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NON-IAB BASED MOBILE
BASE STATION RELAYS
By Rashmi Kamran Bhatia, IIT Bombay
Mobile Base Station Relay (MBSR) is a lucrative option to extend network coverage and
support enhanced capacity. A prime use case of MBSR is Vehicle Mounted Relay (VMR) to
provide connectivity to users inside or nearby outside the vehicle.
The requirements for MBSRs are provided in 3GPP TS 22.261
(stage 1), focusing on efficient mobility and service continuity TSDSI has undertaken a study on
for connected users in different scenarios. While the stage
1 requirements allow for both IAB and non-IAB based MBSR wherein the evolved solution
architectures, the stage 2 development in 3GPP Release 18 has places a gNB-DU at MBSR, and the
considered IAB-based architecture only.
corresponding gNB-CU, called MBSR-
TSDSI has undertaken a study on MBSR wherein the evolved gNB-CU, in the edge cloud.
solution places a gNB-DU at MBSR, and the corresponding
gNB-CU, called MBSR-gNB-CU, in the edge cloud. MBSR
comprises the gNB-DU functionality along with an additional
UE (Mobile Termination (MT)) stack to enable IP connectivity Figure 1 shows the working of this solution for the VMR use
with MBSR-gNB-CU. A unique feature of the TSDSI solution case. Initially, the MT of the MBSR is connected to gNB1 over
is that it utilizes the 5G system’s PDU connectivity service to the radio (Uu) interface, and its PDU session(s) to the MBSR-
connect the MBSR (gNB-DU) to the corresponding MBSR-gNB- gNB-CU are established via gNB1 and UPF1. Multiple UEs
CU as shown in Figure 1. The F1 interface between the gNB-DU within the vehicle are connected to gNB-DU of the MBSR
and gNB-CU is carried in the PDU session established between (VMR) through NR interface. For all UEs connected to gNB-DU
MBSR (MT) and MBSR-gNB-CU via the 5G system. of MBSR, the MBSR-gNB-CU acts as gNB-CU.
Figure 1: Working of the solution for the VMR handover scenario
When the MBSR moves and gets closer to gNB2, a conventional CU) despite the mobility of the MBSR. Therefore, there is no
UE handover is triggered between gNB1 and gNB2 for the handover signaling for the connected UEs. This simplicity and
MBSR (MT function). However, the PDU session(s) between no impact on service continuity for UEs make it a viable option
the MBSR and MBSR-gNB-CU do not get impacted due to for non-IAB based MBSR solution for future 3GPP releases also.
the handover, hence there is no disruption in the IP and F1
connectivity between the two entities. Since the UEs within I would like to acknowledge Prof. Abhay Karandikar, Prof.
the MBSR (VMR) move along with the VMR, it essentially is a Prasanna Chaporkar, Mr. Pranav Jha, Mr. Shashi Ranjan and
no mobility scenario for the UEs as they remain connected to Ms. Shwetha Kiran for their contribution.
the same gNB-DU (MBSR) and the same gNB-CU (MBSR-gNB-
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