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ABSTRACT In orthogonal frequency division multiplexing (OFDM) systems, the time‐selective fading channel causes the signal Doppler expansion in high‐mobility scenarios, leading to intercarrier interference (ICI) in the received signals. People had employed a full‐dimensional weighting matrix method to reduce the Doppler‐assisted ICI, though it required a high implementation complexity. In order to reduce the ICI and produce lower complexities, this paper proposes to exploit the tridiagonal weighting matrix to suppress ICIs, in which an optimization problem is constructed to design the tridiagonal weighting matrix, and the nonzero coefficients within the tridiagonal matrix denote optimization variables. Moreover, the optimization objective exploits the system bit error rate (BER) instead of the conventional signal to interference plus noise ratio (SINR), which results in a highly nonlinear optimization problem. Therefore, an iterative solving approach is proposed according to the successive convex approximation (SCA). Simulations show that the proposed method can achieve a good balance between the complexity and BER degradation, especially in the scenario with moderate Doppler spreads. [ABSTRACT FROM AUTHOR]

The interference has a major detrimental effect on wireless network performance. Today's globe is rapidly focusing on the issue of reducing interference in wireless networks due to the ongoing deployment of larger and more advanced networks. In this research we will discuss the reducing carrier and code interference in wireless communication systems. This paper showed that the critical factor in wireless communication is the carrier-to-interference ratio (CIR). Network operators may improve their systems to provide their customers with high quality telecommunication services by knowing their importance and uses. Requirements for reliable communications will increase along with the development of wireless technology, making proper CIR control more urgent. Furthermore, the signal-to-interference ratio (SIR) is a basic metric in wireless communication systems that evaluate signal quality when interference is present. Better signal quality is indicated by a higher SIR value, while more susceptibility to interference is indicated by a lower value. The effects of SIR on wireless communications are evident in a number of areas, including data speed, bit error rate (BER), and overall quality of service (QoS). [ABSTRACT FROM AUTHOR]

Medium-scale or large-scale receive antenna array with digital beamforming can be employed at receiver to make a significant interference reduction but leads to expensive cost and high complexity of the RF-chain circuit. To deal with this issue, classic analog-and-digital beamforming (ADB) structure was proposed in the literature for greatly reducing the number of RF-chains. Based on the ADB structure, in this paper, we propose a robust hybrid ADB scheme to resist directions of arrival (DOAs) estimation errors. The key idea of our scheme is to employ null space projection (NSP) in the analog beamforming domain and diagonal loading (DL) method in digital beamforming domain. The simulation results show that the proposed scheme performs more robustly, and moreover, it has a significant improvement on the receive signal-to-interference-plus-noise ratio compared to NSP ADB scheme and DL method.

Summary: With the advancement of mobile networks, the demand for increased throughput is continuously rising. Throughput is the amount of error‐free bits transmitted in a given period of time. Heterogeneous networks (HetNet) are widely accepted to enhance the throughput as they do have low pathloss among the others. HetNet deploys another cell under the coverage area of the macro cell. The HetNet offloads the macro cell that avoids congestion and enhances the coverage of the network. In HetNet, however, intercell interference is a major challenge that adversely degrades the throughput. In this paper, coordinated multipoint transmission (CoMP) along with a coordinated beamforming (CBF) is integrated to mitigate the intercell interference (ICI). In general, the results have shown that the proposed technique has resulted into significant interference reduction and hence improved throughput and spectral efficiency. [ABSTRACT FROM AUTHOR]

This article introduces a modular, direct time-of-flight (TOF) depth sensor. Each module is digitally synthesized and features a 2 $\times $ (8 $\times $ 8) single-photon avalanche diode (SPAD) pixel array, an edge-sensitive decision tree, a shared time-to-digital converter (TDC), 21-bit per-pixel memory, and in-locus data processing. Each module operates autonomously, by internal data acquisition, management, and storage, being periodically read out by an external access. The prototype was fabricated in a TSMC 3-D-stacked 45/65-nm CMOS technology, featuring backside illumination (BSI) SPAD detectors on the top tier, and readout circuit on the bottom tier. The sensor was characterized by single-point measurements, in two different modes of resolution and range. In low-resolution mode, a maximum of 300-m and 80-cm accuracy was recorded; on the other hand, in high-resolution mode, the maximum range and accuracy were 150 m and 7 cm, respectively. The module was also used in a flexible scanning light detection and ranging (LiDAR) system, where a 256 $\times $ 256 depth map, with millimeter precision, was obtained. A laser signature based on pulse-position modulation (PPM) is also proposed, achieving a maximum of 28-dB interference reduction. [ABSTRACT FROM AUTHOR]

