1. VDL Mode 4 Airborne Architecture Study (VM4AAS)
ACP WG-M/8 Appendix J
VDL Mode 4 Airborne Architecture Study (VM4AAS)
Study Overview and Conclusions
Nikos Fistas
EATMP / EUROCONTROL
Communications & Surveillance Management

2. Presentation Overview
PART I: General information
Scope, Objectives, Plan, Structure
PART II: Study Summary
Overview of work achieved (Work Packages 1 to 4)
Conclusions
Recommendations
Next Steps

3. PART I: GENERAL INFORMATION

4. VM4AAS scope
Investigate airborne integration issues for VDL Mode 4, considering:
COM / SUR / COM and SUR applications
Large / Small / Light a/c
Forward-fit / Retrofit (digital and analogue) a/c

5. VM4AAS Objectives (cont’d)To
provide answers to questions
identify potential problems
make recommendations
contribute to decision making
provide input/guidance to manufacturers
considering current status and future trends

6. Study Background Information
Performed by Honeywell
Started in June 2002
Finished October 2003
Informal external review group (open to interested “volunteers” )

7. VM4AAS Deliverables D3.2 D3.1 D4 D2 D1 WP4 Implementation Plan
29/10/03
VM4 Airborne
Integration
Meeting
WP3.2
Radio
Frequency
Interference
D3.2
WP4
Implementation
Plan
WP5
Final Report
WP3.1
Avionics
Architectures
D3.1
WP4
Implementation
Plan
and Transition D4
WP2.2
Architecture
Requirements &
Constraints
WP2.1
Applications Data
Requirements D2 D1
WP1.3
Definitions,
Assumptions and
Baselines
WP4
Implementation
Plan
WP5
Draft Final
Report

8. Deliverable Review Process
External Review
group
(“volunteers”)
Airbus
Avtech Sweden
British Airways
Boeing
CNSS
Dittel
EasyJet
PMEI
Rockwell-Collins
SAS
SCAA
Honeywell/
EUROCONTROL
Resolution
External Draft
Deliverable
Internal
Draft
Deliverable
Honeywell/
EUROCONTROL
Resolution
Review
Final Deliverable
on Web
Comment
Resolutions

9. PART II STUDY SUMMARY

10. VM4AAS Work Structure Preparatory work Investigations
WP1 - D1: Assumptions and Baselines
WP2 - D2: Identifications of Requirements
Investigations
WP3 - D3.2: RF Interference Analysis
WP3 - D3.1: Avionics Architectures
WP4 - D4: Implementation and Transition

11. Work Package 1: Assumptions and Baselines
Preliminary work to form the foundations WP3
Establish assumptions
Establish baselines

12. WP1: Assumptions VDL Mode 4 is acceptable to support applications
CDL only
SDL only
combined CDL and SDL
15 other assumptions in 3 broad groups
Group 1:
SSR
Mode-S-based ACAS
Group 2:
Simultaneous VHF Communications
Group 3:
8.33 kHz VHF Voice will be required throughout the study period
The term Communications Data Llink (CDL) is equivalent to the terms point-to-point communications, p2p, and COM used in other EUROCONTROL documents.
The term SDL is equivalent to the term SUR used in other EUROCONTROL documents.

13. WP1: Aircraft Classes Large: take-off mass >15,000 kg
(Citation X, G-IV, ERJ, Airbus, Boeing)
Small: kg < take-off mass < 15,000 kg
(King Air 350, most Citation)
Light: take-off mass < 5700 kg
(Cessna 172, King Air C90B)
The Large class is a combination of the two largest TLAT classes.
The Small class is a combination of the two middle TLAT classes.
The Light class is a combination of the two smallest TLAT classes
Tactical military aircraft and helicopters were not specifically considered. Military cargo and heavy lift aircraft were considered part of the Large class.

14. WP1: Equipment Baselines (1)
Communication
VHF Voice (DSB-AM) x 2
ACARS or Mode 2
Simultaneous operation of voice and data link
Navigation
GNSS
ILS (Localizer and Glideslope)
VOR
All of the equipment assumptions were modified slightly during WP3.1 to provide the widest possible breadth of aircraft equippage.

15. WP1: Equipment Baselines (2)
Surveillance
Mode S Transponder #1
Mode S Transponder #2 or Mode C
ACAS Mode S Interrogator (Large & Small)
CDTI

16. Work Package 2: Identification of Requirements
Identify general functional requirements
Identify internal interfaces
Identify external interfaces
Internal interfaces are those wired interfaces with other avionics.
External interfaces include both desired and undesired RF signals received by and transmitted from the VDL Mode 4 avionics. The RF interference study falls under the considerations of external interfaces.

