Interference-rich Environment Research Articles

Wideband Array Signal Processing with Real-Time Adaptive Interference Mitigation.

Wideband beamforming and interference cancellation for phased array antennas requires advances in signal processing algorithms, software, and specialized hardware platforms. A high-throughput array receiver has been developed that enables communication in radio frequency interference-rich environments with field programmable gate array (FPGA)-based frequency channelization and packetization. In this study, a real-time interference mitigation algorithm was implemented on graphics processing units (GPUs) contained in the data pipeline. The key contribution is a hardware and software pipeline for subchannelized wideband array signal processing with 150 MHz instantaneous bandwidth and interference cancellation with a heterogeneous, distributed, and scaleable digital signal processing (DSP) architecture that achieves 30 dB interferer cancellation null depth in real time with a moving interference source.

Bell–Bloom Magnetometer Linearization by Intensity Modulation Cancellation

This paper describes a technique for enhancing the linearity of a Bell–Bloom optical magnetometer. Both the $M_{x}$ and Bell–Bloom magnetometers are examined, and the characteristics of their photodetector signals are compared. It is noted that the phase signal has better linearity than the quadrature amplitude signal for a $M_{x}$ magnetometer, while phase and quadrature amplitude give similar performance in Bell–Bloom. A cancellation technique is proposed whereby the laser intensity modulation of Bell–Bloom is mitigated to improve the linearity. A cesium microfabricated atomic magnetometer in a frequency-locked-loop configuration is demonstrated, and the improved slew rate and frequency-domain linearity are shown. This linearity enhancement should prove useful for operating atomic magnetometers in interference-rich environments outside of magnetic shields.

Dynamic Enhanced Field Division

Tracking moving objects is always a critical challenge in cyber-physical systems. Researchers have proposed many tracking algorithms. However, most of the proposed algorithms cannot be used for on-demand deployment because of the unavailable preset fingerprints (prior landmark or context information) in their assumption. Another issue is that those algorithms with models built in an interference-free environment cannot work in interference-rich environments. To address those issues, we propose a localizing and tracking algorithm called Enhanced Field Division (EFD), which dynamically divides the field into areas with unique signatures and tracks the target without any fingerprints. We also implemented a proof-of-concept localization platform to demonstrate the tracking accuracy and the algorithm performance in practical, interference-rich environments.

Third-Order Intermodulation Effects and System Sensitivity Degradation in Receive-Mode 5G Phased Arrays in the Presence of Multiple Interferers

Electronically scanned phased-array antennas need to function in an interference-rich environment as an integral part of millimeter-wave 5G networks. In these scenarios, multiple interferers’ incident from different directions can create intermodulation products that can severely degrade the system sensitivity. This paper first presents the theoretical analysis of intermodulation effects in a receive-mode phased array and then shows the detailed experimental verification of multiple interferer effects on a 28-GHz 5G phased array. It is shown that the third-order intermodulation products generated by the interferers peak at certain predictable scan angles depending on the interferer directions of arrival and can limit the sensitivity of the phased array. The interferers degrade the system sensitivity even if incident in the direction of pattern nulls. Two scan-angle-dependent third-order input intercept point (IIP3) definitions are given for a phased array and their implications are discussed. It is shown that while a phased array does result in an input P1dB improvement as the number of elements increases (handles more incident power than a single channel), it does not result in an IIP3 improvement over a single channel as the number of elements increases. Theoretical predictions are also verified by extensive numerical simulations and measurement results for multiple interferers from different directions. Finally, the IIP3 degradation in mechanically scanned antennas is analyzed and it is shown that such antennas are much more robust than phased arrays for wide angle interferers.

Cone of silence

Dense 802.11 wireless networks present a pressing capacity challenge: users in proximity contend for limited unlicensed spectrum. Directional antennas promise increased capacity by improving the signal-to-interference-plus-noise ratio (SINR) at the receiver, potentially allowing successful decoding of packets at higher bit-rates. Many uses of directional antennas to date have directed high gain between two peers, thus maximizing the strength of the sender's signal reaching the receiver. But in an interference-rich environment, as in dense 802.11 deployments, directional antennas only truly come into their own when they explicitly null interference from competing concurrent senders. In this paper, we present Cone of Silence (CoS), a technique that leverages software-steerable directional antennas to improve the capacity of indoor 802.11 wireless networks by adaptively nulling interference. Using in situ signal strength measurements that account for the complex propagation environment, CoS derives custom antenna radiation patterns that maximize the strength of the signal arriving at an access point from a sender while nulling inteference from one or more concurrent interferers. CoS leverages multiple antennas, but requires only a single commodity 802.11 radio, thus avoiding the significant processing requirements of decoding multiple concurrent packets. Experiments in an indoor 802.11 deployment demonstrate that CoS improves throughput under interference.

Spectrum Management for Interference-Limited Multiuser Communication Systems

Consider a multiuser communication system in a frequency selective environment whereby users share a common spectrum and can interfere with each other. Assuming Gaussian signaling and no interference cancelation, we study optimal spectrum sharing strategies for the maximization of sum-rate under separate power constraints for individual users. Since the sum-rate function is nonconcave in terms of the users' power allocations, there can be multiple local maxima for the sum-rate maximization problem in general. In this paper, we show that, if the normalized crosstalk coefficients are larger than a given threshold (roughly equal to 1/2 ), then the optimal spectrum sharing strategy is frequency division multiple access (FDMA). In case of arbitrary positive crosstalk coefficients, if each user's power budget exceeds a given threshold, then FDMA is again sum-rate optimal, at least in a local sense. In addition, we show that the problem of finding the optimal FDMA spectrum allocation is NP-hard, implying that the general problem of maximizing sum-rate is also NP-hard, even in the case of two users. We also propose several simple distributed spectrum allocation algorithms that can approximately maximize sum-rates. Numerical results indicate that these algorithms are efficient and can achieve substantially larger sum-rates than the existing Iterative Waterfilling solutions, either in an interference-rich environment or when the users' power budgets are sufficiently high.