1. Universal Access Transceiver (UAT)
Briefing for
Seminar on Implementation of Data Link and SATCOM Communications
17-19 November 2003
Bangkok, Thailand
Rob Strain
MITRE CAASD
on behalf of
Federal Aviation Administration

2. Outline Status of UAT Standards and Spectrum Planning
Capstone Overview
UAT Technical Overview
History
System Description

3. Status of UAT Standards and Spectrum Planning

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 Commission
Work 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 UAT
UAT 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 UAT
Tasked to develop Minimum Operational Performance Standards (MOPS) for a UAT-based ADS-B system on an accelerated schedule
Document 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)
Eurocontrol
U.S. Department of Defense
AOPA
SSA/FAI
UPSAT
Rockwell Collins
Garmin
Boeing
L3Comm Analytics
BAE Systems
Sensis
Johns Hopkins APL Mitre
Trios
Titan
PMEI

8. UAT MOPS
40 page compliance matrix for ADS-B MASPS (DO-242A) and FIS-B MASPS is available
UAT 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 frequency
Worldwide assignments on this frequency consist of 7 DME/TACAN in Europe
UAT design objective is compatibility with DME without impacting DME/TACAN assignments on channels other than 978
RTCA/FAA analysis indicates that this objective has been achieved
UAT subgroup performing further analysis
For 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.

12. Capstone Overview

13. Capstone Phase I: Yukon - Kuskokwim Delta
JZZ
IIK
5S8
4Z4
SCM
AK85
PTU
KLG
RSH
MOU
Bethel
Region is nearly 100% dependent upon aviation
High accident rates
No surveillance radar coverage below 5000 ft
Bethel is the “hub” for 50+ villages
Equipping 200 single and twin engine aircraft (air taxi)
All costs incurred by the FAA
Planning 10 ground stations for this region
Connectivity with Anchorage ACC

14. Capstone Services ADS-B (air-to-air) CFIT (onboard avionics)
Provides “enhanced see and avoid”
CFIT (onboard avionics)
Provides terrain awareness
ADS-B (air-to-ground)
Enables ATC services via Anchorage ACC
TIS-B (ground-to-air radar targets) *
Completes see and avoid
FIS-B (weather uplink)
Provides weather awareness
Flight Dispatch Services
Provides flight following and asset management services
Future services

15. Avionics Selection
FAA 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 datalink
best overall system cost
avionics package judged to have best probability of implementation within aggressive Capstone schedule

16. Capstone Architecture
ANICS
UAT
Multi-
Function
Display
(CDTI)
TIS-B
FIS-B
ADS-B
GPS
TIS-B
FIS-B
Weather
ADS-B
FIS-B
ATC System
(MicroEarts)
Capstone Communication
and Control System
(CCCS)
ADS-B
UAT
Maint &
Monitor
Archive&
Display
Ground-based transceiver (GBT)
Anchorage Center
Remote Site(s)

17. Capstone Avionics Universal Access Transceiver (UAT)
Multi-function Display
GPS Receiver

18. Avionics Install Kit

19. Ground Broadcast Transceiver (GBT)

20. Typical Capstone Aircraft

21. Traffic and Terrain Display
C182R
+11

22. FIS Weather - Graphics

23. FIS Weather - Text

24. First Operational use of Radar-Like Services-- January 2001 / 0018Z
Controller vectoring Capstone-equipped aircraft to Bethel, Alaska ILS Runway 18, below radar coverage
Maintaining separation from a second Capstone-equipped aircraft using ADS-B
System certified as part of NAS for routine use

25. Capstone ATC Perspective
ADS-B source displayed only if radar unavailable for a given target
ADS-B target positions are updated at 6 second rate (adaptable)
1 sec update of velocity vector provides rapid indication of turns for ADS-B targets
5 nmi separation standard: ADS-B or Radar
Track “bonding” logic ensures single target depicted in cases where radar/ADS-B coverage overlaps
ADS-B targets “auto-acquire” via 24 bit address filed in flight plan remarks
Symbology 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 sensor
ADS-B at 1 second transmission rate:
robust to any single message loss
provides rapid turn indications to ATC
aids 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 range
Flight of FAA’s N40 with
Capstone avionics in vicinity
of Bethel AK, 21 Aug 2000

28. Some Operational Experiences (2)
Possible limitations of ADS-B self-reported integrity (NUC) for some GPS implementations
supplement with independent ground ATC monitoring in Capstone
Capstone providing operational feedback to RTCA
Replicate 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 Alaska
FAA equipping additional 200 aircraft in the Juneau area during.
150 fixed wing and 50 helicopters
Will be UAT MOPS compliant
All Phase I UAT installations to be upgraded per UAT MOPS
THEN “Self Equippage”

30. Summary Points
UAT 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 worldwide
Many 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

31. UAT Technical Overview

32. A Brief History of UAT
Began around 1995 as part of an independent research project on broadcast data link
6 prototype systems flown on small aircraft
ADS-B, TIS-B, and Wx uplink demonstrated
Cargo Airlines incorporate UAT in their evaluation--UPS-AT develops UAT
UAT becomes part of SF-21 Link Evaluation study
UAT part of winning bid for FAA’s Capstone program
UAT 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 UAT
In 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 Overview
Designed specifically for ADS-B and Broadcast Uplink Surveillance-Related Services with no constraints from legacy systems
Simplicity and robustness were paramount design objectives
Operates on a single common wideband channel
1 Mbps channel rate
Capable of supporting multiple broadcast applications to foster early equipage
From 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
Airborne
Transceiver
ADS-B
air-air
FIS-B
TIS- B
ADS-B
air-ground
Observations WX Radar Forecasts Graphics SUAs
ADS-B
ATC Surveillance Radar
FIS-B
Weather Server
Tracker
UAT
Ground
Transceiver
Tracks
TIS-B
(non-ADS
targets)
ATC System

35. Waveform Selection Requirements
Good capture effect
relatively efficient and low cost power amplifier
simple/robust decoder
Binary FM with high modulation index chosen
A 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: MHz
L-band: MHz
C-band: MHz
Extremely difficult to assemble enough contiguous channels at VHF
Propagation loss too high at C band
MHz has best combination of:
channelization (1 MHz)
compatible current usage (pulsed systems)
and propagation characteristics
Where 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 access
ADS-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 Format
Each aircraft transmits exactly one message each second
Standard Forward Error Correction (FEC):
increases message robustness to pulsed interference and noise
provides an extremely low undetected message error rate ~10-9
This 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 payload
Application can perform passive range verification of ADS-B reported position
Flight test data showed time-based slant range estimates to be within 0.2 nmi of that indicated by ADS-B
UAT 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. Summary
System designed specifically for ADS-B performance and for compatibility in the band
Simplicity and robustness drive the design
Every ADS-B message has a complete State Vector without field truncation
no lat/long decompression, participant tracking, multi-message assembly, or ambiguity resolution required
High integrity link layer directly aids certification of applications with stringent requirements
Consistent transmission epoch in all flight domains
No channel sensing required: minimal transmit-only implementations viable
Single fixed frequency operation for full suite of services