Conditional Handover Configuration for Wireless Devices
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Solution Overview
Problem
Legacy handover procedures in 3GPP New Radio (NR) are prone to radio link failures (RLF) and handover failures (HOF) due to the lack of efficient conditional handover mechanisms, which can lead to unnecessary re-establishments and service interruptions, especially when the best target cell is not prepared or when RLF detection triggers re-establishment despite good radio conditions existing among CHO targets.
Innovation Solution
The method involves configuring wireless transmit/receive units (WTRUs) with conditional handover (CHO) configurations that include candidate cells and trigger conditions, allowing the WTRUs to execute handovers only when specific radio conditions are met, and sending measurement reports instead of executing CHO commands if the serving cell meets eligibility criteria, thereby reducing unnecessary re-establishments and improving handover reliability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If legacy handover procedures are used, then handover can be triggered by measurement reports, but radio link failures and handover failures occur due to lack of conditional handover mechanisms
Solution Approach 1:
The patent applies preliminary action by configuring the WTRU with conditional handover (CHO) configurations in advance, including multiple candidate target cells and their associated trigger conditions, before handover is actually needed. This allows the handover to be executed reliably when conditions are met, without requiring complex real-time decision-making during critical handover moments.
Solution Approach 2:
The patent segments the handover process by dividing target cells into multiple candidate cells, each with specific trigger conditions. Instead of a single handover target, the system evaluates multiple candidates (e.g., target cell 1, target cell 2) with different RSRP thresholds and offset values, allowing selective handover to the most appropriate cell based on current radio conditions.
2Reliability
If conditional handover configurations with multiple candidate cells are implemented, then handover reliability improves, but configuration and processing complexity increases
Solution Approach 1:
The patent implements self-service by enabling the WTRU to autonomously evaluate CHO trigger conditions and select appropriate target cells based on measured radio signals. The WTRU independently compares RSRP measurements against configured thresholds and offsets, and automatically executes handover to the suitable target cell without requiring continuous network intervention or complex centralized control.
3Loss of information
If measurement reports are sent for all cells, then network has complete information, but unnecessary re-establishments occur when serving cell meets eligibility criteria
Solution Approach 1:
The patent extracts the handover execution decision from the measurement reporting process. When the serving cell meets measurement reporting eligibility criteria (e.g., RSRP above threshold), the system separates the CHO execution path from the measurement report path, allowing the WTRU to directly execute handover to a candidate cell without sending measurement reports that would trigger unnecessary re-establishment procedures.
Data Source
AI summary
Methods and apparatuses for conditional handover (CHO) are provided herein. CHO configuration information identifying CHO candidate cells may be received. The CHO configuration information may indicate CHO trigger conditions associated with the CHO candidate cells, measurement trigger conditions associated with non-CHO candidate cells, and measurement reporting eligibility criteria associated with a serving cell. If a CHO trigger condition is fulfilled, and if a measurement trigger condition is fulfilled, and if the serving cell does not meet the measurement reporting eligibility criteria, a handover procedure may be executed towards the CHO candidate cell for which the CHO trigger condition is fulfilled. The method may include sending a message indicating completion of the handover procedure and reporting a signal measurement associated with a non-candidate cell. If the serving cell meets the measurement reporting eligibility criteria, the method may include refraining from executing the CHO while still reporting the signal measurement.