This document discusses spectrum requirements for unmanned aircraft systems (UAS) operating beyond line of sight (BLOS). It finds that existing aeronautical mobile satellite allocations do not meet projected needs and additional spectrum is required. Ku and Ka-band satellite systems can support UAS control links but UAS will require small high-gain antennas to operate efficiently in these bands. The document concludes that while studies are underway in ICAO, operation of UAS under fixed-satellite allocations is a potential solution to provide the necessary bandwidth to meet safety requirements and support various UAS applications.

1. Michael Neale
Brooks Cressman
Hau Ho
ICAO ACP WG-F/24
March 21, 2011

2.  UAS Throughput and BLOS Spectrum Requirements (RTCA)
• Spot Beam Satellite Technology and impact on spectrum
 BLOS Candidate Frequency Bands (ITU WP 5B Study)
• Study Summary – Advantages and Disadvantages
 Ku/Ka FSS (Fixed-Satellite Service) Systems Performance
• System Link Availabilities / Rain Fade calculations
• Study Summary
 UAS SWAP Limitations
• Example installations
 Operational Interference Environment
 Conclusions
2

3.  Required Throughput (RTCA & ITU)
• Telecommand: 10 kbps
• Telemetry: 320 kbps
 UA Densities (RTCA)
• 1856 UA in regional beam (3M mi2)
• 501 UA per spot beam (486 mi
diameter footprint)
 Spectrum requirements (M.2171)
• 169 MHz
 1 satellite using global/regional beam
 Small UA not supported
• 56 MHz (169/3)
 ≥ 3 satellites using regional beams
 UA uses directional antenna
• 46 MHz*
 ≥ 3 satellites using spot beams
 UA uses directional antenna
Sat#1 Sat#2 Sat#3
Coverage
area
• The satellites can operate co-
frequency if the UA uses a directional
(high gain) antenna with sufficient off-
axis performance
• The satellites cannot operate co-
frequency if the UA has an Omni
directional (low-gain) antenna due to
interference
3

4.  Used on existing & planned 20/30 GHz band satellites
 Relies on tens/hundreds of beams to achieve high Power
Flux Density (pfd) and spectrum efficiency levels
• Spot beams allow spectrum to be re-used across service area
• Typical scheme is 4x frequency re-use to achieve their required space
isolation (see below). For UAS this means a minimum of 4x46 MHz
is needed, but in reality each beam will have 125 or more MHz of
spectrum to serve many applications.
4
A
A
A
A
A
A
A
B
B
B
B
C
C
C
C
D D
D
D
A B C D
Available spectrum
A
(LH)
B
(LH)
A (LH)
Available spectrum
B (LH)
A (RH) B (RH)
A
(LH)
A
(LH)
A
(LH)
A
(LH)
A
(LH)
A
(LH)
A
(RH)
B
(LH)
B
(LH)
B
(LH)
A
(RH)
A
(RH)
A
(RH)
B
(RH)
B
(RH)
B
(RH)
B
(RH)
Typical 20/30 GHz satellite
3 dB “spot” beamwidths
•0.5º (~310 km beam
diameter/nadir)
•1.0º (630 km beam
diameter/nadir).

5.  5030-5091 MHz
• AMS(R)S allocation
• 20 MHz spectrum in each direction
• Currently no satellite on orbit
 12/14 GHz also known as “Ku-band” satellites
• FSS allocation
• >200 geostationary orbit satellites (GSO) currently on orbit
• 500 MHz (1 polarization) – 1000 MHz (dual pol.) in each direction
 20/30 GHz also known as “Ka-band” satellites
• FSS allocations
• >10 Commercial FSS GSO satellites are currently on orbit
• Several proposed systems will be on orbit in the next few years
• 1000 MHz – 2000 MHz spectrum in each direction
 13/15 GHz & 23/24 GHz
• AMS(R)S allocations
• Unable to share with other services (ITU WP5B studies)
5

