Impulsive interference in communication channels and its mitigation by SPART and other nonlinear filters

Abstract

A strong digital communication transmitter in close physical proximity to a receiver of a weak signal can noticeably interfere with the latter even when the respective channels are tens or hundreds of megahertz apart. When time domain observations are made in the signal chain of the receiver between the first mixer and the baseband, this interference is likely to appear impulsive. The impulsive nature of this interference provides an opportunity to reduce its power by nonlinear filtering, improving the quality of the receiver channel. This article describes the mitigation, by a particular nonlinear filter, of the impulsive out-of-band (OOB) interference induced in High Speed Downlink Packet Access (HSDPA) by WiFi transmissions, protocols which coexist in many 3G smartphones and mobile hotspots. Our measurements show a decrease in the maximum error-free bit rate of a 1.95 GHz HSDPA receiver caused by the impulsive interference from an OOB 2.4 GHz WiFi transmission, sometimes down to a small fraction of the rate observed in the absence of the interference. We apply a nonlinear SPART filter to recover a noticeable portion of the lost rate and maintain an error-free connection under much higher levels of the WiFi interference than a receiver that does not contain such a filter. These measurements support our wider investigation of OOB interference resulting from digital modulation, which appears impulsive in a receiver, and its mitigation by nonlinear filters.

Out-of-band and adjacent-channel interference reduction by analog nonlinear filters

“…Theoretical [9,10] as well as the experimental [11] data suggests that the TX OOB interference in the RX channel (part II of the interference in Figure 2) can appear impulsive under a wide range of conditions, as will be additionally illustrated in Section 2. While this interference cannot be reduced by the subsequent linear filtering in the RX channel, it may be effectively mitigated by the NDLs introduced in Section 3.…”

“…As shown in more detail in [9,10], with additional experimental evidence presented in [11], the signal components induced in a receiver by out-of-band communication transmitters can appear impulsive under a wide range of conditions. For example, in the transmitter-receiver pair schematically shown at the top of Figure 3, for a sufficiently large absolute value of the difference between the transmit and receive frequencies f = f RX − f TX , the instantaneous power I 2 (t, f ) + Q 2 (t, f ) of the in-phase and quadrature components of the receiver signal may appear as a train of pulses consisting of a linear combination of pulses originating at discrete times and shaped as the squared (i.e., raised to the power of 2) impulse response of the receiver lowpass filter.…”

Bit error probability of the M‐QAM scheme subject to multilevel double gated additive white Gaussian noise and η‐μ, κ‐μ, or α‐μ fading

“…In some environments, different noisy sources can generate noise at the same time and with different levels of intensity. Some of these sources may be geographically spaced, such as in industrial environments, or very close, as in smartphones equipped with WiFi transceivers, Bluetooth, and global positioning system . It is in this context that impulsive noise in bursts with multiple levels of intensity can be justified.…”

Nonlinear rank-based analog loop filters in delta-sigma analog-to-digital converters for mitigation of technogenic interference

“…This physical proximity, combined with a wide range of possible transmit and receive powers, creates a variety of challenging interference scenarios. Existing empirical evidence [8], [28], [29] and its theoretical support [6], [7], [10] show that such interference often manifests itself as impulsive noise, which in some instances may dominate over the thermal noise [5], [8], [28].…”