WO2001089114A2

WO2001089114A2 - Method for enhancing the reliability and efficiency of aeronautical data communications networking

Info

Publication number: WO2001089114A2
Application number: PCT/US2001/015197
Authority: WO
Inventors: Stephen Heppe; Prasad Nair; Steven Friedman
Original assignee: Adsi, Inc.
Priority date: 2000-05-12
Filing date: 2001-05-11
Publication date: 2001-11-22
Also published as: WO2001089114A3; AU2001261419A1

Abstract

The present invention uses selected network management data transmitted within VDL/4 RF subnetworks, or information derived from network management data transmitted within VDL/4 subnetworks, to efficiently manage a separate RF subnetwork or set of subnetworks. The present invention uses a VDL Mode 4 RF network as a primary transmission path for data transmitted from aircraft to ground stations, and one or more separate RF network(s) as a primary transmission path for data transmitted from ground stations to aircraft. The unique characteristics of each network provide for cost-effective two-way aeronautical networking.

Description

METHOD FOR ENHANCING THE RELIABILITY AND EFFICIENCY OF

AERONAUTICAL DATA COIvIMUNICATIONS NETWORKING USING DATA

TRANSMITTED BY VHF DATA LINK MODE 4 AIRCRAFT STATIONS

Reference to Related Applications:

The present application claims the benefit of U.S. Provisional Application Nos. 60/203,914, 60/203,918, and 60/203,919, all filed May 12, 2000. The present application further claims continuation-in-part status from each of U.S. Application Nos. 09/848,536, 09/848,541, and 09/848,550, all filed May 4, 2001. The disclosures of all of those applications are hereby incorporated by reference in their entireties into the present disclosure.

Field of the Invention:

The present invention is directed to the economical provision of data networking services to and from aircraft.

Background Of The Invention:

At present it is difficult and costly for airline passengers in commercial aircraft to access modern data communications networks. While a data call can sometimes be configured from a personal computer through an air/ground telephone, the data rate is low, link reliability is low, and line charges are high. Several commercial companies have recently announced plans to deliver higher-quality, higher-speed services at lower cost.

Airlines themselves have poor access to modern data communications networks, with current air/ground data networking for Airline Operational Control (AOC) handled via 2.4 kbps modems within the ACARS family of protocols. The ACARS air/ground environment is described in ARINC Specification 618. The capabilities of onboard equipment are defined in ARINC Characteristics 597, 724 and 724B. Other standards may also apply. ACARS uses a p-persistent carrier-sense multiple-access scheme for packet data communications. Upgrades to ACARS are planned, which will increase the burst data rate but leave the access scheme essentially unchanged. The International Civil Aviation Organization (ICAO) has recently recommended the adoption of standards for a new NHF Data Link Mode 4 (VDL/4). NDL/4 operates at 19.2 kbps and uses a self-organizing time-division multiple-access scheme for packet data communications. Part of the channel management scheme for NDL/4 relies on aircraft position information. Another part relies on accurate time known to all participating stations. A modification of the p-persistent algorithm used by ACARS is also included for some transmissions. NDL/4 has the potential to support several user applications including automatic dependent surveillance - broadcast (ADS-B) and air/ground networking. Management and control information for a telecommunications network frequently consumes valuable bandwidth and data carrying capacity, which correspondingly reduces the quantity of user information that can be transferred in a specified period of time. If two coimnunication networks A and B were available, with differing costs and performance, management and control information could be carried on one network A and user information could be carried on the other network B in order to enhance overall performance and cost-effectiveness. In terrestrial networks such as the public switched telephone network, a shift to out-of-band signaling, wherein call setup and other system configuration information is exchanged via communications resources separate from the resources used for customer data communications, has enabled more efficient communications and also enhanced security.

Out-of-band signaling is not commonly applied in aeronautical RF networks. In aeronautical RF networks where call setup and other system configuration information is segregated from customer data communications by e.g. frequency, time or code division multiplex, out-of-band signaling may be considered to exist in a logical sense, but a common RF resource is nevertheless consumed to a greater or lesser degree.

