Self-interference cancellation in full-duplex wireless systems
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Solution Overview
Problem
Conventional full-duplex wireless communication systems face significant self-interference issues, overwhelming the receiver and preventing proper operation, as they struggle to cancel out self-interference signals effectively and efficiently.
Innovation Solution
A wireless communication system incorporating both analog and digital interference cancellation circuits, with a controller dynamically varying attenuation values based on frequency response characteristics, uses preamble symbols to measure and minimize self-interference, enabling simultaneous transmission and reception by subtracting self-interference from the receive signal.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If full-duplex communication is implemented to reduce frequency spectrum usage, then spectrum utilization is improved, but self-interference overwhelms the receiver preventing proper operation
Solution Approach 1:
The interference cancellation is divided into two separate stages: analog cancellation that processes the raw received signal before digitization, and digital cancellation that processes the digitized signal after ADC. This segmentation allows each stage to optimize for its specific domain characteristics, achieving over 100 dB total cancellation while maintaining full-duplex operation
Solution Approach 2:
The analog cancellation circuit performs preliminary interference removal by subtracting a scaled version of the transmitted signal from the received signal before the ADC stage. This preliminary action reduces the dynamic range requirement of the ADC and prevents receiver saturation, enabling subsequent digital processing to achieve final cancellation goals
2Device complexity
If conventional full-duplex systems operate without advanced cancellation, then system complexity is reduced, but self-interference prevents receiver from operating properly
Solution Approach 1:
An intermediary analog cancellation circuit is introduced between the receiver antenna and the ADC to pre-process the signal. This intermediary stage uses a circulator and variable gain amplifier to create an analog cancellation signal that reduces the overall interference level, enabling the main receiver to operate reliably without requiring extremely complex digital processing
3Object-affected harmful factors
If analog cancellation circuit with multiple delay paths and variable attenuators is used to reduce self-interference, then interference cancellation is improved, but device complexity increases
Solution Approach 1:
The system dynamically adjusts the attenuation parameters of multiple variable attenuators in the analog cancellation circuit based on measured frequency response characteristics. By changing these parameters adaptively, the system achieves high cancellation performance (100+ dB) across varying channel conditions without requiring a permanently complex fixed structure
Data Source
AI summary
A wireless communication device includes, in part, an analog interference cancellation circuit and a controller. The analog cancellation circuit includes a multitude of delay paths each including a delay element and a variable attenuator. The controller dynamically varies the attenuation level of each of the variable attenuators in accordance with the frequency response characteristic of that attenuator to remove a portion of a self-interference signal present in a signal received by the device. The device measures the frequency response characteristic of the communication channel, used in determining the attenuation levels, via one or more preamble symbols. A second portion of the self-interference signal is removed by the device using a multitude of samples of a transmitted signal and a multitude of samples of a signal to be transmitted.