UE Relay Mode Switching for Mission Critical Voice Continuity
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Solution Overview
Problem
Existing technologies face challenges in providing seamless service continuity for ProSe-enabled devices transitioning between network coverage and User Equipment-to-Network Relays (UNRs), resulting in service interruptions and high battery consumption due to inadequate mechanisms for switching between Network Mode Operation (NMO) and Network Mode Operation via Relay (NMO-R).
Innovation Solution
The implementation of methods and devices that enable switching between NMO and NMO-R modes by detecting service deterioration and absence of suitable neighbor cells, initiating relay node discovery, and selecting suitable UNRs to minimize service interruptions and optimize power consumption, using approaches like Break-Before-Make (BBM) and Make-Before-Break (MBB) handover strategies.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a UE switches from NMO to NMO-R after disconnection from LTE network, then the UE can maintain service access, but there is a significant service interruption delay (0.5 to 18 sec)
Solution Approach 1:
The patent applies preliminary action by initiating relay node discovery and selection processes before the UE actually needs to switch from NMO to NMO-R. The UE continuously monitors network conditions and pre-establishes relay connectivity when approaching coverage edges, so that when disconnection occurs, the relay path is already ready to take over service immediately, eliminating the 0.5 to 18 second interruption delay.
2Reliability
If a UE remains connected via UNR when network coverage is available, then service access is maintained, but battery consumption increases excessively
Solution Approach 1:
The patent implements dynamics by making the UE's operational mode flexible and adaptive. The UE dynamically switches between NMO and NMO-R based on real-time network availability and service requirements. When network coverage is available, the UE transitions to NMO to conserve battery; when coverage is lost, it switches to NMO-R to maintain service. This dynamic adaptation optimizes energy consumption while ensuring continuous service access.
3Area of stationary object
If existing handover mechanisms are used for mobility, then network coverage is extended, but the serving cell cannot initiate handover preparation phase with relay
Solution Approach 1:
The patent introduces the relay node as an intermediary element between the UE and the network. The relay acts as a mediator that bridges the gap between out-of-coverage UEs and the core network, enabling handover preparation by pre-establishing relay connections before actual handover is needed. This intermediary approach allows the serving cell to initiate handover preparation phases that would otherwise be impossible with traditional direct UE-to-network connections.
4Ease of operation
If autonomous reselection is allowed in LTE, then mobility flexibility is improved, but it is not allowed in connected mode
Solution Approach 1:
The patent applies segmentation by dividing the UE's operational modes into distinct states (NMO and NMO-R) with different autonomy levels. In NMO mode, the UE follows network-controlled handover procedures, while in NMO-R mode, the UE is enabled for autonomous reselection. This segmentation allows autonomous reselection to be activated only when necessary (when out of coverage), maintaining network control in covered areas while providing mobility flexibility when needed, thus reducing overall system complexity.
Data Source
AI summary
A device, serving cell and method of switching between modes of operation for the device in a cellular network comprises receiving a service via a connection with the serving cell. A condition indicative of deterioration in network service and an absence of a suitable neighbor cell are detected. In response, discovery of relay nodes is initiated. When a suitable relay node is discovered, a mechanism to switch to receiving the service via the suitable relay node is initiated. The service may be a mission critical push-to-talk over Long Term Evolution service. The relay node may be user equipment acting as a user equipment-to-network relay node. When the device is in an RCC_CONNECTED state, the mechanism to switch includes sending a relay mode preference indication to the serving cell, receiving a connection release message from the serving cell, releasing the serving cell connection, and establishing a sidelink connection with the relay.