The following issues among others must be considered in order to deliver high-reliability, high-data-rate and low-cost two-way data networking services to passengers, crew and equipment onboard aircraft:

1. Radio-frequency (RF) subnetworks, providing air/ground connectivity directly or via satellites and other media, must be capable of providing high-data-rate communications : 2. Many existing and planned commercial high-data-rate RF subnetworks assume stationary or slowly-moving user terminals, in contrast to aircraft which move rapidly.

3. AOC and other airline- or crew-related communications are typically supported in a separate frequency band from passenger communications;

4. Many user applications, such as passenger access to the Internet, will tend to be dominated by large quantities of "uplink" data delivered to the aircraft from the ground and relatively small quantities of "downlink" data delivered to the ground from the aircraft (although occasional large downlink file transfers may occur). 5. RF subnetwork services may involve location-dependent pricing mechanisms.

6. Certain RF subnetworks may be constrained to avoid airborne transmissions in certain geographic domains, e.g. regions surrounding radio astronomy observatories. 7. Efficient sharing of a common communications channel by multiple aircraft generally requires the use of a suitable multiple-access protocol, which may be a distributed protocol or a centrally-managed protocol whereas transmissions from one or several ground stations or spacecraft can be managed from a central location so that overlapping transmissions are avoided, and the consequential loss of data is minimized.

Summary Of The Invention:

The present invention uses selected network management data transmitted within NDL/4 RF subnetworks, or information derived from network management data transmitted within NDL/4 subnetworks, to efficiently manage a separate RF subnetwork or set of subnetworks, which may be in the same or a different frequency band of operation, h another embodiment, the present invention uses an ICAO- standard or modified NDL/4 RF network as a primary transmission path for data transmitted from aircraft to ground stations, and one or more separate RF network(s) as a primary transmission path for data transmitted from ground stations to aircraft. The unique characteristics of each network provide for a cost-effective solution to the two-way aeronautical networking problem. Brief Description Of Drawings:

FIG. 1 illustrates a terrestrial air/ground data network comprising several fixed ground stations and an aircraft station.

FIG. 2 illustrates a satellite air/ground data subnetwork comprising a satellite relay, satellite earth station and aircraft station.

FIG. 3 illustrates several aircraft stations 31 and 32, and several aeronautical (fixed ground) stations 33, 34 and 35, operating in a NDL/4 network.

FIG. 4 illustrates a hybrid air/ground data network according to the present invention, comprising a NDL/4 RF subnetwork and additional RF subnetworks, wherein selected NDL/4 network management data is made available to one or more of the facilities of the additional RF subnetworks in order to enhance the efficiency of the additional RF subnetworks.

FIG. 5 illustrates an aircraft operating in a VDL/4 network A as well as another RF communications network B, wherein management and control information for network B is exchanged through the NDL/4 network A.

FIG. 6 illustrates a hybrid air/ground data network according to the present invention, comprising an ICAO-standard or modified NDL/4 RF network and one or more additional RF networks.

Detailed Description Of The Invention:

FIG. 1 illustrates a terrestrial air/ground data network comprising several fixed ground stations 11, 12, 13 and an aircraft station 14. Examples of this type of network are the ACARS network implemented by SITA and the proposed network for NHF Data Link Mode 2. In typical operation an aircraft 14 will frequently operate with the nearest fixed ground station as determined by RF signal strength considerations (although other factors may also apply, and control algorithms may be used to minimize the frequency with which handoffs between ground stations are executed). In FIG. 1, if d_x < (L, and d_λ < d₃, the aircraft 14 would typically operate with fixed ground station 11. During the time period that the aircraft 14 is operating with fixed ground station 11, all uplinlc data addressed to aircraft 14 is handled through fixed ground station 11. As the aircraft moves, it will handoff from one ground station to another. In many aeronautical data communication systems, for example ACARS, an aircraft makes handoff decisions based on RF signal strength of the uplinlc transmissions from the various fixed ground stations which it can detect. However, due to variations in RF propagation, fixed ground station transmit antenna gain and aircraft receive antenna gain, aircraft occasionally make an incorrect decision and lose connectivity. In another type of RF network, the aircraft broadcasts a downlink message and a plurality of ground stations which receive said message will forward it to a central processing site in order to gain space diversity. In this type of RF network, the central site selects, for each uplink transmission, one of the plurality of ground stations for uplink transmission. In this type of network it is also possible to lose connectivity, or require retransmission, due to improper selection of a ground station for uplink transmission.

