Presentation on theme: "Universal Access Transceiver (UAT)"— Presentation transcript:
1 Universal Access Transceiver (UAT) Briefing forSeminar on Implementation of Data Link and SATCOM Communications17-19 November 2003Bangkok, ThailandRob StrainMITRE CAASDon behalf ofFederal Aviation Administration
2 Outline Status of UAT Standards and Spectrum Planning Capstone OverviewUAT Technical OverviewHistorySystem Description
4 SARPs and Technical Manual UAT Standards and Recommended Practices (SARPS) development added formally to ACP work program in May 2003 by the Air Navigation CommissionWork on UAT SARPS began by ACP WG-C (formerly AMCP) in June 2002 (initially “at risk”)Mature drafts of core SARPs and Technical Manual are available.SARPs and Tech Manual development entered a validation phase in Oct 2003 with completion and approval by the full panel targeted for 2005.Validation will include some testing of FAA ground station equipment and certified avionics.Frequency planning criteria for UAT will be finalized during validation period
5 UAT SARPs and TM (Concluded) SARPs and TM development build upon existing UAT equipment certification baseline (MOPS/TSO) and over 2 years of operational experience with UATUAT frequency planning criteria are being developed based upon RTCA/FAA testing, amplified by ACP/UAT subgroup analysis for both en route and terminal/approach scenarios.
6 UAT Certification Baseline Activities initiated by RTCA in December 2000 in response to high priority FAA request for industry-developed standards for UATTasked to develop Minimum Operational Performance Standards (MOPS) for a UAT-based ADS-B system on an accelerated scheduleDocument approved by PMC on August 2002 (DO-282)TSO-C154 approved Nov 2002 as basis for equipment certification
7 Participants in Development of UAT MOPS/TSO FAA (Certification, Spectrum, Technical Center, Flight Standards, Safe Flight 21 Program Office, Alaska Region)EurocontrolU.S. Department of DefenseAOPASSA/FAIUPSATRockwell CollinsGarminBoeingL3Comm AnalyticsBAE SystemsSensisJohns Hopkins APL MitreTriosTitanPMEI
8 UAT MOPS40 page compliance matrix for ADS-B MASPS (DO-242A) and FIS-B MASPS is availableUAT also designed toward, and UAT performance assessed against, extended ADS-B air-to-air range criteria from Eurocontrol (A3-to-A3 air-to-air performance in Core Europe 2015 Scenario of TLAT estimated to be miles)TIS-B requirements are expected to be accommodated by UAT
9 UAT Frequency Planning Criteria (1) 978 MHz selected as candidate UAT frequencyWorldwide assignments on this frequency consist of 7 DME/TACAN in EuropeUAT design objective is compatibility with DME without impacting DME/TACAN assignments on channels other than 978RTCA/FAA analysis indicates that this objective has been achievedUAT subgroup performing further analysisFor the UAT subgroup, DFS has performed a “worst case” enroute environment study on UAT compatibility with DME. DFS has proposed en route frequency planning criteria that involves vacating only the 978 MHz channel
10 UAT Frequency Planning Criteria (2) UAT compatibility with JTIDS/MIDS system has also been achieved with analysis including both future high and low density airspace.US authorities approved 978 MHz UAT frequency for national use on 16 April 2003 based on the “aid to radionavigation” footnote for the band (Footnote 5.328).ICAO is seeking an opinion from ITU on the applicability of the above footnote. If ITU indicates that Radio Regulation changes are needed for UAT operation in the MHz band, any such changes could be addressed under an existing agenda item at WRC 2007.
11 Aircraft Integration of UAT Avionics Integration into small aircraft has been demonstrated through FAA Capstone Program. Success of this integration is evidenced by over 2 years of successful operational use.Integration into air transport class aircraft through sharing of the SSR transponder antennas has been analyzed and tested in detail. Results are positive, and this potential integration path is being coordinated with ICAO SCRSP. Detailed SCRSP consideration of UAT/SSR antenna sharing and cosite compatibility is scheduled for Feb 2004.
