WO2001086893A2 - Data packet communications system with a plurality of antennas - Google Patents

Data packet communications system with a plurality of antennas Download PDF

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Publication number
WO2001086893A2
WO2001086893A2 PCT/US2001/014232 US0114232W WO0186893A2 WO 2001086893 A2 WO2001086893 A2 WO 2001086893A2 US 0114232 W US0114232 W US 0114232W WO 0186893 A2 WO0186893 A2 WO 0186893A2
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WO
WIPO (PCT)
Prior art keywords
radio
lrus
radios
data
shadow
Prior art date
Application number
PCT/US2001/014232
Other languages
French (fr)
Other versions
WO2001086893A3 (en
Inventor
Steven Friedman
Prasad Nair
Stephen Heppe
Original Assignee
Adsi, Inc
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Adsi, Inc filed Critical Adsi, Inc
Priority to AU2001261143A priority Critical patent/AU2001261143A1/en
Publication of WO2001086893A2 publication Critical patent/WO2001086893A2/en
Publication of WO2001086893A3 publication Critical patent/WO2001086893A3/en

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Classifications

    • HELECTRICITY
    • H04ELECTRIC COMMUNICATION TECHNIQUE
    • H04BTRANSMISSION
    • H04B7/00Radio transmission systems, i.e. using radiation field
    • H04B7/02Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas
    • H04B7/04Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas
    • H04B7/08Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the receiving station
    • GPHYSICS
    • G01MEASURING; TESTING
    • G01SRADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S19/00Satellite radio beacon positioning systems; Determining position, velocity or attitude using signals transmitted by such systems
    • G01S19/01Satellite radio beacon positioning systems transmitting time-stamped messages, e.g. GPS [Global Positioning System], GLONASS [Global Orbiting Navigation Satellite System] or GALILEO
    • G01S19/13Receivers
    • G01S19/35Constructional details or hardware or software details of the signal processing chain
    • G01S19/36Constructional details or hardware or software details of the signal processing chain relating to the receiver frond end
    • HELECTRICITY
    • H04ELECTRIC COMMUNICATION TECHNIQUE
    • H04WWIRELESS COMMUNICATION NETWORKS
    • H04W84/00Network topologies
    • H04W84/02Hierarchically pre-organised networks, e.g. paging networks, cellular networks, WLAN [Wireless Local Area Network] or WLL [Wireless Local Loop]
    • H04W84/04Large scale networks; Deep hierarchical networks
    • H04W84/06Airborne or Satellite Networks

Definitions

  • the present invention is directed to the enhancement of air/air packet data communications reliability among aircraft, the enhancement of air/ground packet data communications reliability between aircraft and ground systems, and the reduction in cost for airborne antenna installations associated with packet data communications systems ..that require access to signals from GPS space vehicles.
  • Aircraft commonly transmit and receive analog voice radio communications, to enable air traffic control and provide for other air traffic services (ATS), via radio equipment operating on selected frequency channels.
  • a single aircraft typically supports at least one radio, and may support several radios, each radio tuned to a different frequency channel.
  • Analog voice communications in the NHF band use frequency channels separated by 25 kHz between channel centers, and also 8.33 kHz between channel centers.
  • the aviation industry is currently developing a digital voice and data capability for ATS which will also operate on 25 kHz channels in the VHF band.
  • AOC airline operational control
  • AOC Aircraft Communications Addressing and Reporting System
  • ACARS Aircraft Communications Addressing and Reporting System
  • the ACARS air/ground environment is described in ARI ⁇ C Specification 618.
  • the capabilities of onboard equipment are defined in ARI ⁇ C Characteristics 597, 724 and 724B. Other standards may also apply.
  • the aviation industry is also currently developing enhanced systems for AOC communications which will provide higher data rates and improved networking protocols than those which are available via ACARS.
  • a large commercial aircraft typically provides three VHF antennas for ATS and AOC communications - typically two of these are dedicated to ATS voice and the third is dedicated to AOC.
  • a partial shift to digital voice is planned for the future in some regions.
  • VDL/4 VHF Data Link Mode 4
  • This radio communications system employs a minimum of two frequency channels and can optionally support additional channels.
  • VDL/4 uses aircraft position information, and knowledge of system time, for various functions including the organization of transmissions on the RF channel. Aircraft position information, and knowledge of system time, can be derived from various sources including, as one example, the Global Positioning System (GPS).
  • GPS Global Positioning System
  • a single VDL/4 line replaceable unit comprises a chassis and associated VDL/4 electronics which support a minimum of two frequency channels and can optionally support additional channels.
  • VDL/4 LRU When a VDL/4 LRU is connected to a single antenna it can typically receive on multiple frequencies at once or transmit on any single frequency.
  • a VDL/4 LRU connected to two or more antennas may be capable of simultaneous transmission on frequency f t via one antenna and reception on frequency f 2 via another antenna using current technology.
  • Individual receiver and transmitter units, contained within the two VDL/4 LRUs, can also be dynamically re-assigned to different channels by a human operator or automatic control system capable of commanding the two VDL/4 LRUs (in some cases switching the receive or transmit function for a given frequency channel from one LRU to another LRU) in order to minimize the total number of receiver units and transmitter units needed to achieve a desired level of operational flexibility and reliability.
  • This type of redundant installation is described in working paper 49 of ICAO/AMCP/7 (Montreal, 22-30 March 2000). Since each VDL/4 LRU is connected to a single antenna in this type of installation, each VDL/4 LRU may be incapable of receiving on any frequency while it is transmitting on any single frequency.
  • each VDL/4 LRU would have the potential to receive on frequency/ ; while transmitting on frequency/, but this configuration requires two antennas for each of two VDL/4 LRUs, for a total of four antennas. If two antennas were shared so that each antenna is connected to both
  • the number of antennas can be limited to two but in this case the signal strength available to each VDL/4 LRU is reduced.
  • FIG. 1 illustrates a dual-redundant configuration of antennas and radio LRUs known to the prior art.
  • a first antenna 11 and first radio LRU 12, and a second antenna 13 and second radio LRU 14, operate in parallel and support human (e.g., pilot and copilot) and other avionics systems 15 operational needs.
  • human e.g., pilot and copilot
  • radio LRU For packet data transmission, only one radio LRU may be used at a time on any single frequency since transmission by two radio LRUs at the same time on the same frequency would result in garbled transmissions (even if the data transmitted by the two radio LRUs is the same).
  • one radio LRU may be used with the other reserved as a spare (even if it is active); alternatively both may deliver received data to other onboard systems. In the latter case where both radio LRUs deliver data to other onboard systems, care must be exercised to ensure that the delivery of multiple copies of identical data does not adversely affect onboard operations.
  • a data link layer technical acknowledgement is required to be sent when a data packet is received.
  • the acknowledgement circuit or other device may be contained within the aggregate of other onboard systems 15 and may be connected to only one of the radio LRUs 12 or 14 at any one time. However, this may create a single point of failure unless redundant acknowledgement devices are provided within the aggregate of other onboard systems 15, with appropriate switching mechanisms between the multiple radio LRUs and multiple acknowledgement devices.
  • accurate position and time information is used as part of the nominal channel management scheme, and may be provided by a GNSS antenna 16 and GNSS user receiver device 17 or alternative navigation system and an accurate clock. The position and time information may be passed to the radio LRUs and other onboard systems, as required, via direct interwiring from source systems or via other intermediate systems.
