Use Of Directional Antennas Research Articles

Beam-Tracking Challenges in THz Communications

In recent years, the demand for high data rates has increased drastically. In response to this increasing demand, higher frequencies, such as millimeter wave (mmWave) and terahertz (THz) have been considered that offer much larger bandwidth and potentially much higher data rates. Nevertheless, with the increase in frequency, the pathloss increases significantly, with the non-line-of-sight (nLoS) incurring attenuation levels that can dramatically reduce the quality of a wireless link. The use of directional antennas to counteract the increased pathloss is widely accepted. However, highly directional beams are prone to misalignment and a method to track the tracking object (TO) of the link with consistency, accuracy and low overhead is needed. To this end, the design of beam-tracking algorithms has been proposed. In this work, the main parameters that affect the reliability of beam-tracking are presented along with the challenges that beam-tracking algorithms need to address. Furthermore, the performance merits with respect to three reliability parameters are presented in the case of a simple beam-tracking algorithm.

Directional link attenuation in millimeter-wave range based on empirical model modification

The upcoming fifth and next generation mobile phone systems will use not only the frequencybands of sub-6 GHz but also the millimeter-wave and terahertz bands. From a practical viewpoint,this approach requires the use of directional antennas or beamforming systems. To ensure greaterenergy efficiency of the wireless link, the radio beams on the transmitting and receiving sides shouldbe aligned ones. Path loss models are commonly used for designing the radio communication systemsand networks. However, in the literature, there are no adequate methods of attenuation modellingavailable for the cases of misalignment of antenna beams. In this paper, a method of modifying the pathloss model, based on a multi-elliptical propagation model, is proposed. For this purpose, dedicatedsoftware was developed in the MATLAB environment, which was used to conduct simulation tests.In the remainder of the paper, exemplary results of the adaptation of empirical path loss models inthe range of millime-ter-waves are presented, which were obtained using the developed program.Keywords: wireless communication, radio wave propagation, path loss models, multi-ellipticalpropagation model, directional antennas, directional radio link, millimeter waves, 5G systems,simulation studies

Design of Directional Antennas for Wireless Sensor Networks and the Internet of Things Experiments

The use of directional antennas (DAs) in wireless sensor networks (WSN) and Internet of Things (IoT) applications has been proposed widely in the literature. However, testbed setup for experimental validation is challenging due to the unavailability of a DA module for WSNs. In this letter, a DA is designed using a 2.4-GHz patch antenna and conducting cavity mesh. The dimensions and design of the mesh are optimized using CST Studio Suite SE. The simulated results show the beamwidth of the directional antenna is 60 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$^\circ$</tex-math></inline-formula> , and its directivity is 9.43. Further, a DA is made experimentally with commonly available 2.4-GHz WSN modules by combining them with a conducting cavity. The experimental measurements of the radiation pattern confirm the simulated results.

A beam-tracking framework for THz networks

Millimeter wave (mmWave) and terahertz (THz) frequencies are attractive for increased bandwidth applications, however are vulnerable to blockage and suffer from high pathloss. While the use of directional antennas can potentially mitigate these effects, the need for careful alignment becomes crucial, especially when the user moves. In this context, to ensure a reliable link, several parameters must be taken into account, such as the type of user’s motion, the location of the access point (AP), the shape of the area, the beamwidth, etc. In this work, the link reliability is divided into two main categories, the trajectory tracking resolution and the angular resolution. To address the challenges of both categories, a beam-tracking algorithm that promises high tracking reliability and low pilot overhead is proposed. The algorithm employs multiple cooperating APs and a hierarchical codebook and the performance of the proposed tracking method is evaluated through Monte-Carlo simulations with the probability of success, the average number of pilots per timeslot and the mean square error (MSE) as metrics, for different tracking estimation frequencies and different number of blocked links.

Initial Access &amp; Beam Alignment for mmWave and Terahertz Communications

The initial access in Millimeter wave (mmWave) 5G communications is very challenging and time consuming. In general, mmWave and terahertz communications require the use of directional antennas to seek narrow beams. However, due to this directionality, many issues can impact the beam alignment between transmitter and receiver. In this paper, we present a comprehensive survey of beam alignment and initial access in mmWave and terahertz 5G/6G systems. First, we present a detailed overview of initial access methods, techniques, and beam management procedures. Then, we classify recent works related to beam alignment based on their objective functions (i.e., latency, power allocation, QoS, energy consumption, cost). We also highlight the beam alignment in terahertz 6G, where we find that deep learning and reconfigurable intelligent surface are the two protagonists that help to achieve fast beam alignment.

Towards Environmental RF-EMF Assessment of mmWave High-Node Density Complex Heterogeneous Environments.