The utilization of modal frequency sensors is a feasible and effective way to monitor the settlement problem of the transmission tower foundation. However, the uncertainties and interference in the real operation environment of transmission towers highly affect the accuracy and identification of modal frequency sensors. In order to reduce the interference of modal frequency sensors for transmission towers, a Kriging surrogate model is proposed in this study. The finite element model of typical transmission towers is created and validated to provide the effective original database for the Kriging surrogate model. The prediction accuracy and convergences of the Kriging surrogate model are measured and confirmed. Besides the merits in computational cost and high-efficiency, the Kriging surrogate model is proven to have a satisfied and robust interference reduction capacity. Therefore, the Kriging surrogate model is feasible and competitive for interference filtration in the settlement surveillance sensors of steel transmission towers. [ABSTRACT FROM AUTHOR]

Using light emitting diodes (LED) for the purpose of simultaneous communication and illumination is known as visible light communication (VLC). Interference by ambient light sources is among the most critical challenges. Owing to the wideband VLC spectrum, the efficiency of wavelength-dependent optical filtering is limited, especially in the presence of sunlight. Multi-user VLC causes additional interference, since LEDs are characterized by a wide viewing angle. Although algorithm-based interference suppression is a feasible method, receiver saturation and especially noise enhancement are two challenges that can only by addressed effectively by filtering in the optical domain prior to the photodetector. In this publication, we propose the use of a liquid-crystal display (LCD) as receiver-side filter unit. The main advantage of this technology is the possibility to focus the field-of-view of the receiver on a specific light source and thereby suppress interference. Interference by ambient light, modulated interference and multi-aperture interference are introduced and signal-to-interference ratio improvements are derived using experimental results for a given LCD characteristic. By deriving the bit error rate for MIMO communications, the potential of the proposed interference reduction method is demonstrated. [ABSTRACT FROM AUTHOR]

This study proposes a routing algorithm to enhance throughput and spectrum utilisation efficiency for underwater cognitive acoustic sensor networks (UCASNs). In a UCASN, each cognitive acoustic (CA) user would sense the medium to detect available spectrum resources. However, CA users have no exact knowledge about the communication mechanism of the primary users (PUs) such as sonar users or sonar interference sources. In addition, because of the frequency‐dependent attenuation, the available frequencies in water are severely limited and are still underutilised. Therefore, by analysing the behaviour of the CA users based on the ON–OFF process in the primary channel, an optimisation problem is derived to maximising the spectrum utilisation taking into account the bandwidth requirement of CA users. In this way, an efficient routing algorithm for UCASNs is proposed to enable throughput improvement of the network while reducing interference to PUs. Finally, simulation results are shown to verify the effectiveness of the authors proposed scheme. [ABSTRACT FROM AUTHOR]

In this paper, we study the outage performance of multiuser mixed underlay radio frequency (RF)/multidestinations free-space optical (FSO) links. For RF links, we consider a secondary network with multiple users that can communicate with multiple destinations through a relaying node. The relay is equipped with an antenna array at the RF side, and it uses the amplify-and-forward (AF) protocol. The primary users (PUs) are equipped with multiple antennas at transmit and receive nodes. The RF link is subjected to the aggregate PUs interference effect on the secondary network. To reduce the effect of PUs interference on secondary network at the relay node, two interference cancellation (IC) schemes are adopted, which vary in terms of complexity and achieved performance. On the other hand, the multidestination FSO links can be exploited to further enhance the quality of the second hop, and their associated channel models account for pointing errors, intensity modulation/direct detection, and heterodyne detection. For the aforementioned system model, we obtain exact and asymptotic closed-form expressions for the end-to-end outage probability. To further enhance system performance, optimal power allocation between the two hops is obtained based on the derived asymptotic outage probability expressions.