  • a single common antenna supporting a GNSS user receiving device and a radio communications device is not traditionally considered since the radionavigation function, supported by the GNSS user receiving device, is traditionally considered to be a safety-critical function which cannot tolerate any significant loss in performance, either due to a suboptimal antenna, suboptimal antenna placement, or periods of time when the GNSS user receiving device is effectively disconnected from the antenna (for example during periods of time when the radio communications device is transmitting).
  • This invention is an application of antenna diversity and two or more multichannel radio LRUs, with a novel cooperative sharing strategy among the multichannel radio LRUs, to aeronautical packet data communications and GPS position and time determination.
  • Existing avionics and systems are not designed to accommodate antenna diversity, which is considered to increase the overall level of complexity thereby impairing operational reliability and potentially adding to cockpit workload.
  • the present invention overcomes these concerns and offers the following benefits: a) Enhanced data communications performance in a fading environment; b) Enhanced data communications performance at long range; c) Enhanced data communications performance in the presence of cochannel interference; d) Extendable to an arbitrary number of cooperating peer radio LRUs; e) No single point of failure; f) Improved on-aircraft testing of radio functionality; g) No increase in pilot workload or change in operational procedures; h) Elimination of a separate GPS antenna with consequent reduction in cost.
  • FIG. 1 illustrates a dual-redundant configuration of antennas and radio LRUs known to the prior art.
  • FIG. 2 illustrates an embodiment of the present invention comprising two multi-channel radio LRUs each connected to a separate antenna, wherein each radio LRU contains a data arbitrator designed to operate with one or more peer radio LRUs in a distributed architecture.
  • This embodiment still relies on a separate GPS antenna and electronics to provide position and time information.
  • FIG. 3 illustrates one antenna and LRU for another embodiment of the present invention, wherein each radio LRU contains an internal GPS signal processing capability and a data arbitrator designed to operate with one or more peer radio LRUs in a distributed architecture.
  • FIG. 2 illustrates a preferred embodiment of the present invention wherein a first antenna 21 and radio LRU 22, and a second antenna 23 and radio LRU 24, each contain a data arbitrator element 25.
  • the two radio LRUs operate as cooperative peers and exchange data automatically to assist each other in achieving operational requirements.
  • the radio LRUs may be single-channel or multi-channel, analog or digital or hybrid, and operate in any band, although for the purpose of the present invention they must be tuneable to the same frequencies and the benefits of at least one preferred embodiment of the present invention are only available on frequencies where packet data transmissions are supported.
  • Each radio LRU 22 and 24 receives configuration commands (e.g., tuning frequency, applications to be supported) and data for transmission from external systems, and delivers data it has received, and communicates its current status, to external systems.
  • the interwiring means may be direct or may alternatively pass through intermediate systems.
  • An optional GNSS antenna 26 and GNSS user receiver device 27 may be used as one of several alternative methods to provide time signals and position information to the radio LRUs (as well as other devices not shown).
  • each radio LRU 22 and 24 may be tuned to a separate channel or group of channels in support of operational needs as determined by e.g. internal software configuration or external commands.
  • Each radio LRU also requests "shadow reception service" for its data-oriented applications from its peer radio
  • the peer radio LRUs via the associated data arbitrators 25. If one or more of the peer radio LRUs have unassigned resources available (i.e., ability to tune to and receive RF signals on requested channels in addition to the channels supporting operational need as determined by e.g. internal software configuration or external commands), the one or more of the said peer radio LRUs configure their unassigned resources as required to provide the requested shadow reception sendee.
  • the peer radio LRUs communicate their requests and current configuration via the interwiring means between radio LRUs, said interwiring means carrying mter alia radio coordination and configuration data as well as received signals or u'ser message data received via'the radio channels for which shadow reception service was requested.
  • the coordination protocols between radio LRUs are ideally configured to allow requests for shadow reception service to be specified according to a priority scheme.
  • a peer radio LRU may assign its resources to the requests with the highest priorities.
  • the data arbitrators 25 operate above the Media Access Control (MAC) sublayer of the data protocol supported by the radio LRUs, so for data reception a data arbitrator will handle a packet after it has been checked to ensure error-free reception, but e.g. before generation of a technical acknowledgement.
  • MAC Media Access Control
  • the associated data arbitrator 25 which is a software process internal to the radio LRU.
  • the data arbitrator 25 maintains a data base of appropriate identifying data for all received radio messages associated with frequencies for which it and its associated radio LRU have primary responsibility, which said messages it has received from any source.
  • the nature of the appropriate identifying data for a message can vary from system to system, but should be sufficient to uniquely identify a message received on any frequency, by any radio LRU, within a short span of time on the order of several seconds. Possible examples of such appropriate identifying data include but are not limited to a hash of the message, such as a CRC check, and the message arrival time and ID of the sending aircraft.
  • a data arbitrator receives a message from its associated radio LRU or the interwiring means, said message having been received on a frequency for which the data arbitrator and radio LRU has primary responsibility as determined e.g. by its internal software configuration or external command, the data arbitrator must determine if it has already received and processed the data message from another source.
  • the data arbitrator determines that the data message has not already been processed and passed to external systems, the data message is processed and passed to appropriate external systems and the appropriate identifying data is stored. Otherwise, the data message is cleared without further processing. Periodically or aperiodically, the stored data may be cleared or overwritten.
  • the data arbitrator receives a data message from its associated radio LRU, said data message received on a frequency for which the radio LRU has accepted shadow reception responsibility, it is passed to the data arbitrator of the appropriate peer radio LRU which requested the shadow reception service via the interwiring means.
  • This embodiment is preferred since the data arbitrators operate above the MAC sublayer, minimizing data rate and bandwidth requirements on the interwiring means between data. Selected metadata, such as signal arrival time and signal strength associated with received messages, may also be passed over the interwiring means.
  • the data arbitrators operate below the MAC sublayer and pass either soft-decision metrics from a demodulator, radio-frequency signals downconverted to an intermediate frequency, or radio- frequency signals themselves.
  • This embodiment allows soft-decision combining or antenna beamforming synthesis, which can enhance receive performance, but requires wider bandwidth interwiring means.
  • the data arbitrator is not required to store data relating to messages it has already processed according to its primary responsibility, since the intent of this embodiment is to generate a single estimate of the transmitted message based on the multiple received signals.
  • a data packet may be formatted for transmission and bypass the data arbitrator 25 within a radio LRU.
  • the data arbitrator In the fault-free case there is no need for the data arbitrator to handle data prepared for transmission since the radio LRU with primary responsibility can make the transmission and only a single transmission on any given frequency is desired.
  • the data arbitrators have no ability to re-route data prepared for transmission from one radio LRU A to another radio LRU B.
  • the data arbitrator associated with a radio LRU A may be configured to route a packet prepared for transmission to another compatible data arbitrator for a peer radio LRU B that is able to transmit the data which has been prepared for transmission by radio LRU A, in order to use the transmitter in radio LRU B and compensate for a failed transmitter in radio LRU A.
  • Radio LRUs may be configured to receive simultaneously on multiple frequencies using multiple protocols, but transmit on only one frequency (perhaps using only one protocol).