The densification of multiple wireless communication systems that coexist nowadays, as well as the 5G new generation cellular systems advent towards the millimeter wave (mmWave) frequency range, give rise to complex context-aware scenarios with high-node density heterogeneous networks. In this work, a radiofrequency electromagnetic field (RF-EMF) exposure assessment from an empirical and modeling approach for a large, complex indoor setting with high node density and traffic is presented. For that purpose, an intensive and comprehensive in-depth RF-EMF E-field characterization study is provided in a public library study case, considering dense personal mobile communications (5G FR2 @28 GHz) and wireless 802.11ay (@60 GHz) data access services on the mmWave frequency range. By means of an enhanced in-house deterministic 3D ray launching (3D-RL) simulation tool for RF-EMF exposure assessment, different complex heterogenous scenarios of high complexity are assessed in realistic operation conditions, considering different user distributions and densities. The use of directive antennas and MIMO beamforming techniques, as well as all the corresponding features in terms of radio wave propagation, such as the body shielding effect, dispersive material properties of obstacles, the impact of the distribution of scatterers and the associated electromagnetic propagation phenomena, are considered for simulation. Discussion regarding the contribution and impact of the coexistence of multiple heterogeneous networks and services is presented, verifying compliance with the current established international regulation limits with exposure levels far below the aforementioned limits. Finally, the proposed simulation technique is validated with a complete empirical campaign of measurements, showing good agreement. In consequence, the obtained datasets and simulation estimations, along with the proposed RF-EMF simulation tool, could be a reference approach for the design, deployment and exposure assessment of the current and future wireless communication technologies on the mmWave spectrum, where massive high-node density heterogeneous networks are expected.

Improving Sensor Network Performance with Directional Antennas: A Cross-layer Optimization

The use of directional antennas for wireless communications brings several benefits, such as increased communication range and reduced interference. One example of directional antennas are electronically switched directional (ESD) antennas that can easily be integrated into Wireless Sensor Networks (WSNs) due to their small size and low cost. However, current literature questions the benefits of using ESD antennas in WSNs due to the increased likelihood of hidden terminals and increased power consumption. This is mainly because earlier studies have used directionality for transmissions but not for reception. In this article, we introduce novel cross-layer optimizations to fully utilize the benefits of using directional antennas. We modify the Medium Access Control (MAC) , routing, and neighbor discovery mechanisms to support directional communication. We focus on convergecast investigating a large number of different network topologies. Our experimental results, both in simulation and with real nodes, show when the traffic is dense, networks with directional antennas can significantly outperform networks with omnidirectional ones in terms of packet delivery rate, energy consumption, and energy per received packet.

Internet of Maritime Things Platform for Remote Marine Water Quality Monitoring

In this article, we show the development and implementation of the Internet of Maritime Things (IoMT) platform that supports long-range and high-rate communication for remote and online marine water quality monitoring. We first develop the IoMT device and gateway that interwork with international standard Internet-of-Things (IoT) software platforms for universal utilization in the field of marine monitoring. The proposed IoMT device and gateway play a role similar to the IoT device and gateway on land, but it is optimized for marine use with consideration of the practical characteristics of using sensors in the ocean. Furthermore, to realize long-range and high-rate communication between marine sensors and a control center (CC) on land, an automatic beam adjustment system for directional antennas is developed. This enables the use of directional antennas, which can support long-range and high-rate communication by automatically adjusting the beam angle between the antennas while exchanging their control information, despite the antennas being shifted by undulation from the sea. Finally, we conduct real sea experiments to identify the performances of the proposed IoMT platform in various environments. The results show that the proposed IoMT platform can collect data from marine sensors as well as high definition camera video from distances of 25 and 40 km to the CC on land under one-hop and two-hop transmissions, respectively. These results indicate that the proposed IoMT platform provides at least twofold performance improvement in terms of communication coverage under a similar data rate condition, compared with existing commercial wireless networks (e.g., LTE in the ocean) not utilizing satellite communications.

ADAPT: An Adaptive Directional Antenna Protocol for medium access control in Terahertz communication networks

Terahertz (THz)-band (0.1–10 THz) communication is envisioned as a key technology for the next generation of wireless communications, with the potential to enable Terabit-per-second (Tbps) links. To overcome the high path loss of this band, the use of directional antennas on both transmitter and receiver is necessary even for distances of few meters. This paper presents an Adaptive Directional Antenna Protocol for THz networks (ADAPT), a novel medium access control (MAC) protocol tailored to ultra-high-speed directional networks in a centralized architecture. An access point with a turning antenna divides the space in sectors, and synchronization is achieved with a 3-way receiver-initiated handshake. The protocol implements adaptive sector time and modulation mechanisms. An analytical model to study the stability condition and achievable throughput is presented. The performance of ADAPT is investigated with extensive simulations in ns-3 in terms of throughput and discard rate, using the physical layer defined in IEEE 802.15.3d, the first standard for THz communications. Results show that the proposed solution improves the current protocols and achieves throughput in excess of 100 Gigabit-per-second (Gbps), while reducing latency and packet discard rate.

