OFDM Correlation Canceller for FIR Filter Side Lobe Compensation
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Solution Overview
Problem
The removal of side lobes in OFDM waveforms to prevent adjacent channel interference compromises the orthogonality of the waveform, leading to inner symbol interference and a reduced signal-to-noise ratio, which limits system performance, especially in high-order modulation scenarios.
Innovation Solution
A correlation canceller is introduced that adds the inverse of the interference signals based on known symbols, modulating the data signal over an epoch aperture to generate an inversely correlated communication signal, thereby minimizing self-interference caused by digital filtering.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If side lobes are removed by FIR filter to eliminate adjacent channel interference, then adjacent channel interference is reduced, but inner symbol interference increases and orthogonality is compromised
Solution Approach 1:
The correlation canceller performs preliminary action by calculating and adding the inverse of self-interference signals before transmission. This pre-compensation approach counteracts the orthogonality degradation caused by FIR filtering, allowing the system to maintain signal integrity while using aggressive filtering to reduce adjacent channel interference.
Solution Approach 2:
The system applies preliminary anti-action by introducing inverted interference signals that preemptively counterbalance the self-interference effects. This anti-compensation mechanism ensures that when the filtered signal is transmitted, the pre-added inverse interference cancels out the orthogonality degradation, maintaining effective signal quality.
2Area of stationary object
If side lobes are removed to limit bandwidth, then bandwidth efficiency improves, but system performance degrades due to higher noise floor
Solution Approach 1:
The correlation canceller performs preliminary compensation by adding inverse interference signals before transmission. This pre-processing maintains the effective signal-to-noise ratio despite aggressive bandwidth limiting through FIR filtering, allowing the system to achieve both bandwidth efficiency and reliable performance.
3Object-affected harmful factors
If digital filtering is applied to eliminate side lobe energy, then adjacent channel interference is reduced, but orthogonality is compromised causing implementation loss
Solution Approach 1:
The system converts the harmful effect of orthogonality degradation into a benefit by calculating the exact self-interference pattern introduced by FIR filtering and adding its inverse. This transforms the filtering operation from a source of implementation loss into an effective means of reducing adjacent channel interference while maintaining signal integrity through digital compensation.
Data Source
AI summary
A correlation canceller modulates a communication signal over a plurality of channels and an epoch aperture by a plurality of interference response signals corresponding to linear response by one or more filtering effects to generate an inversely correlated communication signal.