17. WP2: Internal Interfaces
Interconnections
VDLM4 to and from other avionics
Data Flow Diagrams
Data Dictionary
Precision Time Interface (PTI)
CONCLUSION:
Only PTI and baseband interface issues are unique to VDL Mode 4 compared to any other CDL/SDL “modem” technology
A clarification brought up by sidebar conversations: The conclusion does not mean that the interfaces to VDL Mode 4 avionics are the same for CDL, SDL, and CDL+SDL applications, nor does it mean that the interfaces are identical to existing DSB-AM and/or VDL Mode 2 avionics. What it does mean is that the VDL Mode 4-specific interfaces are limited to PTI and the baseband interface. Other interfaces that may be required, such as an FMS interface for enhanced surveillance via ADS-B, are required regardless of the modem technology.

18. WP2: Context-Level DFD An example: Level 1 - external interactions
In keeping with the usual conventions of structured analysis, the OWN_AIRCRAFT entity can be expanded to provide equivalent details at lower levels. This is done through several layers in the deliverable, but discussion of these layers is too detailed for the presentation.

19. WP2: External Interface Issues
RF Interference to/from other avionics
Focus on same-aircraft or co-site problems
Detailed study in WP3.2
Derived work on integrity, availability, and continuity of service
Traffic Loading estimates for 2015 based on MACONDO
In D2, the Integrity, Availability and Continuity of Service are systematic levels for the communications system and are based on MACONDO.

20. Work Package 3.2: Interference Analysis (1)
RF Interference Issues
VHF Communications
Sources: DSB-AM, VDL Mode 2, VDL Mode 4
Communication Victims: DSB-AM, VDL Mode 4, VDL Mode 2
Navigation Victims: Localizer, VOR, VDB, Glideslope
Large, Small, Light Aircraft

21. Work Package 3.2: Interference Analysis (2)
Same-side, Opposite-side antennas
Link-budget analysis using published standards or carefully documented assumptions
3 issues: Desensitization, Off-Channel Emissions, RF (front end) Saturation
Desensitization addresses the IF and DSP designs, specifically the instantaneous dynamic range of the receiver. Off-channel emissions addresses the transmitter design, specifically, the ultimate transmitter noise floor. RF saturation addresses the design of the front end amplifier.

22. WP3.2: VHF COM I/f Problem +20
-180
-140
-100
-60
-20
+20
Power Spectral Density dBm/Hz
thermal noise
minimum signal level
receiver noise floor
reference signal level
minimum digital transmitter output (16 W = +42 dBm)
-98 dBm
-87 dBm
+129 dB (!)
-40 dB
The thermal noise (red curve) is fixed for electronics at –174 dBm/MHz. In practical receivers, this noise level is increased by an implementation dependent factor known as the noise figure.
Typical current VHF noise figures (difference between thermal noise and receiver noise floor) are dB. This fairly large value is driven by the fairly extreme FM Intermodulation requirements for VHF Communications and Navigation radios. The receiver noise floor is above the thermal noise by this factor.
The desired signal level must be sufficiently higher than this noise floor to ensure that the desired Bit Error Rate BER is obtained. For VDL systems, this is approximately 20 dB. For the current VHF systems, this minimum signal level is –98 dBm.
To ensure that thermal noise induced errors do no affect the measurement of interference performance, all of the MOPS require that interference testing be performed at –87 dBm, or 11 dB above the minimum signal level The study used this reference as the standard desired signal level for all systems. This maitains compatibility with other interference tests. On the other hand, assuming –87 dBm ignores the fact that DSB-AM systems typically have a minimum sensitivity of –107 dBm, and data systems may be in the –98 to –103 dBm range. Thus the –87 dBm analysis may understate the true interference by up to 20 dB.
A typical transmitter power on the same aicraft is W. A typical data transmitter will be 16 W or 42 dBm. That is 129 dB ! greater than the reference signal level.
The transmitter signal received at the receiver is reduced by approximately dB due to physical isolation between antennas on the aircraft. For this illustration, we use 40 dB isolation. Therefore, the transmitted signal, as received at the receiver can be as large as +2 dBm, or 89 dB higher than the transmitted signal.
It obvious that the this situation can’t be accommodated on the same channel. As the spacing in frequency is increased, the effective signal on the channel is reduced.
But the fundamental problem is that we need to reduce the effective signal on the victim channel to near or below the noise floor – that is by 110 dB!– in order to fully mitigate the interference.