EFFICIENT mmWAVE BEAM TRACKING FOR 5G AND BEYOND WIRELESS SYSTEMS

Recently, 60 GHz wireless networks have drawn much attention due to availability of huge bandwidth around 60 GHz frequency band which has ability to support very high data rate, i.e., up to 6.7 Gbps. This is also called millimetre wave (mmWave) networking which paves the way for realization of Gigabit WLANs. However, heavy attenuation at 60 GHz frequency band limits the range of transmitted signal up to few meters. In order to extend the range of 60 GHz signal, use of directional antennas have been suggested as the most viable solution. Directional antennas use array of antennas to beamform in a particular direction. The difficulty arises when a user is moving. It is a challenging task to track the movement of a user and thus direct the beam in intended direction. According to the IEEE802.11 ad standard, each deployed mmWave AP in the target environment performs an exhaustive beam forming training (BT) to track the moving user to maintain the link. In this paper, we propose a mmWave user tracking scheme in outdoor environment based on the previous user equipment (UE) context information’s. Where, the preceding beam ID directions used to predict a group of mmWave Tx beams to search on them to find out the best beam ID for the next UE location. Simulations show that the proposed scheme highly reduces BT complexity comparable to conventional scheme with conversing almost same performance.

Virtual Sensing Directional Hub MAC (VSDH-MAC) Protocol with Power Control

Medium access control (MAC) protocols play a vital role in making effective use of a multiple access channel as it governs the achievable performance such as channel utilization and corresponding quality of service of wireless sensor networks (WSNs). In this paper, a virtual carrier sensing directional hub (VSDH) MAC protocol incorporating realistic directional antenna patterns is proposed for directional single hub centralized WSNs. While in most instances, MAC protocols assume idealized directional antenna patterns, the proposed VSDH-MAC protocol incorporates realistic directional antenna patterns to deliver enhanced link performance. We demonstrate that the use of directional antennas with a suitable MAC protocol can provide enhanced communication range and increased throughput with reduced energy consumption at each node, compared to the case when only omnidirectional antennas are used. For the scenarios considered in this study, results show that the average transmit power of the sensor nodes can be reduced by a factor of two, and at the same time offer significantly extended lifetime.

Different Energy Saving Schemes in Wireless Sensor Networks: A Survey

Wireless sensor networks (WSNs) are one of the very active research area. They have many applications like military, health care, environmental monitoring and industrial monitoring. The sensor nodes have limited energy source. Since in many cases the nodes are deployed in unreachable areas, hence recharging or replacing the battery of the sensor nodes is not an option. Therefore, one must employ techniques to conserve the energy by reducing the energy consumption by the nodes. In this paper, we discuss about the different energy saving schemes investigated by different research community in WSNs to reduce the energy consumption of the nodes and thereby improving the lifetime of the overall network. Energy saving protocols such as duty cycle, energy efficient routing, energy efficient medium access control (MAC), data aggregation, cross layer design and error control code (ECC) are discussed. Sleep/wake up method is adopted by the duty cycle approach to reduce the active time of the nodes and conserve their energy. The routing and MAC protocols use suitable energy efficient algorithms for saving energy. The data aggregation aims to save energy by reducing the number of transmissions. On the other side, cross layer approach looks for a cross layer optimization solution to improve the energy efficiency of the network. ECC reduces energy consumption by virtue of coding gain it offers which allows lower signal-to-noise ratio (SNR) to achieve the same bit error rate (BER) as an uncoded system. Some techniques such as use of directional antennas, topology control and transmission power control which have been widely investigated for other ad-hoc networks for energy conservation are also discussed in brief in this paper.

From 2G to 5G Spatial Modeling of Personal RF-EMF Exposure Within Urban Public Trams

The upcoming design and implementation of the new generation of 5G cellular systems, jointly with the multiple wireless communication systems that nowadays coexist within vehicular environments, leads to Heterogeneous Network challenging urban scenarios. In this framework, user's Radiofrequency Electromagnetic Fields (RF-EMF) radiation exposure assessment is pivotal, to verify compliance with current legislation thresholds. In this work, an in-depth study of the E-field characterization of the personal mobile communications within urban public trams is presented, considering different cellular technologies (from 2G to 5G). Specifically, frequency bands in the range of 5G NR frequency range 1 (FR1) and millimeter wave (mm-wave) bands within frequency range 2 (FR2) have been analyzed for 5G scenarios, considering their dispersive material properties. A simulation approach is presented to assess user mobile phone base station up-link radiation exposure, considering all the significant features of urban transportation trams in terms of structure morphology and topology or the materials employed. In addition, different user densities have been considered at different frequency bands, from 2G to 5G (FR1 and FR2), by means of an in-house developed deterministic 3D Ray-Launching (3D-RL) technique in order to provide clear insight spatial E-field distribution, including the impact in the use of directive antennas and beamforming techniques, within realistic operation conditions. Discussion in relation with current exposure limits have been presented, showing that for all cases, E-Field results are far below the maximum reference levels established by the ICNIRP guidelines. By means of a complete E-field campaign of measurements, performed with both, a personal exposimeter (PEM) and a spectrum analyzer within a real tram wagon car, the proposed methodology has been validated showing good agreement with the experimental measurements. In consequence, a simulation-based analysis methodology for dosimetry estimation is provided, aiding in the assessment of current and future cellular deployments in complex heterogeneous vehicular environments.