  • a two-way voice radio may also provide shadow reception service according to certain data protocols without any ability to transmit according to said data protocols. In this way a voice radio A can provide an enhancement of overall data reception performance for separate data radio B, at marginal increase in cost.
  • radio LRUs may be simultaneously configured with primary responsibility for a given frequency/, and these radio LRUs may request shadow reception service for frequency/ from each other as well as other peer radio LRUs.
  • the individual radio LRUs with primary responsibility may each individually rely on a single receiver module for the primary and shadow responsibility, consuming no additional resources but passing received data to the requesting peer radio LRU(s) via the interwiring means.
  • Each radio LRU with primary responsibility which has requested shadow reception service, separately arbitrates the available data and can deliver received messages to external systems independent of its peers. In this way the present invention can mimic the operational architecture of existing systems, while still providing enhanced receive performance.
  • two peer radio LRUs A and B are employed with each connected to a dedicated antenna; radio LRU A takes primary responsibility for all applications and radio LRU B serves as a redundant backup also providing shadow reception service to all applications supported by radio LRU A. Therefore all transmission events are handled by radio LRU A and radio LRU B provides a simultaneous receive capability during periods of transmission by radio LRU A, as well as a second receive capability when radio LRU A is not transmitting.
  • the present invention may be extended in an obvious way to multiple antennas and radio LRUs (greater than 2). For example, on a typical commercial aircraft there may be three VHF antennas available.
  • radio LRU A and B may be operationally associated with ATS voice communications and radio LRU C may be operationally associated with AOC voice and data communications, automatic dependent surveillance broadcast (ADS-B) transmission and reception, weather 'uplink reception and other data applications.
  • ADS-B automatic dependent surveillance broadcast
  • Radio LRUs A and B would not make any requests for shadow reception since they are operationally associated with voice communications.
  • Radio LRU C however would request shadow reception services from radio LRUs A and B for its numerous data-oriented channels. If radio LRUs A and B had resources available, they would tune those resources to the requested channels and deliver any data messages received on those channels to radio LRU C. Radio LRU C would then have the benefit of three diversity antemias for its data-oriented applications.
  • the likelihood of successful data reception by a single antenna/radio LRU pair is determined in part by the strength of the signal in space, the gain of the receiving antenna, and the noise experienced by the radio LRU's demodulator.
  • the present invention is beneficial because antenna gain patterns are not exactly uniform in azimuth and elevation, and noise and interference events are not perfectly identical on all antennas simultaneously.
  • the probability of successful message reception for a given radio LRU k may be denoted p k ( ⁇ , ⁇ , S, N oJc ) ⁇ 0. Assuming that the statistics of successful message reception across the k radio LRUs are uncorrelated, the probability that at least one of a set of radio LRUs ⁇ k ⁇ will receive a given message successfully is
  • Pr ⁇ success ⁇ 1 - J (1 - p k (f, ⁇ , ⁇ , S, N o k )) , which is greater than any of the p k if all k p k > 0.
  • the ability of a radio LRU A to discriminate between them, and successfully demodulate without error at least one of them depends in part on the relative signal strength between the two said signals at the output of the antenna to which the radio LRU A is connected. If a second radio LRU B is tuned to frequency/, in order to provide a shadow reception service for radio LRU A, each of the two radio LRUs has a chance to successfully demodulate at least one of the messages (typically the stronger of the two).
  • each radio LRU A and B tuned to frequency/ according to the present invention will likely experience a different relative signal strength' between the two radio signals. So even if radio LRU A experiences a poor relative signal strength, radio LRU B may experience a better relative signal strength that allows at least one of the radio signals to be successfully demodulated. If a multichannel radio LRU A is required to transmit on frequency/, it may be unable to simultaneously receive on another frequency/ ⁇ /.
  • a peer radio LRU B may be able to receive on frequency/ during a transmission by radio LRU A on frequency/, thereby allowing an effective capability for simultaneous transmission and reception on multiple frequencies.
  • a first embodiment of the present invention does not contemplate the delegation of transmission responsibility from one radio LRU A to a peer radio LRU B in normal fault-free operation.
  • the delegation of transmit responsibility could be used to provide fail-soft operation among a group of peer radio LRUs. For example, if a radio LRU A determines through diagnostic self-test or other means that its transmit capability is failed or degraded, it could potentially delegate transmit responsibility to a given other radio LRU B (possibly selecting a different peer radio LRU for different transmit events).
  • a second embodiment of the present invention contemplates the delegation of transmit responsibility from one radio LRU A to a peer radio LRU B in normal fault- free operation, subject to predefined criteria such as message priority, length, or possible refinements such as known azimuth and elevation to an intended recipient and consideration of known or estimated antenna gain patterns for the multiple antennas associated with the multiple radio LRUs.
  • the present invention provides a full over-the-air loop-back test capability.
  • a radio LRU A can request shadow reception service from another radio LRU B for a frequency channel/, on which radio LRU A is authorized to transmit.
  • Radio LRU A can then transmit a message to itself, which may be received by radio LRU B and delivered to radio LRU A via the associated data arbitrators and interwiring.
  • the benefits of the present invention are foreseen primarily with the application of multi-channel radio LRUs. However, the use of single-channel radio LRUs provides a residual benefit.
  • FIG. 3 illustrates the use of a single antenna 31, in a preferred embodiment according to the present invention, for an integrated radio communications system LRU which relies in part on accurate positioning information and timing signals from the GNSS.
  • the integrated radio communications system comprises an antenna 31, a signal splitter and switch 32, a plurality of receiver/transmitters 33, a GNSS user receiver device 36, and a system controller 37 which contains, in a preferred embodiment, the data arbitrator 25.
  • the GNSS user receiver device 36 provides navigation and system timing for the radio communications system. If installed on an aircraft, the antenna 31 could be bottom-mounted or top-mounted.
  • the signal splitter and switch 32 provides a fan-out of incoming RF signals to a plurality of receiver/transmitters 33, and also provides a switching means to switch a single active transmitter to the shared antenna while blocking the signal flow to the remaining receiver/transmitters, thereby preventing damage to the remaining receiver/transmitters.
  • the signal splitter and switch 32 also provides a fan-out of the incoming RF signals to the GNSS user receiver device 36.
  • the signal splitter and switch 32 also blocks the signal flow from any of the active transmitters 33 to the GNSS user receiver device 36, thereby preventing damage to the GNSS user receiving device 36.
  • the antenna 31 may be designed for radio communications without regard to GNSS signal reception, and may be bottom-mounted.
  • the cabling from the antenna to the signal splitter and switch 32 will introduce some additional loss (this cabling should be selected to accommodate the propagation of RF signals in the GNSS band of operation, as well as the band of operation used for radio communications by the radio communications system, with acceptably low loss).
  • the signal splitter 32 will also reduce the signal strength available to the GNSS user receiver device 36. These factors will impair the signal strength available to the GNSS user receiver device 36. Nevertheless, there will be sufficient signal strength to allow intermittent or continuous (but degraded) operation of the GNSS user receiver device 36. This intermittent or continuous (but degraded) operation of the GNSS user receiver device 36 is sufficient to support the radio cornmumcation system 'management and synchronization requirements of the integrated radio communications system.
  • an optional bandpass filter 34 and amplifier 35 are added in the signal path from the signal splitter 32 to the GNSS user receiver device 36.