23. WP3.2: Key Assumptions MOPS -87 dBm reference signal level
Emissions levels
DO-186A (Voice), DO-281/ED-92 (Mode 2), ED108 (Mode 4)
Assumed noise floors
Using ARINC 716 isolations
MOPS adjacent channel rejection
ACR is a desensitization spec
Figure of merit Es/N0 or S/P
The ARINC 716 isolations are 35 dB between antennas on the same side of the aircraft and 50 dB between antennas on the opposite sides of the aircraft. The study assumes these values, plus a net 3 dB of cable loss in each case, for a total of 38 dB and 53 dB isolation, respectively.

24. WP3.2: 3 VHF-on-VHF i/f scenarios
Voice on digital
RF Saturation
IF Desensitization
Off-channel emissions (residual phase noise)
Digital on voice
Squelch break
Audio S/P concerns
Digital on digital
Desensitization IF
Off-Channel emissions (residual phase noise)
A question has been raised regarding how the audio S/P was evaluated in the study. This question is under review by Honeywell and Eurocontrol. We expect that the resolution will be modification of the actual quantitative values in several tables in WP3.2, but not a change in the overall evaluation of the interference severity.

25. WP3.2: Voice on digital i/f
Mechanism
Primarily phase noise and RF saturation
IF desensitization is lesser effect
Challenges
100% voice duty factor
Mitigations
Better in-band filtering for digital receiver (IF)
“Better-than-MOPS” phase noise of voice transmitter
Increased isolation
Channel separation
Robust application protocols
Clear continuity definitions
Reduced use of AM voice as data use increases

26. WP3.2: Digital on voice i/f
Mechanism
Primarily phase noise and RF saturation
IF desensitization is lesser effect
Challenges
Better than MOPS sensitivity of most AT voice receivers
Mitigations
Better than MOPS emissions for digital transmitter
Increased isolation
Channel separation
Constrain protocols to short pulse widths (adverse impact on “clicks”)
Consider cooperative suppression during transmissions

27. WP3.2: Digital on digital i/f
Mechanism
Primarily phase noise and RF saturation
IF desensitization is lesser effect
Challenges
Multiplicity of antennas/limited isolation
Low-noise figure designs with FM protection
Mitigations
Better emissions for digital transmitter
“Better-than-MOPS” adjacent channel rejection
Increased isolation
Channel separation
Robust applications and protocols
Clear continuity definitions
The communications community at large does not have a good definition of continuity of service that differentiates between fault free rare events and a true failure of the service. Initial attempts at such a definition are contained in RTCA DO-270 and RTCA DO-277.

28. WP3.2: Off-channel & Desensitization
Required frequency separations in (KHz) to solve the interference problem
(additional analysis is being finalised)
Separations in KHz
The resolution of the S/P issue discussed in Slide 24 will result in modification of the lines with DSB-AM as the victim. We do not expect this modification to change any of the red entries to orange, or any of the orange entries to yellow. The numerical values within the affected orange, yellow and green cells may change by a small number of 25 kHz channels.

29. WP3.2: RF Saturation New result (not in original WP3.2)
Supported by Boeing/Honeywell testing (Sept data not yet released)
May be the limiting factor!
The assessment of “probable” is an assessment of how likely a specific radio design is to experience interference problems. For example, there are very few radios on the market today that can sustain interference at –10 dBm within 3 MHz of the desired channel, therefore it is very probable that such levels will cause interference.
Certain: In band signal > +10 dBm and within ~3 MHz
Very Probable: In band signal >-10 dBm and within ~3 MHz
Probable: In band signal >-25 dBm and within ~3 MHz
Possible: In band signal >-33 dBm (MOPS Specification)
None: In band signal <-33 dBm (MOPS Specification)

30. Work Package 3.1: Architecture Descriptions
11 different forward fit architectures
1 radio retrofit architecture
Recommendations
Multi-function VHF radio
8.33 kHz, 25 kHz, VDLm2, VDLm4
Independent transmit and receive capabilities
Baseband control and flexibility
Only 1 retrofit architecture was considered, as more complicated retrofit architectures become essentially equivalent to forward-fit architectures already considered.