In this paper we document the design, development, results, performance and field applications of a compact directive transmit antenna for the long-range High Frequency ocean RADAR (HFR) systems operating in the International Telecommunication Union (ITU) designated 4MHz and 5MHz radiodetermination bands. The antenna design is based on the combination of the concepts of an electrically small loop with that of travelling wave antenna. This has the effect of inducing a radiated wave predominantly in a direction opposed to that of energy flow on the antenna structures. We demonstrate here that travelling wave design allows for a more compact antenna than other directive options, it has straightforward feed-point matching arrangements, and a flat frequency and phase response over an entire radiodetermination band. In situ measurements of the antenna radiation pattern, obtained with the aid of a drone, correlate well with those obtained from simulations, and show between 8dB and 30dB front-to-back suppression, with a 3dB beam width in the forward lobe of 100∘ or more. The broad-beam radiation pattern ensures proper illumination over the ocean and the significant front-to-back suppression guarantees reduced interference to terrestrial services. The proposed antenna design is compact and straight forward and can be easily deployed by minimal modifications of an existing transmission antenna. The design may be readily adapted to different environments due to the relative insensitivity of its radiation pattern and frequency response to geometric detail. The only downside to these antennas is their relatively low radiation efficiency which, however, may easily be compensated for by the available power output of a typical HFR transmitter. Antennas based on this design are currently deployed at the SeaSonde HFR sites in New South Wales, Australia, with operational ranges up to 200 km offshore despite their low radiating efficiency and the extremely low output power in use at these installations. Due to their directional pattern, it is also planned to test these antennas in phased-array Wellen RADAR (WERA) systems in both the standard receive arrays: where in-band radio frequency noise of terrestrial origin is impacting on data quality, and in the transmit array: to possibly simplify splitting, phasing and tuning requirements.

This paper addresses the issues of user association in multi-tier heterogeneous networks (HetNets) to reduce co-channel interference and provide load balancing for proactively offloading users onto mobile personal cells (mPC). Previously, much of the literature discussed the user' association problem for HetNets with conventional fixed small cells. The problem discussed in the existing literature is easy to analyze owing to fix nature of the small cells. In this paper, we focus on the mPC instead of fixed small cells, which complicates the user association problem due to its nature of mobility. In this paper, we propose the public safety (PS) users priority-based mPC user association (PS-UA) scheme for load balancing and interference reduction in highly fluctuating PS long-term evolution systems. The proposed scheme improves the user-association problem by minimizing call blocking probability (CBP) according to the network load conditions and PS user priority. Moreover, it further improves user signal-to-interference-and-noise ratio by implementing enhanced intercell interference coordination scheme to further reduce the interference to the offloaded users. System-level simulations confirmed the validity of the proposed PS-UA scheme, because it convincingly reduces the CBP for PS users as compared with the conventional static user association scheme.

When using a regenerative relay, a trade-off between increasing the energy efficiency versus reducing the generated interference arises. In this paper, the generated interference in the direct link from the base station to a user terminal is compared with the generated interference from both the base station and the relay node in regenerative relay transmissions. In the space of channel losses, in the transceivers' operating region, the lines corresponding to the generated interference ratio comparing the relay scheme and the direct link are depicted. It is shown that it is possible to tune the energy-efficiency vs generated interference trade-off, by adjusting the transmit powers, constellation size and code rate. The trade-off depends on the channel losses along the links. A key enabler of the trade-off is the appropriate placement of the relay node.

