Signal Time-of-Arrival Estimation Using Leading-Edge Correlation
Solution Overview
Problem
Existing position-determination systems face challenges in accurately determining signal propagation time due to susceptibility to multipath interference, particularly when using one-way techniques and standard PN sequences in multipath environments, which affects the accuracy of geographic positioning.
Innovation Solution
The technique involves correlating received signals using a correlation function with a curve matching table that primarily utilizes pre-peak samples and selectively uses post-peak samples for leading edge curve matching, reducing multipath interference and improving resolution by focusing on the leading edge of the correlation function.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If post-peak samples are used in the interpolation calculation to determine time of arrival, then the calculation can be completed, but susceptibility to multipath interference increases
Solution Approach 1:
The patent extracts and uses only the pre-peak portion of the correlation function for time of arrival determination. By taking out the harmful post-peak samples from the calculation and relying solely on pre-peak samples, the method eliminates multipath interference while maintaining measurement precision.
Solution Approach 2:
The patent performs preliminary action by using pre-peak samples that occur before the correlation function peak. These early samples are captured and used for interpolation calculation before multipath interference can corrupt the measurement, effectively preventing harmful effects from degrading accuracy.
2Ease of operation
If a standard PN sequence is used in the ranging waveform, then the system can operate, but the correlation function has high sidelobes and poor performance in multipath environments
Solution Approach 1:
The patent changes the parameter of the ranging waveform by using a modified PN sequence with specific auto-correlation properties. This parameter change results in a correlation function with reduced sidelobes and an asymmetric shape, improving reliability in multipath environments while maintaining system operability.
3Measurement precision
If the correlation function peak is used for time of arrival determination, then the measurement can be made, but resolution is limited by the sampling rate
Solution Approach 1:
The patent applies another dimension by using interpolation between sample points in the time domain. Instead of being limited to discrete sample points, the method creates a continuous time representation through interpolation, adding a dimensional aspect that enables sub-sample resolution and improves measurement precision beyond the original sampling rate limitation.
Data Source
AI summary
A technique for determining the time of arrival of a signal involves correlating a received signal with a correlation function to produce a stream of correlation samples including a peak sample, pre-peak samples, and post-peak samples. A curve matching table includes sets of values, where each set of values represents discrete points of a correlation function having a peak at a respective different time shift relative to the timing of the peak sample. The sets of values include first sets of values that are matched with a first set of samples having no post-peak samples from the correlation samples, and second sets of values that are matched with a second set of samples having at least one post-peak sample. The time of arrival of the signal is determined from the timing of the peak of the correlation function represented by the set of values that produces the best match.