Interference Mitigation Techniques Research Articles

An Interference Mitigation Technique for FMCW Radar Using Beat-Frequencies Interpolation in the STFT Domain

A frequency-modulated continuous-wave (FMCW) radar interference mitigation technique using the interpolation of beat frequencies in the short-time Fourier transform (STFT) domain, phase matching, and reconfigurable linear prediction coefficients estimation for Coherent Processing Interval processing is proposed. The technique is noniterative and does not rely on algorithm convergence. It allows the usage of the fast Fourier transform (FFT) as the radar’s beat-frequency estimation tool, for reasons such as real-time implementation, noise linearity after the FFT, and compatibility with legacy receiver architectures. Verification is done in range and in range-Doppler using radar experimental data in two ways: first by removing interferences from interference-contaminated data and second by using interference-free data as the reference data, and processing it—as if it had interferences—using the proposed technique, inverse cosine windowing and zeroing for comparison. We found that processing with the proposed technique closely matches the reference-data and outperforms the inverse cosine windowing and zeroing techniques in 2-D cross correlation, amplitude, and phase average errors and phase root-mean-square error. It is expected that the proposed technique will be operationally deployed on the TU Delft simultaneous-polarimetric PARSAX radar.

Design of GPS antijamming algorithm using adaptive array antenna to mitigate the noise and interference

This paper describes the Matlab based simulation of radio frequency interference monitoring and mitigation techniques using adaptive array antenna and null steering algorithm. The proposed research is described to show the design and implementation of the GPS transmitter and receiver system for real time navigation, location based services and last but not least tracking applications. Two interferences arriving at 35° and 55° with power greater than seven times of original GPS signals arriving at 45°. Least mean square (LMS) and recursive least square (RLS) algorithms. The proposed system has been evaluated by conducting experiments by using the simulation tool for AntiJammer. The proposed model is useful for developing the smart health care application. Results showed better performance of RLS over LMS to mitigate the effect of interference as well as noise with a higher signal to noise ratio. This system will be useful for enhancing the communication effectiveness of smarthealth care systems.

Uplink Interference Mitigation Techniques for Coexistence of 5G Millimeter Wave Users With Incumbents at 70 and 80 GHz

The millimeter wave spectra at 71-76GHz (70GHz) and 81-86GHz (80GHz) have the potential to endow fifth-generation new radio (5G-NR) with mobile connectivity at gigabit rates. However, a pressing issue is the presence of incumbent systems in these bands, which are primarily point-to-point fixed stations (FSs). In this paper, we first identify the key properties of incumbents by parsing databases of existing stations in major cities to devise several modeling guidelines and characterize their deployment geometry and antenna specifications. Second, we develop a detailed uplink interference framework to compute the aggregate interference from outdoor 5G-NR users into FSs. We then present several case studies in dense populated areas, using actual incumbent databases and building layouts. Our simulation results demonstrate promising 5G coexistence at 70GHz and 80GHz as the majority of FSs experience interference well below the noise floor thanks to the propagation losses in these bands and the deployment geometry of the incumbent and 5G systems. For the few FSs that may incur higher interference, we propose several passive interference mitigation techniques such as angular-based exclusion zones and spatial power control. Simulation results show that the techniques can effectively protect FSs, without tangible degradation of the 5G coverage.

IEEE Access Special Section: Advances in Interference Mitigation Techniques for Device-to-Device Communications

The emergence of data-extensive applications such as online gaming and video sharing has resulted in an exponential increase in mobile data traffic. Advances in the Internet-of-Things (IoT) and 5G also require the fusion of multiple sensors and wireless devices operating in real time. Supporting such high data rate demands within the framework of existing wireless access networks is a challenging task. Addressing this ever-increasing demand of data-hungry devices in an efficient and effective manner has driven the wireless industry to look into new paradigms. Device-to-Device (D2D) and Machine-to-Machine (M2M) communications are viewed as promising solutions to this complex problem and hence a key enabling technology for 5G and IoT applications. The D2D is envisioned to operate either in out-band mode, representing use of a dedicated spectrum, or in-band mode, representing operation within the same spectrum of the existing cellular spectrum. Variations of Vehicle-to-Vehicle (V2V) and Human-to-Human (H2H) are used to deal with the specific nature and application of the wireless network under consideration.

