UE Mobility Measurements in Heterogeneous Networks
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Solution Overview
Problem
In E-UTRAN RRC connected mode, especially in HetNet scenarios, user equipment (UE) mobility is challenged by long DRX cycles and high velocities, leading to delayed handover triggering and increased reaction times, resulting in Radio Link Failures (RLF) due to insufficient measurement sampling in small cells.
Innovation Solution
The UE performs additional mobility measurements for a restricted time period after entering a small cell, independent of existing DRX configurations, with the measurement interval and duration calculated based on the cell type and expected worst-case travel time to ensure robust handover performance without requiring knowledge of UE velocity or DRX details.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If the UE performs measurements according to existing DRX configurations in HetNet scenarios, then power savings are maintained, but mobility robustness deteriorates due to insufficient measurement sampling in small cells
Solution Approach 1:
The network configures the UE with measurement parameters before the UE enters a small cell, preparing the measurement configuration in advance. This preliminary configuration enables the UE to immediately switch to enhanced measurement mode upon entering a small cell, ensuring measurement robustness without requiring continuous high-power operation
Solution Approach 2:
The measurement configuration is made dynamic by introducing a small cell indicator that triggers different measurement behaviors. When the UE enters a small cell (detected via the indicator), it switches to enhanced measurement mode with more frequent sampling. When outside small cells, it returns to standard DRX-based measurements, optimizing the balance between power consumption and measurement robustness based on location
2Use of energy by moving object
If the UE uses long DRX cycles to save power, then energy consumption is reduced, but handover triggering is delayed due to less frequent measurement sampling
Solution Approach 1:
The measurement sampling frequency is made local to specific geographic areas (small cells). Instead of uniformly increasing measurement frequency across all locations, the enhanced sampling is applied only when the UE is within a small cell coverage area, identified by the small cell indicator. This localized approach reduces overall power consumption while ensuring timely handovers specifically where needed
3Productivity
If the network configures the UE with standard measurement parameters for macro-cell layout, then intra-frequency mobility is optimized, but mobility performance deteriorates in heterogeneous networks with small cells
Solution Approach 1:
The measurement parameters are changed based on the cell type. The network configures the UE with standard measurement parameters for macro-cell operation, but introduces additional parameters (small cell indicator, enhanced measurement frequency) that are activated when the UE enters a small cell. This parameter adaptation allows the system to optimize for macro-cell efficiency while ensuring robust performance in small cell environments
Data Source
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AI summary
A method includes performing, responsive to entry into a cell, with a selected interval a number of measurements during a time period. The method also includes ceasing, after expiration of the time period, to perform the measurements that were performed responsive to the entry into the cell. The selected interval may be a maximum interval during which a measurement should be performed. Another method includes determining information to be used by a user equipment to perform, responsive to entry by the user equipment into a cell, a number of measurements using a selected interval during a time period. This other method includes signaling the information to the user equipment. Apparatus, computer program products, and systems are also disclosed.