This Annex presents examples on how two operation modes for V2X communication, i.e. over the PC5 and over LTE-Uu, can be used in a hybrid manner.

In this operation mode, a UE always transmits the V2X messages via PC5. The UE receives V2X messages via PC5 and via MBMS as well. A stationary infrastructure entity acting as a UE, e.g. an RSU, receives V2X messages via PC5, and forwards the application layer processed V2X messages to a V2X Application Server via V1 interface, e.g. using a PDN connection over LTE-Uu or other type of connection (for example fixed). The V2X messages processed by the V2X Application Server can be distributed to UEs via the MBMS system as required. In this manner, a UE can directly receive V2V messages from other UEs in close proximity. Additionally, in this operation mode, the mobile network provides information from an extended range and satisfies the needs of soft safety (e.g. situational awareness at range) or enables more advanced driving assistance applications. This combined sources of information are especially useful in high density use cases, where the UE may not be able to reliably receive V2X messages directly from distant UEs over PC5.

In this operation mode, UEs communicate with other UEs that are in proximity, including with UE-type RSUs, via PC5 for both the transmission and reception of V2X messages. The UE-type RSUs can communicate with the V2X Application Servers in the mobile network, e.g. over LTE-Uu, as needed, for managing the communication of V2X messages beyond the direct PC5 communication range. With such hybrid use of PC5 and LTE-Uu based V2X communication, MBMS broadcast on the downlink is not needed.

Figure C.3-1 is a high level illustration of this operation mode. This operation mode consists of three components:

• Stationary infrastructure entities acting as UEs, e.g. UE-type RSUs, are deployed to provide adequate coverage to vehicular traffic infrastructure. The UEs and the UE-type RSUs are configured or provisioned with information for V2X communication over PC5 as specified in clause 4.4.1. The UE-type RSUs may communicate with the V2X Application Servers.
• The UE-type RSUs receive V2X messages from other UEs via PC5. The V2X application of the RSU(s) decides if the messages need to be routed to the V2X Application Server(s) over LTE-Uu connection, e.g. when the target area is larger than its V2X communication range over PC5. The V2X Application Server(s) determines the target area and the size of the area where the V2X messages need to be distributed. The V2X Application Server may coordinate and communicate with other V2X Application Servers for the determination of the target area and distribution of V2X messages in the target area.
• V2X Application Server(s) send V2X messages downlink to the RSUs in the target distribution area, e.g. over LTE-Uu. The RSUs broadcast the received V2X messages using V2X communication over PC5. UEs within the region receive the RSU broadcasted V2X messages over PC5.

In this manner, a UE, e.g. vehicle UE only needs to operate in the operation mode of V2X communication over PC5, for V2V/V2P services. Only the UEs implemented as RSUs operate in the hybrid mode of simultaneous V2X communication over PC5 and LTE-Uu. Such combination of PC5 based and LTE-Uu based V2X communications is also useful in use cases where the UE may not be able to receive V2X messages directly from distant UEs via PC5. In addition, the UE-type RSUs can use SIPTO connection for the communication with local V2X Servers to reduce latency.