Calibrated Pulse Shapes for GPS Multipath Mitigation
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Solution Overview
Problem
Existing GPS receivers face challenges in accurately synchronizing PRN codes due to multipath signals, which introduce errors and residuals, especially when chip transitions in multipath signals are close to those in the direct path signal, leading to tracking errors and reduced positioning and timing accuracy.
Innovation Solution
The use of calibrated reference pulse shapes, which are specific to each satellite and receiver, to differentiate between direct and multipath signals, and to refine position and time estimates by eliminating range biases, is implemented. These calibrated models are created based on correlation measurements in environments free of multipath and noise, and can be further adjusted for RF and IF path effects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional correlation measurements are used to synchronize PRN codes, then the receiver can acquire and track satellite signals, but multipath signals cause tracking errors and reduce positioning accuracy
Solution Approach 1:
The patent segments the correlation function into multiple discrete samples across the code chip period. Instead of using a single correlation measurement, the system divides the correlation function into N samples, each taken at different time offsets within the chip period. This segmentation allows the system to identify and exclude samples affected by multipath signals while retaining those from the direct path, thereby maintaining synchronization reliability while improving positioning accuracy.
Solution Approach 2:
The patent applies local quality by making the sampling strategy adaptive to local signal conditions. The system selectively weights or excludes specific correlation samples based on their local characteristics - identifying which samples correspond to direct path signals versus multipath reflections. This localized differentiation allows the receiver to maintain robust synchronization while eliminating precision-degrading multipath effects from specific time regions of the correlation function.
2Measurement precision
If the receiver makes correlation measurements separated by one or one-half code chip to acquire PRN code, then the receiver can determine alignment within one code chip, but tracking errors occur when multipath chip transitions are close to direct path transitions
Solution Approach 1:
The patent applies preliminary action by performing multiple correlation measurements at different time offsets before final code alignment is established. The system takes N samples across the chip period during the acquisition and tracking process, allowing it to preliminarily identify the direct path signal characteristics before committing to a final alignment decision. This preliminary sampling enables the receiver to distinguish direct from multipath signals in advance, improving both precision and reliability.
Solution Approach 2:
The patent uses partial action by selecting only the necessary subset of correlation samples for final alignment rather than using all available measurements. From the N samples taken across the chip period, the system identifies and uses only those samples that correspond to direct path signals, excluding multipath-affected samples. This selective use of partial measurements maintains tracking reliability while achieving high precision alignment.
3Productivity
If the receiver uses a single correlation measurement to determine signal alignment, then the processing is simple and fast, but the accuracy of position and time estimation is reduced due to multipath errors
Solution Approach 1:
The patent applies periodic action by taking multiple correlation samples at regular time intervals across the code chip period. Instead of a single measurement, the system periodically samples the correlation function at N different time offsets, creating a structured set of measurements that capture the signal's temporal characteristics. This periodic sampling maintains computational efficiency while enabling accurate distinction between direct and multipath signals for improved time estimation.
Solution Approach 2:
The patent changes the parameter of measurement timing by varying the sample time offsets across the chip period. The system takes correlation measurements at different time parameters (t1, t2, ..., tN) within the chip period, allowing it to observe how the correlation function varies with time. This parameter variation enables the receiver to identify the direct path signal's temporal signature and use it for accurate time estimation while rejecting multipath effects.
Data Source
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AI summary
GPS receivers utilize reference pulse shapes in operations to determine estimates of position and time to correct for range biases in differential operations and in signal quality operations. The reference pulse shapes may be code family based, or may be calibrated on a per satellite basis, to incorporate therein the affects of the satellite hardware on the transmitted signals. The receivers may further manipulate the calibrated pulse shape models on a per receiver basis, to incorporate therein the affects of the IF and RF paths through the respective receivers. The calibrated reference pulse shapes may also be used in multipath mitigation processing operations for the respective codes, to produce estimates of the direct path signals and corrections for the carrier and code tracking loops.