  • signals outside the GNSS frequency band of operations are routed to an enhanced GNSS user receiver device along separate signal paths 39, and processed signals, measurements or data are passed from one or more of the receiver/transmitters 33 along other separate signal paths 38.
  • Said signals, measurements and data, passed to an enhanced GNSS user receiver device along separate optional signal paths 38 and/or 39, are used to stabilize the acquisition and signal tracking performance of the enhanced GNSS user receiver device according to techniques known in the prior art (recently disclosed).
  • Examples of said signals outside the GNSS frequency band of operations which may be used singly or in combination to stabilize the acquisition and signal tracking performance of the enhanced GNSS user receiver device, include but are not limited to NOR signals, FM broadcast signals, TV broadcast signals and NDL Mode 4 signals transmitted from ground stations.
  • an ultra-stable oscillator is also used to stabilize the G ⁇ SS user receiver device. Initial G ⁇ SS signal acquisition while an aircraft is stationary on the ground, using the methods disclosed, can be used to stabilize the oscillator and initiate tracking of G ⁇ SS signals. Once the oscillator state is stabilized, it can coast through short periods of signal loss and maintain G ⁇ SS signal tracking while the aircraft is in flight.
  • position information required by the integrated radio communications system is provided by an external source and the G ⁇ SS user receiver device, operating through the common antenna 31, is used only for the generation of appropriate timing signals.
  • the G ⁇ SS receivers 36 pass unprocessed RF or intermediate-frequency (IF) signals, or a sampled-data equivalent, to the system controllers 37 and the data arbitrators 25 contained therein; said signals are then passed to other peer LRUs with their own embedded G ⁇ SS receivers 36.
  • each GNSS receiver is configured to process separately the signals it has received locally from the antenna connected to its own LRU, and the signals it has received remotely from other peer LRUs.
  • the position and time estimates for these various signal sets will differ slightly due to differences in antenna placement. These differences may be tolerated, or compensated (using external attitude information for the aircraft), or used to determine an independent attitude estimate for the aircraft in addition to the position and time estimate.
  • One hardware implementation of the GNSS receiver involves the use of N-K receiver channels and an enhanced navigation filter, where N is the total number of peer LRUs, K is the maximum number of GNSS spacecraft expected to be visible at any instant of time, and the enhanced navigation filter estimates aircraft attitude as well as position and velocity.
  • N is the total number of peer LRUs
  • K is the maximum number of GNSS spacecraft expected to be visible at any instant of time
  • the enhanced navigation filter estimates aircraft attitude as well as position and velocity.
  • other hardware implementations are feasible.
  • the GNSS receivers can generate position and time estimates with greater reliability than if only a single set of signals are available, and the GNSS receivers can "track through" outages of the local signal set due to transmission events associated with its local LRU.
  • the one or more GNSS receivers embedded in the radio LRUs receive "cuing" information from an external GNSS user receiver that is itself directly-connected to a dedicated GNSS user receiver antenna, said cuing information comprising GNSS downlink navigation data and aircraft position and velocity estimates, and said cuing information delivered to the embedded GNSS receivers through the data arbitrators.
  • the embedded GNSS receivers can provide time and attitude information, as well as position and velocity information (if desired) without the need to actually demodulate the downlink GNSS navigation data.
  • the radio communications system implements the ICAO standard VDL Mode 4 protocol.

Abstract

Antenna diversity and antenna reuse are provided by a system comprising two or more multi-channel radios, which may optionally contain embedded GNSS user receiving equipment, with a cooperative sharing strategy among the multi-channel radios, to aeronautical packet data communications and other communications. It offers the following benefit: enhanced data communications performance in a fading environment; enhanced data communications performance at a long range; enhanced data communications performance in the presence of cochannel interference; extendable to an arbitrary number of cooperating peer radios; no single point of failure; no increase in pilot workload or change in operational procedures. If the two or more multi-channel radios contain embedded GNSS user receiving equipment, the shared data can be used to enhance the performance of the embedded GNSS user receiving equipment.

Description

ANTENNA TECHNOLOGY FOR ENHANCED AND COST-EFFICIENT OPERATION OF MULTIPLE AVIONICS SYSTEMS
Reference to Related Applications: The present application claims the benefit of U.S. Provisional Patent
Application Nos. 60/202,116 and 60/202,120, both filed May 5, 2000, whose disclosures are hereby incorporated by reference in their entireties into the present disclosure.
Field of the Invention:
The present invention is directed to the enhancement of air/air packet data communications reliability among aircraft, the enhancement of air/ground packet data communications reliability between aircraft and ground systems, and the reduction in cost for airborne antenna installations associated with packet data communications systems ..that require access to signals from GPS space vehicles.
Background of the Invention:
Aircraft commonly transmit and receive analog voice radio communications, to enable air traffic control and provide for other air traffic services (ATS), via radio equipment operating on selected frequency channels. A single aircraft typically supports at least one radio, and may support several radios, each radio tuned to a different frequency channel. Analog voice communications in the NHF band use frequency channels separated by 25 kHz between channel centers, and also 8.33 kHz between channel centers. The aviation industry is currently developing a digital voice and data capability for ATS which will also operate on 25 kHz channels in the VHF band.
Commercial aircraft may additionally support analog and digital air/ground communications for airline operational control (AOC). One example used in the NHF band is the Aircraft Communications Addressing and Reporting System (ACARS). The ACARS air/ground environment is described in ARIΝC Specification 618. The capabilities of onboard equipment are defined in ARIΝC Characteristics 597, 724 and 724B. Other standards may also apply. The aviation industry is also currently developing enhanced systems for AOC communications which will provide higher data rates and improved networking protocols than those which are available via ACARS.
A large commercial aircraft typically provides three VHF antennas for ATS and AOC communications - typically two of these are dedicated to ATS voice and the third is dedicated to AOC. A partial shift to digital voice is planned for the future in some regions.
The International Civil Aviation Organization (ICAO) has recently recommended for adoption a new radio communications system and protocol known as VHF Data Link Mode 4 (VDL/4). This radio communications system employs a minimum of two frequency channels and can optionally support additional channels. VDL/4 uses aircraft position information, and knowledge of system time, for various functions including the organization of transmissions on the RF channel. Aircraft position information, and knowledge of system time, can be derived from various sources including, as one example, the Global Positioning System (GPS).
A single VDL/4 line replaceable unit (LRU) comprises a chassis and associated VDL/4 electronics which support a minimum of two frequency channels and can optionally support additional channels. When a VDL/4 LRU is connected to a single antenna it can typically receive on multiple frequencies at once or transmit on any single frequency. A VDL/4 LRU connected to a single antenna is typically incapable of receiving on any channel during periods when it is transmitting on any single channel, although future advances in technology could enable simultaneous transmission on frequency f, and reception on frequency f2 if the frequency separation Δf = fj - f2 is sufficiently great. A VDL/4 LRU connected to two or more antennas (for example top-mounted and bottom-mounted) may be capable of simultaneous transmission on frequency ft via one antenna and reception on frequency f2 via another antenna using current technology.
