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This paper presents a full‐duplex and multi‐antenna relay‐aided transmission scheme for the user‐oriented perspective in cooperative non‐orthogonal multiple access (NOMA) systems. Relying on the service requirements, two legitimate users with security demands (SU) and quality of service (QoS) demands (QU) are paired for NOMA execution. The security of SU is enhanced through inverse power allocation of the conventional NOMA. The QoS requirements for QU are guaranteed, simultaneously. Then, the precoding design at the multi‐antenna relay has been exploited to improve the reliability demands of SU. Closed‐form expressions for SU's outage probability (OP) and intercepted probability, as well as QU's OP, are derived. The security–reliability trade‐off is also presented. Additionally, performance analysis under the half‐duplex and multi‐antenna scheme is provided as a benchmark for comparison. Finally, numerical simulations are performed to confirm the accuracy of the theoretical derivations under different schemes. Results demonstrate the superiority of the proposed scheme over benchmark schemes in terms of improving the security and reliability of SU, as well as saving power consumption of the system. [ABSTRACT FROM AUTHOR]

The author addresses the question, under which conditions an active jammer will be successful in corrupting a wireless communication link, when both the desired link and the jamming link are subject to multipath signal fading. To this end, a simple closed‐form analytical expression is derived for the resulting block‐error probability (BLEP) under Nakagami‐m$m$ fading with in general unequal fading parameters for the desired and the jamming link. As a by‐product, a novel expression for the corresponding probability of a capacity outage is obtained. An asymptotic analysis and numerical evaluation of the BLEP expression show that in the single‐antenna case the jammer will indeed be successful in corrupting the wireless link, unless there is a rather high signal‐to‐noise ratio (SNR) advantage for the desired link. This even holds true, when signal fading for the jamming link is significantly more severe than for the desired link. Finally, the case of multiple antennas is considered and the benefits of array processing and diversity reception at the desired receiver are explored. It is found that receive array processing can significantly improve the resulting BLEP, provided that the desired link is characterized by favorable fading conditions. On the other hand, diversity reception can significantly improve the BLEP, if the desired link has favorable SNR conditions. [ABSTRACT FROM AUTHOR]

Abstract Modern radar systems often face various interference signals in complex and rapidly changing electronic environments. The task of suppressing this interference in the radar echo signal to extract vital information is challenging. A radar interference suppression method is proposed based on a generative adversarial network (GAN). This method effectively recovers the target signal from the echo signal, which contains interference and noise, by leveraging the powerful fitting ability of GAN. Specifically, this method was tested using coherent suppression interference, smart noise interference, and noise frequency modulation suppression interference. We compared the proposed GAN method with recurrent neural network, short‐time Fourier transform time‐varying filtering, short‐time fractional Fourier transform time‐varying filtering algorithms and RNN approach. The results show that the interference suppression algorithm based on GAN is superior to the other three algorithms.

Modern radar systems often face various interference signals in complex and rapidly changing electronic environments. The task of suppressing this interference in the radar echo signal to extract vital information is challenging. A radar interference suppression method is proposed based on a generative adversarial network (GAN). This method effectively recovers the target signal from the echo signal, which contains interference and noise, by leveraging the powerful fitting ability of GAN. Specifically, this method was tested using coherent suppression interference, smart noise interference, and noise frequency modulation suppression interference. We compared the proposed GAN method with recurrent neural network, short‐time Fourier transform time‐varying filtering, short‐time fractional Fourier transform time‐varying filtering algorithms and RNN approach. The results show that the interference suppression algorithm based on GAN is superior to the other three algorithms. [ABSTRACT FROM AUTHOR]

A hybrid CS-DL method for aircraft classification in complex electromagnetic environment is introduced. To classify aircraft from interfered radar echoes, the authors propose a novel classification method based on compressed sensing (CS) and deep-learning (DL). After recovering the spectrum polluted by jamming signals by using CS, they exploit sparse auto-encoder (SAE) to extract modulation features and then classify aircraft. The method is tested by 536 flights of three types of airplanes, and the results show that the correct classification rate reaches 75% even when 41% of the pulses are interfered.

A hybrid CS-DL method for aircraft classification in complex electromagnetic environment is introduced. To classify aircraft from interfered radar echoes, the authors propose a novel classification method based on compressed sensing (CS) and deep-learning (DL). After recovering the spectrum polluted by jamming signals by using CS, they exploit sparse auto-encoder (SAE) to extract modulation features and then classify aircraft. The method is tested by 536 flights of three types of airplanes, and the results show that the correct classification rate reaches 75% even when 41% of the pulses are interfered. [ABSTRACT FROM AUTHOR]

Here, the authors develop a prototype filter design for filter bank multi‐carrier (FBMC) systems focusing on short‐length pulses (K≤3) with near‐perfect reconstruction features, favouring operational conditions for FBMC systems. The proposed design is formulated as the optimisation of the weights of a discrete prototype filter that takes into account high symbol reconstruction rates and desirable spectrum features. Despite not being convex, the formulated optimisation problem is relaxed via semi‐definite programming (SDP), enabling solutions that can over‐perform other popular prototype filters. Numerical results show that the proposed design considering overlapping factors K={1,2,3} can deliver prototype filters with a good signal‐to‐interference ratio (SIR) versus spectrum performance trade‐off. Indeed, for K≤2, the proposed methodology delivered prototype filters with the highest SIR levels among the available options. Furthermore, the proposed methodology can be extended and combined with other filter optimisation criteria, enabling to comply with different FBMC design requirements. [ABSTRACT FROM AUTHOR]

