1. UAS Control and Non Payload Communications (CNPC) Link Availability
ICAO ACP-WG-F Meeting #24
Paris, March Michael Neale and Brooks Cressman

2. Overview
What levels of UAS Control and Non-Payload Communications (CNPC) Link Availability will be required?
Safety driven analysis of Collision Avoidance Scenario.
Dependent on Aircraft type, Class of Airspace, Operation.
ICAO AMS(R)S Manual.
What levels of Availability can be achieved?
LOS and BLOS (satellite).
Using frequencies likely to be approved at ITU WRC-12.
An overall system view.
A candidate UAS CNPC design solution

3. Safety Analysis Analysis of a Collision Avoidance Scenario
Conflict Avoidance Period 5-10 seconds.
Collision Avoidance Period 5-10 seconds.
CNPC Link temporary outage must last for less than 1-2 seconds during this second period.

4. Safety Analysis
Target UAS Midair Collision Rates per flight hour to be the same as manned aircraft
AOPA NALL Report shows about 10 Part 91 (GA) manned aircraft midair collisions per year during approximately 25 million flight hours = 4x10^-7 per flight hour.
NTSB and FAA data shows for manned Part 121 (airline and large cargo) aircraft no midair collisions during over 400 million flight hours = 2.5x10^-9 per flight hour.
Collision Likelihood
Current estimates of the likelihood of an intruder, on a collision course with a UA, entering the UA's self conflict avoidance volume (self separation volume) is once every 10,000hrs. Collision Likelihood = 1x10^-4 per flight hour.
Sense and Avoid and CNPC systems must reduce this Collision Likelihood to the target Midair Collision rates achieved by manned aircraft

5. Safety Analysis Assuming no autonomous UA operation
Collision Likelihood x SA & CNPC Unavailability < Manned Aircraft Midair Collision Rate
Part 91 Type UA Unavailability Case
4x10^-7/1x10^-4 = 4x10-3
Assume SA and CNPC systems share equal Unavailabilities.
CC link Unavailability 1/2 x 4x10^3 = 2x10-3 = 0.2%
99.8% CNPC Link Availability = Total outage of 2.88min per day.
Part 121 Type UA Unavailability Case
2.5x10^-9/1x10^-4 = 2.5x10-5
CNPC Link Unavailability 1/2 x 2.5x10-5 = 1.25x10-5 = %
% CNPC Link Availability = Total outage of 1.08 seconds per day.

6. Safety Analysis Part 91 Type UA Unavailability Case
Required CNPC Link Availability approximately 99.8%
Part 121 Type UA Unavailability Case
Required CNPC Link Availability approximately %
ICAO Manual on Required Communications Performance Doc AN/462, 2008 prescribes a similar level of availability based on supporting ATC separation service.

7. LOS CNPC Link Availability
LOS Availability impairments compared to free space
Multipath and Diffraction – low altitude e.g. takeoff and landing as well as earth curvature obstruction near maximum range.
Airframe antenna obstruction - maneuvering during takeoff and landing as well as when flying straight and level en-route.
LOS Multipath
Using ITU-R P.530 Propagation data and prediction methods required for the design of terrestrial line of sight systems – Section
Additional propagation loss of 11-19dB (depending on frequency and aircraft altitude) added for 99.8% availability.

8. LOS CNPC Link Availability
LOS Installed antenna performance analysis
Using a single antenna yields dB nulls.
Using two diversity controlled antennas gives 12dB nulls.
Additional loss (12dB) added to link budgets to account for airframe obstruction

9. LOS CNPC Link Availability
Assuming
Control - Telecommand and telemetry data rates 10kbps
Pilot Voice Communication data rates 5kbps
SA/TCAS support data rates 10kbps
Weather radar and nose camera video 270kbps
L Band (circa 1GHz) and C Band (circa 5GHz) ITU preferred AM(R)S LOS frequencies.
10 Watt transmitters
2dB Noise Figure receivers
Realistic system losses
Two Omnidirectional antennas on the aircraft
High gain antenna(s) at Control Station
Include 6dB safety margin
Approximately 150km (80nm) range
Single Link Availability of 99.8% can be achieved

10. BLOS CNPC Link Availability
BLOS Satellite Availability impairments compared to free space
L and C Band scintillation loss (<0.5dB).
Ku and Ka Band.
Rain and scintillation fading.
Use ITU-R P Propagation data and prediction methods required for the design of Earth-space telecommunication systems - Section
Additional propagation loss of dB depending on rain rate and altitude for 99.8% availability.
Other Ku and Ka Band limitations
Aircraft size and power capability, limits antenna size and transmit amplifier power output which limits EIRP and G/T and link margin.

