Lower Layer Triggered Mobility Recovery in Wireless Systems
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Solution Overview
Problem
Existing wireless communication systems face increased latency and interruption when user equipment (UE) moves between cells, as lower layer triggered mobility may fail to complete a switch to a target cell, necessitating a recovery mechanism to ensure successful cell switching.
Innovation Solution
The apparatus and method implement a recovery mechanism by selecting and attempting a switch to a further target cell from a list of candidate cells provided by the network node, using layer 1 or layer 2 triggered mobility, with timers and quality threshold settings to manage the switching process, allowing for repeated attempts until successful or reaching a predetermined time or number of attempts.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If lower layer triggered mobility is used to reduce latency, then switching speed is improved, but reliability deteriorates when switch completion fails
Solution Approach 1:
The network node pre-configures multiple candidate target cells with all necessary mobility parameters and configuration information before the actual cell switch is needed. When a cell switch attempt fails, the UE can immediately try another pre-configured candidate cell without waiting for new configuration messages, thus maintaining fast switching while improving reliability through multiple pre-prepared options.
Solution Approach 2:
The system prepares multiple candidate target cells in advance as a buffer against potential switch failures. This cushioning approach ensures that if the first target cell switch attempt fails, there are already alternative cells ready with all configuration parameters, preventing service interruption and maintaining reliability without sacrificing the fast switching benefit.
2Reliability
If multiple candidate cells are prepared in advance, then reliability of successful switching is improved, but device complexity increases
Solution Approach 1:
The network node uses a universal configuration approach where multiple candidate cells share the same configuration structure and parameters. The UE applies the same mobility procedure and evaluation criteria to all candidate cells, simplifying the complexity despite having multiple options. The system treats all candidate cells uniformly rather than requiring separate management mechanisms for each.
Solution Approach 2:
The system changes parameters such as cell quality thresholds and signal strength criteria dynamically based on current radio conditions. Instead of complex decision logic, the UE evaluates candidate cells using parameter-based criteria (e.g., RSRP thresholds, signal quality metrics), which simplifies the complexity while maintaining high reliability through adaptive parameter adjustment.
3Productivity
If multiple candidate cells are indicated, then productivity of mobility recovery is improved, but loss of time for processing increases
Solution Approach 1:
The network node provides pre-configured candidate cells with all necessary parameters, measurement references, and mobility information in advance. When a switch failure occurs, the UE can immediately evaluate and attempt switching to alternative candidates without waiting for additional configuration messages or network responses, thus improving recovery productivity while minimizing additional processing time.
Data Source
AI summary
Lower layer triggered mobility LTM for a user equipment moving through a communication network with multiple network nodes supporting radio coverage in multiple cells is considered. The user equipment receives a message from a network node indicating a plurality of lower layer mobility candidate cells and in response attempts a switch to a target cell selected from one of the plurality of candidate cells. Where the attempt fails the user equipment attempts completion of a switch to a further target cell selected from the plurality of candidate cells.