Adaptive beamforming methods are sensitive to underlying assumptions on the environment, sources, or sensor array violation, especially when interferences are moving fast. In this study, the non‐stationary interference source is estimated during the period in which snapshots are taken. Then, a new interference‐plus‐noise covariance matrix reconstruction is introduced which is derived from a simplified power spectral density function that can be used to shape the directional response of the beamformer. Finally, the beamformer is designed to impose nulls towards the regions of the moving interference based on the reconstructed covariance matrix. The essence of the proposed method is to express the inverse of the reconstructed covariance matrix which needs less computational complexity calculation. The effectiveness of the proposed method is demonstrated by numerical results. [ABSTRACT FROM AUTHOR]

In this study, the authors propose a novel method that provides weapon sound (WS) interference reduction of military instruction sound or instructions sound (IS). This method comprises of the following steps. In the first step, the mixed signal is split into its basic constituents using principal component analysis. The second step provides the intrinsic mode functions using the empirical mode decomposition method. In the third step, the fundamental frequency component is extracted by cepstrum analysis. The localisation of WS is done using the grid search window‐dominant signal subspace‐based method in the fourth step. Multiscale prediction and filtering using Daubechies wavelet‐based prediction are applied in the final step. The proposed method provides better results than existing baseline methods, for various signal‐to‐noise ratios. The simulations have also been performed on recorded WS corrupted IS signals from three different distances for the various input signal‐to‐weapon noise ratios, to verify the accuracy of the proposed method. [ABSTRACT FROM AUTHOR]

A simple and effective adaptive beamforming technique is proposed for uniform linear arrays, which are based on projection processing for covariance matrix construction and desired‐signal steering vector estimation. The optimal minimum variance distortion‐less response beamformer is closely achieved through approximating the interference‐plus‐noise covariance matrix by utilising the eigenvalue decomposition of the received signal's covariance matrix. Moreover, the direction‐of‐arrival (DOA) of the desired signal is estimated by maximising the beamformer output power in a certain angular sector. In particular, the proposed beamformer utilises the aforementioned DOA in order to estimate the desired‐signal's steering vector for general steering vector mismatches. Simulation results indicate the better performance of the proposed method in the presence of the different errors compared with some of the recently introduced techniques. [ABSTRACT FROM AUTHOR]

Filters with antenna arrays are widely used for interference suppression in the temporal domain, frequency domain, space domain and so on. Meanwhile, the interference mitigation performance of a single‐domain‐based filter depends on a noticeable difference between the target signal and interference in the corresponding domain. However, the interference cannot be efficiently suppressed by a single‐domain‐based filter when the difference in this individual domain is small. To solve this problem, a multi‐domain collaborative oblique projection filter is proposed in this study. First, multi‐domain spaces are theoretically derived to distinguish the target signal and the interference, and then a multi‐domain oblique projection operator is provided to recover the original target and suppress the interference. Depending on the multi‐domain spaces, the filter has excellent performance when the difference is insignificant in each individual domain, whereas the performances of the single‐domain‐based filter and cascade filter degrade significantly. Finally, a space–polarisation–frequency domain collaborative filter based on oblique projection is given as an illustration. Performance analysis and simulation results are provided to illustrate the superiority of the proposed filter for interference mitigation. [ABSTRACT FROM AUTHOR]

A novel design of ternary signal sets is proposed for estimation of multiuser fibre‐wireless (Fi‐Wi) uplink channels. The design overcomes the current limitation in the maximum number of users that the system can accommodate by separating the signals in a set into subsets. The signals are uncorrelated between subsets, but correlated within subsets, thus forming a semi‐correlated ternary pseudo‐random signal (SC‐TPRS) set. An iterative channel estimator based on the SC‐TPRS scheme is then proposed for joint estimation of the Fi‐Wi uplink channel. The computational complexity associated with the existing and the proposed estimators is derived and it is shown that the latter incurs substantially lower computational cost than the former. Numerical results show that despite using signals which are a few hundred times shorter, the proposed scheme can improve estimation accuracy dramatically over the existing scheme at low signal‐to‐noise ratios. The proposed scheme has a further advantage of allowing the designer to optimise the Fi‐Wi system under the constraint of maximum permissible level of multiple access interference, since the amount of interference can be tuned by adjusting the number and size of the ternary signal subsets. [ABSTRACT FROM AUTHOR]

Optical see-through head-mounted displays enable augmented reality (AR) applications that display virtual objects overlaid on the real world. At the core of this new generation of devices are low-cost tracking technologies that allow us to interpret users' motion in the real world in relation to the virtual content for the purposes of navigation and interaction. The advantages of pervasive tracking come at the cost of limiting interaction possibilities, however. To address these challenges the authors introduce GyroWand, a raycasting technique for AR HMDs using inertial measurement unit (IMU) rotational data from a handheld controller. [ABSTRACT FROM PUBLISHER]

In high‐impedance grounded distribution networks which are common in many countries, single line‐to‐ground (SLG) fault diagnosis is difficult due to weak fault characteristics, noise interference, three‐phase unbalanced operation's influence and so on. Upon thorough analysis on the space‐time characteristics of SLG fault, this study applies signal processing and analysis techniques to do SLG fault location detection. First, finite impulse response (FIR) filter is applied to effectively strain out interference factors and extract pure fault characteristics for each line. Afterwards, hierarchical clustering is used to classify lines based on the extracted fault characteristics. According to the clustering result, the fault line could be determined. If there are monitoring terminals distributed in the fault line, the fault section could also be further identified. Simulation shows that the proposed method works well under various fault conditions and has a higher reliability compared with wavelet analysis. Besides, this method makes full use of the existing hardware conditions in the grid and the cost is low, hence it has high practical value. [ABSTRACT FROM AUTHOR]

