Handover Offset Configuration for Wireless Terminal
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Solution Overview
Problem
In LTE-based communication systems, handovers often result in increased data interruption times due to delayed measurement report messages and handover command messages, leading to degraded communication quality and radio link failures.
Innovation Solution
A method for a terminal to receive configuration information for handover events, measure channel states of serving and target base stations, and transmit measurement and handover indication messages based on predefined offsets for normal, abnormal, and radio link failure states, allowing for timely handover execution and reducing data interruption times.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the terminal waits for the received signal strength difference to exceed a predetermined threshold before triggering handover, then the handover decision is more reliable, but the data interruption time increases and communication quality degrades
Solution Approach 1:
The terminal performs preliminary actions by transmitting the measurement report message immediately when the handover preparation event occurs (difference >= handover preparation offset), rather than waiting for the handover execution event. This allows the base station to prepare the handover in advance, reducing the actual data interruption time when handover is executed.
Solution Approach 2:
The handover process is segmented into two distinct events: handover preparation event (when difference >= handover preparation offset) and handover execution event (when difference >= handover execution offset). This segmentation allows the terminal to trigger preparation actions earlier while maintaining reliable execution criteria, effectively separating the decision-making phases to reduce overall interruption time.
2Device complexity
If the terminal uses a single handover threshold for all channel states, then the system is simpler to implement, but the handover performance degrades in abnormal and radio link failure states
Solution Approach 1:
The patent applies local quality by configuring different handover parameters (handover preparation offset and handover execution offset) according to the specific channel state. In normal state, larger offsets are used for stable operation; in abnormal state and RLF state, smaller offsets are used to enable faster handover execution. This state-dependent configuration optimizes handover performance for each specific scenario without requiring a completely different system.
Solution Approach 2:
The handover offsets are made dynamic by adapting them according to the channel state (normal, abnormal, or RLF state). The terminal determines the appropriate offsets based on the current radio link quality, allowing the handover criteria to dynamically adjust to changing conditions. This dynamic adaptation improves reliability in critical states while maintaining system simplicity through a unified configuration framework.
3Speed
If the terminal transmits measurement report messages in real time, then the base station can make faster handover decisions, but the message may not be received due to poor radio link conditions
Solution Approach 1:
The terminal transmits the measurement report message in advance when the handover preparation event occurs, before the radio link condition deteriorates to the point of failure. This preliminary transmission ensures the base station receives the measurement information while the link is still reliable, enabling faster handover decisions without sacrificing message transmission reliability.
4Reliability
If the terminal performs AS RLF recovery or NAS RLF recovery procedures, then the radio link failure can be recovered, but the data interruption time increases to several hundreds of milliseconds or seconds
Solution Approach 1:
By transmitting the measurement report message at the handover preparation event and enabling the base station to prepare the handover in advance, the system reduces the likelihood of handover failure that would trigger RLF recovery procedures. When the handover is properly prepared beforehand, the execution is more successful, preventing the need for time-consuming AS or NAS RLF recovery procedures.
Data Source
AI summary
An operation method of a terminal includes receiving configuration information from a serving base station; measuring channel states of the serving base station and a target base station; when a difference between received signal strengths of the serving base station and the target base station is not less than a handover preparation offset, determining that a handover preparation event has occurred and transmitting a measurement report message to the serving base station; and when the difference is equal to or greater than a handover execution offset, determining that a handover execution event has occurred and transmitting a handover indication message informing of execution of a handover to the target base station. The channel state is normal state, abnormal state, or RLF state, and the configuration information indicates a different handover preparation offset and a different handover execution event according to the channel state.