6. 6
Band
Type of
Allocation
UA
Terminal
Antenna
Study
Summary
Disadvantages/
Potential Issues Advantages
 10 MHz of the
1525-1559 &
1625-60.5
MHz MSS
Allocation
 GSO satellites
 AMS(R)S
Allocation
 Low-Gain
antenna
(Omni)
 Can support
UAS control
links
 Link availability
needs further
study
 Spectrum limitation
 One satellite per
region
 Shared with MSS
systems
 Operate in
AMS(R)S allocation
 Satellites on orbit
 Global coverage
 1610-1626.5
MHz
 NGSO - MSS
satellites
 AMS(R)S
Allocation
 Two
NGSO
MSS in
this band
 Low-Gain
antenna
(Omni)
 Can support
UAS control
links
 Link availability
needs further
study
 Spectrum limitation -
only 4 MHz in each
direction (HIBLEO 2)
 One satellite per
region
 Shared with MSS
systems
 Operate in
AMS(R)S allocation
 Satellites on orbit
 Global coverage
L-Band spectrum not sufficient for all projected UAS Requirements

7. 7
Band Study summary Disadvantages Advantages
5 GHz bands May be able to support UAS
control links (BLOS)
• Sharing difficulties (MLS)
• No satellite on orbit
• Only ~5 MHz per spot beam
and1 satellite per region
greatly constrains spectrum
• Operate in ARNS allocation
• UA operates with omni antenna
12/14 GHz
bands --
commercial
satcom
• Support UAS control Links
• Meet the UAS system link
availability
Operate in FSS allocation,
not AMSRS
• 100’s of satellites on orbit
• Global coverage
• Used for decades to provide BLOS
service to UAS
• > 500 MHz in each direction
13/15 GHz
bands
• Can’t share with the existing and
planned systems in these bands
• Unacceptable interference to passive
sensors in adjacent bands
Spectrum limitation
22/23 GHz
bands
• Can’t share with the existing and
planned systems in these bands
• Unacceptable interference to passive
sensors in adjacent bands
Spectrum limitation
20/30 GHz
bands –
commercial
satcom
• Support UAS control links
• Meet the UAS system link
availability
Allocated to the FSS and,
in some bands, the MSS.
No specific AMS(R)S
allocation.
• Several satellites on orbit
• Many more planned
• > 1000 MHz in each direction
• Service UAV using small antenna

8.  Ku and Ka-band satellite
systems can support UAS
control links and meet the
system link availability
 Ka-band appears more
suitable than Ku-band
because it allows UA to
operate with smaller antennas
 Ka-band is more impacted by
rain than Ku, but still achieves
higher link availability
• Ka-band operates at higher pfd
and Uplink EIRP density
 To meet the safety levels, the UA
control link availability is ~
99.999%
 UA will be equipped with more
than one control link. If UA has
two control link subsystems, each
link only required to achieve
99.8%
• CS (control station): 99.95%
• UA: 99.85%
 ITU-R WP 3M, 4A, 4B are
currently reviewing WP5Bs
analysis.
8

9. 0
1
2
3
4
5
6
7
8
9
10
10 20 30 40 50 60 70 80 90 100
Rq.
Fade
Margin
(dB)
Rain Rate (mm/hr)
.1 km
.5 km
1 km
1.5 km
2.0 km
3.0 km
UA - Fade
Margin
UA Altitude
Freq: 14.25 GHz
Link Availability: 99.85%
3.8 dB Fade Margin
(-14dBW/4 kHz, 0.8 m antenna
0
1
2
3
4
5
6
10 20 30 40 50 60 70 80 90 100
Rq.
Fade
Margin
(dB)
Rain Rate (mm/hr)
.1 km
.5 km
1 km
1.5 km
2.0 km
3.0 km
UA - Fade
Margin
UA Altitude
Freq: 11.95 GHz
Link Availability: 99.85%
1 dB Fade Margin
(10 dBW/4 kHz, 0.8 m antenna
Ku-band- Telemetry link - 20º E.L.
Ku-band- Telecommand link - 20º E.L.
Ku-band
0
3
6
9
12
15
18
21
24
27
30
10 20 30 40 50 60 70 80 90 100
Rq.
Fade
Margin
(dB)
Rain Rate (mm/hr)
.1 km
.5 km
1 km
1.5 km
2.0 km
3.0 km
UA - Fade
Margin
UA Altitude
Freq:30 GHz
Link Availability: 99.85%
14.6 dB Fade Margin
(320 kbps,0.5m ant. & 10 W)
0
3
6
9
12
15
10 20 30 40 50 60 70 80 90 100
Rq.
Fade
Margin
(dB)
Rain Rate (mm/hr)
.1 km
.5 km
1 km
1.5 km
2.0 km
3.0 km
UA - Fade
Margin
UA Altitude
Freq:20 GHz
Link Availability: 99.85%
6.7 dB Fade Margin
(-118 dB(W/m²/MHz, 0.5m antenna
Ka-band
Ka-band- Telemetry link - 20º E.L.
Ka-band- Telecommand link - 20º E.L.
9

