Hybrid Self-Interference Cancellation for Full-Duplex Transceivers
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Solution Overview
Problem
Full-duplex wireless communication systems face challenges with self-interference due to simultaneous transmission and reception, limiting their effectiveness, especially in environments where self-interference is frequency-dependent or hampered by receiver dynamic range issues.
Innovation Solution
A hybrid self-interference cancellation system that performs RF, IF, and digital self-interference cancellation simultaneously and in parallel using a combination of analog and digital circuitry, including a signal coupler, downconverter, upconverter, RF self-interference canceller, IF self-interference canceller, and digital self-interference canceller, to mitigate receiver dynamic range issues and enhance cancellation performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If full-duplex wireless communication systems are implemented to transmit and receive signals simultaneously, then spectral efficiency is improved, but self-interference increases
Solution Approach 1:
The self-interference cancellation process is segmented into three distinct stages operating at different frequency levels: RF-stage cancellation processes the transmit signal at radio frequency, IF-stage cancellation processes at intermediate frequency after downconversion, and baseband digital cancellation processes after full downconversion. Each stage handles specific portions of the self-interference spectrum, dividing the complex cancellation task into manageable segments that can be processed independently and simultaneously.
Solution Approach 2:
The system adds a frequency dimension to the self-interference cancellation approach by implementing parallel cancellation paths at three different frequency levels (RF, IF, and baseband). This multi-dimensional approach allows the system to address self-interference across the entire frequency spectrum of the transmit signal, with each dimension targeting specific frequency-dependent characteristics of the interference.
2Device complexity
If digital self-interference cancellation is used, then implementation simplicity is improved, but performance deteriorates in frequency-dependent environments and when hampered by receiver dynamic range issues
Solution Approach 1:
The cancellation system is segmented across three frequency domains, with the RF and IF stages handling frequency-dependent cancellation tasks using analog circuitry, while the baseband digital stage handles residual cancellation. This segmentation allows each stage to operate within its optimal performance range, with analog stages managing high-power frequency-dependent interference and digital stages providing precise residual correction.
Solution Approach 2:
The IF-stage canceller acts as an intermediary between the RF and baseband digital cancellation stages. It downconverts the RF transmit signal to intermediate frequency and provides cancellation signals to both the RF stage (via upconversion) and the baseband digital stage, mediating the transition from analog to digital processing and ensuring coherent cancellation across all stages.
3Reliability
If high dynamic range receivers are used to handle self-interference, then receiver capability is improved, but system cost and complexity increase
Solution Approach 1:
The RF and IF-stage cancellers perform preliminary self-interference cancellation before the signal reaches the receiver's analog-to-digital converter. By subtracting processed versions of the transmit signal from the received signal at high frequency levels, the system pre-reduces the power of self-interference components, allowing standard dynamic range receivers to handle the residual signal without requiring specialized high dynamic range components.
Solution Approach 2:
The system converts the harmful self-interference signal into a useful cancellation reference by tapping the transmit signal path and processing it through the same RF and IF chains. The processed transmit signal becomes a beneficial reference that accurately models the self-interference present in the receive path, enabling effective subtraction and transforming the interference source into a cancellation resource.
Data Source
AI summary
A system for hybrid self-interference cancellation includes a transmit coupler that samples an RF transmit signal, a RF self-interference canceller that transforms the sampled RF transmit signal to an RF self-interference cancellation signal, an IF self-interference canceller that transforms a downconverted version of the RF transmit signal to an ISRF self-interference cancellation signal, and a receive coupler that combines the RF and ISRF self-interference cancellation signals with an RF receive signal.