In transport category aircraft, overall operational reliability is typically enhanced by use of dual-redundant and sometimes triple-redundant systems. When applied to packet data communications e.g. VDL/4, operational reliability may be enhanced with a dual installation comprising two VDL/4 LRUs and two antennas, each VDL/4 LRU connected to a single antenna. In this type of installation the two VDL/4 LRUs are typically denoted as a "left" and "right" LRU. Failure of the "left" LRU can be compensated by the coήtinuedJoperation of the "right'" LRU. Individual receiver and transmitter units, contained within the two VDL/4 LRUs, can also be dynamically re-assigned to different channels by a human operator or automatic control system capable of commanding the two VDL/4 LRUs (in some cases switching the receive or transmit function for a given frequency channel from one LRU to another LRU) in order to minimize the total number of receiver units and transmitter units needed to achieve a desired level of operational flexibility and reliability. This type of redundant installation is described in working paper 49 of ICAO/AMCP/7 (Montreal, 22-30 March 2000). Since each VDL/4 LRU is connected to a single antenna in this type of installation, each VDL/4 LRU may be incapable of receiving on any frequency while it is transmitting on any single frequency. If two antennas were provided to each VDL/4 LRU, each VDL/4 LRU would have the potential to receive on frequency/; while transmitting on frequency/, but this configuration requires two antennas for each of two VDL/4 LRUs, for a total of four antennas. If two antennas were shared so that each antenna is connected to both
VDL/4 LRUs simultaneously, the number of antennas can be limited to two but in this case the signal strength available to each VDL/4 LRU is reduced.
A concern of aeronautical radio communications systems, as for all radio communications systems, is the need to minimize the effects of environmental noise, cosite noise, radio-frequency propagation anomalies and antenna gain effects which can adversely affect communications reliability. In the aeronautical VHF bands, these factors are typically much more significant that receiver-generated noise.
FIG. 1 illustrates a dual-redundant configuration of antennas and radio LRUs known to the prior art. In this configuration a first antenna 11 and first radio LRU 12, and a second antenna 13 and second radio LRU 14, operate in parallel and support human (e.g., pilot and copilot) and other avionics systems 15 operational needs. Two antennas and two radio LRUs exist in this configuration, but the radio LRUs do not cooperate at a peer level. Instead they operate in accordance with commands issued by human operators or other avionics systems. For packet data transmission, only one radio LRU may be used at a time on any single frequency since transmission by two radio LRUs at the same time on the same frequency would result in garbled transmissions (even if the data transmitted by the two radio LRUs is the same). For packet data reception, again one radio LRU may be used with the other reserved as a spare (even if it is active); alternatively both may deliver received data to other onboard systems. In the latter case where both radio LRUs deliver data to other onboard systems, care must be exercised to ensure that the delivery of multiple copies of identical data does not adversely affect onboard operations. In some cases involving packet data communications, a data link layer technical acknowledgement is required to be sent when a data packet is received. In order to prevent the simultaneous transmission of this technical acknowledgement by radio LRU 12 and radio LRU 14, which could lead to garbled transmissions, the acknowledgement circuit or other device may be contained within the aggregate of other onboard systems 15 and may be connected to only one of the radio LRUs 12 or 14 at any one time. However, this may create a single point of failure unless redundant acknowledgement devices are provided within the aggregate of other onboard systems 15, with appropriate switching mechanisms between the multiple radio LRUs and multiple acknowledgement devices. For some radio systems, e.g. VDL/4, accurate position and time information is used as part of the nominal channel management scheme, and may be provided by a GNSS antenna 16 and GNSS user receiver device 17 or alternative navigation system and an accurate clock. The position and time information may be passed to the radio LRUs and other onboard systems, as required, via direct interwiring from source systems or via other intermediate systems.
If the GNSS is used for determination of position and time, current industry practice is that an appropriate antenna must also be installed (if it does not already exist), along with appropriate interwiring to connect the antenna to the GNSS user receiving device. This represents a significant expense. A single common antenna supporting a GNSS user receiving device and a radio communications device is not traditionally considered since the radionavigation function, supported by the GNSS user receiving device, is traditionally considered to be a safety-critical function which cannot tolerate any significant loss in performance, either due to a suboptimal antenna, suboptimal antenna placement, or periods of time when the GNSS user receiving device is effectively disconnected from the antenna (for example during periods of time when the radio communications device is transmitting). Summary Of The Invention:
This invention is an application of antenna diversity and two or more multichannel radio LRUs, with a novel cooperative sharing strategy among the multichannel radio LRUs, to aeronautical packet data communications and GPS position and time determination. Existing avionics and systems are not designed to accommodate antenna diversity, which is considered to increase the overall level of complexity thereby impairing operational reliability and potentially adding to cockpit workload. The present invention overcomes these concerns and offers the following benefits: a) Enhanced data communications performance in a fading environment; b) Enhanced data communications performance at long range; c) Enhanced data communications performance in the presence of cochannel interference; d) Extendable to an arbitrary number of cooperating peer radio LRUs; e) No single point of failure; f) Improved on-aircraft testing of radio functionality; g) No increase in pilot workload or change in operational procedures; h) Elimination of a separate GPS antenna with consequent reduction in cost.
Brief Description Of Drawings:
FIG. 1 illustrates a dual-redundant configuration of antennas and radio LRUs known to the prior art.
FIG. 2 illustrates an embodiment of the present invention comprising two multi-channel radio LRUs each connected to a separate antenna, wherein each radio LRU contains a data arbitrator designed to operate with one or more peer radio LRUs in a distributed architecture. This embodiment still relies on a separate GPS antenna and electronics to provide position and time information.
FIG. 3 illustrates one antenna and LRU for another embodiment of the present invention, wherein each radio LRU contains an internal GPS signal processing capability and a data arbitrator designed to operate with one or more peer radio LRUs in a distributed architecture. Detailed Description Of The Invention:
Various preferred embodiments of the present invention will be set forth in detail with reference to Figs. 2 and 3.
FIG. 2 illustrates a preferred embodiment of the present invention wherein a first antenna 21 and radio LRU 22, and a second antenna 23 and radio LRU 24, each contain a data arbitrator element 25. In this embodiment the two radio LRUs operate as cooperative peers and exchange data automatically to assist each other in achieving operational requirements. The radio LRUs may be single-channel or multi-channel, analog or digital or hybrid, and operate in any band, although for the purpose of the present invention they must be tuneable to the same frequencies and the benefits of at least one preferred embodiment of the present invention are only available on frequencies where packet data transmissions are supported.
Each radio LRU 22 and 24 receives configuration commands (e.g., tuning frequency, applications to be supported) and data for transmission from external systems, and delivers data it has received, and communicates its current status, to external systems. An interwiring means 29, such as a wiring harness, connects the data arbitrators 25 of the various radio LRUs. The interwiring means may be direct or may alternatively pass through intermediate systems.
An optional GNSS antenna 26 and GNSS user receiver device 27 may be used as one of several alternative methods to provide time signals and position information to the radio LRUs (as well as other devices not shown).
