised test-plan for MLS external interference susceptibility measurements was presented to the group. The goal of such measurement would be, to perform the tests to establish the MLS protection criteria against wideband aeronautical telemetry signals. The group agreed in general with the proposed test plan, which is based on a test procedure established in document ICAO/NSP WGW-WP/50, St. Petersburg, Russia, 25 May-4 June 2004 prepared by P. Gayraud and S. Devaux of Thales. One member of the group expressed the view if the receiver characteristics of a tested receiver differ considerably from the SARPs, that fact needs to be taken into account in the conclusions or the test procedure. Furthermore, the sliding window techniques, i.e. the MLS measurement methodology as defined in Figure G-12 of the MLS guidance material should be applied.
6c19) Members of the group mentioned that the results of such measurements may have implications not only for AMT, but also for the compatibility of other services with MLS. Other members of the SSG expressed there opinion that very long measurement times may be necessary to determine the expected very small increases of Control Motion Noise near the interference threshold ( = 0.005°) with a reasonable statistical confidence, making such a measurement not achievable in practice
6c20) Members of the group pointed out, that it had been announced to the SSG already at its last meeting, that results of such tests would be available to this meeting. It was told to the group that, this was not possible due to lack of resources. However, it was likely, that such material will be presented to the SSG meeting in March 2007.
Agenda Item 6 d) Update of guidance material on VOR and DME service volumes
WP32, “DME Power Availability Curves and Service Volumes -How to deal with DME service volumes straddling at 18,000 feet”
6d1) WP32 presents the answer to Question SSG9/10 on DME service volumes straddling at 18,000 feet. The issue, how to deal with DME service volumes straddling at 18,000 feet arose during the discussion of SSG9/WP38. In this paper it was mentioned, that in the United States, there are three different categories of DME facilities, namely high altitude en-route DME (upper limit 60,000 feet), low altitude en-route DME (upper limit 18,000 feet) and terminal DME facilities (upper limit 12,000 feet). Some low altitude DME facilities have service volumes that extent into airspace above 18,000 feet. For these expanded service volumes there are two different min. power density values, namely -91.5 dBW/m² in the part of the service volume above 18,000 feet and 86dBW/m², below 18,000 feet.
WP37, “DME Power Availability Curves and Service Volumes - To provide further background information on the “discontinuities” in the DME propagation curves”
6d2) WP37 is in response to action item SSG9/9, which request to provide further background information on the “discontinuities” in the DME propagation curves, whether they are due to antenna lobing or due to multipath. The meeting was informed that the power density curves in the applicable national standards for DME in the United States are based on the IF-77 wave propagation model considers various tropospheric radio propagation effects, lobing and time availability as well as specific ground equipment parameters such as vertical/horizontal antenna pattern, antenna height, EIRP, diameter of counterpoise. Reflection or multipath due to any man-made objects is not considered in the IF-77 model. However single ground reflection is considered. The paper did not provide a firm conclusion on the cause of the “discontinuities”.
6d3) During the discussion of WP37 several members of the group expressed the view that the most likely cause of the “discontinuities” single ground reflection.
Action item SSG10/1: Robert Frazier (US) to further clarify the reason for “discontinuities” in the DME propagation curves.
WP31, “IF-77 Radio Frequency Propagation Model Description”
6d4) WP31 is in response to action item SSG9/7, which requests the United States to provide background information on the “IF-77” model for radio coverage analysis for a variety of systems. The group learned, that this model is applicable to air/ground, air/air, ground/satellite, and air/satellite paths at radio frequencies from about 0.1 to 20 GHz. Currently the model is available only as a DOS executable from the web site of the NTIA-Institute of Telecommunication Service. However, FAA is developing a windows front-end interface to allow for more efficient use of the model.
Typical outputs of the IF77 Windows software are plots of “Power Density vs. Distance for a given aircraft altitude” and “Power density contour”, i.e. distance vs. aircraft altitude”. Appendices of WP31 provide IF-77 model input variable definitions as well as a sample input file and a sample output file.
6d5) A general discussion on the way forward concerning the update of guidance material on VOR and DME service volumes took place. Various members of the group pointed out, that a recommendation to use of the IF77 propagation model would yield more realistic results, than the usage of the curves in the existing guidance material. However, it was also made clear, that the pre-requisite of such a recommendation would be that the IF77 model is public domain.
6d6) One member of the group offered to provide background material on the algorithms used in IF77 and the comparison of the results of calculations of IF77 and flight inspections. The group learned from the US that it is likely that these documents are releasable, but this needs to be checked. The group learned that the MS-Windows interface for a DOS-implementation of IF77, which is being developed by the US, is likely to be made publicly available shortly, but this needs to be verified.
6d7) An ad-hoc group was established to develop mature guidance material on VOR and DME service volumes based on WP26, WP37, WP38 and IP10 of the previous ICAO NSP SSG meeting in Brussels in May 2006 (SSG9), as well as WP31 of this meeting and other available documentation of the IF77 propagation model. This group will be chaired by Joachim Wollweber (Germany). It shall work by correspondence with the goal to present proposed guidance material at the March 2007 meeting of the group. Russia, the United States and Great Britain offered their contribution. The group agreed that also the characteristics of typical DME and VOR ground facilities should be taken into account. A recommendation to use the IF77 model and inclusion of the results of the IF77 model with typical input scenarios is desirable.
6d8) In the context of the discussion of Flimsy4, which is dealing with a request of CN&TSG to SSG to make a consolidated proposal of revised guidance material for conventional navaids it was decided to widen the task of the group to the preparation of proposed revised guidance material for GBAS frequency coordination (see discussion of Flimsy4). Since there may also be an impact on GRAS due to any change of guidance material for GBAS, Australia offered also its cooperation.
Note: The group agreed to delete action item SSG10/2 during its review of the draft report by the meeting.