Universal Access TransceiverSystem DescriptionChris MoodyOctober 2000 1999 The MITRE Corporation
2Outline HistoryUAT Description–– System OverviewSome DetailsUAT Role in CNS Architecture and TransitionSpectrum and StandardsSummary Attributes 1999 The MITRE Corporation. All rights reserved.
3A Brief History of UAT Began around 1995 as part of larger CAASD IR&Dinitiative on broadcast data link–– 6 prototype systems flown on small aircraftADS-B, TIS-B, and Wx uplink demonstratedCargo Airlines incorporate UAT in theirevaluation--UPS-AT develops UATUAT becomes part of SF-21 Link Evaluation studyUAT part of winning bid for FAA’s CapstoneprogramRTCA PMC approves establishment of UATMOPS working group 1999 The MITRE Corporation. All rights reserved.
4UAT Overview Designed specifically for ADS-B with noconstraints from legacy systemsSimplicity and robustness were paramountdesign objectivesOperates on a single common wideband channel1 Mbps channel rateCapable of supporting multiple broadcastapplications to foster early equipage 1999 The MITRE Corporation. All rights reserved.
5UAT: Broadcast Data Link Supporting ADS-B, TIS-B & FIS-BUATAirborneTransceiverS-BAD -airairFIS-BTIS- ckerTracksATC System 1999 The MITRE Corporation. All rights reserved.UATTIS-BGround(non-ADStargets) TransceiverFIS-BWeatherServerObservationsWX RadarForecastsGraphicsSUAs
6Waveform Selection Requirements– Good capture effect– relatively efficient and low cost power amplifier– simple/robust decoder Binary FM with high modulation index chosen 1999 The MITRE Corporation. All rights reserved.
7Frequency Band Selection ADS-B requires ARNS allocation--3 alternatives:––– VHF: 108-118 MHzL-band: 960-1215 MHzC-band: 5000-5250 MHzExtremely difficult to assemble enoughcontiguous channels at VHFPropagation loss too high at C band960-1215 MHz has channelization and currentusage most compatible with UAT operation 1999 The MITRE Corporation. All rights reserved.
8UAT Media Access Approach Requirement: Simple and Robust logic for aircraft mediaaccessADS-B transmissions occur based on pseudorandomselection of one of 3200 Message Start Opportunities(MSO)UAT Frame 1 sec.GroundBroadcast(32 time slots)Aircraft Reports (random)Ground Message (464 bytes payload) 1999 The MITRE Corporation. All rights reserved.ADS-B Message (16/32 bytes payload)
9ADS-B Message FormatSymbols/Bits4368SyncLengthIdent128 or 256Payload2448CRCFEC4 Each aircraft transmits exactly one message each second Standard Forward Error Correction (FEC) increasesmessage robustness to noise and interference FEC plus Error Checking (CRC) combine for an extremelylow undetected message error rate 10-10 1999 The MITRE Corporation. All rights reserved.
10State Vector Component of Every ADS-BMessageByte #Bit 7Bit 6Bit 5Bit 4Bit 3012Bit 2Bit 1Bit 0.A23A24 (LSB)ICAO 24-Bit Aircraft AddressA1 gn)9(MSB)NUC R(LSB)10N-S Velocity11(LSB)12(Sign)15(LSB)Pressure Altitude Rate 1999 The MITRE Corporation. All rights reserved.1 PPS OK(LSB)H.Pos.OK(Sign)Pressure AltitudeAir/Ground StateNUC PE-W Velocity1314(MSB)Anon.(LSB)(sign)(LSB)(MSB)
11ADS-B Message Set and TransmissionSchedule for Full Capability Participant State Vector Call SignState Vector TCP TCP 1State Vector TCP TCP 1State Vector [future payload]One transmitted message every second--4second message rotation 1999 The MITRE Corporation. All rights reserved.
12Independent ADS-B Report Validation:Aircraft Perspective ADS-B message payload includes the precise transmissiontime (MSO)Receiving aircraft UAT reports precise time of receptionwith decoded message payloadApplication can perform passive range verification of ADSB reported positionPreliminary UPSAT flight test data showed time-based slantrange estimates to be within 0.2 nmi of that indicated byADS-BADS-B message plustransmission time 1999 The MITRE Corporation. All rights reserved.