In normal operation each radio LRU 22 and 24 may be tuned to a separate channel or group of channels in support of operational needs as determined by e.g. internal software configuration or external commands. Each radio LRU also requests "shadow reception service" for its data-oriented applications from its peer radio
LRUs, via the associated data arbitrators 25. If one or more of the peer radio LRUs have unassigned resources available (i.e., ability to tune to and receive RF signals on requested channels in addition to the channels supporting operational need as determined by e.g. internal software configuration or external commands), the one or more of the said peer radio LRUs configure their unassigned resources as required to provide the requested shadow reception sendee. The peer radio LRUs communicate their requests and current configuration via the interwiring means between radio LRUs, said interwiring means carrying mter alia radio coordination and configuration data as well as received signals or u'ser message data received via'the radio channels for which shadow reception service was requested. The coordination protocols between radio LRUs are ideally configured to allow requests for shadow reception service to be specified according to a priority scheme. Thus, if a peer radio LRU has limited resources which can accommodate some but not all of the requests for shadow reception service from its peer radio LRUs, it may assign its resources to the requests with the highest priorities.
In one preferred embodiment of the present invention, the data arbitrators 25 operate above the Media Access Control (MAC) sublayer of the data protocol supported by the radio LRUs, so for data reception a data arbitrator will handle a packet after it has been checked to ensure error-free reception, but e.g. before generation of a technical acknowledgement. When a data message is successfully received without error by e.g. radio LRU 24, it is passed to the associated data arbitrator 25 which is a software process internal to the radio LRU. The data arbitrator 25 maintains a data base of appropriate identifying data for all received radio messages associated with frequencies for which it and its associated radio LRU have primary responsibility, which said messages it has received from any source. The nature of the appropriate identifying data for a message can vary from system to system, but should be sufficient to uniquely identify a message received on any frequency, by any radio LRU, within a short span of time on the order of several seconds. Possible examples of such appropriate identifying data include but are not limited to a hash of the message, such as a CRC check, and the message arrival time and ID of the sending aircraft. When a data arbitrator receives a message from its associated radio LRU or the interwiring means, said message having been received on a frequency for which the data arbitrator and radio LRU has primary responsibility as determined e.g. by its internal software configuration or external command, the data arbitrator must determine if it has already received and processed the data message from another source. It does this by comparing the appropriate identifying data, for the data message received, with the stored identifying data for messages it has already processed and passed to external systems according to its primary responsibility as determined e.g. by its internal software configuration or external command. If the data arbitrator determines that the data message has not already been processed and passed to external systems, the data message is processed and passed to appropriate external systems and the appropriate identifying data is stored. Otherwise, the data message is cleared without further processing. Periodically or aperiodically, the stored data may be cleared or overwritten. If the data arbitrator receives a data message from its associated radio LRU, said data message received on a frequency for which the radio LRU has accepted shadow reception responsibility, it is passed to the data arbitrator of the appropriate peer radio LRU which requested the shadow reception service via the interwiring means. This embodiment is preferred since the data arbitrators operate above the MAC sublayer, minimizing data rate and bandwidth requirements on the interwiring means between data. Selected metadata, such as signal arrival time and signal strength associated with received messages, may also be passed over the interwiring means. hi a second embodiment of the present invention, the data arbitrators operate below the MAC sublayer and pass either soft-decision metrics from a demodulator, radio-frequency signals downconverted to an intermediate frequency, or radio- frequency signals themselves. This embodiment allows soft-decision combining or antenna beamforming synthesis, which can enhance receive performance, but requires wider bandwidth interwiring means. In this embodiment the data arbitrator is not required to store data relating to messages it has already processed according to its primary responsibility, since the intent of this embodiment is to generate a single estimate of the transmitted message based on the multiple received signals.
For data transmission, a data packet may be formatted for transmission and bypass the data arbitrator 25 within a radio LRU. In the fault-free case there is no need for the data arbitrator to handle data prepared for transmission since the radio LRU with primary responsibility can make the transmission and only a single transmission on any given frequency is desired.
In one embodiment of the present invention the data arbitrators have no ability to re-route data prepared for transmission from one radio LRU A to another radio LRU B.
In another embodiment of the present invention the data arbitrator associated with a radio LRU A may be configured to route a packet prepared for transmission to another compatible data arbitrator for a peer radio LRU B that is able to transmit the data which has been prepared for transmission by radio LRU A, in order to use the transmitter in radio LRU B and compensate for a failed transmitter in radio LRU A. Radio LRUs may be configured to receive simultaneously on multiple frequencies using multiple protocols, but transmit on only one frequency (perhaps using only one protocol). For example, a two-way voice radio may also provide shadow reception service according to certain data protocols without any ability to transmit according to said data protocols. In this way a voice radio A can provide an enhancement of overall data reception performance for separate data radio B, at marginal increase in cost.
Multiple radio LRUs may be simultaneously configured with primary responsibility for a given frequency/, and these radio LRUs may request shadow reception service for frequency/ from each other as well as other peer radio LRUs. In this case the individual radio LRUs with primary responsibility may each individually rely on a single receiver module for the primary and shadow responsibility, consuming no additional resources but passing received data to the requesting peer radio LRU(s) via the interwiring means. Each radio LRU with primary responsibility, which has requested shadow reception service, separately arbitrates the available data and can deliver received messages to external systems independent of its peers. In this way the present invention can mimic the operational architecture of existing systems, while still providing enhanced receive performance. In one embodiment of the present invention, two peer radio LRUs A and B are employed with each connected to a dedicated antenna; radio LRU A takes primary responsibility for all applications and radio LRU B serves as a redundant backup also providing shadow reception service to all applications supported by radio LRU A. Therefore all transmission events are handled by radio LRU A and radio LRU B provides a simultaneous receive capability during periods of transmission by radio LRU A, as well as a second receive capability when radio LRU A is not transmitting. The present invention may be extended in an obvious way to multiple antennas and radio LRUs (greater than 2). For example, on a typical commercial aircraft there may be three VHF antennas available. Each can be connected to a different multichannel radio LRU A, B and C and those three multichannel radio LRUs A, B and C may be interwired in an extension of the concept described herein. In operation, radio LRU A and B may be operationally associated with ATS voice communications and radio LRU C may be operationally associated with AOC voice and data communications, automatic dependent surveillance broadcast (ADS-B) transmission and reception, weather 'uplink reception and other data applications. Radio LRUs A and B would not make any requests for shadow reception since they are operationally associated with voice communications. Radio LRU C however would request shadow reception services from radio LRUs A and B for its numerous data-oriented channels. If radio LRUs A and B had resources available, they would tune those resources to the requested channels and deliver any data messages received on those channels to radio LRU C. Radio LRU C would then have the benefit of three diversity antemias for its data-oriented applications.
The likelihood of successful data reception by a single antenna/radio LRU pair is determined in part by the strength of the signal in space, the gain of the receiving antenna, and the noise experienced by the radio LRU's demodulator. The present invention is beneficial because antenna gain patterns are not exactly uniform in azimuth and elevation, and noise and interference events are not perfectly identical on all antennas simultaneously. Consider an incoming radio signal arriving on frequency /from azimuth φ and elevation θ with field strength S, a d no onboard transmission. Considering the gain patterns of the k antennas connected to the k radios tuned to frequency/ and the noise statistics NoJc experienced by the k radio LRUs, the probability of successful message reception for a given radio LRU k may be denoted pk( φ, θ, S, NoJc ) ≥ 0. Assuming that the statistics of successful message reception across the k radio LRUs are uncorrelated, the probability that at least one of a set of radio LRUs {k} will receive a given message successfully is
Pr {success} = 1 - J (1 - pk (f, φ, θ, S, No k )) , which is greater than any of the pk if all k pk > 0.