Interference Mitigation via Rate-Splitting and Common Message Decoding in Cloud Radio Access Networks

Cloud-radio access networks (C-RAN) help in overcoming the scarcity of radio resources by enabling dense deployment of base-stations (BSs) and connecting them to a central-processor (CP). This paper considers the downlink of a C-RAN, where the cloud is connected to the BSs via limited-capacity backhaul links. We propose and optimize a C-RAN transmission scheme that combines rate splitting, common message decoding, and beamforming vectors design and clustering. To this end, this paper optimizes a transmission scheme that combines rate splitting (RS), common message decoding (CMD), and clustering and coordinated beamforming. In this paper, we focus on maximizing the weighted sum-rate subject to per-BS backhaul capacity and transmit power constraints, so as to jointly determine the RS-CMD mode of transmission, the cluster of BSs serving private and common messages of each user, and the associated beamforming vectors of each user private and common messages. This paper proposes solving such a complicated non-convex optimization problem using $l_{0}$ -norm relaxation techniques, followed by inner-convex approximations (ICA), so as to achieve stationary solutions to the relaxed non-convex problem. The numerical results show that the proposed method provides significant performance gain as compared to conventional interference mitigation techniques in C-RAN which simply treat interference as noise (TIN).

On Performance Analysis of Single Frequency Network With C-RAN

Centralized-RAN (C-RAN) is an architectural trend that uses resource sharing and a set of interference mitigation techniques to reduce capital and operational expenditures for mobile network operators (MNOs). One of the technical enablers of a C-RAN solution is single frequency network (SFN) that curbs the interference and allows MNOs to transmit over single frequency across coordinated cells. One of the main advantages of SFN is that it reduces the number of handovers between neighboring cells while improving the overall system performance. In contrast to previous approaches that demonstrate some of the most prominent C-RAN features, in this paper, we first investigate two different SFN deployment scenarios’ characteristics, benefits, and limitations. Second, we perform a simulation analysis of non-SFN and SFN without joint scheduling to observe signal to interference ratio heatmap distribution of the experimental test-site using similar system configurations. Finally, we perform an experimental analysis of joint scheduling in SFN based on coordinated inter baseband units scenario using C-RAN in a realistic environment. The experimental results are tested on a real operating site of a major MNO’s infrastructure in Turkey. Through experimental results, we show overall performance gains of SFN feature in terms of different key performance indicators that are obtained from coordinating remote radio units in an SFN cell. Finally, we discuss about the main takeaways, lessons learned, and challenges of the considered SFN implementation.

On the Complexity Reduction of the Second-Order Volterra Nonlinear Equalizer for IM/DD Systems

To cope with the various nonlinear signal distortions in intensity-modulation/direct-detection transmission systems, a theoretical analysis on the Volterra nonlinear equalizer (VNLE) is provided, focusing on computational complexity aspects. The analysis yields a simple reduced-complexity scheme for the second-order VNLE (R2-VNLE) based on a performance-complexity tradeoff. An experimental verification is performed with single-sideband 28-GBaud PAM-4 signals, generated by an electroabsorption modulated distributed-feedback laser, over transmission distances of up to 80 km of standard single-mode fiber in the C-band. A comparison of the results for different equalization schemes, including a signal-signal beat interference mitigation technique, shows superior performance for the R2-VNLE.

