Mobile Device RSTD Estimation Using Dynamic Search Window Modes
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Solution Overview
Problem
The existing methods for determining reference signal time difference in mobile communication systems, such as LTE, face challenges in accurately estimating the time difference within a capture range smaller than the search window, leading to ambiguous results and increased processing time due to the need for sliding window approaches.
Innovation Solution
The introduction of acquisition and tracking modes in the mobile device assisted multilateration method, which dynamically adjusts the search window based on the capture range capability and employs non-coherent combining of OFDM frames to mitigate frequency offsets, allowing for efficient estimation of reference signal time differences.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a sliding window approach is used to search for PRS occasions within a search window larger than the capture range, then the complete search range is covered, but the processing complexity and time consumption increase significantly
Solution Approach 1:
The patent divides the search window into multiple overlapping segments, where each segment is processed independently to find local peaks. This segmentation allows the system to cover a large search window without processing the entire window at once, reducing computational complexity while maintaining complete search coverage.
Solution Approach 2:
The patent performs preliminary coarse timing estimation using a reduced search window before refining the estimate. This preliminary action narrows down the search space, allowing subsequent fine timing estimation to focus only on relevant regions, thereby reducing overall processing time while maintaining accuracy.
2Productivity
If the capture range is limited by subcarrier spacing, then the FFT processing is computationally efficient, but the search window must be larger than the capture range, requiring additional sliding window approaches
Solution Approach 1:
The patent dynamically adjusts the search window size and position based on the capture range determined by subcarrier spacing. The search window is adapted to match the available capture range, and multiple passes are performed with different window positions, optimizing the balance between processing efficiency and search completeness.
Solution Approach 2:
The patent implements a nested structure where a coarse search is performed first with a larger window, followed by refined searches with smaller windows centered on detected peaks. This nesting allows the system to efficiently handle the relationship between capture range and search window size without requiring complex algorithms.
3Reliability
If multiple sliding FFTs are performed to cover the maximum search window span, then complete coverage is achieved, but power consumption and processing complexity increase
Solution Approach 1:
The patent applies local quality by focusing computational resources on regions of interest. After detecting local peaks in initial processing, subsequent FFT operations are concentrated only around these peak regions rather than uniformly across the entire search window. This maintains search completeness while significantly reducing the number of FFT operations and associated power consumption.
Data Source
AI summary
Acquisition and tracking modes for a mobile device assisted multilateration based localization are disclosed. A relative time difference is determined between a positioning reference cell and at least two other detectable positioning cells. A reference signal of a positioning cell is detected to determine timing of a detectable positioning cell by either applying sliding window approach to acquire the positioning cell or a single window approach to track the positioning cell. The sliding window approach within a search window is applied to acquire the positioning cell when a coarse timing of the positioning cell has not yet been achieved. A single window approach is applied to track the positioning cell when a coarse timing of the positioning cell has been achieved or when the search window is not larger than a capture range capability of the mobile device.