Abstract This paper addresses the Co-Channel Interference (CCI) reduction in Relay Assisted (R-A) cellular systems using Beamforming (BF) techniques. Analytical treatments are conducted. The network performance improvements through reducing the CCI are evaluated using three different configurations of applying BF. These configurations represent Relay Station (RS) do BF only, Base Station (BS) do BF only and both RS and BS do BF. Additionally, the considered BF techniques denote the horizontal, vertical, and Three Dimensional (3D) BF techniques. Therefore, each configuration consists of three different scenarios. Accordingly, nine different scenarios are studied. A comparison of these scenarios is introduced to enhance the network Quality of Service (QoS). Moreover, closed-form expressions for worst-cases Cell Edge User's (CEU's) Signal to Interference Ratio (SIR), Cell Center User's (CCU's) SIR and inner radius are implemented. Furthermore, various performance evaluation metrics are used to compare the different scenarios. The results reveal, that the performance of vertical BF is close to that of the 3D BF in low Path-loss (PL) exponent range. Therefore, applying vertical BF is preferable from the network cost and power consumption perspectives. Furthermore, it is observed, that the configuration of RS do BF is superior to other configurations when horizontal or vertical BF technique is employed. Additionally, the configuration of both RS and BS do BF outperforms the other configurations when 3D BF is applied. However, as unexpected it performs worse than them when the other BF techniques are applied. The work outcomes attain much higher CEU's SIR improvement. Therefore, the coverage probability is increased. Thus, more users can be served by the network. Accordingly, the total network cost is reduced. So, this treatment not only improves the network performance, but also it reduces the total network cost. [ABSTRACT FROM AUTHOR]

This paper reviews the background phenomenon of various cloaking techniques such as transformation optics, transmission line network, microwave network cloak, scattering cancellation techniques in the applications of antenna field particularly in hiding the obstacle from the electromagnetic source and reducing the mutual coupling between two antennas that was placed closed to each other. Cloaking at multiple frequencies in each cloaking techniques are also compared. The comparative study showed that the scattering cancellation technique based on aperiodic Frequency Selective Surfaces (FSS) structure will dominate the electromagnetic cloaking field in near future. [ABSTRACT FROM AUTHOR]

The utilization of modal frequency sensors is a feasible and effective way to monitor the settlement problem of the transmission tower foundation. However, the uncertainties and interference in the real operation environment of transmission towers highly affect the accuracy and identification of modal frequency sensors. In order to reduce the interference of modal frequency sensors for transmission towers, a Kriging surrogate model is proposed in this study. The finite element model of typical transmission towers is created and validated to provide the effective original database for the Kriging surrogate model. The prediction accuracy and convergences of the Kriging surrogate model are measured and confirmed. Besides the merits in computational cost and high-efficiency, the Kriging surrogate model is proven to have a satisfied and robust interference reduction capacity. Therefore, the Kriging surrogate model is feasible and competitive for interference filtration in the settlement surveillance sensors of steel transmission towers.

Using light emitting diodes (LED) for the purpose of simultaneous communication and illumination is known as visible light communication (VLC). Interference by ambient light sources is among the most critical challenges. Owing to the wideband VLC spectrum, the efficiency of wavelength-dependent optical filtering is limited, especially in the presence of sunlight. Multi-user VLC causes additional interference, since LEDs are characterized by a wide viewing angle. Although algorithm-based interference suppression is a feasible method, receiver saturation and especially noise enhancement are two challenges that can only by addressed effectively by filtering in the optical domain prior to the photodetector. In this publication, we propose the use of a liquid-crystal display (LCD) as receiver-side filter unit. The main advantage of this technology is the possibility to focus the field-of-view of the receiver on a specific light source and thereby suppress interference. Interference by ambient light, modulated interference and multi-aperture interference are introduced and signal-to-interference ratio improvements are derived using experimental results for a given LCD characteristic. By deriving the bit error rate for MIMO communications, the potential of the proposed interference reduction method is demonstrated.

In this paper, we study the outage performance of multiuser mixed underlay radio frequency (RF)/multidestinations free-space optical (FSO) links. For RF links, we consider a secondary network with multiple users that can communicate with multiple destinations through a relaying node. The relay is equipped with an antenna array at the RF side, and it uses the amplify-and-forward (AF) protocol. The primary users (PUs) are equipped with multiple antennas at transmit and receive nodes. The RF link is subjected to the aggregate PUs interference effect on the secondary network. To reduce the effect of PUs interference on secondary network at the relay node, two interference cancellation (IC) schemes are adopted, which vary in terms of complexity and achieved performance. On the other hand, the multidestination FSO links can be exploited to further enhance the quality of the second hop, and their associated channel models account for pointing errors, intensity modulation/direct detection, and heterodyne detection. For the aforementioned system model, we obtain exact and asymptotic closed-form expressions for the end-to-end outage probability. To further enhance system performance, optimal power allocation between the two hops is obtained based on the derived asymptotic outage probability expressions. [ABSTRACT FROM PUBLISHER]

