Self-interference Cancellation Circuit Using Feedforward and Feedback Paths
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Solution Overview
Problem
Full-duplex wireless communication systems face significant self-interference issues due to simultaneous transmission and reception on the same frequency, rendering them ineffective in receiving desired signals.
Innovation Solution
A circuit and method utilizing multiple signal paths with passive couplers, delay elements, and variable attenuators to generate delayed and weighted samples of the transmit signal, forming feedforward and feedback paths that combine to reconstruct and subtract self-interference signals, employing IIR filters and sinc functions to optimize attenuation levels for effective cancellation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If full-duplex mode is used for simultaneous transmission and reception, then communication efficiency is improved, but self-interference increases
Solution Approach 1:
The patent segments the self-interference cancellation into multiple signal paths (first signal path, second signal path, first group of P signal paths, second group of M signal paths) with different delays and weights. Each path processes a portion of the interference signal, and their combined output effectively cancels the total self-interference, enabling full-duplex operation
Solution Approach 2:
The patent implements feedback paths that feed back canceled signal components to further refine the cancellation process. The feedback paths include delay elements and variable attenuators that adjust based on the residual interference, creating a closed-loop system that continuously optimizes cancellation performance
2Reliability
If multiple signal paths with delay elements and variable attenuators are used, then self-interference cancellation performance is improved, but device complexity increases
Solution Approach 1:
The patent uses universal building blocks (passive couplers, delay elements, variable attenuators) that can be configured in multiple ways to create different signal paths. These same components serve multiple functions: signal splitting, phase shifting, amplitude control, and combination, reducing the need for specialized components for each function
Solution Approach 2:
The patent employs variable attenuators with controllable attenuation levels that can be dynamically adjusted to optimize cancellation performance for different interference conditions. The delay elements can also be tuned to match varying signal characteristics, making the system adaptable rather than fixed
Data Source
AI summary
A circuit that cancels a self-interference signal includes, in part, a pair of signal paths that are substantially in phase, each of which paths includes a passive coupler, a delay element and a variable attenuator. The circuit further includes, in part, a first group of P signal paths each of which is substantially in phase with the pair of paths, a second group of M signal paths each of which is substantially out-of-phase relative to the pair of signal paths, and at least a pair of feedback paths. Each of the P and M signal paths, as well as the feedback paths includes a delay element and a variable attenuator. Optionally, each of the M signal paths is optionally 180° out-of-phase relative to the pair of signal paths.