FIG. 2 illustrates an aeronautical satellite network comprising a fixed ground station (satellite earth station) 21, a relay satellite 22 supporting an operational coverage area 23, and an aircraft 24 within the operational coverage area. Also shown is an operational exclusion zone 25, for example as may be associated with a radio- quiet zone surrounding an observatory operating in the Radio Astronomy Service. The control system of the aeronautical satellite network may be required to ensure that no aircraft transmissions take place while the aircraft 24 is within the operational exclusion zone 25. Accurate and timely aircraft position and velocity information can increase the efficiency and reliability of aeronautical communication system control, improve user quality of service, provide a means to verify compliance with regulatory constraints and serve as an aid in regional pricing. Certain avionics on the aircraft may have accurate and timely position and velocity information, but most traditional aeronautical communication systems do not have direct access to this information and most therefore estimate the relevant parameters from signal features available within the communications system itself. Alternatively, if an aeronautical communications system has access to aircraft navigation information and transports this information within the aeronautical communications system, an overhead penalty is incurred due to the opportunity cost of transporting said information.

The ICAO-standard NHF Data Link Mode 4 (NDL/4) is an aeronautical communications protocol wherein position and velocity information is exchanged by stations compliant with the protocol. FIG. 3 illustrates several aircraft stations 31 and 32, and several aeronautical (fixed ground) stations 33, 34 and 35, operating in a VDL/4 network. Aircraft 31 is within range of aircraft 32 and ground station 33; aircraft 32 is within range of aircraft 32 and all 3 ground stations 33, 34 and 35. Each aircraft and aeronautical station periodically or aperiodically broadcasts 3D position and velocity information, as well as selected other information, which may be received by other VDL/4 stations within range. This information is used for certain network management and access control protocols within the VDL/4 network, and also supports safety-related surveillance applications such as enhanced situational awareness and flight path deconfliction planning. FIG. 4 illustrates one embodiment of the present invention, wherein synchronization messages transmitted by a VDL/4 - compliant aircraft station 40 are received by a VDL/4 - compliant aeronautical ground station 41 and relevant synchronization information contained therein is then transmitted to one or more communications control facilities (CCFx) 30, 35 of one or more other aeronautical communication networks, via appropriate internetworking means, where said relevant synchronization information may be used for e.g. precise ground station handoff control, precise emissions control in the vicinity of defined exclusion zones, selection of appropriate ground transmit stations to enhance aircraft reception probability or selection of appropriate ground transmit stations to maximize spectrum utilization efficiency (i.e., by allowing simultaneous uplink transmission, from several co- frequency ground stations, directional or omnidirectional, to several aircraft in different geographic locations, wherein each aircraft has high probability of error-free reception given the known directionality of the ground stations, if any, and the known distance ratios between the aircraft and the simultaneously-transmitting ground stations). In this illustration, CCFl 30 is a communications control facility for a satellite network comprising ground station 31, satellite 32 and communicating with aircraft 40. Similarly, CCF2 35 is a communications control facility for a terrestrial network comprising ground stations 36, 37, 38 and communicating with aircraft 40. Relevant synchronization information, derived from VDL/4 synchronization bursts received at VDL/4 - compliant ground station 41, can also be delivered to Application Service Providers 39 where said information may be used e.g. to select one of several alternative networks for carriage of particular information to/from the aircraft 40. This might be used, for example, to switch between network service providers based on cost or policy considerations, or to switch between network service providers based on the anticipated communications reliability given the known location of aircraft 40.

