NR connectivity for UEs capable of Aerial communication is supported via the following functionalities:
subscription-based Aerial UE identification and authorization, as specified in clause 184.108.40.206.1 of TS 23.502;
height reporting based on the measurement event(s) where the UE's altitude has crossed a network-configured reference altitude threshold;
height-dependent configurations which apply only to specific height regions;
interference detection based on a measurement reporting that is triggered when a configured number of cells (i.e. larger than one) fulfils the triggering criteria simultaneously;
signalling of flight path information from UE to NG-RAN and from the source gNB to target gNB during handover;
location information reporting, including UE's horizontal and vertical velocity;
broadcasting of BRID and DAA messages via PC5 interface.
Support for Aerial UE functions is stored in the user's subscription information in UDM. UDM transfers this information to the AMF during Registration, Service Request and Mobility Registration Update procedures.
The Aerial UE subscription information can be provided by the AMF to the NG-RAN node via the NGAP INITIAL CONTEXT SETUP REQUEST message during the Registration, Mobility Registration Update and Service Request procedures. The subscription information can also be updated via the NGAP UE Context Modification procedure and NGAP Path Switch Acknowledge procedure. In addition, for Xn-based handover, the source NG-RAN node can include the Aerial UE subscription information in the XnAP HANDOVER REQUEST message and RETRIEVE UE CONTEXT RESPONSE message to the target NG-RAN node.
For intra- and inter-AMF NG-based handover, the AMF provides the Aerial UE subscription information to the target NG-RAN node after the handover procedure.
An Aerial UE can be configured with height-dependent, event-based measurement reporting (i.e., eventH1
as defined in TS 38.331
). An Aerial UE sends a measurement report when its altitude becomes higher or lower than configured threshold. The UE includes its height and location information in the measurement report if configured to do so by NG-RAN. RSRP/RSRQ measurement results are always reported when height reporting is configured.
The Aerial UE can also be configured to trigger measurement reporting only when both a height-dependent condition and a RSRP/RSRQ/SINR-based condition are met (i.e., eventA3H1
in TS 38.331
, commonly denoted as eventAxHy
). For the content of eventAxHy
measurement report, the same rules as described above for eventH1
An Aerial UE can be configured with multiple height-dependent configurations, each of which is applied in its corresponding height range. Height-dependent configurations can be provided independently in measurement object (i.e. SSB-ToMeasureAltitudeBased
in TS 38.331
) and an Aerial UE can use those when in RRC_CONNECTED.
For interference detection, an Aerial UE can be configured with RRM event A3, A4, A5 or AxHy that triggers measurement report when individual (per cell) RSRP values for a configured number of cells fulfil the configured event. Once such condition is met and a measurement report is sent, the list of triggered cells is updated when subsequent cell(s) fulfil the event. However, further measurement reports are not sent while the list of triggered cells remains larger than or equal to the configured number of cells unless reportOnLeave
is configured (see TS 38.331
Following an indication from the Aerial UE that flight path information is available, NG-RAN can request the Aerial UE to report flight path information consisting of a number of waypoints defined as 3D locations, as defined in TS 37.355
. Aerial UE reports up to a configured number of waypoints if flight path information is available at the UE. The report can also contain a time stamp per waypoint if configured by the NG-RAN and if available at the UE. The flight path information can be also provided by the source gNB to the target gNB during handover. If configured by the NG-RAN and if the associated distance- or time-based condition (see flightPathUpdateDistanceThr
in TS 38.331
, respectively) for indication reporting are met for any of the waypoints, the Aerial UE indicates the availability of the updated flight path information. The Aerial UE can also indicate the availability of the updated flight path information if a new waypoint has been added or if a future waypoint has been removed from the flight path information.
Location information for Aerial UE communication can include horizontal and vertical speed if configured. Location information can be included in RRM report and in height-based reporting (as described in 16.18.3).
The Aerial UE supports A2X communication which is broadcasting of BRID and DAA messages using NR sidelink. DAA can also be provided via unicast transmissions in NR sidelink. BRID and DAA message transmission is supported in both in-coverage and out-of-coverage scenarios and relies only on UE autonomous resource selection for NR sidelink communication. BRID and DAA follow the QoS framework defined for NR sidelink and dedicated A2X PQI values are stored in Table 220.127.116.11-1 of TS 23.256
. The NG-RAN can configure a separate SL Tx resource pool for BRID and DAA. The SL Tx pool selection for A2X is described in clause 5.22 of TS 38.321