13 Capstone Phase I: Yukon - Kuskokwim Delta JZZIIK5S84Z4SCMAK85PTUKLGRSHMOUBethelRegion is nearly 100% dependent upon aviationHigh accident ratesNo surveillance radar coverage below 5000 ftBethel is the “hub” for 50+ villagesEquipping 200 single and twin engine aircraft (air taxi)All costs incurred by the FAAPlanning 10 ground stations for this regionConnectivity with Anchorage ACC
14 Capstone Services ADS-B (air-to-air) CFIT (onboard avionics) Provides “enhanced see and avoid”CFIT (onboard avionics)Provides terrain awarenessADS-B (air-to-ground)Enables ATC services via Anchorage ACCTIS-B (ground-to-air radar targets) *Completes see and avoidFIS-B (weather uplink)Provides weather awarenessFlight Dispatch ServicesProvides flight following and asset management servicesFuture services
15 Avionics SelectionFAA solicits avionics proposals for integrated system of GPS, terrain data base, cockpit display and broadcast data link.UPSAT awarded the avionics contract--with UAT as the datalinkbest overall system costavionics package judged to have best probability of implementation within aggressive Capstone schedule
24 First Operational use of Radar-Like Services-- January 2001 / 0018Z Controller vectoring Capstone-equipped aircraft to Bethel, Alaska ILS Runway 18, below radar coverageMaintaining separation from a second Capstone-equipped aircraft using ADS-BSystem certified as part of NAS for routine use
25 Capstone ATC Perspective ADS-B source displayed only if radar unavailable for a given targetADS-B target positions are updated at 6 second rate (adaptable)1 sec update of velocity vector provides rapid indication of turns for ADS-B targets5 nmi separation standard: ADS-B or RadarTrack “bonding” logic ensures single target depicted in cases where radar/ADS-B coverage overlapsADS-B targets “auto-acquire” via 24 bit address filed in flight plan remarksSymbology allows differentiation of Radar and ADS-B targets
26 Some Operational Experiences (1) ADS-B accuracy found consistently superior to radar for ranges greater than 5 nmi from sensorADS-B at 1 second transmission rate:robust to any single message lossprovides rapid turn indications to ATCaids track “bonding”BUT, increases communications/processing load for ATC automation (LAN upgrade recently completed to accommodate additional ADS-B sites)
27 Capstone avionics in vicinity of Bethel AK, 21 Aug 2000 Radar returns (12 second scan interval)ADS-B reports (1 second transmission interval)Cape Newenham radar 130 nmi rangeFlight of FAA’s N40 withCapstone avionics in vicinityof Bethel AK, 21 Aug 2000
28 Some Operational Experiences (2) Possible limitations of ADS-B self-reported integrity (NUC) for some GPS implementationssupplement with independent ground ATC monitoring in CapstoneCapstone providing operational feedback to RTCAReplicate transponder indicators (IDENT, 4096 code)Adjustments to the way GPS integrity is reported (NIC vs NUC)Integrity of 24 bit address (installer discipline, pilot access)
29 Capstone Phase II: Southeast Alaska Extend ADS-B coverage with up to 30 additional sites in Southeast AlaskaFAA equipping additional 200 aircraft in the Juneau area during.150 fixed wing and 50 helicoptersWill be UAT MOPS compliantAll Phase I UAT installations to be upgraded per UAT MOPSTHEN “Self Equippage”
30 Summary PointsUAT has been proven to support the provision of radar-like services in actual ATC operations in Alaska for nearly 3 years--the first ATC operational use of airborne ADS-B worldwideMany areas of the world with little or no radar coverage could benefit from ADS-B in a similar manner. UAT has been proven to be an attractive, cost-effective ADS-B data link for this type of environment.Work currently in progress on UAT SARPS allows its consideration by other States as an ADS-B data link
32 A Brief History of UATBegan around 1995 as part of an independent research project on broadcast data link6 prototype systems flown on small aircraftADS-B, TIS-B, and Wx uplink demonstratedCargo Airlines incorporate UAT in their evaluation--UPS-AT develops UATUAT becomes part of SF-21 Link Evaluation studyUAT part of winning bid for FAA’s Capstone programUAT began as part of an Internally funded project at MITRE/CAASD to assess architcture alternatives for broadcast data link services. This project resulted in the flight testing of 6 prototype units in 1996 and This effort reuslted in the successful demonstration of ADS-B, TIS-B and uplink broadcast weather products.In 1997 representatives from the Cargo Airline Association were invited to witness flight demonstrations of the MITRE prototype systems. This resulted in a decision to include UAT in their multi datalink ADS-B evaluation along with 1090 and VDL4. UPSAT (then IIM corporation) began UAT development as part of the multilink Link Data Processing Unit to be developed for Cargo Aircraft use.FAA’s Safe Flight 21 programtakes on the task of ADS-B Link Evaluation--to include UATIn Spetember 1999 FAA Alaska Region awards contract to UPSAT for large scale trial of new avionics to inlcude UAT data link avionics for approximately 140 aircraft and ground station transceivers for 12 sites
33 UAT OverviewDesigned specifically for ADS-B and Broadcast Uplink Surveillance-Related Services with no constraints from legacy systemsSimplicity and robustness were paramount design objectivesOperates on a single common wideband channel1 Mbps channel rateCapable of supporting multiple broadcast applications to foster early equipageFrom the beginning UAT was designed specifically for the function of ADS-B. The design was a “clean slate” approach in order to remove any constraints from legacy systems that could impose constraints on parameters like message length or channel bandwidth for example.Since ADS-B is seen as the basis for future surveillance and separation assurance, it was important that the system be designed to be both affordable to all classes of users and exhibit a minimum of possible failure conditions. Therefore simplicity and robustness were the key design objectives.To meet these objectives the system was designed for operation on a single widband channel (eliminating the need for tuning procedures or multiple receivers) operating at a 1Mbps data rate.In order to foster early equipage and to appeal to the widest group of aircraft operators, the system also accomodates uplink broadcast traffic to include traffic reports from surveillanc eradars and weather products.UAT was NOT designed to support ATN-style addressed communications
34 UAT Applications and Connectivity AirborneTransceiverADS-Bair-airFIS-BTIS- BADS-Bair-groundObservations WX Radar Forecasts Graphics SUAsADS-BATC Surveillance RadarFIS-BWeather ServerTrackerUATGroundTransceiverTracksTIS-B(non-ADStargets)ATC System
35 Waveform Selection Requirements Good capture effectrelatively efficient and low cost power amplifiersimple/robust decoderBinary FM with high modulation index chosenA key objective in the waveform selection was a high tolerance to self interference. This allows air-air surveillance performance to degrade gracefully under extreme load conditions by allowing a stronger ADS-B report to be received with minimal signal margin relative to an overlapping weaker ADS-B report. This is sometimes referred to as “capture effect”.Waveform level simulations showed a binary FM waveform with high modulation index to be the best choice.
