UAV Communications

Unmanned Aircraft Communication Scenarios

The communications scenarios during the phases of an Unmanned Aircraft mission

Meaning of acronyms used Air Traffic Control ATC

A service provided for the purposes of: a) preventing collisions between aircraft and in the manoeuvring area between aircraft and obstructions; and b) expediting and maintaining an orderly flow of air traffic. - STANAG 4586

FIS-B

Flight Information Service - Broadcast

GCS

Ground Control System

LOS

Line-Of-Sight: maximum seperation = 5 km

R

Request

TWR

Airport Control Tower

UA

Unmanned Aircraft Very High Frequency

VHF

FM analog radio communications in the 118 MHz to 132 MHz band

Notes 

payload communications requirements (such as ground monitoring video data) are considered to be a separate issue from the command and control requirements



the GPS navigation signals received from the US GPS satellites at 1,575.42 MHz (the civilian L1 signal) and at 1,227.60 MHz (the civilian L2 signal) are acknowledged, but are excluded from the following discussion



for Beyond-Line-Of-Sight operation of the UA, we assume a Sense and Avoid system is fitted and operational in the UA, and that this system operates autonomously on the UA, with reports of what is sensed and being tracked included in the status reports which are transmitted each second



for video data transmission via a satellite link, we have suggested the use of MPEG-2 video compression in which a 720 x 480 pixel frame at a rate of 30 frames per second requires a bit rate of about 4 Mbps.



EUROCONTROL, FAA and ICAO plan to equip high traffic densities areas with ATC data links for man and unmanned aircrafts by 2020. The ATC data link will require an availability of 99.999% and must meet the 95th percentile one-way transit times shown in the following table (from Pelmoine):



Domain

Threshold

Objective

En Route

3.0 sec

1.5 sec

Tower

3.0 sec

1.5 sec

Terminal

3.0 sec

1.5 sec

for US military systems, the proposed: o o

o

Line-Of-Sight data link frequency = 14,500 to 15,350 MHz satellite communications uplink (satellite to Unmanned Aircraft) frequency = 30 GHz to 31 GHz satellite downlink (Unmanned Aircraft to satellite) frequency = 20.2 GHz to 21.2 GHz

Communications systems requirements based on following scenarios Here are the communications requirements we derive from the following scenarios. communications requirements 3 OFF COFDM video channels, each 8 MHz bandwidth, in an ISM band such as the 5.8 GHz ISM band 3 OFF MPEG-2 video channels, each 4 Mbps bit rate, for video information, on a SAT comms link

scenario

reason / use 

continuous situation awareness and following while the UA is on the runway



in an emergency landing, where the UA is remotely flown from the GCS

UA is in LOS of GCS

UA is BLOS of GCS

CHA = 4.8 kbps 9.6 kbps satellite links with backup GSM 900 / 1800 modem links



download status messages (typically one per second) and video line scan data



upload flight plan changes / remote operation of UA

all

primarily when close to, or at, an airport

CHB = 4.8 kbps for digitised, duplex, TWR VHF voice relay

primarily when climb out and cruise + when cruise / mission

CHA = 4.8 kbps for digitised (CELP) duplex, ATC1 VHF voice relay

9.6 kbps satellite links with backup GSM 900 / 1800 modem links

primarily when on cruise / mission and passing from one ATC centre to another



CHB = 4.8 kbps for digitised (CELP) duplex, ATC2 VHF voice relay



this VHF channel is also used to pick up the weather FIS

Notes 

 

The GSM 900 / 1800 link is used to reduce the latency in satellite communication link, but the satellite link is also used to ensure back-up in the event of failure, or, unavailability of the GSM link. The Sense and Avoid (S+A) system, if fitted, functions autonomously and no S+A video information is relayed back to the GCS. COFDM can be used as a modulation scheme to transmit video information from the UA at or near the airport to a GCS that is within LOS of the UA on an ISM band, such as the 5.8 GHz ISM band. The 5.8 GHz ISM band has a contiguous 125 MHz bandwidth that can be subdivided into 15 channels of 8 MHz each for the purposes of video information transmission. This band is at present not as heavily used as the 2.4 GHz ISM band, which is heavily used for WLAN communications links. It must be noted that COFDM is sensitive to Doppler shift, and is degraded in situations where the difference in speed between the transmitter on the UA and the receiver at the static ground station exceeds 185 kph.

Case 1A

From gate to take-off From landing to gate

 UA within local line-of-sight of Airport  UA within line-of-sight of GCS  Local weather FIS data picked up by GCS

sensing of obstacles on the runway sensing runway and runway number reading signs beside the runway

3 OFF video cameras each COFDM BW = 8 MHz 5.8 GHz ISM band

data downlink UA to GCS

(1) GSM 900 / 1800 modem

data uplink GCS to UA

(2) satellite phone modem 4.8 kbps of a 9.6 kbps link

digitised (eg. using CELP) voice: downlink UA to GCS uplink GCS to UA

voice relay: TWR, ATC to UA voice relay: UA to TWR, ATC

(1) GSM 900 / 1800 modem (2) satellite phone modem

UA status monitoring 1 msg / second UA control

ATC acknowledge

4.8 kbps of a 9.6 kbps link VHF channel x (TWR - UA) VHF channel y (ATC - UA) VHF FM 118 - 132 MHz

Notes 

continuous for situation awareness and following

latency in the satellite voice relay is an issue.

R engine start R push back R taxi clearance R take off

Case 1B



From gate to take-off From landing to gate If a field is used rather than an airport, then Case 1B is as per Case 1A, except that there will be no ATC communications.

