Full Duplex Radio Self-Interference Cancellation via Waveform Extraction
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Solution Overview
Problem
Existing wireless networks, such as 802.11a/b/g/n, are designed for half-duplex radios, limiting bandwidth utilization and throughput, and previous attempts to achieve full duplex wireless communication by using RF noise cancellation chips and antenna positioning have been unsuccessful due to limitations in canceling wide band signals and achieving π shift for all frequency components.
Innovation Solution
A method and system for full duplex radio communications that involves transmitting a training signal, extracting a waveform from the receive chain, generating a cancellation signal, and applying it to the receive chain to cancel interference, using waveform extraction and generation circuitry, and potentially employing multiple antennas and prefilters to reduce self-interference across the same frequency channel.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If separate frequency channels are used for transmitting and receiving, then full duplex wireless communication is achieved, but bandwidth requirement increases and bandwidth efficiency decreases
Solution Approach 1:
The patent segments the transmitted signal into multiple components and processes them differently. Specifically, it divides the signal path into direct path components and reflected path components, applying different cancellation techniques to each segment. This allows the system to handle wideband signals more effectively by treating different frequency components separately through multiple antenna elements.
Solution Approach 2:
The patent introduces an intermediary cancellation signal generated from a training sequence that mediates between the transmitted and received signals. This intermediary signal is used to estimate and cancel self-interference, enabling the receiver to distinguish between transmitted and received signals on the same frequency channel without requiring separate channels.
2Object-generated harmful factors
If RF noise cancellation chip is used to cancel transmitted signal, then self-interference reduction is achieved, but the system fails to effectively cancel wide band signals due to narrow band design limitations
Solution Approach 1:
The patent transitions from single-antenna narrowband cancellation to a multi-antenna spatial dimension approach. By positioning multiple transmitting antennas at different spatial locations, the system creates multiple propagation paths with different characteristics. This spatial dimension allows effective cancellation across wide bandwidth by exploiting the different path lengths and reflections that arrive at the receiving antenna.
Solution Approach 2:
The patent changes the parameters of the transmitted signal by using different time delays and amplitude weights for signals from different antenna elements. The system adjusts these parameters dynamically based on channel conditions estimated from training sequences, enabling effective wideband interference cancellation through parameter optimization rather than relying on fixed narrowband phase-shifting techniques.
3Object-generated harmful factors
If two transmitting antennas with half-wavelength distance are positioned, then signal cancellation is achieved at center frequency, but cancellation effectiveness decreases for wide band signals due to frequency-specific optimization
Solution Approach 1:
The patent makes the antenna system universal by designing it to perform multiple functions: transmitting signals, receiving signals, and generating cancellation signals for different frequency components simultaneously. The multiple transmitting antennas are configured to serve both data transmission and interference cancellation purposes across a wide frequency range, rather than being optimized for a single center frequency.
Solution Approach 2:
The patent introduces dynamics into the antenna system by continuously adapting the amplitude and phase of signals from different antenna elements based on real-time channel conditions. The system dynamically adjusts these parameters using feedback from training sequences and received signal measurements, allowing it to maintain effective cancellation across varying frequencies and channel conditions rather than relying on fixed geometric positioning.
4Device complexity
If half duplex radio design is used, then protocol complexity is reduced, but bandwidth utilization and throughput are limited
Solution Approach 1:
The patent implements a feedback mechanism where the receiver estimates the self-interference channel using training sequences and feeds this information back to the transmitter. The transmitter then uses this feedback to adjust its transmission parameters and generate appropriate cancellation signals. This feedback loop enables full-duplex operation with manageable complexity by continuously adapting to channel conditions.
Solution Approach 2:
The patent performs preliminary actions by pre-characterizing the self-interference channel using training sequences before actual data transmission. The system estimates channel parameters, determines optimal cancellation weights, and prepares cancellation signals in advance. This preliminary characterization reduces the complexity of real-time processing during data transmission while enabling efficient full-duplex operation.
Data Source
AI summary
A node of a full duplex wireless transmission system may include cancellation signal generation elements. The cancellation signal generation elements may extract a waveform from received signals, for example signals transmitted from the node, and use the waveform to generate a prefilter or cancellation signal to apply to further received signals. The cancellation signal may cancel interference in received signals caused by signals transmitted from the node.