Extensive deployment of small cells in heterogenous cellular networks introduces both challenges and opportunities. Challenges come with reuse of limited frequency resources, which always introduce both intra- and inter-interference among small cells and macrocells. The opportunities refer to more potential inter- and intra-tier cooperation gains, in particular for ultra-dense heterogeneous and small cell networks. In addition to current spectral efficiency optimization, energy efficiency will also be a critical performance requirement for future green communications, especially when small cells are densely deployed to enhance the user?s quality of experience. In this article, potential cooperation gains are explored via a cooperative bargaining game to counter challenges of mitigating interference and saving energy, thus improving both spectral and energy efficiency. We survey the current optimization and trade-offs of spectral and energy efficiency, and introduce the basics of cooperative game theory. Then a utility function is presented with spectral and energy efficiency coupled together. Furthermore, we present the bargaining cooperative game theoretic framework to explore potential cooperation gains. Moreover, two applications are investigated for the dedicated and co-channel deployment cases, including cooperative relay with spectrum leasing and cooperative capacity offload. Finally, we conclude the article with potential challenges of the presented cooperative framework and some thoughts for future research directions. [ABSTRACT FROM PUBLISHER]

In this study, primary user (PU) interference in a cognitive amplify-and-forward relay network is considering over a Nakagami-m fading channel, and the outage probability is derived for the secondary users. This PU interference has not previously been considered in the literature. Results are presented which show that PU interference can significantly degrade secondary user performance, and thus should be considered in the design of a cognitive radio network.

A robust adaptive filtering algorithm based on the convex combination of two adaptive filters under the maximum correntropy criterion (MCC) is proposed. Compared with conventional minimum mean square error (MSE) criterion-based adaptive filtering algorithm, the MCC-based algorithm shows a better robustness against impulsive interference. However, its major drawback is the conflicting requirements between convergence speed and steady-state mean square error. In this letter, we use the convex combination method to overcome the tradeoff problem. Instead of minimizing the squared error to update the mixing parameter in conventional convex combination scheme, the method of maximizing the correntropy is introduced to make the proposed algorithm more robust against impulsive interference. Additionally, we report a novel weight transfer method to further improve the tracking performance. The good performance in terms of convergence rate and steady-state mean square error is demonstrated in plant identification scenarios that include impulsive interference and abrupt changes. [ABSTRACT FROM AUTHOR]

Wireless sensor network communication in industrial environments is compromised by interference, multipath fading, and signal attenuation. In that respect, accurate channel diagnostics is imperative to selecting the adequate countermeasures. This paper presents the lightweight packet error discriminator (LPED) that infers the wireless link condition by distinguishing between errors caused by multipath fading and attenuation, and those inflicted by interfering wideband single-channel communication systems (e.g., IEEE 802.11b/g), based on the differences in their error footprints. The LPED uses forward error correction in a novel context, namely, to determine the symbol error density, which is then fed to a discriminator for error source classification. The classification criteria are derived from an extensive set of error traces collected in three different types of industrial environments, and verified on a newly collected set of error traces. The proposed solution is evaluated both offline and online, in terms of classification accuracy, speed of channel diagnostics, and execution time. The results show that in ≥91% of cases, a single packet is sufficient for a correct channel diagnosis, accelerating link state inference by at least 270%, compared with the relevant state-of-the-art approaches. The execution time of LPED, for the worst case of packet corruption and maximum packet size, is below 30 ms with ≤3% of device memory consumption. Finally, live tests in an industrial environment show that LPED quickly recovers from link outage, by losing up to two packets on average, which is only one packet above the theoretical minimum. [ABSTRACT FROM PUBLISHER]

Purpose: Myocardial perfusion imaging (MPI) is used for diagnosis and prognosis of coronary artery disease. When MPI studies are performed with positron emission tomography (PET) and the radioactive tracer rubidium-82 chloride (82Rb), a small but non-negligible fraction of studies (~10%) suffer from extracardiac interference: high levels of tracer uptake in structures adjacent to the heart which mask the true cardiac tracer uptake. At present, there are no clinically available options for automated detection or correction of this problem. This work presents an algorithm that detects and classifies the severity of extracardiac interference in 82Rb PET MPI images and reports the accuracy and failure rate of the method. Methods: A set of 200 82Rb PET MPI images were reviewed by a trained nuclear cardiologist and interference severity reported on a four-class scale, from absent to severe. An automated algorithm was developed that compares uptake at the external border of the myocardium to three thresholds, separating the four interference severity classes. A minimum area of interference was required, and the search region was limited to that facing the stomach wall and spleen. Maximizing concordance (Cohen's Kappa) and minimizing failure rate for the set of 200 clinician-read images were used to find the optimal population-based constants defining search limit and minimum area parameters and the thresholds for the algorithm. Tenfold stratified cross-validation was used to find optimal thresholds and report accuracy measures (sensitivity, specificity, and Kappa). Results: The algorithm was capable of detecting interference with a mean [95% confidence interval] sensitivity/specificity/Kappa of 0.97 [0.94, 1.00]/0.82 [0.66, 0.98]/0.79 [0.65, 0.92], and a failure rate of 1.0% ± 0.2%. The four-class overall Kappa was 0.72 [0.64, 0.81]. Separation of mild versus moderate-or-greater interference was performed with good accuracy (sensitivity/ specificity/Kappa = 0.92 [0.86, 0.99]/0.86 [0.71, 1.00]/0.78 [0.64, 0.92]), while separation of moderate versus severe interference severity classes showed reduced sensitivity/Kappa but little change in specificity (sensitivity/specificity/Kappa = 0.83 [0.77, 0.88]/0.82 [0.77, 0.88]/0.65 [0.60, 0.70]). Specificity was greater than sensitivity for all interference classes. Algorithm execution time was <1 min. Conclusions: The algorithm produced here has a low failure rate and high accuracy for detection of extracardiac interference in 82Rb PET MPI scans. It provides a fast, reliable, automated method for assessing severity of extracardiac interference. [ABSTRACT FROM AUTHOR]

