Self-Interference Cancellation via Cyclic Prefix Delay Alignment
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Solution Overview
Problem
In LTE relay systems, self-interference is difficult to predict due to misalignment between the desired signal and interference feedback signals, leading to interference leakage across subcarriers, which complicates self-interference cancellation and requires costly time-domain filtering.
Innovation Solution
Constraining the loop delay to a fraction of the cyclic prefix (CP) length to align OFDM symbol boundaries, allowing self-interference cancellation to be performed more efficiently in the frequency domain, and optionally shortening the impulse response duration using dedicated signal processing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If time-domain filtering is used for self-interference cancellation, then cancellation accuracy can be achieved, but computational complexity increases significantly
Solution Approach 1:
The patent extracts and eliminates the misalignment component from the self-interference cancellation problem by constraining loop delay to be a fraction of the cyclic prefix length. This ensures OFDM symbol boundaries align between desired signal and interference feedback signal, allowing frequency-domain cancellation without requiring complex time-domain filtering operations
Solution Approach 2:
The patent changes the loop delay parameter from an arbitrary value to a specific constrained value (a fraction of the cyclic prefix length). This parameter change enables the system to achieve accurate self-interference cancellation in the frequency domain, avoiding the computational complexity of time-domain filtering while maintaining cancellation accuracy
2Adaptability or versatility
If loop delay is not constrained, then system flexibility is maintained, but self-interference becomes difficult to predict and leaks across subcarriers
Solution Approach 1:
The patent changes the loop delay parameter from an unconstrained variable to a constrained value (a fraction of the cyclic prefix length). This parameter constraint eliminates misalignment between OFDM symbol boundaries, making self-interference predictable and preventing leakage across subcarriers, while the constraint itself is simple enough to maintain system flexibility
3Device complexity
If frequency-domain cancellation is used, then computational complexity is reduced, but it requires alignment of OFDM symbol boundaries which constrains loop delay
Solution Approach 1:
The patent changes the loop delay parameter to a specific constrained value (a fraction of the cyclic prefix length). This parameter change enables frequency-domain cancellation by ensuring OFDM symbol boundaries align, reducing computational complexity while the constraint remains simple and does not significantly limit system adaptability
Data Source
AI summary
The present invention relates to a method and arrangement for receiving an OFDM signal and forwarding the received OFDM signal comprising OFDM symbols of a wireless OFDM communication network. The wireless OFDM communication network includes self-interference cancelling functionality and each received OFDM symbol to be forwarded is prefixed with a cyclic prefix (CP) which is a copy of the last part of the OFDM symbol. In the method a delay for delaying an interference generating feedback signal is determined such that an OFDM symbol of the interference generating feedback signal overlaps within a margin of a length of the CP with an OFDM symbol of the received OFDM signal, and interference generating feedback signal is delayed with the determined delay. Furthermore may the duration of the impulse be shortened as well.