Shielding Effectiveness, Coupling Path, and EMI Mitigation for QSFP Cages With Heatsink

Quad form-factor pluggable (QSFP) interconnections shielding cages with heatsinks are often optimized for thermal, mechanical, and volume manufacturing. In this paper, shielding effectiveness (SE) of QSFP cages, including two configurations of 1 × 1 and 1 × 6 with three cases of normal (i.e., rising) heatsink, without a heatsink, and with a modified heatsink, is measured for the frequency range of 1–40 GHz using a dual reverberation chamber. For each measurement, three different vendors of optical modules are utilized and averaged SE is achieved for each case, indicating that the rising heatsink degrades the SE around 5–10 dB compare to the no heatsink or modified heatsink. Further, energy parcels and their trajectory concept are applied to visualize the coupling paths in a rising heatsink. The rising heatsink creates a new coupling path for EM waves to leak to the cage and emit from the chassis faceplate. From the energy parcel results, an electromagnetic interference (EMI) mitigation technique is proposed for the newly created coupling path by the rising heatsink, and its performance is evaluated with SE measurements. Further, a measurement is performed with an active board using a 40-Gbps optical module with and without the EMI mitigation technique.

Interference mitigation technique with coverage improvement in indoor VLC system

AbstractWe consider an indoor visible light communication system in which an arbitrary number of light‐emitting diodes are transmitting the information to the users. Due to the circular field of view of the light‐emitting diode transmitters, there is always a trade‐off between the coverage and interference at the receiving end. Any approach to increase the coverage area increases the overlapping area of two or more field of views resulting in severe interference at the receiver. In this paper, we propose a method that simultaneously reduces the interference due to multiple sources in an indoor visible light communication system and improves the coverage area. The signal‐to‐interference ratio (γSIR)–based approach is used for analyzing the outage and error performances. Specifically, the effect of the proposed method is investigated on various performance metrics such as signal‐to‐interference ratio, coverage probability, and bit error rate. The effect of ambient light on system performance is also incorporated in the analysis.

Network-enabled MIMO systems with distributed data processing

Traditional network MIMO systems with joint data processing usually require a large amount of backhaul data and a central processing station with very high processing power. In order to address this problem, the capacity of access network with network-enabled MIMO systems with distributed data processing is investigated in this paper. A study of network throughput for a system with interference mitigation and base station cooperation techniques is given. We also propose a distributed iterative decoding network structure as an alternative of joint detection/decoding scheme with network-enabled MIMO configurations, where iterative signal processing is performed at network level. Simulation results show that, with the proposed schemes, the complexity of data processing required to compute the detection solution is restricted and the complexity is distributed across access base stations, which results in a significant reduction in complexity of signal processing in hub base stations.

Analysis of Packet Throughput in Small Cell Networks Under Clustered Dynamic TDD

Small cell networks under dynamic time-division duplex (D-TDD) transmission have emerged as a promising solution to accommodate the varied uplink (UL) and downlink (DL) traffic in next generation cellular mobile communication networks. By allowing each cell to individually configure its communication direction, D-TDD allocates resources to accommodate whichever transmission direction needs it most. However, with unaligned transmissions, the interference increases and limits the performance of mean packet throughput (MPT). In this paper, we study the small cell networks under D-TDD with cell clustering being the interference mitigation technique (clustered D-TDD). By leveraging stochastic geometry and queuing theory, we develop an analytical framework that captures both spatial and temporal randomness. We study the MPT whose analytical expression is verified via simulation, and based on the analysis, we explore the impact from different network and service parameters. In particular, numerical results show that there is an optimal cluster size for DL MPT, while UL MPT always benefits from increasing cluster size. By grouping cells into clusters, the clustered D-TDD can provide the flexible service compared with static time-division duplex (S-TDD), and provide significant improvement over a traditional D-TDD in terms of UL MPT at a small cost of DL MPT.

