# Complementary Intermittently Nonlinear Filtering for Mitigation of Hidden Outlier Interference

## TL;DR

This paper introduces Complementary Intermittently Nonlinear Filters (CINFs) to effectively mitigate hidden outlier interference in complex communication scenarios, especially when outliers are obscured by signals or other interference.

## Contribution

The paper presents a novel implementation of CINFs for real-time mitigation of hidden outlier interference, including practical analog-to-digital filtering methods for challenging signal environments.

## Key findings

- CINFs effectively mitigate hidden outlier interference in complex scenarios.
- The approach works across wide interference power ranges and outlier rates.
- Demonstrated effectiveness with radar, sonar, and spread-spectrum signals.

## Abstract

When interference affecting various communication and sensor systems contains clearly identifiable outliers (e.g. an impulsive component), it can be efficiently mitigated in real time by intermittently nonlinear filters developed in our earlier work, achieving improvements in the signal quality otherwise unattainable. However, apparent amplitude outliers in the interference can disappear and reappear due to various filtering effects, including fading and multipass, as the signal propagates through media and/or the signal processing chain. In addition, the outlier structure of the interference can be obscured by strong non-outlier interfering signals, such as thermal noise and/or adjacent channel interference, or by the signal of interest itself. In this paper, we first outline the overall approach to using intermittently nonlinear filters for in-band, real-time mitigation of such interference with hidden outlier components in practical complex interference scenarios. We then introduce Complementary Intermittently Nonlinear Filters (CINFs) and focus on the particular task of mitigating the outlier noise obscured by the signal of interest itself. We describe practical implementations of such nonlinear filtering arrangements for mitigation of hidden outlier interference, in the process of analog-to-digital conversion, for wide ranges of interference powers and the rates of outlier generating events. To emphasize the effectiveness and versatility of this approach, in our examples we use particularly challenging waveforms that severely obscure low-amplitude outlier noise, such as broadband chirp signals (e.g. used in radar, sonar, and spread-spectrum communications) and ``bursty," high crest factor signals (e.g. OFDM).