Full-Duplex Self-Interference Cancellation Using Temporal Derivative
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Solution Overview
Problem
Full-duplex communication systems face significant challenges in reducing self-interference signals, particularly when the envelope of the transmission signal varies, due to the insufficient insulation between transmission and reception channels, and existing solutions are either unsatisfactory in terms of size and cost or require clock synchronization.
Innovation Solution
A device comprising a first reduction module that generates a first reduction signal by aligning the phase and amplitude of a replica transmission signal with the reception signal, and a second reduction module that generates a second reduction signal based on the temporal derivative of the baseband signal, both modules working together to subtract from the reception signal to eliminate self-interference, without requiring clock synchronization and with a minimal footprint.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a single antenna is used for both transmission and reception in a full-duplex system, then spectral occupancy is reduced by a factor of two, but self-interference signal reduction becomes insufficient (only 20-30 dB insulation)
Solution Approach 1:
The self-interference cancellation is divided into multiple stages: a first reduction module that processes the transmission signal to generate a first reduction signal, and a second reduction module that processes the baseband signal to generate a second reduction signal. This segmented approach allows each module to address specific components of the self-interference problem, achieving over 100 dB total reduction.
Solution Approach 2:
The first reduction module performs preliminary cancellation of the dominant self-interference components before the signal reaches the second reduction module. By addressing the major interference sources first (through complex gain adjustment and temporal derivative processing), the system prepares the signal for finer cancellation in the second stage, making the overall process more efficient.
2Measurement precision
If variable delays are applied to different delay lines to handle envelope variations, then self-interference reduction accuracy is improved, but silicon surface area occupation increases significantly
Solution Approach 1:
Instead of using multiple delay lines with different fixed delays, the invention changes the temporal characteristics of the signal by applying a temporal derivative operation. This parameter transformation allows the system to handle envelope variations without requiring multiple physical delay paths, thereby reducing the silicon footprint while maintaining cancellation accuracy.
Solution Approach 2:
The invention replaces the mechanical/digital delay line approach with a signal processing substitution: applying a temporal derivative to the baseband signal. This substitution eliminates the need for multiple physical delay elements while achieving the same goal of accommodating envelope variations, thus reducing hardware complexity and area.
3Measurement precision
If clock synchronization is implemented between transmission and reception, then signal alignment accuracy is improved, but device complexity and cost increase
Solution Approach 1:
The system achieves signal alignment without external clock synchronization by using the transmission signal itself as the reference. The first reduction module uses a replica of the transmission signal, and the second reduction module uses the temporal derivative of the baseband signal, allowing the system to self-align based on the inherent temporal relationships in the transmitted signal.
Solution Approach 2:
The temporal derivative of the baseband signal acts as an intermediary that captures the envelope variations without requiring synchronized clocks. By processing this derivative signal through the second reduction module, the system achieves accurate alignment through the natural temporal correspondence between transmission and reception signals.
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
Effectively reduces self-interference contributions in full-duplex wireless communication systems, even when the envelope of the transmission signal varies, by using a digital delay and complex gains to generate destructive interference, thereby improving signal quality without occupying significant silicon space or requiring clock synchronization.
Implementation Method 1
The first reduction module takes, at an instant t, a replica of the transmission signal TXOUT, and aligns the phase of the replica of the transmission signal TXOUT on the signal received by the antenna interface RXIN at an instant t+δt
Implementation Method 2
a second reduction module, arranged so as to be able to take a replica of the baseband signal, and capable of generating a second reduction signal that is a function of the temporal derivative of the baseband signal
Implementation Method 3
a subtractor, linked to the first reduction module and to the second reduction module, and configured to subtract from the reception signal the first reduction signal and the second reduction signal
Data Source
AI summary
A device for reducing a self-interference contribution in a full-duplex wireless communication system configured to transmit a transmission signal and modulated by a baseband signal, and configured to receive a reception signal containing a self-interference contribution corresponding to the transmission signal, the reduction device comprising a first reduction module, configured to take a replica of the transmission signal, and configured to generate a first reduction signal, the device further comprising: a second reduction module, arranged so as to be able to take a replica of the baseband signal, and capable of generating a second reduction signal that is a function of the temporal derivative of the baseband signal, a subtractor, linked to the first reduction module and to the second reduction module, and configured to subtract from the reception signal the first reduction signal and the second reduction signal.