31. WP3.1: requirements and constraints
Integrity
RMER to 10-8
Continuity
Loss of Continuity 1 x to 5 x 10-4
Availability
Communication system MTBF 1000 days
Surveillance system MTBF 1000 day
These values are largely based on MACONDO

32. WP3.1: Architecture Candidate #5
ARINC 750 form factor New VHF Digital Radio (NVDR)
4R1T, half duplex transceivers (not available today)
High-speed baseband information sharing
Independently reconfigurable R/T capabilities
The driver was “no new antennas”.

33. WP3.1: Architecture Candidate #9
Remote mount high-end B/RA New VHF Digital Radio (NVDR)
4R1T, half duplex transceivers (not available today)
High-speed baseband information sharing
Independently reconfigurable R/T capabilities
Architecture #9 is the same internal architecture as #5, but with different package.

34. WP3.1: Architecture Candidate #10
Retains existing analog voice radio for GA aircraft
Small form factor (panel mount?) NVDR
4R1T, half duplex transceivers (not available today)
Independently reconfigurable R/T capabilities
Somewhat limited under certain failure conditions
Again, the internal architecture is the same as for large and small aircraft. The intent is to capitalize on economies of scale.

35. WP3.1: Architecture Candidate #11
Retains existing analog voice radio for GA aircraft
Small form factor (panel mount?) NVDR
4R1T, half duplex transceivers (not available today)
Independently reconfigurable R/T capabilities
Somewhat limited under certain failure conditions
This architecture could support some Small aircraft that only desire two VHF comm radios. Once again, the internal architecture is the same.

36. WP3.1: Other Products
Allocation table showing how each transmitter and receiver is used
Availability/continuity analysis tables
Analytical Appendices

37. Work Package 4: Implementation and Transition
Relative normalized costs of installation in a variety of configurations
“Typical” and “Best-Case” schedules

38. WP4: Summary of Relative Costs
For each class, the normalizing factor is the current catalog price of a VHF DSB-AM transceiver. The values are comparable among options within each aircraft class, but not between classes.

39. WP4: Serial Task Schedule

40. WP4: Aggressive Schedule

41. Work Package 5: Final Report & Summary
Summarize WPs 1, 2, 3.2, 3.1, and 4
Review external comments
Conclusions
Recommendations
Open Items and Future Work

42. WP5: Review of External Comments
Comments critical of WP 3.2
VHF Voice assumptions were too severe
Worst-case and not statistical analysis
Not supported by field data and/or trial experience
Comments about cost analysis with lack of benefit analysis
Comments about intermodulation
Comments about saturation

43. WP5: Study Conclusions (1)
Interference Problem:
VHF-on-VHF interference will exist
VHF-on-VHF interference may prevent simultaneous voice and data usage provided by separate systems (valid for all VDLs)
Voice-on-VDL interference is more critical
Only half-duplex is achievable
Uplink data applications must be made sufficiently robust to sustain transfer delay due to downlink voice
Technical mitigations seem insufficient

44. WP5: Study Conclusions (2)
Aircraft Integration Problem:
Recommended architectures are based on multi-function half-duplex VHF transceiver with 1 TX and 4 RXs
Recommended architectures require interconnected transceivers
VDL Mode 4 specific integration issues limited to PTI and baseband connections

45. WP5: Study Conclusions (3)
General
VDL Mode 4 installation plans should be coordinated with ADS-B and/or advanced data link upgrades
Simultaneous operation of multiple VDLs and voice should be avoided

46. WP5: Study Recommendations
Investigate operational impact of VDL Mode 4 interference to voice and vice versa to determine if and which applications can be supported
Complete feasibility analysis (safety, ..) of recommended architectures and facilitate as appropriate the development of multi-function 4R1T transceiver with
8.33/25 kHz analog voice, VDL Mode 2, VDL Mode 4
common baseband coordination
quasi-independent R/T functions
Use VMAAS results as input to other efforts to complete VDL Mode 4 specific cost/benefit analysis (CBA) to support link decision
Coordinate any aircraft upgrades with ADS-B and advanced CDL application upgrades

47. WP5: Open Items/Future Work (1)
Assess operational impact of voice-on-data interference
Adopt GFSK BER analysis as part of a standard for reference
Adopt VDL Mode 4 link budget to level of detail comparable with other VDL data links

48. WP5: Open Items/Future Work (2)
Perform or refine system-level cost benefit analysis based on relative costs provided by WP4
Perform, publish, and publicize additional measurements of VHF-on-VHF interference effects

49. VM4AAS Remarks & Questions More info and available draft deliverables:
Comments and input welcome