In this paper, an optical code-division multiple-access (OCDMA) system employing overlapping pulse-position modulation (OPPM) is proposed to support multimedia services with different bit-rate and quality-of-service (QoS) requirements in OCDMA networks. Both wrapped OPPM (WOPPM) and unwrapped OPPM (UOPPM) are considered. The proposed system achieves multirate and multi-QoS transmission by using multilength variable-weight optical orthogonal codes (MLVW-OOCs) as signature sequences and using different values of OPPM modulation parameters. Furthermore, numerical analysis is performed for two different receiver structures, namely, correlation receivers with and without hard-limiters. In our analysis, the multiple-access interference (MAI) is considered as the main performance limiting factor. In addition, the performance of the proposed system is evaluated and compared to that of traditional OOK-OCDMA system. Our results reveal that under both pulsewidth and throughput constraints, the performances of the proposed WOPPM- and UOPPM-OCDMA systems are significantly superior to that of OOK-OCDMA system. [ABSTRACT FROM PUBLISHER]

User environments for wireless devices are complex and include many sources of interference. As RF power is spread over wider bandwidths to increase data rates, wireless devices encounter increased interference. As designers look to create robust solutions that perform in these environments, it is essential to recreate those conditions in the lab. This article describes the problems associated with RF interference in modern wireless devices and techniques that can be used to analyze these interference issues. [ABSTRACT FROM PUBLISHER]

The presence of the desired signal (DS) in the training snapshots makes the adaptive beamformer sensitive to any steering vector mismatch and dramatically reduces the convergence rate. Even the performance of the most of the existing robust adaptive beamformers is degraded when the signal‐to‐noise ratio (SNR) is increased. In this study, a high converging rate robust adaptive beamformer is proposed. This method is a promoted eigenspace‐based beamformer. In this paper, a new signal‐plus‐interferences (SPI) covariance matrix estimator is proposed. The subspace of the ideal SPI covariance matrices is exploited and the estimated covariance matrix is projected into this subspace. This projection effectively reduces the covariance matrix estimation error and the proposed estimator yields a more accurate estimation of the SPI covariance matrix. In addition, a computationally efficient steering vector estimator has been proposed. To prevent the absence of the DS steering vector in the estimated SPI subspace, the estimated SPI covariance matrix is compensated. Hence, the proposed method can attain the optimal beamformer in the both high and low SNR cases. The numerical examples indicate that this method has excellent signal‐to‐interference plus noise ratio performance and offers a higher converging rate compared with the existing robust adaptive beamforming algorithms. [ABSTRACT FROM AUTHOR]

The effects of signal contamination of secondary data are investigated in the framework of adaptive target detection in remotely sensed hyperspectral images. In contrast to previous studies on signal contamination, the focus of this paper is the detection of targets with unknown spectral signatures (i.e., anomalies) and adaptive detection methods based on a local estimation of the background covariance matrix. Contamination due to the target signal is expected to have a more severe impact when the number of secondary data is limited. An analytical model for signal contamination is developed that allows variability in the extent of contamination. Several parameters, such as the contamination fraction of secondary data and the contaminating signal energy, are introduced, and a contaminating signal-to-interference-plus-noise ratio is derived as an objective measure of contamination. The proposed model is employed to experimentally evaluate signal contamination effects and the impact of its variability on the performance of adaptive detection of local anomalies. The outcomes of the experimental study are substantiated by validation with real hyperspectral data. The results obtained highlight the relevance that the impact of signal contamination, assessed with respect to different system parameters, may have for practical applications. This paper represents a starting point for the development of detection performance forecasting models that consider signal contamination. [ABSTRACT FROM PUBLISHER]

This letter studies feedback topologies for interference alignment (IA) in a multiple-input multiple-output (MIMO) K-user interference channel with M = (K - 1)d antennas at each node, where d is the number of data streams per user. Under this antenna configuration, Cho propose two two-hop centralized feedback topologies, as well as a channel state information (CSI) exchange structure which requires 2(K - 1) time slots to compute IA precoders. In order to reduce the CSI overhead or shorten the time delay for the existing feedback topologies, we propose three new ones: 1) a two-hop distributed one with reduced CSI overhead; 2) a modified CSI-exchange topology that has the same CSI overhead but shortened delay compared to its existing counterpart; and 3) a four-hop novel one with smaller CSI overhead rather than that of the conventional CSI-exchange topology. [ABSTRACT FROM AUTHOR]

