OFDM Interference Estimation and Mitigation
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Solution Overview
Problem
Existing communication systems face challenges in reliably mitigating OFDM interference without prior knowledge of the interfering OFDM signal's structure and parameters, as previous methods require decoding and cancellation of both signals, which is not always feasible.
Innovation Solution
A method that estimates and mitigates OFDM interference by using a reference modulation symbol set to hypothesize modulation symbols, generating a frequency-domain channel sequence to minimize error between the product and observed samples, allowing for cancellation of the interfering signal without demodulating it.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If parallel- or successive-interference cancellation methods are used to decode and cancel the interfering OFDM signal, then interference mitigation performance is improved, but the requirement for knowledge of the interfering signal structure and parameters increases
Solution Approach 1:
The patent creates a model copy of the interfering OFDM signal using hypothesized modulation symbols from a reference constellation and estimated channel response, rather than requiring direct access to the actual interfering signal parameters. This model copy is then subtracted from the received composite signal to mitigate interference, achieving cancellation without needing precise knowledge of the original interfering signal's structure or parameters
Solution Approach 2:
The patent introduces an intermediary estimation process that uses the received composite signal itself to derive channel response and hypothesize modulation symbols, serving as a mediator between the unknown interfering signal and the cancellation process. This intermediary approach allows the system to build its own model of the interference rather than requiring external knowledge of the interfering signal's parameters
2Reliability
If decoding of both the signal of interest and interfering OFDM signal is performed, then accurate interference cancellation is achieved, but system complexity increases
Solution Approach 1:
The patent extracts only the essential components needed for interference cancellation - specifically the channel response and hypothesized modulation symbols - from the complex task of full signal decoding. By separating the interference estimation function from complete signal demodulation, the system achieves cancellation accuracy without requiring full decoding capability for both signals
Solution Approach 2:
The patent segments the interference mitigation process into distinct functional blocks: channel response estimation, modulation symbol hypothesis generation, interference signal reconstruction, and cancellation subtraction. This segmentation allows each function to be implemented independently with optimized complexity, avoiding the need for a monolithic high-complexity decoder
3Ease of operation
If a reference modulation symbol set different from the interference modulation symbol set is used for estimation, then mitigation can proceed without demodulating the interfering signal, but estimation error increases
Solution Approach 1:
The patent changes the parameter of the modulation symbol set from requiring exact match with the interfering signal to using a reference constellation that may differ. This parameter change is compensated by adjusting the channel response estimation and using least-squares optimization to minimize the impact of constellation mismatch, allowing the system to operate without precise knowledge of the interfering signal's modulation parameters while maintaining acceptable estimation accuracy
Data Source
AI summary
Methods and systems for estimating and mitigating OFDM interference to enable reliable communications with minimal a priori knowledge of the interfering OFDM signal are presented. Embodiments of the present invention hypothesize modulation symbols from a reference signal set, which may not be identical to the interference signal set, and compute a channel sequence to minimize an error between the observed samples and a product of the channel sequence and the hypothesized modulation symbols. The interfering OFDM signal may be estimated and mitigated with no reliance on knowledge of the interference signal set, although this may result in the inability to decode and demodulate the interfering OFDM signal when embodiments of the present invention are extended from single-input single-output systems to multiple-input single-output systems.