A terrestrial or satellite-based system A, or application service provider B, which relies in part on estimates of the 3D position or velocity for aircraft served, benefits by the accuracy of the data contained in or derived from VDL/4 synchronization bursts and avoids the cost and overhead penalty of determining this information autonomously, i.e. using the resources and means wholly contained within system A or otherwise available to the application service provider B. The relevant information is delivered to appropriate facilities of the terrestrial or satellite- based system A, or application service provider B, via terrestrial internetworking means or interwiring means which are typically more cost-effective than the RF networking resources comprising the terrestrial or satellite-based system A.

FIG. 5 illustrates an aircraft 50 operating in a VDL/4 network A comprising radio Rl 51 installed on the aircraft and ground station 52, as well as auxiliary elements not shown. FIG. 5 also illustrates another RF communications network B comprising radio R2 53 with associated management unit 54 installed on the aircraft, ground station 55, and communications control facility 56. Management and control information for network B is exchanged through the VDL/4 network A, appropriate interwiring means between radio Rl and the airborne management unit 54, and appropriate interwiring means or internetworking means between ground station 52 operating in the VDL/4 network and CCF2 56 operating as an element of communications network B. Management unit 54 and CCF2 56 perform management and control tasks for communications network B including e.g. hardware configuration control, handoff between ground stations, frequency tuning and channel access. Management and control information for communications network B, exchanged through the VDL/4 network A, is treated as user data in VDL/4 network A and routed to/from the airborne management unit 54 and ground-based CCF2 56 using e.g. a standard internetworking protocol such as IPv6 or the ATN. Management and control information for communications network B may also be exchanged within communications network B as an adjunct to the exchange of management and control information through VDL/4 network A, either as an alternative route or for the exchange of different classes of management and control information.

FIG. 6 illustrates a hybrid air/ground data network according to the present invention, comprising an ICAO-standard or modified VDL/4 RF network A and one or more additional RF networks B, C, etc. wherein the VDL/4 RF network A is the primary transmission path for data transmitted from aircraft to ground stations, and the separate one or more non- VDL/4 RF network(s) B, C, etc. is(are) the primary transmission path for data transmitted from ground stations to aircraft. The VDL/4 network A comprises an airborne radio R_x 61 with associated antenna, ground station GS_j 62 with associated antenna, and ground-based network control facilities (not shown). There may be several aircraft participating in one VDL/4 network, and there may be several ground stations. The other RF network B comprises an airborne radio R₂ 63 with associated antenna, ground station GS₂ 64 with associated antenna, and ground-based network control facilities (not shown). There may be several aircraft participating in RF network B, and there may be several ground stations associated with RF network B. If more than one other RF network is available, e.g. network C, D, etc. as illustrated in FIG. 6 by additional radios R,. and ground stations GS_n, they may use different technologies and frequency bands from those used by the first other RF network B comprising radio R₂ 63 and GS₂ 64. For example, RF network B could be terrestrial UHF while an additional RF network C could be satellite-based. In general each RF network A, B, C, etc. provides two-way communications between aircraft and ground stations, however certain RF networks may be primarily or strictly limited to "forward link" communications only (i.e. transmissions to the aircraft).

An airborne server 65 and ground-based server 66 provide means to route data to/from desired applications and ground-based facilities (not shown) via the various available networks A, B, C, etc.