If two radio signals arrive at the same time on frequency/, the ability of a radio LRU A to discriminate between them, and successfully demodulate without error at least one of them, depends in part on the relative signal strength between the two said signals at the output of the antenna to which the radio LRU A is connected. If a second radio LRU B is tuned to frequency/, in order to provide a shadow reception service for radio LRU A, each of the two radio LRUs has a chance to successfully demodulate at least one of the messages (typically the stronger of the two). Furthermore, since each antenna provides a different gain pattern over azimuth and elevation, and the two radio signals are likely to arrive from different azimuths and elevations, each radio LRU A and B tuned to frequency/ according to the present invention will likely experience a different relative signal strength' between the two radio signals. So even if radio LRU A experiences a poor relative signal strength, radio LRU B may experience a better relative signal strength that allows at least one of the radio signals to be successfully demodulated. If a multichannel radio LRU A is required to transmit on frequency/, it may be unable to simultaneously receive on another frequency/ ≠/. However, a peer radio LRU B may be able to receive on frequency/ during a transmission by radio LRU A on frequency/, thereby allowing an effective capability for simultaneous transmission and reception on multiple frequencies. A first embodiment of the present invention does not contemplate the delegation of transmission responsibility from one radio LRU A to a peer radio LRU B in normal fault-free operation. However, the delegation of transmit responsibility could be used to provide fail-soft operation among a group of peer radio LRUs. For example, if a radio LRU A determines through diagnostic self-test or other means that its transmit capability is failed or degraded, it could potentially delegate transmit responsibility to a given other radio LRU B (possibly selecting a different peer radio LRU for different transmit events). This capability would not preclude the ability of a pilot or other operator (human or automatic) to reconfigure the primary responsibilities of the radio LRUs in accordance with normal failure procedures. A second embodiment of the present invention contemplates the delegation of transmit responsibility from one radio LRU A to a peer radio LRU B in normal fault- free operation, subject to predefined criteria such as message priority, length, or possible refinements such as known azimuth and elevation to an intended recipient and consideration of known or estimated antenna gain patterns for the multiple antennas associated with the multiple radio LRUs.
The present invention provides a full over-the-air loop-back test capability. Under the control of appropriate diagnostic software, a radio LRU A can request shadow reception service from another radio LRU B for a frequency channel/, on which radio LRU A is authorized to transmit. Radio LRU A can then transmit a message to itself, which may be received by radio LRU B and delivered to radio LRU A via the associated data arbitrators and interwiring. The benefits of the present invention are foreseen primarily with the application of multi-channel radio LRUs. However, the use of single-channel radio LRUs provides a residual benefit.
FIG. 3 illustrates the use of a single antenna 31, in a preferred embodiment according to the present invention, for an integrated radio communications system LRU which relies in part on accurate positioning information and timing signals from the GNSS. The integrated radio communications system comprises an antenna 31, a signal splitter and switch 32, a plurality of receiver/transmitters 33, a GNSS user receiver device 36, and a system controller 37 which contains, in a preferred embodiment, the data arbitrator 25. The GNSS user receiver device 36 provides navigation and system timing for the radio communications system. If installed on an aircraft, the antenna 31 could be bottom-mounted or top-mounted. The signal splitter and switch 32 provides a fan-out of incoming RF signals to a plurality of receiver/transmitters 33, and also provides a switching means to switch a single active transmitter to the shared antenna while blocking the signal flow to the remaining receiver/transmitters, thereby preventing damage to the remaining receiver/transmitters. According to the present invention, the signal splitter and switch 32 also provides a fan-out of the incoming RF signals to the GNSS user receiver device 36. The signal splitter and switch 32 also blocks the signal flow from any of the active transmitters 33 to the GNSS user receiver device 36, thereby preventing damage to the GNSS user receiving device 36.
The antenna 31 may be designed for radio communications without regard to GNSS signal reception, and may be bottom-mounted. The cabling from the antenna to the signal splitter and switch 32 will introduce some additional loss (this cabling should be selected to accommodate the propagation of RF signals in the GNSS band of operation, as well as the band of operation used for radio communications by the radio communications system, with acceptably low loss). The signal splitter 32 will also reduce the signal strength available to the GNSS user receiver device 36. These factors will impair the signal strength available to the GNSS user receiver device 36. Nevertheless, there will be sufficient signal strength to allow intermittent or continuous (but degraded) operation of the GNSS user receiver device 36. This intermittent or continuous (but degraded) operation of the GNSS user receiver device 36 is sufficient to support the radio cornmumcation system 'management and synchronization requirements of the integrated radio communications system.
In another embodiment of the present invention intended to enhance the operational availability and reliability of the GNSS user receiver device 36, an optional bandpass filter 34 and amplifier 35 are added in the signal path from the signal splitter 32 to the GNSS user receiver device 36. Alternatively or in addition to said optionalbandpass filter and amplifier, signals outside the GNSS frequency band of operations are routed to an enhanced GNSS user receiver device along separate signal paths 39, and processed signals, measurements or data are passed from one or more of the receiver/transmitters 33 along other separate signal paths 38. Said signals, measurements and data, passed to an enhanced GNSS user receiver device along separate optional signal paths 38 and/or 39, are used to stabilize the acquisition and signal tracking performance of the enhanced GNSS user receiver device according to techniques known in the prior art (recently disclosed). Examples of said signals outside the GNSS frequency band of operations, which may be used singly or in combination to stabilize the acquisition and signal tracking performance of the enhanced GNSS user receiver device, include but are not limited to NOR signals, FM broadcast signals, TV broadcast signals and NDL Mode 4 signals transmitted from ground stations. hi a third embodiment of the present invention, an ultra-stable oscillator is also used to stabilize the GΝSS user receiver device. Initial GΝSS signal acquisition while an aircraft is stationary on the ground, using the methods disclosed, can be used to stabilize the oscillator and initiate tracking of GΝSS signals. Once the oscillator state is stabilized, it can coast through short periods of signal loss and maintain GΝSS signal tracking while the aircraft is in flight.
In a fourth embodiment of the present invention, position information required by the integrated radio communications system is provided by an external source and the GΝSS user receiver device, operating through the common antenna 31, is used only for the generation of appropriate timing signals. In a fifth embodiment of the present invention, the GΝSS receivers 36 pass unprocessed RF or intermediate-frequency (IF) signals, or a sampled-data equivalent, to the system controllers 37 and the data arbitrators 25 contained therein; said signals are then passed to other peer LRUs with their own embedded GΝSS receivers 36. In this embodiment, each GNSS receiver is configured to process separately the signals it has received locally from the antenna connected to its own LRU, and the signals it has received remotely from other peer LRUs. The position and time estimates for these various signal sets will differ slightly due to differences in antenna placement. These differences may be tolerated, or compensated (using external attitude information for the aircraft), or used to determine an independent attitude estimate for the aircraft in addition to the position and time estimate. One hardware implementation of the GNSS receiver involves the use of N-K receiver channels and an enhanced navigation filter, where N is the total number of peer LRUs, K is the maximum number of GNSS spacecraft expected to be visible at any instant of time, and the enhanced navigation filter estimates aircraft attitude as well as position and velocity. However, other hardware implementations are feasible.
