Analog Filter Self-Interference Cancellation for Inband Full Duplex
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Solution Overview
Problem
Inband full duplex systems face challenges in canceling self-interference signals, which limits their ability to achieve high spectrum efficiency and adapt to changing environments, particularly in small devices where physical spacing of antennas is not feasible, leading to high costs, complexity, and power consumption.
Innovation Solution
A transmitting and receiving node equipped with an analog filter operated in the analog domain and a controller that determines filter coefficients based on baseband-sampled signals, allowing for efficient self-interference cancellation in both inband full duplex and half duplex schemes, using a finite impulse response (FIR) filter and channel/signal estimator to adapt to environmental changes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If physical spacing of antennas is used to cancel self-interference, then self-interference cancellation is achieved, but device size increases and it becomes infeasible for small devices
Solution Approach 1:
The patent replaces the mechanical/physical solution (antenna spacing) with an electronic/digital solution (signal processing). Specifically, it uses digital signal processing techniques including channel estimation, interference signal generation, and subtraction of the self-interference component from the received signal, thereby eliminating the need for physical antenna separation while achieving self-interference cancellation in small devices
Solution Approach 2:
The patent introduces intermediate processing steps between signal reception and final processing. It uses channel estimators to characterize the self-interference channel, generates an estimated self-interference signal, and subtracts this intermediate signal from the received signal. This intermediary approach enables effective self-interference cancellation without requiring physical antenna separation
2Object-affected harmful factors
If complex self-interference cancellation techniques are used, then cancellation performance is improved, but device complexity and power consumption increase
Solution Approach 1:
The patent divides the self-interference cancellation process into distinct functional segments: channel estimation phase (using training signals), data detection phase, and interference subtraction phase. This segmentation allows each component to be optimized independently and enables the system to achieve effective cancellation without requiring all components to operate at maximum complexity simultaneously
Solution Approach 2:
The patent performs channel estimation and characterizes the self-interference channel in advance during a training phase before actual data transmission. By pre-characterizing the interference channel and storing channel estimates, the system avoids the need for complex real-time adaptation during data transmission, thereby reducing overall system complexity and power consumption
3Productivity
If inband full duplex is implemented, then spectrum efficiency is doubled, but self-interference from transmitted signal degrades received signal quality
Solution Approach 1:
The patent converts the harmful self-interference signal into a useful component for channel estimation. By using the transmitted signal that causes self-interference as a known reference, the system can estimate the self-interference channel characteristics. This estimated channel information is then used to generate and subtract the interference signal, effectively transforming the harmful interference into a beneficial resource for improving received signal quality
Solution Approach 2:
The patent implements a feedback mechanism where the received signal is processed to estimate channel characteristics, which are then used to generate an estimated self-interference signal that is subtracted from the original received signal. This feedback loop continuously adapts to changing channel conditions and maintains effective interference cancellation, enabling reliable inband full duplex operation with high spectrum efficiency
Data Source
AI summary
There are provided a method and an apparatus for performing a self-interference cancellation by determining a filter coefficient of an analog filter operated in an analog domain; and canceling self-interference generated in a received signal received by the node by a transmitted signal transmitted from the node, based on the filter coefficient.