As an important class of non‐Gaussian statistic model, α ‐stable distribution has received much attention because of its generality to represent impulsive interference. Unfortunately, it does not have a closed‐form probability density function (PDF) except for a few cases. For this reason, suboptimal zero‐memory non‐linearity (ZMNL) function has to be used as an approximation in designing locally optimal detector, such as classical Cauchy and Gaussian‐tailed ZMNL (GZMNL). To enhance the performance of detectors, the authors first investigate the approximate PDFs for the symmetric α ‐stable. In particular, a simplified version of Cauchy–Gaussian mixture (CGM) model, called bi‐parameter CGM (BCGM) model is detailed. This BCGM model has a concise closed‐form, and hence is more tractable than the classical Gaussian mixture model and CGM model. Then based on the preset false alarm ratio (FAR), the test threshold is adaptively evaluated by using BCGM to maintain a constant FAR. The authors further devise an algebraic‐tailed ZMNL (AZMNL) with a simplified form. Simulation results show that the detector with AZMNL outperforms the ones with classical Cauchy and GZMNL, and achieves near‐optimal performance in varying impulsive interference. [ABSTRACT FROM AUTHOR]

The main focus of this paper is the acoustic feedback path neutralisation during online operation of the single‐channel active noise control (ANC) systems. Invasive techniques, in which additive auxiliary noise is injected for online feedback path modelling (FBPM), degrade the noise‐reduction performance of ANC systems. In the existing methods for online FBPM, additive auxiliary noise with fixed variance is injected during all operating conditions of ANC systems. In this paper, a scheduling strategy is proposed to have time‐varying gain for additive auxiliary noise. The time‐varying gain is computed on the basis of (i) the convergence status of the FBPM filter, and (ii) the power of the interference term in the error signal of the FBPM filter. Simulation results show that, compared to the existing methods, the proposed method can better achieve the conflicting requirements of fast convergence of the FBPM filter, and reduced steady‐state power of the residual error at the error microphone. For sake of completeness, appendix presents typical simulation results when both the secondary path and feedback path are simultaneously identified during online operation of ANC systems. [ABSTRACT FROM AUTHOR]

The ZPW‐2000 track circuit is the dominant track circuit system used in China. On standard plain line track it is used as a jointless track circuit where 'tuned zones' are used to separate adjacent tracks operating at different frequencies. Owing to the complexities of station layouts it is not possible to use the ZPW‐2000 as a jointless track circuit within stations, so a solution incorporating mechanical joints is commonly used. The station environment is known to have high levels of electromagnetic interference, and such environments can cause interference in the track circuit resulting in signal degradation and failure. An integrated solution that allows the ZPW‐2000 track circuit to be used dependably in jointed operation that is able to cope with the electromagnetic environment found in stations is therefore required. In this study, a solution based on impedance bonds is developed to alleviate interference problems with the ZPW‐2000 in harsh electromagnetic environments. The study presents an innovative design of impedance bond incorporating an air gap transformer and a double function filter circuit. The impedance bond was found to have an impedance of below 0.01 Ω at the resonant frequency of 50 Hz, and in excess of 17 Ω at other signal frequencies. The impedance bond is shown to eliminate interference while meeting the requirements of signal transmission on rail tracks. In this study, both theoretical analysis and the results of laboratory tests are presented. [ABSTRACT FROM AUTHOR]

A new approach for protecting sensitive receivers through large attenuation and its realization on-chip is presented for the first time. This paper demonstrates the use of absorptive bandstop filters that gives anomalously deep notches for a given quality factor. This approach is used in a fabricated design example to isolate a sensitive wideband LNA from interference in 45-nm SOI complementary metaloxide-semiconductor (CMOS). For reconfigurable RF front-ends, a frequency-agile design is newly developed with Q tunable resonators because an absorptive bandstop filter must balance both intrinsic Q of the resonators and the resonant frequency of the filter. Therefore, the design requires variable resistors, variable capacitors, and intimate coupling of inductors of disparate values. The layout of overlapping inductors on closely spaced metal layers is required for proper absorptive properties. The size of one filter presented in this paper is 310 by 340 μm, making it the smallest absorptive bandstop filter demonstrated so far. Despite using small-size, on-chip low-Q resonators in the bandstop filter design, an attenuation level from 31 to 63 dB and a frequency tuning range from 2.9 to 4.3 GHz are achieved with potential to suppress potential interference or an image frequency signal. [ABSTRACT FROM AUTHOR]

We study the performance region of a general multicell downlink scenario with multiantenna transmitters, hardware impairments, and low-complexity receivers that treat interference as noise. The Pareto boundary of this region describes all efficient resource allocations, but is generally hard to compute. We propose a novel explicit characterization that gives Pareto optimal transmit strategies using a set of positive parameters-fewer than in prior work. We also propose an implicit characterization that requires even fewer parameters and guarantees to find the Pareto boundary for every choice of parameters, but at the expense of solving quasi-convex optimization problems. The merits of the two characterizations are illustrated for interference channels and ideal network multiple-input multiple-output (MIMO). [ABSTRACT FROM PUBLISHER]

We show that the maximization of the sum degrees-of-freedom for the static flat-fading multiple-input multiple-output (MIMO) interference channel (IC) is equivalent to a rank constrained rank minimization problem (RCRM), when the signal subspaces span all available dimensions. The rank minimization corresponds to maximizing interference alignment (IA) so that interference spans the lowest dimensional subspace possible. The rank constraints account for the useful signal subspaces spanning all available spatial dimensions. That way, we reformulate the IA requirements to requirements involving ranks. Then, we present a convex relaxation of the RCRM problem inspired by recent results in compressed sensing and low-rank matrix completion theory that rely on approximating rank with the nuclear norm. We show that the convex envelope of the sum of ranks of the interference matrices is the normalized sum of their corresponding nuclear norms and replace the rank constraints with asymptotically equivalent and tractable ones. We then tune our heuristic relaxation for the multicell interference channel. We experimentally show that in many cases the proposed algorithm attains perfect interference alignment and in some cases outperforms previous approaches for finding precoding and receive matrices for interference alignment. [ABSTRACT FROM PUBLISHER]