Since multiple sets of GNSS signals are available, the GNSS receivers can generate position and time estimates with greater reliability than if only a single set of signals are available, and the GNSS receivers can "track through" outages of the local signal set due to transmission events associated with its local LRU.
In a sixth embodiment of the present invention, the one or more GNSS receivers embedded in the radio LRUs receive "cuing" information from an external GNSS user receiver that is itself directly-connected to a dedicated GNSS user receiver antenna, said cuing information comprising GNSS downlink navigation data and aircraft position and velocity estimates, and said cuing information delivered to the embedded GNSS receivers through the data arbitrators. In this embodiment the embedded GNSS receivers can provide time and attitude information, as well as position and velocity information (if desired) without the need to actually demodulate the downlink GNSS navigation data.
In a specific seventh embodiment of the present invention, the radio communications system implements the ICAO standard VDL Mode 4 protocol.
While various 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 specifically set forth above can be implemented. Therefore, the present invention should be construed as limited only by the appended claims.

Claims

CLAIMS We claim:
1. A system for packet data communications for data-oriented applications, the system comprising: a plurality of radios, each of the plurality of radios supporting at least one packet- oriented data protocol common to all of the plurality of radios, and each of the plurality of radios comprising a receiver; a plurality of antennas in one-to-one communication with the plurality of radios for the packet data communications; and interwiring means for interconnecting the plurality of radios, wherein: each of the plurality of radios further comprises a data arbitrator, in communication with the data arbitrators of the others of the plurality of radios through the interwiring means, for requesting shadow reception service for said data-oriented applications from the other radios, controlling the radio associated with that data arbitrator to provide the shadow reception service in response to requests received from the other radios if the radio can provide the shadow reception service with the resources available, and arbitrating among possible multiple copies of a received packet data message associated with one of the data-oriented applications, said possible multiple copies received by the radio's receiver or by the interwiring means from the other radios, so that only a first copy of said possible multiple copies is further processed and subsequent copies of said possible multiple copies are not further processed.
2. The system of claim 1, wherein the plurality of radios implement a common priority scheme for the requests for shadow reception service, thereby allowing each of the radios to determine a most preferred set of shadow reception service requests.
3. The system of claim 1, wherein each of the radios further comprises a transmitter, and wherein the data arbitrators delegate transmit responsibility among the plurality of radios.
4. The system of claim 1, wherein, when a first one of the radios transmits a self- addressed message, and when a second one of the radios receives the self-addressed message, the second one of the radios transmits the self-addressed message over the interwiring means to the first one of the radios, providing shadow reception service to enable over-the-air loop-back testing.
5. The system of claim 1, wherein each Of the plurality 'of radios comprises a radio LRU for aeronautical packet data communications.
6. The system of claim 5, wherein the plurality of radio LRUs implement a common priority scheme for the requests for shadow reception service, thereby allowing each of the radio LRUs to determine a most preferred set of shadow reception service requests.
7. The system of claim 5, wherein each of the radio LRUs further comprises a transmitter, and wherein the data arbitrators delegate transmit responsibility among the plurality of radio LRUs.
8. The system of claim 5, wherein, when a first one of the radio LRUs transmits a self-addressed message, and when a second one of the radio LRUs receives the self- addressed message, the second one of the radio LRUs transmits the self-addressed message over the interwiring means to the first one of the radio LRUs, providing shadow reception service to enable over-the-air loop-back testing.
9. The system of claim 1, wherein each of the plurality of radios comprises a radio
LRU for packet data conrmunications as well as other communications.
10. The system of claim 9, wherein the plurality of radio LRUs implement a common priority scheme for the requests for shadow reception service, thereby allowing each of the radio LRUs to determine a most preferred set of shadow reception service requests.
11. The system of claim 9, wherein each of the radio LRUs further comprises a transmitter, and wherein the data arbitrators delegate transmit responsibility among the plurality of radio LRUs.
12. The system of claim 9, wherein, when a first one of the radio LRUs transmits a self-addressed message, and when a second one of the radio LRUs receives the self- addressed message, the second one of the radio LRUs transmits the self-addressed message over the interwiring means to the first one of the radio LRUs, providing shadow reception service to enable over-the-air loop-back testing.
13. A system for aeronautical communications, the system comprising: a plurality of radio LRUs; a plurality of antennas in one-to-one communication with the plurality of radio LRUs; and interwiring means for interconnecting the plurality of radio LRUs, wherein: the plurality of radio LRUs are individually configured'to request shadow reception service from other ones of the radio LRUs and to provide the shadow reception service in response to requests received from the other ones of the radio LRUs if said shadow reception service can be provided with resources available, said shadow reception service comprising RF, downcoverted RF or a soft-decision demodulator output signal stream.
14. The system of claim 13, wherein the plurality of radio LRUs implement a common priority scheme for the requests for shadow reception service, thereby allowing each of the radio LRUs to determine a most preferred set of shadow reception service requests.
15. The system of claim 13, wherein each of the radio LRUs further comprises a transmitter, and wherein the data arbitrators delegate transmit responsibility among the plurality of radio LRUs.
16. The system of claim 13, wherein, when a first one of the radio LRUs transmits a self- addressed message, and when a second one of the radio LRUs receives the self- addressed message, the second one of the radio LRUs transmits the self-addressed message over the interwiring means to the first one of the radio LRUs, providing shadow reception service to enable over-the-air loop-back testing.
17. A system comprising: a GNSS user receiving device; a radio communications device; a single antenna shared by the GNSS user receiving device and the radio communications device; and a signal splitter and switch for selectively connecting the single antenna to the GNSS user receiving device or to the radio communications device.
18. The system of claim 17, further comprising a means to enhance performance of the GNSS user receiving device based on tracking of signals available outside the GNSS frequency band of operations.
19. The system of claim 17, wherein the radio communications device comprises a VHF radio communications device installed on an aircraft.
20. The system of claim 19, further comprising a means to enhance performance of the GNSS user receiving device based on tracking of signals available outside the GNSS frequency band of operations.
21. The system of claim 17, wherein the radio communications device comprises a VDL Mode 4 radio communications device installed on an aircraft.
22. The system of claim 21, further comprising a means to enhance performance of the GNSS user receiving device based on tracking of signals available outside the GNSS frequency band of operations.
23. The system of claim 21, wherein the GNSS user receiving device is employed for the limited purpose of generating appropriate time signals.
24. A system comprising: a plurality of communications devices, each with an embedded GNSS user receiving device; and a single separate antenna to which each communications device with the embedded GNSS user receiving device is connected locally; wherein the plurality of communications devices with the embedded GNSS user receiving devices exchange RF, IF or sampled-data equivalent signals associated with the GNSS, and the embedded GNSS user receiving devices process said exchanged signals in addition to the GNSS signals received via said locally-connected antenna.
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Cited By (7)

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US8940292B2 (en) * 2003-01-28 2015-01-27 Wake Forest University Health Sciences Enhancement of angiogenesis to grafts using cells engineered to produce growth factors
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CN103675848A (en) * 2013-12-26 2014-03-26 东莞市泰斗微电子科技有限公司 Signal transmission method and system based on multichannel GNSS signals
CN113472378A (en) * 2021-08-11 2021-10-01 中国商用飞机有限责任公司 Civil aircraft wireless avionics network system architecture and special wireless transmission device

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