The resolution 421 (WRC-07) defines the scope of the WRC-11 A.I. 1.3 which aims at supporting the safe operation of UAS (unmanned air vehicle systems) in non segregated airspaces. The document deals with the issue of the possible spectrum requirements for the transmission of video streams that may be needed for UA aeronautical safety in mixed airspace with piloted aircraft.
It is proposed :
- to take into consideration this issue arising from transmission of high data rates associated ed with video streams if needed for UAS admission into unsegregated airspace
- that WGF seeks the point of view of all the other ICAO working groups concerned with the UAS topic .
To date, only a few U.A (unmanned air vehicles) fly in very specific segregated airspaces. The scope of the WRC-11 A. I. 1.3 invites studies to be performed within ITU-R to identify under what conditions future U.A could be granted access to all kinds of airspace unrestrictively .
The resolution 421 invites to study the requirements for UA ‘’command and control’’ (C2) as well as the ‘’sense and avoid ‘’(SAA) functions. For the flight of the U.A. in conventional airspace, the UA operator, i.e. the remote pilot may need to receive a real-time visual picture of the airspace environment in the immediate vicinity the unmanned aircraft, if confirmed as an operational safety requirement, with respect to both conventional piloted aircraft and to persons and facilities on ground.
It is worth noting that today’s experience with UAS operated in segregated airspace has established :
that some UA can routinely fly autonomously both during their en-route and initial take-off and final landing phases of their flight, without continuous radio communications from their operators to initiate, or change on-board flight control software, generally pre-loaded before departure, with the remote UA operator on ground involved in radio telemetry monitoring the “UA” health status and ready to intervene by tele-command should a contingency situation arises
that the on-board software can be designed to implement a return flight and landing procedure back to its home base in case of accidental loss of radio contact1,
Furthermore experience with ACAS (Airborne collision avoidance systems) design and operations for conventional piloted aircraft has repetitively shown that the reaction time needed to perform an evasive manoeuvre to avoid a perceived collision with either a neighbouring aircraft or approaching ground obstacle is much shorter than the time required for the tactical surveillance and control loop between aircraft and ground control ATC ; and accordingly such a threat requires an immediate evasive action under automatic on-board implementation, with evasive action reporting to ground control facilities as a second priority.
The informative document ‘’ACP-WGF-IPXX_UAS_Links’’ submitted in parallel to this meeting indicates the technical possibility to transmit real time video from the U.A to the remote piloting centre under C2(Command and Control) or SAA (sense and avoid) functions. It shows also that there may be a requirement to do so for the payload but not necessarily on a real time transmission basis . These transmissions could occur directly or could be relayed by satellite or aircraft.
Spectrum issue related to the video streams
Below is a highly preliminary sizing of the considered UA video transmission capabilities that may be employed between the UA and its remote pilot control (RPC) station needed for its command and control (C2). Further study work is needed to :
reach a consensus first within ICAO and then within ITU-R that they should be considered, as part of the studies needed to prepare for AI 1.3 Res 421,
agree on the aeronautical telecommunication standards requirement to be developed and associated spectrum needed for their implementation .
Considering a current standard definition video stream (720 x 576 pixels) with a frame rate of 20 images/s and 256 colours (8 bits) of each pictures, this leads approximately to a bit rate of : 720 x 576 x 20 x 8 = 66.4 Mbits/s
Knowing that the current spectrum efficiency used for aeronautical telemetry is around 1bit/s/Hz, the above rough video requirement leads to a spectrum need of around 66 MHz. Future spectrum efficiencies figures greater than 1 bit/S/Hz achievable at the time of UAS deployment into unsegreagated airspace, should also be considered Such a value is for one U.A. only.
Data and video compression method could significantly reduce this value by several tens of percent and lead to final spectrum requirements in the order of several MHz instead of several tens of MHz. On the opposite, these compressions methods bring some drawbacks such as important processing workloads and significant latency. Essential characteristics of such video data transmission and compression would need to be determined as part of the aeronautical C2 and SAA telecommunications standards mentioned above.
Latency in the order of a few seconds may probably be unacceptable for the video if confirmed to be required for the safety C2 or SAA functions identified in Res 421, contrary to video radio links operated for the UA mission payload which may very well accept such a latency or even a greater one.
The interest of this simple example is to show that the scarce spectrum resource could not be sufficient if video streams, in both up and down direction from the RPC are ultimately confirmed to be needed for the SAA or C2 functions of the UAS. as part of UAS air-worthiness certification mandated for their safe design and flight operations in unsegregated airspace. This is particularly true in ICAO classes E to G airspaces as well as in the unclassified ones.
3- Action by the meeting
The ACP WGF is invited:
to consider the issues of:
a) video transmission links between UA and ground control: whether they constitute essential requirements for the implementation of the C2 and SAA functions identified in the WRC’11 AI 1.3 under Res 421
b) the importance of the associated spectrum that could be required in case video transmissions are confirmed to be needed for these functions implementation;
to improve the above spectrum sizing example as necessary;
to inform all other ICAO working groups involved in this UAS matter and invite them to formulate their point of view on works related to UAS, considering that the outcome of such an action would progress the preparatory work to the WRC-11 A.I. 1.3.
1 This in line with the EUROCONTROL-SPEC-01 -02 :
A back-up mode of operation should enable the UAV to revert to autonomous flight in the event of total loss of control data-link between the pilot-in-command and the UAV. This back-up mode of operation should ensure the safety of other airspace users.