36 Frequency Band Selection Aeronautical band alternatives:VHF: MHzL-band: MHzC-band: MHzExtremely difficult to assemble enough contiguous channels at VHFPropagation loss too high at C bandMHz has best combination of:channelization (1 MHz)compatible current usage (pulsed systems)and propagation characteristicsWhere in the spectrum would a system like UAT be most suitable? FAA has stated their position that ADS-B is most consistent with the spectrum allocation called Aeronautical Radio Navigation Service(ARNS) as this receives the highest level of protection. Three candidate bands with this designation were examined.VHF has favorable long range propagation characteristics, however within this band the channelization is 50 kHz. This would require vacating many contiguous channels of their current uses to make room for UAT. This eliminated the possibility of experimental use and reduces its attractiveness for UAT in all but the longest term.C-band exhibits propagation losses that are very high for ADS-B systems that must operate air-air with omni-directional antennas.The L-band has channelization (1 Mhz) and current usage most compatible with UAT operation. All experimental assignments to date have been at 966 MHz
37 UAT Media Access Approach Requirement: Simple and Robust logic for aircraft media accessADS-B transmissions occur based on pseudorandom selection of one of 3200 Message Start Opportunities (MSO)Ground Broadcast (32 time slots)UAT Frame = 1 sec.Aircraft Reports (random)Ground Message (432 bytes payload)ADS-B Message (18/34 bytes payload)All UAT media access is based on a one second frame. The first 20% of the frame time is bandwidth allocated to UAT ground stations. This portion of the frame contains 32 time slots that are assigned to ground stations on a static basis much like VHF voice frequencies are assigned to ATC sectors. These time slots are reused similarly to VHF voice frequencies based on spectrum management procedures. Each of the 32 time slots can support a 3.7 kbps continuous uplink data rate.The remaining 80% of the frame is devoted to ADS-B message transmissions. Within this portion of the frame transmission time is determined by each aircraft. Every second transmission time is based on pseudorandom selection of one of approximately 3200 discrete Message Start Opportunities (MSO). The selection algorithm was designed to prevent any two stations from repeatedly selecting the same MSO. The MSO is encoded in certain ADS-B messages to allow the receiver to perform a passive ranging calculation on the transmitter--allowing an independent validation of the ADS-B data. A Time Of Transmission and Time Of Reception facility is included in the UAT evaluation units.Note that for purposes of media access, precise timing is not required. Receipt of even one ground message could also serve to establish timing in the absence of GPS were another source of navigation data available
38 ADS-B Message FormatEach aircraft transmits exactly one message each secondStandard Forward Error Correction (FEC):increases message robustness to pulsed interference and noiseprovides an extremely low undetected message error rate ~10-9This slide shows the format of the ADS-B message.The UAT message set includes a “Basic” Message that includes only State Vector information, and a set of 4 “Extended Length” Messages that each inlcude the State Vector plus other variable information required by the RTCA MASPS. Each aircraft transmits one message every second.UAT includes a Reed Solomon Foweard Error Correction (FEC) code that increase the systems toleerance to bit errors caused by noise or interference.Collectively the error checking plus FEC combine to provide for an extremely low undetected message error rate.
39 Independent ADS-B Report Validation: Aircraft Perspective ADS-B message payload includes the precise transmission time (MSO)Receiving aircraft UAT reports precise time of reception with decoded message payloadApplication can perform passive range verification of ADS-B reported positionFlight test data showed time-based slant range estimates to be within 0.2 nmi of that indicated by ADS-BUAT evaluation units encode MSO of ADS-B message transmission in one of the Extended Length messages. Each message received is also appended with a Time Of Reception. This allows the receiver to perform a continuous range validation and time tracking.ADS-B message plus transmission time
40 SummarySystem designed specifically for ADS-B performance and for compatibility in the bandSimplicity and robustness drive the designEvery ADS-B message has a complete State Vector without field truncationno lat/long decompression, participant tracking, multi-message assembly, or ambiguity resolution requiredHigh integrity link layer directly aids certification of applications with stringent requirementsConsistent transmission epoch in all flight domainsNo channel sensing required: minimal transmit-only implementations viableSingle fixed frequency operation for full suite of services