Femtocell Calibration for Timing-Based Location Accuracy
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Solution Overview
Problem
Existing timing-based locating systems in wireless communications face inaccuracies when trying to determine the location of mobile devices due to unsynchronized macrocells, resulting in location errors of up to +/-200-500 meters.
Innovation Solution
The implementation of a femtocell calibration method that uses the known location of a femtocell access point to calculate a reference time difference from measured time differences between macrocells and mobile devices, allowing for more accurate location determination of other mobile devices by compensating for the asynchronous signals from macrocells.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If timing-based locating systems use unsynchronized macrocells, then the system coverage area is large, but location accuracy deteriorates to +/-200-500 meters
Solution Approach 1:
A femtocell access point with known location is introduced as an intermediary to mediate between macrocells and mobile devices. The femtocell receives signals from multiple macrocells and measures time differences, providing a reference point that enables accurate location calculation without requiring macrocell synchronization. This intermediary resolves the contradiction by allowing large coverage area while maintaining high location accuracy.
Solution Approach 2:
The system changes the reference parameter from unsynchronized macrocell timestamps to femtocell-measured time differences. By using the femtocell's known location and its measurements of macrocell signal arrival times, the system transforms the location determination problem into one that can achieve high precision without requiring the macrocells to be synchronized.
2Measurement precision
If macrocells are synchronized to improve location accuracy, then location precision improves, but system complexity and synchronization requirements increase
Solution Approach 1:
The femtocell access point serves as a mediator that eliminates the need for macrocell synchronization. Instead of requiring macrocells to be synchronized, the femtocell measures the time differences of signals from unsynchronized macrocells and uses its known location to calculate reference time differences, thereby achieving accurate location determination without synchronization infrastructure.
Solution Approach 2:
The patent extracts the synchronization requirement from the macrocell system by introducing a separate reference mechanism. The femtocell's known location and its independent timing measurements replace the need for macrocell synchronization, effectively removing the complexity of maintaining synchronized macrocells while preserving location accuracy.
3Measurement precision
If femtocell calibration is implemented to improve location accuracy, then location precision improves to +/-10-12 meters, but system complexity increases due to additional calibration procedures
Solution Approach 1:
The femtocell access point performs self-calibration by using its own known location to measure time differences from macrocells and calculate reference time differences autonomously. This self-service approach minimizes external calibration intervention while achieving high location accuracy, reducing the perceived complexity for system operators.
Solution Approach 2:
The system performs preliminary calibration by having the femtocell measure macrocell signal time differences and establish reference time differences before actual location determination. This preliminary action prepares the system for accurate location measurement without requiring complex real-time calibration during operation.
Data Source
AI summary
A femtocell calibration solution is provided that uses the known location of the femtocell to calibrate timing based locating systems. The calculated time differences of different signals sent between macrocells and a mobile device can be used to solve for a reference time difference that accounts for the timing differences of the unsynchronized macrocells. The reference time difference can then be used to solve for the location of another mobile device if the calculated time differences between that mobile device and the macrocells are known. The solution can include taking many measurements of the calculated time difference at the first mobile device in order to average them to get a more accurate reference time difference. The solution can further include ceasing measurements at the first mobile device when the mobile device is no longer within range of the femtocell.