In a preferred embodiment of the present invention, the NDL/4 network is modified from the ICAO standard to operate in the UHF portion of the frequency band (300-3000 MHz) and at least one of the other RF networks B, C, D, etc. is a satellite-based wideband network providing "forward link" communications only. The modifications to the VDL/4 network, in order to operate efficiently in the UHF portion of the frequency spectrum, may involve changes in data rate, modulation index, coding, etc., but the media access protocols defined by the ICAO standard are entirely or substantially unchanged. In this preferred embodiment the modified VDL/4 network provides efficient access to one or several UHF frequency channels by a multiplicity of participating aircraft, allowing efficient return link data transfer (i.e., transmissions from an aircraft to the ground) as well as an optional path for forward link data transfer. Control traffic and network management data for the modified VDL/4 network are transmitted and received by aircraft and ground stations. Since the satellite-based wideband network B provides a primary path for forward link communications only, aircraft operate in receive-only mode (for network B) which reduces weight and complexity of airborne equipment, and the network B can be operated as a multiplexed broadcast channel with high throughput efficiency. This maximizes the utility and cost-effectiveness of the satellite-based network resources associated with network B. The aircraft position and velocity information, transferred as part of the network management and synchronization protocol of the modified VDL/4 network A, can be used to enhance the operation of the satellite-based network B (e.g. by allowing the selection of one of several spot beams, or doppler pre- compensation).

In another embodiment of the present invention, the VDL/4 network operates in the VHF portion of the frequency spectrum according to the ICAO standard, communications data associated with safety and regularity of flight are carried with a high priority, and communications data for passenger correspondence are carried at a lower priority which avoids excessive time delay for higher-priority communications.

In another embodiment of the present invention, a network B (which may be satellite-based) provides two-way communications (forward link and return link). , The two-way communications capability may be available at all times of desired transmission or only a subset of said times of desired transmission. This embodiment requires aircraft to support transmit capability within the network B, but provides enhanced or redundant coverage considering the two networks together and still allows the network B to preferentially operate with a large fraction of its resources configured for forward-link communications. As used herein, interwiring and internetworking means can include any suitable wiring or networking infrastructure capable of providing the necessary communications, such as a wiring harness or a LAN or WAN. While preferred embodiments of the present invention have been set forth above, those skilled in the art who have reviewed the present disclosure will readily appreciate that other embodiments can be realized within the scope of the invention. For example, protocols other than those disclosed can be used. Therefore, the present invention should be construed as limited only by the appended claims.

Claims

CLAIMS We claim:

1. A method to enhance the reliability, efficiency or quality of service of a terrestrial or satellite-based aeronautical radio coimnunications subnetwork, provide a means to verify compliance with regulatory constraints, or serve as an aid in regional pricing, said method comprising:

(a) receiving synchronization bursts transmitted by VDL/4 - compliant aircraft stations by ground station receiving stations; and

(b) transmitting information contained in or derived from the synchronization bursts to facilities associated with said terrestrial or satellite-based aeronautical radio communications subnetworks via appropriate internetworking or interwiring means.

2. A method to enhance the reliability, efficiency or quality of service provided by an application service provider, provide a means to verify compliance with regulatory constraints, select among network service providers or serve as an aid in regional pricing, said method comprising:

(b) transmitting information contained in or derived from the synchronization bursts to facilities associated with said application service provider via internetworking or interwiring means.

3. A communication method comprising: establishing communication between two locations over an aeronautical RF network; and out-of-band signaling between the two locations over a NDL Mode 4 subnetwork or network for management and control information exchange.

4. The out-of-band signaling method of claim 3, wherein the management and control information exchanged via the NDL Mode 4 subnetwork or network is treated as Airline Operational Control information, or Airline Administrative Control information contributing to the safety and regularity of flight.

5. A dual-band radio communications system for aeronautical data communications comprising: avionics and ground systems supporting an ICAO standard or modified NDL Mode 4 network; and avionics and ground systems supporting at least one other RF network; wherein the ICAO standard or modified NDL Mode 4 network provides a primary return link path for user data and the at least one other RF network provides a primary forward link path for user data.

6. The dual-band radio communications system for aeronautical data communications of claim 5, wherem the NDL Mode 4 network is modified to operate in a portion of the RF spectrum other than the 108-137 MHz band.

7. The dual-band radio communications system for aeronautical data communications of claim 5, wherein at least one RF network is satellite-based.

8. The dual-band radio communications system for aeronautical data communications of claim 5, wherein one or more of the RF networks provide two- way communications capability for user communications.