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ACP-WGWF23/WP-XX
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International Civil Aviation Organization
WORKING PAPER / ACP-WGWF23/WP-02
07/06/05

AERONAUTICAL COMMUNICATIONS PANEL (ACP)

23rd MEETING OF WORKING GROUP (WG F)

Cairo, Egypt 25 – 27 September 2010

Agenda Item 3: / Development of material for ITU-R meetings

AM(R)S-ARNS/MLS compatibility analysis in the 5030 – 5091 MHz band

(Presented by Gerlof Osinga)

SUMMARY
The NSP/SSG has engaged in a detailed review of WP 65 Annex 1 band sharing study and specifically of an AM(R)S-ARN/MLS compatibility analysis, with the proposed AM(R)S limited to line-of-sight radio links of unmanned aircraft systems(UAS) for control and non payload communications, operating in the band 5030-5091 MHz , where the MLS requirements have precedence over all other uses .
ACTION
Correct equation (1) section 3 and verify the consequent tables.
Concur with the NSP recommendation to ICAO not to endorse the WP 65 findings in terms of decreased distance and frequency separations proposed therein to ensure AM(R)S-MLS compatibility using the afore mentioned reduced alternative MLS interference threshold
To note that Table 3 is not consistent with previous studies that ICAO submitted to ITU that for the co-channel protection of MLS receiver it requires a separation distance to be over the horizon. See Annex 10 Volume I, Attachment G paragraph 9.3.1.
To note that Table 4 implies that the freedom of ICAO to re-assign MLS channels in an ICAO region , as is the case in Europe with in the COM-3 assignments table, will be lost and that since part of the MLS band would have to be assigned exclusively to the proposed UAV AM(R)S ]
To update the WP65 Annex 1 equation (10) calculation assuming a w.c. MLS DPSK/OCI gain of 8 dBi, i.e. with an MLS EIRP of 51 instead of 43 dBm
To take into account the capacity constraints as given in section B2 of this paper.
To note the comments as provided by a manufacturer of UAV systems with respect to the data-link requirements.

1.  INTRODUCTION

1.1  The NSP/SSG has engaged in a detailed review of WP 65 Annex 1 band sharing study and specifically of an AM(R)S-ARN/MLS compatibility analysis, with the proposed AM(R)S limited to line-of-sight radio links of unmanned aircraft systems(UAS) for control and non payload communications, operating in the band 5030-5091 MHz , where the MLS requirements have precedence over all other uses ....

2.  discussion

2.1  The review by the NSP/SSG resulted in the following detailed comments.

a) Equation (1) of section 3 contains errors in its numerical coefficients.

Using guidance from ITU-REC M. 1829, Annex 1 this equation formulation , with the parameters definition given in WP65 can be corrected as:

Puas – 10 log (4000p) + − 20log(1852dmin) − FDR − LPOL = TMLS

Puas – 20 log [300/(4π 1852) ] − 20log(f dmin) − FDR − LPOL = TMLS (1)

Since this equation is used throughout this Annex to establish the subsequent equations in order to derive numerical results in distance and frequency separations, these results in subsequent tables should be checked after reformulation of these equations

b) The WP65 makes a reference to an internal ICAO paper that proposes an alternative MLS interference threshold level. (A. Delrieu et al., Aeronautical Communications Panel (ACP), Seventeenth Meeting of Working Group F, Definition of the MLS aggregate in-band interference protection limit based on recent analytical and test results, ACP-WGF17- /WP15, September 2007.)

The ICAO Aeronautical Communications Panel Working Group F at its 17th meeting, reviewed the paper and decided the paper should be passed on to the Navigation Systems Panel for further consideration. At its May 2010 session in Montreal, the ICAO NSP spectrum sub-group (SSG) re-addressed this matter. During its discussions it was stated that no further testing nor analytical MLS interference susceptibility assessments have been reported by any ICAO-contracting State since the reported WGF17/WP15 activities took place. In the absence of such additionnal information the NSP/SSG has taken the view that the referenced paper ,does not contain sufficient evidence to support the proposed change of the MLS interference threshold level defined as –130 dBm(or -160 dBW) within 150 kHz.. Accordingly the NSP/SSG cannot recommend to ICAO to endorse the WP 65 findings in terms of decreased distance and frequency separations proposed therein to ensure AM(R)S-MLS compatibility using the afore mentioned reduced alternative MLS interference threshold

c) Because of the mobile nature of the proposed AM(R)S systems and that they need to be used in non-segregated airspace, separation by distance as protection for the MLS receiver does not seems to be a valid approach for band sharing, for reasons explained below:

Table 3 is not consistent with previous studies that ICAO submitted to ITU that for the co-channel protection of MLS receiver it requires a separation distance to be over the horizon. See Annex 10 Volume I, Attachment G paragraph 9.3.1.

