Content for TS 23.280 Word version: 19.1.0

1… 5… 5.2.8… 6 7… 7.3.2 7.4… 7.4.3… 7.5… 8… 9… 9.2.2… 9.2.2.2… 9.3… 10… 10.1.2… 10.1.3… 10.1.4.3… 10.1.4.5… 10.1.5… 10.1.6… 10.2… 10.2.3… 10.2.4.2… 10.2.4.3… 10.2.5… 10.2.7… 10.3… 10.6… 10.7… 10.7.3… 10.7.3.4… 10.7.3.7… 10.7.3.7.3 10.7.3.8… 10.7.3.10… 10.8… 10.8.4… 10.8.5… 10.9… 10.9.3… 10.9.3.5… 10.9.3.8… 10.9.3.9… 10.9.3.9.3… 10.9.3.9.4… 10.9.3.10… 10.9.3.10.4… 10.9.3.10.6… 10.10… 10.10.1.2.3… 10.10.2… 10.10.3… 10.10.3.3… 10.10.3.4… 10.11… 10.11.5… 10.12… 10.13… 10.13.3… 10.13.7… 10.13.10… 10.14… 10.15… 10.15.3… 10.15.3.3… 10.15.3.4… 10.16… 10.17… 11… 11.3… 11.5… 11.5.2… 11.5.3… 11.5.3.3.2A… 11.5.4… A… B… C…

10.7.3.7.3 Service continuity with a UE-to-Network relay
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10.7.3.7.3 Service continuity with a UE-to-Network relay p. 149

This procedure handles a scenario when UE is moving from a location when the UE is experiencing good reception of the MBMS bearer to a location outside the MBMS service coverage. The MC service client apply a service continuity procedure to ensure that the service can be maintained and that the packet loss can be minimized during transition to a UE-to-Network relay connection. The solution also provides the benefit that it offloads the cell when UEs that normally would trigger a transfer from MBMS bearers to unicast bearers when moving outside the MBMS coverage area.

Figure 10.7.3.7.3-1 below illustrates the concept of this procedure. In the Figure UE A (with the MC service client) is first within the MBMS coverage (the far right most location). The MBMS coverage is represented by the dashed circle. The UE A is the moving outside the MBMS coverage and first enters a location in which the MBMS signal is not good enough, but in this location there is still coverage to use unicast bearers. Unicast bearers use link adaption and retransmission so the coverage area for unicast bearers is larger than the coverage of the MBMS bearers. The solid circle outer line represents the coverage of the unicast bearer.

A UE that is leaving the area of MBMS coverage may in this scenario trigger a ProSe discovery procedure to initiate the establishment a relay communication path to UE-R. A UE that is receiving media over an MBMS bearer (and is in idle mode) and for the moment does not need a unicast bearer is costly (from a resource efficiency point of view) to transfer to a unicast bearer due to the need for retransmissions and robust coding in the outer part of cell.

When the ProSe communication path is established the UE A may continue to receive the media over the relay UE-R.

Reproduction of 3GPP TS 23.280, Fig. 10.7.3.7.3-1: UE A is moving from a position in MBMS coverage to outside the network coverage passing an area where only unicast is possible

Figure 10.7.3.7.3-1: UE A is moving from a position in MBMS coverage to outside the network coverage passing an area where only unicast is possible

The procedure defined in this subclause allows for MBMS bearer service continuity when UE is moving from a MBMS coverage area to outside the MBMS coverage area. The procedure applies when the UE is not finding a target cell with good RSRP/RSRQ (receiving strong reference signals from other cells), which could trigger normal cell reselection procedure. In such scenario other aspects should be evaluated to trigger to a relay communication path.

Pre-conditions:

The MC service client UE is not using a unicast bearer when this procedure applies.

Reproduction of 3GPP TS 23.280, Fig. 10.7.3.7.3-2: Service continuity over MBMS bearer using UE-to-network relay

Figure 10.7.3.7.3-2: Service continuity over MBMS bearer using UE-to-network relay

Step 1.

The MC service client estimate the MBMS bearer quality. The MC service clients also measure the reference signals from other cells to estimate the possibilities to transfer to unicast and perform a cell reselection procedure.

Step 2.

If the MBMS bearer quality has reach a certain threshold the MC service client performs ProSe UE-to-network relay discovery over PC5 and establishes a secure point-to-point link with the relay (UE-R) over PC5. As part of this process the remote UE is mutually authenticated at PC5 layer with either the relay or with the network as specified in TS 23.303.

Step 3.

Normal service continuity procedure for a UE-to-network relay. This may be done according to Annex B.

Step 4.

The MC service client informs the UE-R about the reception of media over the MBMS bearer. This includes sending the TMGIs, MBMS SAIs and ProSe per packet priority to the UE-R. This procedure is specified in TS 23.303.

Step 5.

The UE-R will relay the MBMS media using one-to-many ProSe Direct Communication. The UE-R may also relay requests to transfer the media flow from multicast to unicast and vice versa.