With the recent development of solid-state lighting (SSL) technologies, visible light communication (VLC) systems using light-emitting diodes (LEDs) has been a promising technology to complement wireless communication. While LEDs offers advantageous properties such as high brightness, lower power consumption, long lifetime, and short transient time for high transmission rates, few researches have been exploited on the receiver side. Conventionally, photoelectric-diodes are implemented to convert optical signals into electronic signals. Since conventional photoelectric-diodes cannot distinguish inputs of different spectra, using conventional photoelectric-diodes have the disadvantage that the system is vulnerable to interference, and that it is hard to achieve wavelength-division-multiplexing (WDM) for light sources of different wavelengths. In this work, a spectrum sensor array is proposed to be implemented on the receiver side to achieve interference rejection. Due to recent advances in semiconductor technologies, spectrum sensors with different spectral transmission properties can be integrated into a chip-scale sensor-array. By proper design of the weightings for individual spectrum sensor, the effective output signal-to-interference ratio (SIR) can be maximized. Following the concept of coherent multi-antenna communication systems, signal fusion algorithms are presented. Our simulation is conducted based on the specification of a prototype filter-array spectrum sensor from nanoLambda. Simulation results demonstrate that robust interference rejection is possible using the low-cost spectrum sensor array. [ABSTRACT FROM PUBLISHER]

The backscattering from man-made point targets like passive corner reflectors and active transponders is often used as a radiometric calibration standard for synthetic aperture radar (SAR) calibration. As new systems emerge and the demand for more accurate systems increases, it becomes necessary to better understand the effects of real or imperfect targets on the radiometric calibration results. Therefore, a point-target SAR simulator is presented which models the complete external radiometric calibration process. It incorporates a number of target properties like frequency response, transponder internal calibration strategies, noise, and interference signals, and it takes the instrument SAR mode settings into consideration. Thereby, the relevant target backscatter variation as observed in the processed SAR image with respect to an ideal or any other target can be determined. The simulation results are relevant during the design process of a new target as well as during the actual calibration of a SAR system. Based on these point-target simulations, correction coefficients can be stated for each target and SAR mode, therefore decreasing the remaining radiometric point-target uncertainties. The quantitative examples in this paper show that these corrections can influence the absolute radiometric calibration by more than 1 dB. [ABSTRACT FROM AUTHOR]

In a molecular communication via diffusion (MCvD) system, enzymes are known to reduce molecular signal interference caused by eliminating unwanted chemicals that persist in the system. An MCvD system with a fixed amount of enzymes around the spherical receiver is considered. Since the enzyme amount is fixed, increasing the size of the enzyme region increases the probability of entering the enzyme region while it decreases the effectiveness of the enzymes. Therefore, the size of the enzyme region needs to be optimised. Thus, the effect of system parameters on the optimal enzyme region radius is analysed. [ABSTRACT FROM AUTHOR]

In orthogonal frequency division multiplexing‐based spectrum sharing networks, due to inefficient coordination or imperfect spectrum sensing, the signals from femtocells or secondary users appear as interference in a subset of subcarriers of the primary systems. For pilot‐based doubly‐selective channel estimation, the embedded pilots in pilot subcarriers would inevitably be harmed by the unpredictable interference. This unsolved issue is considered and proposed is a variational expectation maximisation‐based method to iteratively learn the distribution of thermal noise plus interference, and refine doubly‐selective channel estimates. Simulations demonstrated the superiority of the proposed approach over existing algorithms without considering interference mitigation. [ABSTRACT FROM AUTHOR]

A novel robust algorithm for the interference‐plus‐noise covariance matrix (IPNCM) reconstruction according to its definition is addressed. Unlike the previous works, each interference steering vector (SV) is estimated as the prime eigenvector of the interference covariance matrix obtained by integrating over each interference angular sector and its power through the Capon spectral estimator is also estimated. Then, a more precise IPNCM based on these accurate estimates is reconstructed. In addition, the same idea is used to estimate the SV of the signal of interest over the signal angular sector. Simulation results demonstrate that the proposed beamforming has much more robustness against the large look direction errors of the interferences, and can attain the optimal beamformer in both high and low signal‐to‐noise ratio cases with low computational complexity. [ABSTRACT FROM AUTHOR]

A multiple antenna downlink channel where limited channel feedback is available to the transmitter is considered. In a vector downlink channel (single antenna at each receiver), the transmit antenna array can be used to transmit separate data streams to multiple receivers only if the transmitter has very accurate channel knowledge, i.e., if there is high-rate channel feedback from each receiver. In this work it is shown that channel feedback requirements can be significantly reduced if each receiver has a small number of antennas and appropriately combines its antenna outputs. A combining method that minimizes channel quantization error at each receiver, and thereby minimizes multi-user interference, is proposed and analyzed. This technique is shown to outperform traditional techniques such as maximum-ratio combining because minimization of interference power is more critical than maximization of signal power in the multiple antenna downlink. Analysis is provided to quantify the feedback savings, and the technique is seen to work well with user selection and is also robust to receiver estimation error. [ABSTRACT FROM PUBLISHER]

