Optical Filter Interference Cancellation for Multi-Tap RF Systems
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Solution Overview
Problem
Existing methods for self-interference cancellation in wireless and communications devices using electrical circuits and filters in the radio frequency domain face challenges such as bulkiness, difficulty in implementing multiple filter taps and delays, thermal noise, power issues, and the need for high-resolution digital-to-analog converters, which are costly and difficult to implement.
Innovation Solution
The use of optical filters to generate an analog interference cancellation signal in the optical domain, which is then converted to the radio frequency domain, allowing for a larger number of filter taps, reduced thermal noise, and elimination of the need for high-resolution digital-to-analog converters.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If electrical circuits and filters are used to generate interference cancellation signal in RF domain, then interference cancellation can be achieved, but the device becomes bulky and difficult to implement with multiple filter taps and delays
Solution Approach 1:
The patent substitutes electrical/RF filter circuits with optical filter circuits. The optical filter receives an optical signal corresponding to the transmitted signal and generates an optical interference cancellation signal, which is then converted to RF domain. This replacement eliminates the bulkiness and implementation difficulties of electrical filters while maintaining interference cancellation effectiveness.
Solution Approach 2:
The patent changes the frequency domain parameter from RF to optical domain for filter operation. By operating the filter in optical domain rather than RF domain, the system achieves better performance characteristics and easier implementation of multiple filter taps and delays, then converts back to RF domain for interference cancellation.
2Reliability
If electrical circuits operate in RF frequency domain, then interference cancellation signal can be generated, but thermal noise and power issues preclude generation of meaningful cancellation signal for weak interference
Solution Approach 1:
The patent replaces electrical circuit operation in RF domain with optical circuit operation. The optical filter operates in optical domain which has lower thermal noise characteristics, generating a cleaner interference cancellation signal. The optical signal is then converted to RF domain to match the received signal for effective cancellation.
Solution Approach 2:
The patent introduces an optical domain as an intermediary for signal processing. The transmitted signal is converted to optical domain, filtered there to generate cancellation signal, then converted back to RF. This intermediary optical domain provides noise-free signal generation that avoids the thermal noise problems of direct RF electrical circuits.
3Productivity
If RF filters are used for interference cancellation, then signal processing can be performed, but additional self-interference is generated as filter components radiate interference
Solution Approach 1:
The patent substitutes electrical RF filters with optical filters. Since optical components do not radiate RF interference, the filter components themselves do not generate self-interference. The optical filter processes the signal without creating the harmful electromagnetic radiation problem that plagues electrical RF filter implementations.
4Measurement precision
If high-resolution digital-to-analog converters are used to generate accurate analog interference cancellation signal, then cancellation accuracy improves, but cost and implementation difficulty increase significantly
Solution Approach 1:
The patent replaces the need for high-resolution digital-to-analog converters with an optical filter-based system. The optical filter directly generates the analog interference cancellation signal in the optical domain, which is then converted to RF. This approach achieves high accuracy without requiring expensive high-resolution DACs, as the filtering operation occurs in the optical domain where precision is naturally maintained.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach enables effective self-interference cancellation with improved responsiveness and support for a wide range of frequencies, reducing interference by 50dB or more, facilitating full duplex communication in wireless and wired devices with reduced space and cost.
Implementation Method 1
an RF interference signal is converted into an optical signal using an RF-to-optical converter
Implementation Method 2
The optical filter assembly includes a plurality of optical filters, each optical filter having a different delay and/or gain
Implementation Method 3
an optical to RF converter converts the optical interference cancellation signal into an RF interference cancellation signal
Data Source
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AI summary
Methods and apparatus for interference cancelation in a radio frequency communications device are described. In various embodiments a signal to be transmitted in converted into an optical signal and processed using an optical filter assembly including one or more optical filters to generate an optical interference cancelation signal. The optical interference cancelation signal is converted into an analog radio frequency interference cancelation signal using an optical to electrical converter prior to the analog radio frequency interference cancelation signal being combined with a received signal to cancel interference, e.g., self interference. The optical filter assembly can include a large number of taps, e.g., 30, 50, 100 or more. Each tap may be implemented as a separate optical filter or series of optical filters. Delays and/or gain of the optical filters can be controlled dynamically based on channel estimates which may change due to changes in the environment and/or communications device position.