10. • Telecommand downlink (satellite-to-UA): If the
UA operates with a 0.5 m antenna the system can
achieve 6.7 dB rain fade margin.
• Telemetry uplink (UA-to-satellite): If the UA
operates with a 0.5 m antenna and a 10 W
transmitter the system can achieve a 14.6 dB rain
fade margin.
• These rain fade margins would be adequate to
achieve the desired link availability for most
locations around the globe particularly when the
UA is operating at altitudes higher than 1.5 km.
10

11.  UA’s are size, weight & power (SWAP) limited
• Satcom equipment (antenna) impacts airframe design / size
• Large antenna, or multiple equipment requires larger airframe,
increasing cost, complexity and limiting applications
 Antenna solutions tied to system architecture and UA design
• At lower frequencies, omni antenna on UAS is used with large G/T on
satellite
– Drawback is spectrum cannot be re-used and only 1 satellite can be used per region so
more spectrum is required or UAS density is limited. Benefit is that antenna
implementation is simple.
• At higher frequencies, rain fade is pronounced and high gain antennas
are used to reduce SWAP, offset losses and meet off-axis requirements
– Examples : for a constant gain of 38 dB,
• X band = 1.18 meter
• Ku band = .86 m
• Ka band = .47 m
– Upper limit on frequency due to increasing rain fade, and availability of satellite
infrastructure.
– Ka band is a practical limit for rain fade (up to 14 db)
 CNPC satcom must also carry payload sensor data for
practical SWAP
11

12. 12

13. 13
Sensors
Flight Computer
Sensor data
processor

14.  FSS Coordination process
• FSS operators use ITU API/Coordination/Notification/BIU Filing process
• Examination by ITU triggers Coordinations based upon proximity (arc) or
potential noise floor impact (ΔT/T). Operators can also separately request a
Coordination if they find a ΔT/T exceedance
• Operators coordinate operating parameters to meet performance
requirements
• ITU examines notices with respect to compliance with the Radio
Regulations (RR)
• ITU definitively records assignments with favorable findings with respect to
compliance with RR, including completions of coordination
• Assignment may be recorded if coordination is incomplete after 4 months of
interference free operation
 ICAO SARPS for UAS could require users to provide for
backup spectrum for use in the event their channel was to
receive interference
 Aviation regulator will certify UAS operators based upon
successfully meeting ICAO SARPS and national regulations
14

15.  ITU and RTCA studies indicate UAS requires 46
to 169 MHz of spectrum
• SWAP requirements and practical satellite design drive
UAS toward low gain omni or smaller directional
antennas in Ka band
• Resulting actual spectrum needs become 169, 184 MHz
or more (500 MHz…)
 Existing AMS(R)S allocations do not meet
projected UAS needs
 Additional spectrum is needed and FSS can be explored as
a way to provide ready bandwidth, meet safety
requirements, and support future UAS applications
15

16. 16
 Call for additional studies in ICAO 1.3 background text
 Currently: "Spectrum for UAS for safety and regularity
of flight, and in particular when the UAS operates in civil
airspace, needs to be accommodated under an allocation
to the aeronautical mobile (R) service, aeronautical mobile
satellite (R) service, or the aeronautical radionavigation
service in order to receive the sufficient status and
protection from harmful interference.“
 Add: “STUDIES ARE REQUIRED AND UNDERWAY
TO DETERMINE IF OPERATION OF UA UNDER OTHER
RADIO SERVICES CAN BE ACCOMMODATED WHILE
SATISFYING THE NECESSARY ICAO TECHNICAL
REQUIREMENTS.”