## 3 Review of Sensor Requirements for A3R
### Ensure Communications  
To complete A3R, reliable data links that support both voice and data transfer are critical. Data transfer is important for automation functions and monitoring; voice transfer is needed for coordination and communication to support humans that are monitoring and/or interacting with the system. Communications are needed between the tanker and the receiver for automated operations, and the requirements for apertures include both transmission (T) and receiver (R) capabilities. In addition to communication between the tanker and the UA, there must be communication with the GCS for the AVO to monitor the UA. Communication with the AVO enables a human or team of humans to monitor the operation of the tanker and potentially multiple receivers. Similarly, multiple GCSs controlling multiple UAs must be able to transmit both data and voice for humans to coordinate operations. A GCS serves as the command and control (C2) node for a UA or team of UAs while providing flight information to the AVO in a similar fashion to that of a cockpit instrument display panel in a crewed aircraft [51]. Depending on the level of autonomy onboard the UA, a data link may or may not be required to the AVO. The airworthiness officials certifying the UA at the platform level may not require a human either in (interacting with operations) or on the loop (monitoring operations) to conduct A3R if additional assurance is provided by a certified Run Time Assurance (RTA) [52]. A RTA serves as a monitor to the autonomy under test (AUT), and in the event the AUT encounters a problem or suffers from a degradation, the RTA will revert control back to an automated recovery controller, similar to an Auto Ground Collision Avoidance System (Auto GCAS), to ensure safe operations [53]. A data link to an AVO may be installed for redundancy and/or oversight, but it may not be required for operation. Unless the UA employs a computer vision (CV)-only solution with no fusion of additional location information, such as differential global positioning system (DGPS) data [29], a data link between the receiver and tanker is required for the transmission of position data. For this paper, it is assumed that a data link must exist between both the tanker and receiver, as well as between the AVO and the UAs (Figure 11). To transmit data and voice between multiple GCSs, if the GCSs are geographically located in a close area, a fiber optic cable or ethernet may be routed to pass information between GCSs [51]. Alternatively, mobile networks operating in ultra-high-frequency (UHF, 300 MHz to 3 GHz), low-frequency (L, 30 to 300 kHz), or S Band (2 to 4 GHz) frequency bands using Commercial Off The Shelf (COTS) components [54] or wireless sensor networks (WSN) in the C frequency Band (4 to 8 GHz, reserved for satellite communications) [55] could be leveraged to pass data and voices between GCSs. If the range between GCSs does not allow for a fiber, ethernet, mobile network, or WSN, either a Line-Of-Sight (LOS) or Beyond LOS (BLOS) solution would be required. To transmit data between the GCS and UA, either a LOS or BLOS data link will be required depending on the anticipated range between the GCS and UA [56]. Operations within LOS of the GCS allow the UA to have faster and more reliable data transmission. LOS operations are typically limited to operations within the radar horizon, a function of the UA altitude, but also may be further limited due to environmental limitations. For the LOS data link, both the GCS and UA must have a radio installed, such as a software-defined radio (SDR) [57] or a purpose-built radio, capable of producing a LOS data link waveform and an aperture capable of transmitting and receiving the waveform. LOS data links employed by the DoD include the older Link-1 waveform in a high-frequency Band (HF, 2  
Figure 11: Visual depiction of data links required between multiple UAs and GCSs/AVOs.