Conditional L1/L2 Serving Cell Change for Low-Latency Handover

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Solution Overview

Problem

Existing wireless communication networks face challenges in executing handovers efficiently due to poor radio conditions, leading to increased latency, signaling overhead, and battery depletion, particularly in conditional handover (CHO) scenarios, which rely on Radio Resource Control (RRC) signaling.

Innovation Solution

Implementing Layer-1 (L1) or Layer-2 (L2) based inter-cell mobility serving cell change using conditional reconfigurations, where the UE receives a message containing execution conditions and lower layer commands to switch to a candidate target cell upon fulfilling specific measurements, reducing reliance on RRC signaling.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If RRC signaling is used for conditional handover, then handover control is reliable, but latency and signaling overhead increase

Engineering Contradiction:

Improvehandover control reliabilityVSAvoidhandover latency

Core Design Contradiction:

ReliabilityVSLoss of time

Solution Approach 1:

The patent segments the handover process into preparation phase (RRC signaling for conditional reconfiguration) and execution phase (MAC CE for actual cell switch). This segmentation allows reliable control during preparation while enabling fast execution through lower-layer signaling, resolving the contradiction between reliability and latency.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent introduces MAC CE as an intermediary mechanism between RRC layer and physical layer. MAC CE serves as a mediator that receives conditional reconfiguration from RRC and executes the actual cell switch at L1/L2, enabling fast execution without requiring continuous RRC signaling during the handover execution.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Reliability

If RRC signaling is used for conditional handover, then handover control is reliable, but signaling overhead increases

Engineering Contradiction:

Improvehandover control reliabilityVSAvoidsignaling overhead

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The patent segments signaling into two phases: comprehensive RRC signaling for conditional reconfiguration setup (preparation phase) and concise MAC CE signaling for execution (execution phase). This reduces overall signaling overhead by avoiding repetitive RRC signaling during the actual handover execution.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

MAC CE acts as an intermediary that condenses the handover execution information into a compact format, reducing signaling overhead compared to using full RRC signaling for the execution phase while maintaining the reliability established during the RRC preparation phase.

Inventive Principle:

Principle #24Intermediary (Mediator)

3Speed

If handover is executed quickly, then latency is reduced, but connection stability may be compromised

Engineering Contradiction:

Improvehandover execution speedVSAvoidconnection stability

Core Design Contradiction:

SpeedVSStability of the object's composition

Solution Approach 1:

The patent applies preliminary action by configuring conditional reconfiguration in advance through RRC signaling, including all necessary parameters and conditions. When execution is triggered, the UE only needs to execute the pre-configured MAC CE command, enabling fast handover execution while maintaining connection stability through thorough preparation.

Inventive Principle:

Principle #10Preliminary action

4Loss of time

If L1/L2 based inter-cell mobility is implemented, then latency and overhead are reduced, but implementation complexity increases

Engineering Contradiction:

Improvehandover latencyVSAvoidimplementation complexity

Core Design Contradiction:

Loss of timeVSDevice complexity

Solution Approach 1:

The patent makes MAC CE universal by enabling it to serve multiple functions: normal MAC control functions plus conditional handover execution. This multi-functionality reduces implementation complexity by reusing existing MAC layer structures rather than requiring entirely new L1/L2 mechanisms.

Inventive Principle:

Principle #6Universality (Multi-functionality)

Solution Approach 2:

MAC CE serves as an intermediary that bridges RRC layer configuration and physical layer execution. This intermediary approach reduces implementation complexity by leveraging existing MAC layer processing capabilities while achieving L1/L2 based mobility performance.

Inventive Principle:

Principle #24Intermediary (Mediator)

Data Source

PatentUS20260040157A1Conditional Execution of L1/L2 Inter-Cell Mobility Serving Cell Change

Publication Date: 2026.02.05 TELEFONAKTIEBOLAGET LM ERICSSON (PUBL)

AI summary

Methods are described for a wireless device, such as a UE, to execute a Layer-1 (LI) or Layer-2 (L2) based inter-cell mobility serving cell change, based on the fulfillment of an execution condition (e.g., based on measurements), using a conditional reconfiguration. The UE receives, from a serving network node, a message containing at least one conditional reconfiguration for L1/L2 based inter-cell mobility serving cell change. The at least one conditional reconfiguration includes at least one of an execution condition, an indication of a candidate target cell for L1/L2 mobility, and a lower layer command. When an execution condition associated to the candidate target cell for L1/L2 inter-cell mobility is fulfilled, the UE executes the conditional reconfiguration that results in a L1/L2 based inter-cell mobility serving cell change to the candidate target cell. The UE then starts to operate according to a configuration of the candidate target cell in the L1/L2 based inter-cell mobility serving cell change.