Using multiple depth cameras can extend the field of view, which is beneficial to three-dimensional (3D) reconstruction. However, multiple active depth cameras would interfere with each other, which degrades the quality of depth images significantly. In this paper, we first present a depth extraction method based on sampling of the space at camera viewpoints to address the interference problem. Compared with the previous plane-sweeping method based on structured-light stereo and multiview stereo, depth images with less depth errors and better shape of objects are generated. Then, we analyze factors affecting depth accuracy for light-coding-based depth cameras and demonstrate the proposed depth extraction method also improves the accuracy of depth images by utilizing multiple projected patterns. Based on the analysis, subpixel-based matching (SPM) is finally applied to further improve the depth accuracy obtained by the depth extraction method. In the image matching process of our method, nearest neighbor interpolation is utilized to each projector's image plane to increase their resolution, which leads to the improved depth accuracy at subpixel level and avoids the drawbacks of changing parameters of light-coding-based depth cameras. Experimental results under simulated and real-world examples validate our analysis and show that the proposed method not only mitigates the impacts of interference effectively but also further improves the accuracy of depth images by using SPM. [ABSTRACT FROM PUBLISHER]

In this paper, we propose an interference reduction routing protocol for ad-hoc networks. The interference is one of the degradation factors in wireless communications. In the ad-hoc network, some nodes communicate simultaneously. Therefore, these communications cause interference each other, and some packets are corrupted due to interference from another node. In the proposed protocol, each node estimates required transmission power according to hello messages. Therefore, the node can transmit a data packet with minimum required transmission power. Consequently, the interference against neighbor nodes can be reduced. From simulation results, we can find that the proposed protocol can reduce the number of control messages and can improve the throughput performance.

The fifth-generation (5G) communications systems are expecting to support users with diverse quality-of-service (QoS) requirements. Beside these requirements, the task with utmost importance is to support the emergency communication services during natural or man-made disasters. Most of the conventional base stations are not properly functional during a disaster situation, so deployment of emergency base stations such as mobile personal cell (mPC) is crucial. An mPC having moving capability can move in the disaster area to provide emergency communication services. However, mPC deployment causes severe co-channel interference to the users in its vicinity. The problem in the existing resource allocation schemes is its support for static environment, that does not fit well for mPC. So, a resource allocation scheme for mPC users is desired that can dynamically allocate resources based on users’ location and its connection establishment priority. In this paper, we propose a public safety users priority-based context-aware resource allocation (PS-CARA) scheme for users sum-rate maximization in disaster environment. Simulations results demonstrate that the proposed PS-CARA scheme can increase the user average and edge rate around 10.3% and 32.8% , respectively because of context information availability and by prioritizing the public safety users. The simulation results ensure that call blocking probability is also reduced considerably under the PS-CARA scheme.

Dense wireless local area networks (WLANs) have emerged as a promising design paradigm recently. While partially overlapped channels (POCs) have proved to be able to improve network capacity significantly in the dense network, they are usually considered the fixed number of access points (APs) in traditional research works. The network capacity can be scaled by providing additional APs in a given area since the expected distance from users to the associated APs becomes shorter. On the other hand, the additional increment of network capacity by means of deploying more APs is limited. It can be accredited to the substantial interference among the high number of deployed APs assigned with POCs. Furthermore, the impact of the POC model makes the design more complex. To cope with these challenges in this work, we study the problem of interaction between density of APs and POC assignment with parameter tuning and propose the approach called DAPA, in which we derive that the optimal density of APs lies in the feasible region consisting of the lower bound and upper bound density. Thus, the solution can be obtained by searching for the feasible region by means of the proposed POC assignment. Through analysis and numerical results in DAPA, we provide recommendations on the optimal dimension of high density and POC assignment, with consideration of the network configuration. [ABSTRACT FROM AUTHOR]