13Independent ADS-B Report Validation:Ground ATC Perspective Single ground site can perform same range validation asaircraftMultiple networked sites allows position estimate based ondifferential burst arrival times at ground stationsGS1 1999 The MITRE Corporation. All rights reserved.GS2GS3
14Independent Position Estimate from GroundMessages Time slot and ground station location provided in each uplinkmessage headerAllows aircraft to derive independent position estimateAbsolute time not required on aircraftAbsolute time required at ground stationsGS1 1999 The MITRE Corporation. All rights reserved.GS2GS3
15Spectrum and Standards All experimental assignments to date have beenat 966 MHzFAA shifting frequency to 981 MHz for futureCapstone (for greater international viability)RTCA PMC go ahead for MOPS developmentICAO AMCP WG C to consider SARPsdevelopment in their future work program 1999 The MITRE Corporation. All rights reserved.
16960-1215 MHz ARNS BandAll UAT experimentalassignments to dateFuture Capstone UAT960970“NationalAllotment”(TACAN USEIN U.S.) 1999 The MITRE Corporation. All rights reserved.9809901200Internationally Coordinated(TACAN/DME USE)(GPS 1164-1188)12101215
17Summary Intended for a dedicated channel--so capacity andperformance limited mainly by system self interferenceEvery ADS-B message has a complete State Vector––– no tracking or message assembly requiredno lat/lon decompression or ambiguity resolution requiredno need to burden application with detection of transmissionerrorsFull resolution position reportingConsistent operation in all flight domainsNo channel sensing required for tx--minimal tx-onlyimplementations are viableNo tuning procedures required to access full suite ofbroadcast servicesSimple, proven frequency modulation technique 1999 The MITRE Corporation. All rights reserved.
Backup Material 1999 The MITRE Corporation
19Evaluation Unit Airborne Subsystem30 Watts transmit powerADS-B ReportsT/RUAT TransceiverT/R(Internal to LDPU)TIS-B, FIS-BApplicationProcessor(s)Antenna Switching(each second): Receive--TBTB Transmit--TTBBTTBB. 1999 The MITRE Corporation. All rights reserved.
20UAT Spectrum (Measured)Source: UPS-AT 1999 The MITRE Corporation. All rights reserved.
Possible UAT Transition and Role in CNSArchitectureC/A based on active interrogations augmented by UAT-based ADS-Bhybrid surveillanceC/A based on passiveUAT ranging andADS-BOther aircraft(e.g., GeneralAviation)Final A-Asurveillancevia TCAS txpdrinterrogationvia TIS-BuplinkInterim A-Asurveillancevia UATA-AUAT EquipageAir Carrieraircraft withcollision avoidance(C/A) mandateUATEquipagetimeSpecialized fleetepuipage beginsGround stationdeployment beginsTIS-B, FIS-Bservices available 1999 The MITRE Corporation. All rights reserved.Integrated UAT/GPSnavigator avionicsavailable,VOR/DME avionicsbegin to be displacedUAT-based groundinfrastructurecomplete. UAToffers nav backupin medium endhigh density airspaceSSR transpondersdisplaced,ADS-B requiredin designatedairspace
22Considerations in Choosing UAT Frequency Frequency should be below 1025 OR above 1150 minimize cosite effects from airborne DME interrogators avoid UAT interaction with ground DME transponders Avoid proximity to 1030 (TCAS) and L5 also for airborne cosite Minimize displacement of LOC assignments (more limited than VOR) Low end of band preferable for best ADS-B air-air propagationUAT CenterFrequencyUATGuardDME GroundReply Frequency980VHF NavPairing108.2(VOR)# U.S. Assignmentsthat Include DME25 1999 The MITRE Corporation. All rights reserved.UATGuard981982108.3(LOC)108.4(VOR)820
Considerations in Choosing UAT Frequency 980 981 982 DME Ground Reply Frequency UAT Center Frequency UAT Guard UAT VHF Nav Pairing 108.2 (VOR) 108.3 (LOC) 108.4 # U.S. Assignments that Include DME 25 8 20 Frequency should be below 1025 OR above 1150 minimize cosite effects from airborne DME interrogators avoid UAT interaction with .