Successive Interference Cancellation and Fractional Frequency Reuse for LTE Uplink Communications

Cellular networks are increasingly densified to deal with the fast growing wireless traffic. Interference mitigation plays a key role for the dense cellular networks. Successive interference cancellation (SIC) and fractional frequency reuse (FFR) are two representative inter-cell interference (ICI) mitigation techniques. In this paper, we study the application of both SIC and FFR for LTE uplink networks, and develop an analytical model to investigate their interactions and impact on network performance. The performance gains with FFR and SIC are related to key system functionalities and variables, such as SIC parameters, FFR bandwidth partition, uplink power control and sector antennas. The ICIs from individual cell sectors are approximated by log-normal random variables, which enables low complexity computation of the aggregate ICI with FFR and SIC. Then, network performance of site throughput and outage probability is computed. The model is fast and has small modeling deviation, which is validated by simulations. Numerical results show that both SIC and FFR can largely improve network performance, but SIC has a stronger impact than FFR. In addition, most of the network performance gains with SIC could be obtained with a small number of SIC stages applied to a few sectors.

A new implementation of narrowband interference detection, characterization, and mitigation technique for a software-defined multi-GNSS receiver

Due to the very low power of satellite signals when reaching the earth’s surface, global navigation satellite system receivers are vulnerable to various types of radio frequency interference, and, therefore, countermeasures are necessary. In the case of a narrowband interference (NBI), the adaptive notch filtering technique has been extensively investigated. However, the research on the topic has focused on the adaptation of the notch frequency, but not of the notch width. We present a fully adaptive solution to counter NBI. The technique is capable of detecting and characterizing any number of narrow interfered bands, and then optimizing the mitigation process based on such characterization, namely the estimates of both interference frequency and width. Its full adaptiveness makes it suitable to cope with the unpredictable and diverse nature of unintentional interfering events. In addition to a thorough performance evaluation of the proposed method, which shows its benefits in terms of signal quality improvement, an analysis of the impact of different NBI profiles on GPS L1 C/A and Galileo E1 is also conducted.

High-Rate Ultrasonic Through-Wall Communications Using MIMO-OFDM

This paper investigates methods to achieve high-rate data transmission through metallic barriers using ultrasound. Multiple-input-multiple-output-orthogonal frequency division multiplexing (MIMO-OFDM) is employed in conjunction with interference mitigation techniques to reduce throughput-limiting crosstalk. Several crosstalk mitigation strategies are investigated and their theoretical and practical bit-loaded data rates are determined for the general case of A transmitters and A receivers (A×A MIMO). A physical MIMO acoustic-electric channel array is formed using a 40 mm (1.575 in) thick steel barrier with seven pairs of 4 MHz nominal resonant frequency piezoelectric disk transducers, each with 10 mm (0.394 in) diameter. To investigate the effects of crosstalk, the transducers are closely spaced, and each transmitter-receiver pair is coaxially aligned on opposing sides of the metallic barrier. It is shown that, with the use of crosstalk mitigation techniques, the aggregate multichannel theoretical capacity performance scales linearly with the number of channels. This paper also investigates the use of novel power allocation techniques in a MIMO-OFDM acoustic-electric channel, which show significant throughput performance gains over conventional bit-loading and greedy bit-filling techniques. Finally, this paper presents a study on the effects of transducer misalignment on the multichannel theoretical capacity and achievable data transmission rates using bit-loading techniques.

An Adaptive Parallel Interference Mitigation Technique using Artificial Neural Network in Complementary Coded MC-CDMA

An Adaptive Parallel Interference Mitigation Technique using Artificial Neural Network in Complementary Coded MC-CDMA

Interference Mitigation for Indoor Optical Attocell Networks Using an Angle Diversity Receiver

In this paper, interference mitigation techniques based on angle diversity receivers (ADRs) are studied for optical attocell networks. Consisting of multiple photodiodes (PDs), an ADR requires appropriate signal combining schemes in order to mitigate intercell interference (ICI) in optical attocell networks. Four signal combining schemes, namely select best combining, equal gain combining, maximum ratio combining, and optimum combining are investigated. To further mitigate ICI, a novel double-source cell configuration with two transmission modes is also proposed. Results show that the systems with ADRs significantly outperform those with single-PD receivers in terms of signal-to-interference-plus-noise ratio (SINR). Also, compared to the conventional single-source cell configuration, the double-source cell configuration can provide an SINR improvement of over $\text{20}$ dB. Furthermore, an analytical framework is proposed to analyze the performance of optical attocell networks with ADRs, where different propagation scenarios such as line-of-sight and nonline-of-sight are considered. The accuracy of the proposed analytical model is validated by Monte Carlo simulations.

