GNSS Pseudorange Correction for Urban Multipath Positioning
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Solution Overview
Problem
GNSS receivers in urban environments suffer from significant position calculation errors due to multipath effects, which can distort pseudorange measurements, leading to inaccuracies of over 100 meters, as seen in urban canyons where signals are reflected multiple times off surrounding buildings.
Innovation Solution
The method involves classifying pseudoranges as line-of-sight (LOS) or non-line-of-sight (NLOS) and computing excess path length (EPL) corrections for NLOS pseudoranges using a weighted least squares (WLS) algorithm, combined with extended Kalman filters to smooth and predict EPL corrections over time, and transmitting these corrections to a cloud-based assistance service for database creation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If pseudorange measurements are used in urban environments, then position calculation can be performed, but multipath effects cause large position errors exceeding 100 meters
Solution Approach 1:
The patent segments pseudorange measurements into two distinct categories: LOS (line-of-sight) measurements and NLOS (non-line-of-sight) measurements. This segmentation is achieved through classification algorithms that analyze signal characteristics. By treating these two types of measurements separately, the system can apply different processing strategies - using LOS measurements directly for position calculation while applying EPL corrections to NLOS measurements, thereby resolving the contradiction between maintaining position calculation capability and eliminating multipath errors.
Solution Approach 2:
The patent introduces an intermediary correction mechanism called Excess Path Length (EPL) estimation and correction. This intermediary process acts as a mediator between the problematic NLOS measurements and the final position calculation. The EPL correction estimates the additional path length caused by signal reflections and uses this information to adjust the NLOS pseudorange measurements, effectively removing the multipath error component while preserving the useful positioning information.
2Measurement precision
If signal classification and EPL correction processing are implemented, then position accuracy is improved, but computational complexity and processing time increase
Solution Approach 1:
The patent applies preliminary action by performing signal classification and EPL correction processing before the final position calculation. The system classifies measurements as LOS or NLOS in advance, estimates EPL values for NLOS signals beforehand, and applies corrections prior to position computation. This preliminary processing organizes the data in advance, allowing the position calculation algorithm to work with pre-processed, corrected measurements, thereby reducing the overall computational burden during real-time positioning.
Solution Approach 2:
The patent implements dynamic processing by adapting the correction application strategy based on measurement quality and availability. The system dynamically selects which NLOS measurements to correct and apply based on their reliability indicators and the overall measurement set quality. This dynamic approach allows the system to increase processing complexity only when necessary to achieve the required position accuracy, rather than applying fixed complex processing to all measurements uniformly.
Data Source
AI summary
Methods and systems for estimating and using excess path length (EPL) corrections in GNSS receivers are described. A method can estimate the EPLs using a selection of line of sight and non line of sight pseudorange measurements, and these EPLs can be used to correct non selected non-line of sight pseudoranges. In one embodiment, a cloud based system can receive data from a crowd source set of EPL corrections (e.g., from GNSS receivers in an urban canyon environment) and then can develop a crowd sourced set of EPL corrections and then provide to GNSS receivers (some of which may part of the crowd of GNSS receivers) the crowd sourced set of EPL corrections. The EPL corrections can be used to improve position solutions in, for example, an urban canyon.