LTE CS Fallback Target Cell Selection
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Solution Overview
Problem
In LTE networks, CS fallback procedures often result in unnecessary location registration and delayed CS service handling due to handovers to undesired non-LTE cells when user equipment is at the boundary of two LTE cells, as the current methods lack efficient selection criteria for target cells based on signal quality.
Innovation Solution
A method is introduced to select a target cell for CS fallback by using a CS fallback parameter and signal quality measurements of non-LTE candidate cells, where the parameter is added to the signal quality measurement of one candidate cell and compared with another, ensuring handover to a cell with significantly better signal quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If user equipment performs CS fallback procedure in expanded service area of serving LTE cell, then CS service can be provided, but handover may occur to undesired non-LTE cell causing unnecessary location registration and delay
Solution Approach 1:
The patent applies parameter changes by introducing a CS fallback parameter that modifies the signal quality measurement threshold. This parameter is added to the signal quality measurement of non-LTE candidate cells mapped to the serving LTE cell, effectively changing the decision criterion for target cell selection. This resolves the contradiction by adjusting the parameter (signal quality threshold) to distinguish between desired and undesired handovers, preventing unnecessary location registration while maintaining CS service availability.
2Area of stationary object
If handover is initiated when target LTE cell has significantly better communication environment, then service area expands, but CS fallback may hand over to undesired non-LTE cell
Solution Approach 1:
The patent changes the parameter used for target cell selection by introducing a CS fallback parameter that is added to signal quality measurements. This modifies the effective threshold for selecting target cells during CS fallback, ensuring that even when service area expansion occurs, the handover targets appropriate non-LTE cells based on enhanced signal quality criteria rather than merely geographic coverage boundaries.
Solution Approach 2:
The patent replaces the simple geographic/service-area-based handover mechanism with a signal quality-based selection mechanism. Instead of relying solely on service area boundaries to determine target cells, the system substitutes a measurement-based approach that evaluates actual signal quality of non-LTE candidate cells, adding the CS fallback parameter to ensure accurate target cell selection even at service area boundaries.
3Device complexity
If simple mapping from LTE cell to non-LTE cell is used, then CS fallback procedure is simple, but handover may occur to cell with poor signal quality
Solution Approach 1:
The patent maintains procedural simplicity while improving reliability by changing the evaluation parameter from basic cell mapping to signal quality measurement with CS fallback parameter addition. The procedure remains straightforward - measure signal quality, add parameter, compare, and select - but the enhanced parameter ensures the selected cell has superior signal quality, resolving the contradiction between simplicity and reliability.
Data Source
AI summary
Described embodiments provide a method of effectively selecting a target cell to hand over user equipment from a LTE network to a non-LTE network when the user equipment requests a CS service. A LTE cell may determine a CS fallback hysteresis parameter in advance. The LTE cell may receive signal quality measurements of at least two candidate non-LTE cells from the user equipment. The LTE cell may select one target cell among the at least two candidate non-LTE cells based on the CS fallback hysteresis parameter and the received signal quality measurements of the at least two candidate non-LTE cells.