VDL Mode 2 Multifrequency Guidance

ACP-WGW015/IP- International Civil Aviation Organization 10x 07/06/05 WORKING PAPER

AERONAUTICAL COMMUNICATIONS PANEL (ACP)

FIFTHTEENTH MEETING OF THE WORKING GROUP M

Montreal, Canada 16 – 18 November 2009

Agenda Item 4: Maintenance of VDL Mode-2 Documents

Proposed Updates to Doc 9776, Part I – VDL Mode 2 Manual Guidance

(Presented by Rob Morgenstern, MITRE)

SUMMARY

This working paper proposes amendments to Doc 9776 Part I Implementation Aspects regarding multiple frequency operations.

ACTION Consider attached amendment proposal

1. INTRODUCTION

1.1 AEEC’s Data Link Systems subcommittee developed technical specifications to handle multiple frequency operation for the VDL Mode 2 system. Proposal to update the technical provisions of Doc 9776 have been presented to ACP WG-M.

2. DISCUSSION

2.1 This paper proposes updates to the Implementation Aspects in Part I of Doc 9776 to be consistent with the proposed updates to the Technical Provisions in Part II.

(3 pages) 089ab020fd3990c69ae33739569f3540.doc 2 ACP-WGWM01/IP- xx

3. AMENDMENT PROPOSAL

Title: Multiple Frequency operation guidance AP working paper number and date M15/WPx 16 Nov 2009 Document(s) Affected: Manual on VDL Mode 2 Technical Specifications Document Version: Doc 9776 Sections of Documents Affected: Part I, 3.4.2.1.2.2, 3.4.2.1.3.3, 3.4.2.1.4.3 Coordinator: Robert Morgenstern Coordinator's Address: 7515 Colshire Drive, M/S N660 McLean, VA 22102 USA Coordinator's Phone: +1 703 983 7846 Coordinator's Fax: +1 703 983 1367 Coordinator's E-mail Address: [email protected] Category: CLARIFICATION Problem description: Added guidance relating to updated frequency handoff capabilities between different frequencies Background: It was recognized that implementations vary how they handle unrecognized XID parameters. It is desired that stations operate consistently in this area. Backwards compatibility: Guidance material. Amendment Proposal: See below. WG-M Status: SUBMITTED 11/16/09

Amend the document as follows:

3.4.2.1.2.2 Supported facilities. The GSIF identifies all frequencies and protocols that the ground station supports. It may also identify alternate and surrounding ground stations. The aircraft LME stores this information to be used when trying to contact the stations during ground station changes. This allows the LME to re-tune the radio and know information about ground stations on that frequency without having to wait for several GSIFs to be transmitted. All GSIF transmissions will also include the HDLC and AVLC options parameters to also factor into any handoff decisions. When an aircraft establishes a link with the ground system, it will provide a list of the facilities that it supports. The ground system LME stores this information to be used when deciding what type of service to provide the aircraft.

3.4.2.1.3.3Autotune. The autotune frequency parameter allows the ground station to manage multiple frequencies in a congested area. The ground station may request that an aircraft re-tune to a different frequency and initiate link establishment on the new frequency. The replacement ground station parameter will be included to inform the aircraft of which ground station to attempt to contact. The new ground station may belong to a different service provider. Alternately, if only two frequencies are in use, the Frequency Support List parameter contained within the GSIF can be used to identify separate surface and enroute frequencies. This enables the aircraft to switch based on the weight-on- wheels indication without explicit frequency management by the ground system. 3 ACP-WGW01/IP-xx

Note 1.— In order to properly implement make- before-break across two frequencies, the aircraft will need two VDL radios. With only one VDL radio, the system will operate with a break-before-make paradigm. The system will silently disconnect the link before retuning to the newfrequency.

Note 2.— When VDL handoff takes place between ground stations connected to different ATN air-ground routers, a potential exists for ambiguity in ATN Routes over the air-ground link during the link overlap period. The issue arises due to the establishment of a new IDRP route following handoff to a ground station connected to a different air-ground router, while the original IDRP route is retained until expiry of TG5. It is desirable that PDUs should be transferred via the new IDRP Route, since the Route via the old VGS may be compromised. However, both Routes may have equal merit and the IDRP protocol, as currently specified by ATN standards, cannot be expected to select the most appropriate route. In the aircraft, it is recommended that in these circumstances, there should be a local preference for sending downlinks via the new SVC to the newly-established air-ground router. On the ground, other measures may be applied to minimize the impact of routing ambiguity. Close alignment of default values of TG5 on the air and ground may be desirable, to avoid maintenance of an IDRP route that is incapable of reaching the aircraft after expiry of TG5 in the air. Additional system management action may be necessary by the service provider to transfer uplinks via the most appropriate IDRP route prior to TG5 expiry.

3.4.2.1.4.3Handoff. In general, the aircraft LME will monitor the signal quality parameter (SQP) values of all transmissions from ground stations. When it determines that a ground station change is needed, it will send an XID to the selected (new) ground station. It may also trigger a ground station change, based on the aircraft’s weight-on-wheels indication to indicate a change between airport surface and enroute frequencies. The aircraft LMEIt may include a list of alternate (acceptable) ground stations. The ground service provider may, at its discretion, reply from another ground station (usually in the alternate list). This allows, among other functions, a means of load-balancing the ground stations.

4. ACTION BY THE MEETING

4.1 The ACP WG-M is invited to consider the amendment proposal to Doc 9776 presented in this paper.