With the impossibility of co-channel sharing , Table 4 implies that the freedom of ICAO to re-assign MLS channels in an ICAO region , as is the case in Europe with in the COM-3 assignments table, will be lost and that since part of the MLS band would have to be assigned exclusively to the proposed UAV AM(R)S ] communication system.

2.2  Issues and further work

B.1 DPSK transmission over OCI antenna outside the MLS scanning beams coverage:

One cannot dismiss a potential worst case MLS interference associated with DPSK data transmitted over a worst case 8 dBi OCI antenna gain as explained in the extract of last NSP/SSG , May 2010, report, on the subject of MLS OCI antenna gain clarification , ref output document : “Flimsy 22 “:

“The MLS OCI (Out of Coverage) high gain antenna is used to suppress strong multi-path occurrences outside the proportional guidance sector. This scenario can occur if specular reflectors are present very close to the MLS ground stations. The OCI high gain antenna is not used to transmit DPSK data over 360 o azimuth coverage.

The wide-beam OCI antennas are used to suppress moderate multi-path occurrences outside the proportional guidance sector. This is the more common multi-path scenario.

The wide-beam OCI antennas may also be used to transmit DPSK data words in order to achieve 360 o data coverage. However the EIRP achieved with these antennas when used simultaneously is smaller than that achieved with the dedicated DPSK antenna that has a horizontal beam width of 120 o because the same RF amplifier is used to feed the antennas”

Accordingly the WP65 Annex 1 equation (10) calculation needs to be updated assuming a w.c. MLS DPSK/OCI gain of 8 dBi, i.e. with an MLS EIRP of 51 instead of 43 dBm

B. 2 Determination of capacity taking into account existing constraints :

•  WP 65 Annex 1 has so far analyzed the radio compatibility of single UAS stations , on aircraft or on-ground with single MLS stations in the band 5030-5091 MHz.

•  It still has to address the assessment of UA AM(R)S capacity taking into account the existing system planning constraints such as the MLS channels deployment plan of the European ICAO –COM3 table. As a starting point a worst case MLS deployment situation could be envisaged for such an assessment consisting of several high air-traffic airport platforms within close geographical distance of each other (less than 30 Nmi) such as the London or Paris areas .

2.3  Comment to the proposed scenario’s

The proposed scenario’s seem top aim at direct control of the UAS by the remote pilot, this kind of remote control requires a very short latency between the commands given en the response of the UAS to the commands as this will a direct input to the control loop of the UAS.

It was explained by a manufacturer of UAS that this concept is not feasible as it would certainly lead to a loss of the UAS or worse a collision with other air traffic. For that reason UAS are controlled in reality at the level of a change in the trajectory that the UAS is ordered to fly. This does not require a short latency between the change of trajectory and the order to change the flight-path. Also the amount of data to change the trajectory is very small, in the order of a few kBytes.

For this way of control a slow data link over satellites between the remote pilot and the UAS would be sufficient. The direct contact between the remote pilot and ATC would be over secure terrestrial data and/or voice communication links. This would probably only require the transmission to the ATC of the confirmation of the execution of the change in trajectory and the trajectory itself to the UAS and ATC.

3.  ACTION BY THE MEETING

3.1  The ACP WGF is invited to: Correct equation (1) section 3 and verify the consequent tables.

3.2  Concur with the NSP recommendation to ICAO not to endorse the WP 65 findings in terms of decreased distance and frequency separations proposed therein to ensure AM(R)S-MLS compatibility using the afore mentioned reduced alternative MLS interference threshold

3.3  To note that Table 3 is not consistent with previous studies that ICAO submitted to ITU that for the co-channel protection of MLS receiver it requires a separation distance to be over the horizon. See Annex 10 Volume I, Attachment G paragraph 9.3.1.

3.4  To note that Table 4 implies that the freedom of ICAO to re-assign MLS channels in an ICAO region , as is the case in Europe with in the COM-3 assignments table, will be lost and that since part of the MLS band would have to be assigned exclusively to the proposed UAV AM(R)S ]

3.5  To update the WP65 Annex 1 equation (10) calculation assuming a w.c. MLS DPSK/OCI gain of 8 dBi, i.e. with an MLS EIRP of 51 instead of 43 dBm

3.6  To take into account the capacity constraints as given in section B2 of this paper.

3.7  To note the comments as provided by a manufacturer of UAV systems with respect to the data-link requirements.