We investigate a space-time coding scheme with four or more transmit antennas based on a matrix-Alamouti scheme in a quasi-static fading environment. The receiver consists of an Alamouti combiner followed by an iterative joint detection and decoding process. A priori probabilities fed back from the decoder are used to both get more reliable estimates of the transmitted symbols and efficiently remove inter-block interference. Interblock interference is removed using techniques known in multiuser communication. The theoretical bounds of this scheme are established through the study of its outage probability. [ABSTRACT FROM PUBLISHER]

Using relays in wireless networks can potentially lead to significant capacity increases. However, within an asynchronous multi-user communication setting, relaying might cause more interference in the network, and significant sum-rate deterioration may be observed. In this work the effect of cooperation in an interference limited, narrow-band wireless network is investigated. It is crucial to determine the optimal trade-off between the amount of throughput gain obtained via cooperation and the amount of interference introduced to the network. We quantify the amount of cooperation using the notion of a cooperative region for each active node. The nodes which lie in such a region are allowed to cooperate with the source. We adopt the decode-and-forward scheme at the relays and use the physical interference model to determine the probability that a relay node correctly decodes its corresponding source. Through numerical analysis and simulation, we study the optimal cooperative region size to maximize the network sum-rate and energy efficiency, based on network size, relay availability, node decoding threshold, and destination reception capability. It is shown that optimized system performance in terms of the network sum-rate and the power efficiency is significantly improved compared with cases where relay nodes are not exploited or where the cooperative region size is suboptimal. [ABSTRACT FROM PUBLISHER]

Previously, an optical code-division multiplexing (OCDM)-based network architecture was proposed to improve the wavelength utilization and to provide finer bandwidth granularities to users. By this technology, different channels using distinct optical codes (OCs) can be multiplexed onto the same wavelength, in which an OC is considered as the basic unit in lightpath provisioning. In the ideal case, multiaccess interference (MAI) inherent to the OCDM technology is assumed to be removed completely at intermediate nodes and cannot be propagated or accumulated along the lightpath. However, since no optical-electrical (O/E) or electrical-optical (E/O) conversion is allowed in transparent OCDM-based optical networks, the MAI cannot be removed completely at intermediate nodes with current all-optical regeneration techniques. As a result, the residual MAI may be propagated and accumulated along the lightpath and affect other active lightpaths carried by the same wavelength in the network. The affected active lightpaths may build unintended cycles along which the MAI is accumulated. Furthermore, this MAI keeps increasing when the lightpaths traversed by the cycle are active, which deteriorates the lightpath signal quality. Since this deterioration may eventually result in unacceptable signal quality and service disruption, the phenomenon caused by the MAI is termed as cycle attack in this paper. The explanations of the MAI propagation mechanism and the cycle attack problem are given. A depth-first search (DFS)-based algorithm is proposed to diagnose such cycle attacks under dynamic traffic conditions. The numerical results show that our DFS-based cycle attack diagnostic algorithm enables one to detect cycle attacks effectively, and the two-way resource reservation method associated with heuristic wavelength assignment is shown to mitigate the blocking performance degradation due to cycle attacks greatly with some proper wavelength and OC configuration. [ABSTRACT FROM PUBLISHER]

An analytic model for interchannel four-wave mixing (FWM) is developed for return to zero differential phase shift keying (RZ-DPSK) single span transmission including interchannel walk-off for degenerate FWM (D-FWM) and nondegenerate FWM (ND-FWM). The model is verified by simulations and reasonable agreement is obtained for a 10-Gb/s single span link. Results are presented for different channel spacing, launch pulse duty-cycle, and launch power. The model is strictly valid for systems with low fiber dispersion as it ignores dispersion related pump pulse distortion. It is found that the walk-off effect makes a significant contribution to the detected unfiltered FWM noise and this contribution is mostly concentrated at high frequencies determined by the channel spacing alone. The contribution of the walk-off and its frequency content is understood in terms of intracollision and intercollision interference. In the typical situation when a sub-bit-rate electrical low-pass filter is used, the walk-off effect is effectively removed for all types of FWM. The analytic model is validated by comparing to split-step-Fourier (SSF) simulations. Extension to the general case of multiple FWM lines is considered. It is found that the FWM noise standard deviation is 2 times smaller for RZ-DPSK as compared to that for return to zero on-off keying (RZ-OOK) at the same average launch power for a system with 25-GHz channel spacing. [ABSTRACT FROM PUBLISHER]

An adaptive beamforming algorithm that enhances the quality of the signal recorded by a microphone array is presented. The system described here attenuates the interference from spatially scattered sources while preserving the desired signal quality in the speech frequency range. A novel method for defining additional constraints within the adaptation process and performing beamforming in parallel across several frequency bands achieves undistorted recording even with slight errors in localizing the speaker. Moreover, a tracking algorithm is developed which adjusts the beamformer parameters while keeping its wideband characteristics and the interference reducing capabilities. Simulation results show nearly optimal improvement of speech quality in various noisy environments. The algorithm is modified to perform in a real environment by introducing two modes of adaptation that switch according to the speaker activity. The implementation of this modified system demonstrates signal-to-noise ratio (SNR) gain close to that of the original simulated system. It is robust to localization errors and non-ideal environmental effects. [ABSTRACT FROM PUBLISHER]

In the framework of control methods for adaptive phased-arrays, this paper deals with complex communication scenarios by considering a memory-enhanced cooperative algorithm. Compared to existing approaches where far-field interferences are taken into account, the proposed analysis considers a more realistic situation where the jamming sources are located either in the near-field or in the far-field of the receiving antenna. In order to carefully address the arising challenges and to effectively deal with such complex environments, an optimization approach based on an enhanced particle swarm optimizer (PSO)-based algorithm is used. The obtained results seem to confirm the effectiveness of the proposed technique in terms of both signal-to-noise ratio and computational costs and complexity. [ABSTRACT FROM PUBLISHER]

