Time-Varying Harmonic Interference Cancellation in Wireless Receivers
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Solution Overview
Problem
Current tone suppression techniques in wireless communications are inadequate for effectively addressing radio frequency interference (RFI) caused by spread spectrum clock harmonics, as they fail to exploit the time-varying nature of these harmonics, leading to unnecessary removal of signal energy.
Innovation Solution
A system that includes a phase estimator to determine the phase between a periodic spreading signal and an effective spreading signal, an amplitude estimator to estimate the amplitude of the interfering harmonic, and a tone suppressor to cancel the interfering harmonic from the received signal, treating spread clock harmonics as time-varying narrow interferers rather than wide interferers, thereby minimizing signal degradation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If current tone suppression techniques (tone excision, notch filtering, adaptive filtering) are used to remove interferers, then the interference is suppressed, but much of the signal energy near the interferer is unnecessarily removed
Solution Approach 1:
The patent applies dynamics by treating the spread clock harmonic as a time-varying narrow interferer rather than a static wide interferer. The tone suppressor dynamically tracks the interferer's frequency and phase variations over time, adjusting the suppression parameters accordingly. This dynamic approach allows precise targeting of the interferer while preserving nearby signal energy that would otherwise be removed by static wideband suppression methods.
Solution Approach 2:
The patent applies local quality by selectively suppressing only the specific time-varying frequency components identified as interferers, rather than applying broad suppression across a wide frequency band. The tone suppressor locally targets the narrowband interferer at each time instant based on its current frequency and phase, preserving the quality and energy of adjacent signal components that are not interferers.
2Object-affected harmful factors
If spread spectrum clocking is used to reduce average amplitude of clock harmonics, then interference to radio receivers is reduced, but it is not sufficient for GPS on small form factor devices
Solution Approach 1:
The patent introduces an intermediary tone suppressor component that sits between the received signal and the GPS processing chain. This intermediary actively identifies and removes the specific spread clock harmonic interferers that spread spectrum clocking fails to sufficiently suppress, thereby enabling reliable GPS operation in small form factor devices where the interferer power relative to GPS signal strength is high.
Solution Approach 2:
The patent employs feedback mechanisms where the tone suppressor continuously monitors the received signal for presence of spread clock harmonics, tracks their time-varying frequency and phase characteristics, and adjusts suppression parameters in real-time. This feedback loop ensures that the suppression adapts to changing interferer conditions while preserving GPS signal integrity.
3Device complexity
If tone suppression techniques assume fixed frequency or slowly time varying interferers, then implementation is simplified, but the known structure of spread clock harmonics is not exploited
Solution Approach 1:
The patent resolves this contradiction by implementing a dynamic tone suppressor that tracks the time-varying frequency and phase of spread clock harmonics. Rather than assuming fixed frequency, the system continuously estimates these parameters and adapts the suppression accordingly. This dynamic approach maintains reasonable implementation complexity while dramatically improving RFI suppression effectiveness by exploiting the known structure of spread clock harmonics.
Solution Approach 2:
The patent applies parameter changes by dynamically adjusting the suppression parameters (frequency, phase, amplitude) of the tone suppressor based on real-time estimation of the spread clock harmonic characteristics. This allows the system to adapt to the time-varying nature of the interferer while maintaining a relatively simple implementation structure compared to more complex adaptive filtering approaches.
Data Source
AI summary
In some embodiments a phase between a periodic spreading signal and an effective spreading signal modulating an interfering harmonic is determined, an amplitude of the interfering harmonic is estimated, and the interfering harmonic is canceled from a received signal. Other embodiments are described and claimed.