Priority Access and General Authorized Access Interference Mitigation in the Spectrum Access System

To meet the capacity needs of next generation wireless communications, the U.S. Federal Communications Commission has recently introduced the spectrum access system. Spectrum is shared between three tiers—incumbents, priority access licensees (PAL), and general authorized access (GAA) licensees. When the incumbents are absent, PAL and GAA share the spectrum under the constraint that GAA ensure the interference to PAL is no more than $-$ 40 dBm with at least 99% confidence. We consider the scenario where locations are not shared between PAL and GAA. We propose a PAL–GAA cochannel interference mitigation technique that does not expose base station locations. Our approach relies on GAA sharing the distribution and maximum number of transmitters in a finite area. We show how PAL can derive the distribution of the aggregate interference using the probability density function and characteristic function, and notify GAA about the exclusion zones in space that will guarantee that the interference requirement is met. We also propose a numerical approximation using inverse fast Fourier and discrete Fourier transforms. Analytically calculated distribution aligns well with the numerical results. Additionally, we formulate an optimization problem for the optimal exclusion zone size. We analytically prove convexity of the problem. Our approach reduces the exclusion zone size by over 42%, which gives significantly more spectral opportunities to GAA in the spatial domain.

Spectrum Sharing Backhaul Satellite-Terrestrial Systems via Analog Beamforming

Current satellite and terrestrial backhaul systems are deployed in disjoint frequency bands. This fact precludes an efficient use of the spectrum and limits the evolution of wireless backhauling networks. In this paper, we propose an interference mitigation technique in order to allow the spectrum coexistence between satellite and terrestrial backhaul links. This interference reliever is implemented at the terrestrial backhaul nodes, which are assumed to be equipped with multiple antennas. Due to the large bandwidth and huge number of antennas required in these systems, we consider pure analog beamforming. Precisely, we assume a phased array beamforming configuration so that the terrestrial backhaul node can only reduce the interference by changing the phases of each beamforming weight. Two cases are considered: the 18 and 28 GHz band where transmit and receive beamforming optimization problems shall be tackled, respectively. In both cases, the optimization problem results in a nonconvex problem that we propose to solve via two alternative convex approximation methods. These two approaches are evaluated and they present less than 1 dB array gain loss with respect to the upper bound solution. Finally, the spectral efficiency gains of the proposed spectrum sharing scenarios are validated in numerical simulations.

Adaptive Interference Mitigation with User Grouping for Fast Transmission in Cellular Networks

Designing uplink systems which group users with adaptive interference mitigation techniques is the objective of this research. Reduction in error rates and improvement in the energy efficiency is expected with this approach in addition to spectral efficiency. This paper reports a study on interference mitigation and transmission designs for groups of users in the uplinks. New formulations for the interference mitigation are produced based on the minimum mean square error and successive interference cancellation approach. By reducing the interference, the energy efficiency can be maintained and improved although the number of users per group increases. The measured error rates of this approach with user grouping achieve gains between 1 to 3 dB against that of the existing approach. With reduced complexity, the proposed scheme should be viable for practical deployment.

Adaptive Interference Mitigation with User Grouping for Fast Transmission in Cellular Networks

Designing uplink systems which group users with adaptive interference mitigation techniques is the objective of this research. Reduction in error rates and improvement in the energy efficiency is expected with this approach in addition to spectral efficiency. This paper reports a study on interference mitigation and transmission designs for groups of users in the uplinks. New formulations for the interference mitigation are produced based on the minimum mean square error and successive interference cancellation approach. By reducing the interference, the energy efficiency can be maintained and improved although the number of users per group increases. The measured error rates of this approach with user grouping achieve gains between 1 to 3 dB against that of the existing approach. With reduced complexity, the proposed scheme should be viable for practical deployment.