VSWR Estimation via Cross-Correlation and Phase Rotation
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Solution Overview
Problem
In wireless transmission systems, monitoring the condition of antennas and cable/connector systems in real-time is challenging due to interference and noise, leading to false alarms and inaccurate return loss measurements, especially with complex modulation schemes and co-sited transmitters.
Innovation Solution
A method using cross-correlation and spectrum analysis techniques with single axis sampling, where the transmitted signal is mathematically rotated in phase and sampled over equally spaced intervals to suppress interference and estimate VSWR without the need for strict time alignment, allowing for accurate return loss calculation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional power detectors are used to measure reflected power, then the measurement process is simple, but the measurement precision deteriorates due to noise from other transmitters and co-sited transmitters
Solution Approach 1:
The patent converts the harmful interference from co-sited transmitters into a beneficial signal by using cross-correlation between the known transmitted signal and the received reflected signal. The interference, which has different statistical properties than the desired signal, is suppressed through the correlation process, allowing accurate return loss measurement even in noisy environments
Solution Approach 2:
The patent introduces cross-correlation as an intermediary processing step between the reflected signal and the power measurement. This intermediary operation separates the desired reflected signal from the interfering noise by exploiting the known structure of the transmitted signal, thereby improving measurement accuracy
2Productivity
If complex modulation schemes with multiple carriers are used to improve transmission capacity, then the data rate increases, but the reliability of VSWR monitoring deteriorates due to detector inaccuracies
Solution Approach 1:
The patent replaces traditional hardware power detectors with a software-based cross-correlation measurement approach. This substitution allows for accurate power measurement of complex modulation schemes without relying on the linearity and calibration of physical detectors, thereby maintaining VSWR monitoring reliability while supporting high-data-rate transmissions
3Measurement precision
If directional couplers and bridges are used to separate forward and reflected signals, then the signal separation is effective, but the device complexity increases
Solution Approach 1:
The patent extracts only the necessary information for VSWR measurement by using cross-correlation to directly measure the reflected power from the received signal, eliminating the need for complex hardware signal separation devices. This extraction approach maintains measurement accuracy while significantly reducing system complexity
Data Source
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AI summary
Methods, apparatus, and computer program products using spectrum analysis or cross correlation techniques to discriminate against interference. These approaches are straight forward if both the forward and reflected signals contain complex or quadrature (I and Q) samples. But, if only single axis samples are available as is often the case to reduce the sampling rate, the resulting samples could represent the I component, the Q component or, more likely, some combination of the two. This generally requires some type of time alignment procedure to ensure proper phase. Assuming that the transmitted signal exists in complex form, this signal can be mathematically rotated in phase and then single axis sampled for comparison against the single axis reflected signal. If the rotation is done over equally spaced intervals that spans one complete cycle, the average of the absolute value all such return loss ratios will approach the actual return loss ratio and the interference will be suppressed. The resultant can be compared to a threshold value and trigger an alarm.