ZCZ Training Signals for Full-Duplex Self-Interference Cancellation
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Solution Overview
Problem
Full-duplex communications systems face significant challenges with self-interference, where the interference from the transmitter is much higher than the receiver's sensitivity level, necessitating effective channel impulse response estimation and interference cancellation methods.
Innovation Solution
The use of zero-correlation-zone (ZCZ) sequences for training signals, which are transmitted over the transmit antenna and received over the receive antenna, allowing for accurate channel impulse response estimation and subsequent self-interference cancellation, is proposed. These sequences have a correlation matrix that is a scaled identity matrix, derived from Zadoff-Chu sequences, and are designed to optimize channel estimation accuracy and cancellation performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If conventional training signals are used for channel estimation in full-duplex systems, then the system can operate in full-duplex mode, but self-interference from the transmitter overwhelms the receiver sensitivity
Solution Approach 1:
The patent applies preliminary action by transmitting training signals (preamble sequences) before actual data transmission. These training signals enable the receiver to pre-estimate the channel impulse response and pre-cancel self-interference components. The training signals are specifically designed with properties (ZCZ sequences) that facilitate accurate channel estimation despite the presence of strong self-interference, allowing the system to prepare for full-duplex operation in advance.
Solution Approach 2:
The patent employs parameter changes by using specially designed ZCZ (Zero Correlation Zone) sequences with specific mathematical properties. These sequences have auto-correlation and cross-correlation properties that create a zero-correlation zone, which helps in accurately estimating the channel impulse response even when self-interference is present. The sequences are derived from Zadoff-Chu sequences with specific root indices and lengths optimized for the communication system parameters.
2Measurement precision
If training signals are transmitted for channel impulse response estimation, then interference cancellation can be enabled, but the correlation matrix properties affect estimation accuracy and numerical stability
Solution Approach 1:
The patent applies parameter changes by selecting training signals with specific mathematical properties - ZCZ sequences derived from Zadoff-Chu sequences. These sequences have the property that their correlation matrix is a scaled identity matrix or has a large condition number, which improves numerical stability during channel estimation. The sequences are designed with specific lengths and root indices that optimize both the zero-correlation zone property and the correlation matrix properties for reliable estimation.
Solution Approach 2:
The patent uses copying by transmitting known training sequences (preambles) that are predetermined and stored at both transmitter and receiver. The receiver correlates the received training signal with the known transmitted sequence to estimate the channel impulse response. This copying approach allows for accurate estimation by comparing the expected signal with the actual received signal, accounting for channel effects and self-interference.
Data Source
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AI summary
A method includes transmitting a training signal derived from a sequence, the training signal facilitates an estimation of a channel impulse response (CIR) for a communications channel between a transmit antenna of the device and a receive antenna of the device, estimating the CIR for the communications channel, and receiving signals corresponding to a first transmission at the receive antenna. The method also includes cancelling self-interference present in the received signals in accordance with the estimated CIR, the self-interference arising from a second transmission made by the transmit antenna of the device, thereby producing an interference canceled received signal, and processing the interference canceled received signal.