Abstract
In addition to ever-present thermal noise, various communication and sensor systems can contain significant amounts of interference with outlier (e.g., impulsive) characteristics. Such outlier noise can be efficiently mitigated in real time using intermittently nonlinear filters. Depending on the noise nature and composition, improvements in the quality of the signal of interest will vary from “no harm” to substantial. In this paper, we explain in detail why the underlying outlier nature of interference often remains obscured, discussing the many challenges and misconceptions associated with state-of-the-art analog and/or digital nonlinear mitigation techniques, especially when addressing complex practical interference scenarios. We then focus on the methodology and tools for real-time outlier noise mitigation, demonstrating how the “excess band” observation of outlier noise enables its efficient in-band mitigation. We introduce the basic real-time nonlinear components that are used for outlier noise filtering and provide examples of their implementation. We further describe complementary nonlinear filtering arrangements for wideband and narrowband outlier noise reduction, providing several illustrations of their performance and the effect on channel capacity. Finally, we outline “effectively analog” digital implementations of these filtering structures, discuss their broader applications, and comment on the ongoing development of the platform for their demonstration and testing.
Highlights
At any given frequency, a linear filter affects all signals proportionally
This paper provides an overview of the methodology and tools for real-time mitigation of outlier noise in general and ‘‘hidden’’ wideband outlier noise in particular
C. ‘‘EXCESS BAND’’ OBSERVATION FOR IN-BAND MITIGATION As discussed in Section II-A, a linear filter affects the amplitudes of the signal of interest, wideband Gaussian noise, and wideband outlier noise differently
Summary
A linear filter affects all signals proportionally. when linear filtering is used to suppress interference, the resulting signal quality is largely invariant to a particular makeup of the interfering signal and depends mainly on the total power and the spectral composition of the interference in the passband of interest. Properly implemented nonlinear filtering enables in-band, real-time mitigation of interference with distinct outlier components to levels unattainable by linear filters. This is illustrated by the toy example of Fig. 1. When a linear filter is used to suppress this impulsive interference while letting through the signal of interest, it neither restores the ‘‘missing’’ tone nor reduces the power of the signal’s tone affected by the constructive interference This is shown in the upper right of the figure. This paper provides an overview of the methodology and tools for real-time mitigation of outlier noise in general and ‘‘hidden’’ wideband outlier noise in particular Such mitigation is performed as a ‘‘first line of defense’’ against interference ahead of, or in the process of, reducing the bandwidth to that of the signal of interest. We briefly discuss broader applications of these nonlinear filtering techniques, discuss the ongoing development of the platform for their demonstration and testing, and outline the direction of future work
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