In this paper, a generalized spectral subtraction approach for reducing additive impulsive noise, narrowband signals, white Gaussian noise and DS-CDMA interferences in MIMO channel DS-CDMA wireless communication systems is investigated. The interference noise reduction or suppression is essential problem in wireless mobile communication systems to improve the quality of communication. The spectrum subtraction scheme is applied to the interference noise reduction problems for noisy MIMO channel systems. The interferences in space and time domain signals can effectively be suppressed by selecting threshold values, and the computational load with the FFT is not large. Further, the fading effects of channel are compensated by spectral modification with the spectral subtraction process. In the simulations, the effectiveness of the proposed methods for the MIMO channel DS-CDMA is shown to compare with the conventional MIMO channel DS-CDMA.

The beam system of multiple input and multiple output (MIMO) radar needs lower peak sidelobe level for reducing interference, in addition, broad nulls placed at undesired directions are also an alternative method. A hybrid method based on the whale optimisation algorithm is proposed to implement sidelobe suppression and broad nulls. To the best of the authors' knowledge, relative works based on the whale optimisation algorithm applied to MIMO radar are not reported so far. By introducing chaotic optimisation into the whale optimisation algorithm scheme, performance of origin algorithm is improved substantially in suppressing peak sidelobe level with constraint of broad nulls. Furthermore, it is found in the experiment that the proposed algorithm can avoid the premature of origin algorithm effectively, and only takes a short time during the optimum accomplishment. Finally, simulation results demonstrate the good performance of the proposed method. [ABSTRACT FROM AUTHOR]

The paper presents the methodology including the deployment of a structure comprising of C-clamp magnetic stripes and a self-calibration scheme using a four-coil design to resolve the issues of the interference and misplacement problems existing in the flexible nonintrusive current sensor tag for the current detection of household two-wire power lines. Experimental results show that the stripe structure can effectively screen out the magnetic flux originating from the nearby power line for the reduction of sensing error caused by the electromagnetic field interference and the calibration scheme containing the correction of horizontal misplacement and the analysis of power cable thickness via the four-coil design can provide the information of sensor location for accurate current sensing. Less than 4% of sensing error indicates that the proposed methodology can indeed facilitate the flexible current sensor tag for practical use. [ABSTRACT FROM PUBLISHER]

Mobile ad hoc networks (MANETs) are networks that are created on the fly (ad hoc) between various mobile nodes and do not require infrastructure. The mobile nodes can move around, and the network would automatically reconfigure itself to allow connectivity. Vehicular ad hoc networks (VANETs) are a subclass of MANETs that is expected to have a key role in the intelligent transportation systems of the future. VANETs provide vehicle-to-vehicle and vehicle-to-roadside communication in order to support safety and comfort applications. Despite being a subclass of MANETs, VANETs have fundamentally different behavior. This paper presents a scheme consisting of a media access control protocol and a clustering algorithm designed to reduce interferences in VANETs. Our scheme, which is intended for safety applications in highway environments, employs dynamic multihop clustering, allows better utilization of network resources, and improves network performance. [ABSTRACT FROM PUBLISHER]

Energy conservation and interference reduction are the two important goals of any topology control algorithms in wireless multi-hop sensor networks, but impacts of network traffic load on interference have been largely ignored in mostly all previous works on topology control algorithms. Inspired by this challenge, we set out to investigate the impact of traffic load on nodes' energy consumption and having demonstrated its significance and, a relation between traffic load and interference was established by using collision numbers. Then we went on to formulate an optimization model for our topology control with the goal of minimizing the maximum power consumption among network's nodes. Analysis showed that due to the NP-hardness of the preliminary model it could not be used to achieve our objective in a reasonable time span. Thus, to overcome the shortcoming of optimization model, a novel heuristic algorithm called cell based optimization tree (CBOT) was finally introduced that was capable of constructing a suboptimal topology in a reasonable time bound by considering traffic load and interference. Simulation results verified superiority of the proposed approach over a number of reported techniques in the literature. [ABSTRACT FROM AUTHOR]