11. BLOS CNPC Link Availability
Rain at lower altitudes causes additional propagation loss on Ku/Ka satellite links
UA can only use Ku/Ka Band satellites at aircraft altitudes where rain loss is not excessive. This limits the lowest altitude the UA can fly. UA will switch to LOS for takeoff and landing.
Manned Aircraft avoid weather radar level 3 (red) and above regions where rain is higher than an R 0.01 of approximately 20mm/hr.

12. BLOS CNPC Link Availability
Assuming
Control - Telecommand and telemetry data rates 10kbps
Pilot Voice Communication data rates 5kbps
SA/TCAS support data rates 10kbps
Weather radar and nose camera video 270kbps
L Band (circa 1.6GHz), C Band (circa 5GHz), Ku (12/14GHz) and Ka Band (20/30GHz) frequencies
10 Watt transmitters
Realistic system losses
Omnidirectional antennas on the aircraft at L and C Band
0.8m and 0.5m dish antennas on aircraft at Ku and Ka Band
EIRP limited by uplink power flux density regulations
Single Link Availability 99.8% can be achieved

13. Candidate Design
A single CNPC link is probably adequate for Part 91 Type UA operating in class E or G airspace
A very effective way to achieve the availability needed for a Part 121 Type UA operating in class A, B or C airspace is to use two non- correlated CNPC systems
x = or % Availability
Also mitigates against hardware and software failures.
Use the multiple frequency bands that are being considered by ITU to provide the diversity.
Dual links for larger UA already assumed in ITU-R M spectrum analysis.
Allows some margin for other parts of the CNPC link.

14. Candidate Design Part 91 Type UA Part 121 Type UA
Operation in Class E or G airspace.
LOS - Use Single L (1GHz) or C (5GHz) Band LOS link.
BLOS - Use Single L (1.6GHz) or C (5GHz) BLOS link – only required for operation outside Visual LOS.
If desiring to operate in class A, B or C airspace may be treated as a Part 121 Type UA if suitably equipped.
Part 121 Type UA
Operation in Class A, B, C or D airspace.
LOS - Use Dual L (1GHz) and C (5GHz) Band LOS Links.
BLOS – Use Dual L(1.6GHz) or C (5GHz) Band link and Ku (12/14GHz) or Ka (20/30GHz) Band Link.
If desiring to operate in Class E, or G airspace may do so.

15. Conclusions
A flexible dual band approach can deliver the levels of safety anticipated while affording a number of advantages:
Redundancy
Using two non-correlated frequencies offers protection against equipment failure as well as improvements in availability.
Scalability
A smaller UA only requires a simple single AM(R)S L (1GHz) or C (5GHz) Band system for Visual LOS or Radio LOS operation.
A larger UA, that can support more equipment, can achieve higher levels of availability.
Interference Protection
Combining an L(1.6GHz) or C (5GHz) Band AMS(R)S BLOS system with a Ku or Ka Band FSS system provides the interference protection of AMS(R)S with the ubiquity and payload data rate capability of FSS.

16. Future Liaison
RTCA SC203 Control and Communications Work Group has developed a number of papers on:
UAS CNPC Spectrum
UAS CNPC Security
UAS CNPC messaging and data requirements
UAS Candidate CNPC Architectures
UAS CNPC Required Communications Performance
Latency, Availability Continuity, Integrity etc.
Contact Michael Neale for copies of SC203 papers or to participate in RTCA UAS MASPS and MOPS development
Michael Neale –
Brooks Cressman –