TDOA Location Estimation Mitigating Multipath Delay Bias
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Solution Overview
Problem
Existing location estimation systems face accuracy degradation due to multipath delays, especially in environments where gateways experience varying levels of multipath delay spread, leading to biased Time of Arrival (TOA) and Time Difference of Arrival (TDOA) measurements.
Innovation Solution
The system employs an Extended Least Median Error algorithm that filters and eliminates gateways with significant multipath delay, combines TOA with Received Signal Strength Indication (RSSI) and Signal to Noise Ratio (SNR) metadata to validate measurements, and adaptively selects between Least Median Error and Least Mean Square Error methods to improve accuracy, while mitigating bias from multipath delays.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional Least Mean Square Error algorithm is used for location estimation, then computational efficiency is maintained, but location accuracy degrades in the presence of multipath delay
Solution Approach 1:
The patent extracts and eliminates gateways with heavy multipath delay from the location estimation process. By identifying problematic gateways and removing them from calculations, the system prevents multipath bias from degrading location accuracy, thereby resolving the contradiction between maintaining computational efficiency and achieving accurate location estimation in multipath environments.
Solution Approach 2:
The patent changes the estimation criterion from Least Mean Square Error to Least Median Error. This parameter change in the optimization objective makes the algorithm robust against outliers and multipath delays, as the median is less sensitive to extreme values than the mean, thus improving location accuracy without requiring complex preprocessing.
2Reliability
If all gateways are used for location estimation, then the system operates with available infrastructure, but accuracy degrades when some gateways suffer from heavy multipath delay
Solution Approach 1:
The patent performs preliminary evaluation of TOA variations for each gateway before conducting location estimation. By assessing the multipath delay characteristics of each gateway in advance, the system can identify and eliminate problematic gateways before they corrupt the location calculation, ensuring reliable and accurate results.
Solution Approach 2:
The patent uses TOA variation metrics as feedback to evaluate gateway quality. This feedback mechanism allows the system to adaptively select gateways with acceptable multipath characteristics, creating a closed-loop process that continuously monitors and adjusts gateway selection based on observed signal quality, thereby maintaining high location accuracy.
3Productivity
If TDOA measurements are taken from all gateways, then sufficient data is available for location calculation, but biased measurements from multipath-affected gateways degrade the estimate
Solution Approach 1:
The patent applies partial action by using only a subset of gateways for location estimation rather than all available gateways. By selectively including only those gateways with acceptable TOA variation (below threshold), the system achieves accurate location estimation without the computational overhead and accuracy degradation that would result from using all gateways, including those with heavy multipath delay.
Data Source
Figure 1a~1b
Figure 2a
Figure 2b
AI summary
A system comprising at least a mobile device (110) and a plurality of gateways (120a-120g) whose positions are known, wherein the gateways (120a-120g) are operatively arranged to determine for each gateway a time differences of arrival (TDOA) of a signal originated by the mobile device (110). A solver unit (160) computes the position of the mobile device (110), based on said time difference of arrival (TDOA). The solver unit (160) implements ELM and a LMS algorithm to compute the mobile device's one-shot location estimate based on one or several packet transmissions, and includes a procedure to decide if an LMS algorithm needs to be run and a procedure to select or combine the location output from ELM and LMS for the one-shot location output. Further the solver unit comprises a tracking algorithm to realise the tracking of the moving device or to improve location accuracy should the device static.