OTDOA Reference Cell Selection for Femto and Inter-Frequency Positioning
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Solution Overview
Problem
Existing OTDOA positioning systems face challenges in determining the location of mobile stations when the serving cell cannot be included in the OTDOA assistance data, particularly in cases where femto cells are involved or when there is a frequency layer mismatch, leading to inefficiencies and potential failures in position determination.
Innovation Solution
The system provides OTDOA assistance data by selecting a suitable reference cell from neighboring cells for which the mobile station can obtain timing information, allowing it to determine PRS occasions and perform measurements even when the serving cell is not included in the assistance data, using methods such as idle periods and autonomous gaps to synchronize with neighbor cells.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the serving cell is included in OTDOA assistance data, then positioning accuracy is improved, but the system fails when the serving cell is a Femto cell or operates on a different frequency layer
Solution Approach 1:
The patent introduces a neighboring cell as an intermediary reference cell to bridge the gap when the serving cell cannot be used. The location server provides assistance data for a neighboring cell instead of the serving cell, allowing the MS to perform OTDOA measurements using this intermediate reference point, thus resolving the incompatibility issue while maintaining positioning functionality
Solution Approach 2:
The patent segments the reference cell selection process by allowing the MS to choose from multiple neighboring cells based on signal quality and timing information. Instead of relying on a single serving cell, the system divides the reference cell pool into multiple candidates, enabling the MS to select the most suitable reference cell for accurate positioning
2Reliability
If the MS obtains timing information from neighboring cells using idle periods and autonomous gaps, then positioning functionality is enabled, but the time and complexity of obtaining cell timing information increases
Solution Approach 1:
The patent applies preliminary action by having the location server pre-calculate and provide expected RSTD values and timing information for neighboring cells in the assistance data. This allows the MS to skip lengthy timing acquisition procedures and directly perform measurements using the pre-provided timing references, significantly reducing the time required
Solution Approach 2:
The system uses feedback mechanisms where the MS reports measured RSTD values to the location server, which then refines future assistance data provisioning. This iterative feedback loop optimizes the timing information provided in subsequent assistance data sets, reducing the time and complexity of timing acquisition over time
Data Source
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AI summary
Disclosed embodiments pertain to the obtaining and utilization of Observed Time Difference of Arrival (OTDOA) assistance data. Cell timing information obtained based on measurements by a Mobile Station (MS) of neighbor cells may comprise cell timing offsets of the neighbor cells relative to a serving cell for the MS. OTDOA assistance data may be generated, where the OTDOA assistance data may comprise an OTDOA assistance data reference cell and a cell timing offset between the serving cell and an OTDOA assistance data reference cell, the reference cell being selected based on the received neighbor cell measurements. Embodiments disclosed also pertain to methods on an MS for performing measurements of neighbor cells comprising cell timing information for neighbor cells by requesting idle periods with a desired length from a base station to perform the measurements, and performing the requested measurements upon receiving confirmation that the idle periods have been configured.