Notes 

Case 1C



 UA within local line-of-sight of Airport  UA beyond line-of-sight of GCS

sensing of obstacles on the runway sensing runway and runway number reading signs beside the runway

3 OFF video cameras each MPEG-2 at 4 Mbps via SAT COMMS link

(1) GSM 900 / 1800 modem data downlink UA to GCS data uplink GCS to UA



(1) GSM 900 / 1800 modem



ATC acknowledge  latency of SatComms link

could be a problem

(2) satellite phone modem

 need live link through take-

4.8 kbps of a 9.6 kbps link

 availability / integrity is

off sequence safety critical

voice relay: TWR, ATC to UA voice relay: UA to TWR, ATC

VHF CH x (TWR - UA) VHF CH y (ATC - UA) VHF FM 118 - 132 MHz

R engine start R push back R taxi clearance R take off

picked up on VHF CH z weather FIS information

relayed via GSM 900/1800

not time critical

back-up is 4.8 kbps SAT comms voice relay link Notes 


Case 1D




If a field is used rather than an airport, then Case 1D is as per Case 1C, except that there will be no ATC communications.



This case could also apply to an emergency landing situation.

Case 2A

Climb out and cruise

 UA within local line-of-sight of Airport  UA within line-of-sight of GCS  Local weather FIS data picked up by GCS

3 OFF video cameras sensing of other aircraft

data processed on-board status reported each sec

data downlink GCS to UA data uplink GCS to UA

(1) GSM 900 / 1800 modem (2) satellite phone modem

continuous for situation awareness

UA status monitoring 1 msg / second

4.8 kbps of a 9.6 kbps link (1) GSM 900 / 1800 modem

digitised (eg. using CELP) voice: downlink UA to GCS


uplink GCS to UA

UA control

ATC acknowledge

4.8 kbps of a 9.6 kbps link R flight level / bearing

voice relay: ATC1, ATC2 to UA voice relay: UA to ATC1, ATC2

VHF channel x (ATC1 - UA)

R enter / leave sector

VHF channel y (ATC2 - UA)

Freq change instr

VHF FM 118 - 132 MHz

ALT ref QNH transition Mode S transponder setting

Notes 


Emergency management 

Case 2B

In case of emergency, ATC and GCS notified, UA identified

Climb out and cruise

 UA within local line-of-sight of Airport  UA beyond line-of-sight of GCS


data processed on-board status reported each sec (1) GSM 900 / 1800 modem

data downlink UA to GCS data uplink GCS to UA





(1) GSM 900 / 1800 modem

ATC acknowledge  latency of SatComms link

could be a problem


 need live link through take-


 availability / integrity is

off sequence safety critical

R flight level / bearing voice relay: TWR, ATC to UA voice relay: UA to TWR, ATC

VHF CH x (TWR - UA)

R enter / leave sector

VHF CH y (ATC - UA)

Freq change instr

VHF FM 118 - 132 MHz

ALT ref QNH transition Mode S transponder setting

picked up on VHF CH z weather FIS information

relayed via GSM 900/1800

not time critical

back-up is 4.8 kbps SAT comms voice relay link Notes 

latency in the satellite voice relay is an issue


In case of emergency, ATC and GCS are notified, the UA is identified



If the Sense and Avoid system fails, and is reported, the emergency situation is flagged to ATC



A major safety problem arises if a failure of the on-board Sense and Avoid system is not detected, or, if a failure of the S+A system is detected, but not then reported (two failures).

Case 3A

Cruise / mission

 UA beyond line-of-sight of Airport  UA beyond line-of-sight of GCS

 No local weather FIS data available  OCEANIC with ATC seperation service



data downlink UA to SAT to GCS

satellite phone modem

data uplink GCS to SAT to UA


digitised (eg. using CELP) voice: downlink UA to SAT to GCS uplink GCS to SAT to UA voice relay: ATC to UA voice relay: UA to ATC

satellite phone modem 4.8 kbps of a 9.6 kbps link VHF channel x (ATC1 - UA)


ATC acknowledge



infrequent: 1 or 2 msg every 10 minutes



ATC clearances

VHF channel y (ATC2 - UA) VHF FM 118 - 132 MHz

802.11g or 802.11n (draft) UA-to-UA WLAN data link


WLAN link operating in the 2.4 GHz ISM band

for a formation (swarm) of Unmanned Aircraft, in which only one UA maintains a SAT comms link (although all carry the equiment for this link)

Notes 

latency in a satellite communication link is considered tolerable



no GSM 900 / 1800 service available


ATC identified



UA identified



S+A system failure: detected and reported: flag emergency to ATC



S+A system failure: not detected and / or not reported: not serious in oceanic arena: serious if UA then processed into more crowded air space on land.

Case 3B

Cruise / mission

 UA beyond line-of-sight of Airport  UA beyond line-of-sight of GCS  No local weather FIS data available  Flying over REMOTE area with no ATC seperation service



data downlink UA to SAT to GCS

satellite phone modem

data uplink GCS to SAT to UA


digitised (eg. using CELP) voice: downlink UA to SAT to GCS uplink GCS to SAT to UA voice relay: ATC to UA voice relay: UA to ATC

satellite phone modem 4.8 kbps of a 9.6 kbps link


ATC acknowledge

VHF channel x (ATC1 - UA) VHF channel y (ATC2 - UA) VHF FM 118 - 132 MHz

802.11g or 802.11n (draft) UA-to-UA WLAN data link


WLAN link operating in the 2.4 GHz ISM band

for a formation (swarm) of Unmanned Aircraft, in which only one UA maintains a SAT comms link (although all carry the equiment for this link)

Notes 

latency in a satellite communication link is considered tolerable



GSM 900 / 1800 coverage unreliable or unavailable


ATC identified



UA identified



S+A system failure: detected and reported: flag emergency to ATC and / or perform emergency landing

** The above information was jointly developed by Tony Henley and Joe Barnard.

UAV Communications

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