Global positioning system receivers sometimes operate under severe multipath conditions, including those which include a ground specularly reflected signal along with a direct signal. Here, such a case is discussed which involves a dielectric-covered flat ground reflector, with incident energy at 1.57542-GHz right-hand circularly polarized at elevation angles between 5^circ and 50 ^circ. The relative received powers produced by the sum of the specularly reflected and direct signals are computed from conventional theory and are measured for various thicknesses of dielectrics. Both theory and measurement show that the received powers produced by the sum of the specularly reflected and direct signals have the same behavior throughout a range of elevation angles. A snow case study shows potential for inferring snow depth by fitting the theory to the measurements. [ABSTRACT FROM PUBLISHER]

Current ultra-high frequency air interface protocols help users get the true benefits of second-generation RFID standards. However, these technologies also have some security drawbacks and limitations. [ABSTRACT FROM PUBLISHER]

This issue combines an array of interesting articles that address recent activities in this important and highly evolving field. In closing, the guest editors would like to acknowledge the many experts in the field who participated in the reviewing process for providing helpful suggestions to the authors on improving the content and presentation of their articles. [ABSTRACT FROM PUBLISHER]

We have investigated both theoretically and experimentally the elimination of multiple-access interference (MAI) in an incoherent optical code-division multiple access (OCDMA) system by using a novel incoherent dual code OCDMA receiver incorporating an ultrafast all-optical time gate (AOTG). A theoretical analysis was performed based on (3,11) frequency-hopping time-spreading OCDMA codes with a chip size of 73 ps. To experimentally demonstrate the elimination of MAI, the novel receiver comprising an ultrafast 2 ps-AOTG was developed and tested in a representative OCDMA network testbed. Experimental measurements confirmed by simulations show error-free [bit error rate (BER) < 10-2] operation for up to four users. Simulations also predict that receivers equipped with 2 ps-AOTG will more than triple the number of simultaneous users without degrading BER. [ABSTRACT FROM PUBLISHER]

In this paper, we propose a novel multiple-access interference (MAI) cancellation technique using a reference signal, which contains no data components (data-free) of the desired signal, and then simplifies the receiver configuration in synchronous M-ary frequency-shift keying optical code-division multiple-access (FSK-OCDMA) network. In doing so, we have taken advantage of a recently introduced energy-saving unipolar prime-code family, referred to as double-padded modified prime-code (DPMPC) as the spreading codes. In the theoretical analysis, the system upper bounded bit error rate (BER) is derived taking into account the Poisson effect on the I/O characteristics of the photodetectors. We have found that when the bit rate is constant, the capacity of this system increases by employing the proposed interference canceller and spreading code as compared with the synchronous M-ary pulse-position modulation OCDMA system with an existing interference canceller. In contrast to wavelength-division multiple access, a fewer set of wavelengths is needed as a result of only M-ary source coding. [ABSTRACT FROM PUBLISHER]

Adaptive parallel interference cancellation (PIC) has been recently proposed for the signal detection in multiple- input multiple-output (MIMO) systems. However, it suffers from error propagation when operated in time-varying channels. In this letter, an adaptive two-stage PIC with the minimum variance (MV) criterion is proposed to solve the problem. Adaptation with the MV criterion is realized with a decision feedback generalized sidelobe canceller (DFGSC). In the first-stage cancellation, a special structure involving dual DFGSCs is developed. All adaptation operations are implemented with the least-mean-square (LMS) algorithm. Simulations show that the proposed adaptive PIC detection can significantly outperform the conventional adaptive PIC detection in time-varying MIMO channel environments. [ABSTRACT FROM PUBLISHER]

This paper deals with a signal processing precorrelation method to detect the presence of interference at a global navigation satellite system (GNSS) receiver site. In particular, a nonparametric spectral estimation approach based on the Welch windowed periodogram will be considered here. The performance of the proposed detector, in terms of detection probability, for a given false-alarm probability value, will be derived by means of an analytical approach and resorting to computer simulations. A performance comparison with previously proposed precorrelation methods will also be presented in order to highlight the better behavior of the proposed approach that makes it suitable for safety of life (SoL) applications. [ABSTRACT FROM PUBLISHER]

Multi-antenna transmission and reception (known as MIMO) is widely touted as the key technology for enabling wireless broadband services, whose widespread success will require 10 times higher spectral efficiency than current cellular systems, at 10 times lower cost per bit. Spectrally efficient, inexpensive cellular systems are by definition densely populated and interference-limited. But spatial multiplexing MIMO systems- whose principal merit is a supposed dramatic increase in spectral efficiency- lose much of their effectiveness in high levels of interference. This article overviews several approaches to handling interference in multicell MIMO systems. The discussion is applicable to any multi-antenna cellular network, including 802.16e/WiMAX, 3GPP (HSDPA and 3GPP LTE), and 3GPP2 (lxEVDO). We argue that many of the traditional interference management techniques have limited usefulness (or are even counterproductive) when viewed in concert with MIMO. The problem of interference in MIMO systems is too large in scope to be handled with a single technique: in practice a combination of complementary countermeasures will be needed. We overview emerging system-level interference-reducing strategies based on cooperation, which will be important for overcoming interference in future spatial multiplexing cellular systems. [ABSTRACT FROM PUBLISHER]