Hybrid area exploration–based mobility‐assisted localization with sectored antenna in wireless sensor networks

SummaryIn common practice, sensor nodes are randomly deployed in wireless sensor network (WSN); hence, location information of sensor node is crucial in WSN applications. Localization of sensor nodes performed using a fast area exploration mechanism facilitates precise location‐based sensing and communication. In the proposed localization scheme, the mobile anchor (MA) nodes integrated with localization and directional antenna modules are employed to assist in localizing the static nodes. The use of directional antennas evades trilateration or multilateration techniques for localizing static nodes thereby resulting in lower communication and computational overhead. To facilitate faster area coverage, in this paper, we propose a hybrid of max‐gain and cost‐utility–based frontier (HMF) area exploration method for MA node's mobility. The simulations for the proposed HMF area exploration–based localization scheme are carried out in the Cooja simulator. The paper also proposes additional enhancements to the Cooja simulator to provide directional and sectored antenna support. This additional support allows the user with the flexibility to feed radiation pattern of any antenna obtained either from simulated data of the antenna design simulator, ie, high frequency structure simulator (HFSS) or measured data of the vector network analyzer (VNA). The simulation results show that the proposed localization scheme exhibits minimal delay, energy consumption, and communication overhead compared with other area exploration–based localization schemes. The proof of concept for the proposed localization scheme is implemented using Berkeley motes and customized MA nodes mounted with indigenously designed radio frequency (RF) switch feed network and sectored antenna.

New Radio Beam-Based Access to Unlicensed Spectrum: Design Challenges and Solutions

This paper elaborates on the design challenges, opportunities, and solutions for New Radio-based access to Unlicensed spectrum (NR-U) by taking into account the beam-based transmissions and the worldwide regulatory requirements. NR-U intends to expand the applicability of 5th generation New Radio access technology to support operation in unlicensed bands by adhering to Listen-Before-Talk (LBT) requirements for accessing the channel. LBT was already adopted by different variants of 4th generation Long Term Evolution (LTE) in unlicensed spectrum, i.e., Licensed-Assisted Access and MulteFire, to guarantee fair coexistence among different radio access technologies. In the case of beam-based transmissions, the NR-U coexistence framework is significantly different as compared to LTE in unlicensed spectrum due to the use of directional antennas, which enhance the spatial reuse but also complicate the interference management. In particular, beam-based transmissions are needed in the unlicensed spectrum at millimeter-wave (mmWave) bands, which is an attractive candidate for NR-U due to its large amount of allocated spectrum. As a consequence, some major design principles need to be revisited to address coexistence for beam-based NR-U. In this paper, different problems and the potential solutions related to channel access procedures, frame structure, initial access procedures, re-transmission procedures, and scheduling schemes are discussed. A simulation evaluation of different LBT-based channel access procedures for NR-U/Wi-Fi indoor mmWave coexistence scenarios is also provided.

Learning Automaton-Based Neighbor Discovery for Wireless Networks Using Directional Antennas

This letter studies the problem of neighbor discovery (i.e., finding 1-hop neighbor nodes) in a wireless adhoc network, with exclusive use of directional antennas. We model the neighbor discovery process as a learning automaton, operating in a non-stationary learning environment with unknown dynamics. The node learns about its environment from its past observations and adjusts its strategy to achieve a faster discovery rate. The asymptotic behavior of the proposed learning scheme is analyzed and is shown to converge to an equi-probable probability distribution. The proposed scheme achieves significantly faster network-wide neighbor discovery in densely populated networks.

Centralized Cooperative Directional Spectrum Sensing for Cognitive Radio Networks

Most previous spectrum sensing techniques use omni-directional antennas. Unlike omni-directional antennas, the use of directional antennas for spectrum sensing is a promising technique that can realize fine-grained sensing for the primary user (PU) with a longer sensing range. In this paper, we propose a centralized cooperative directional sensing technique for cognitive radio networks. We assume that one secondary coordinator called the fusion center (FC), gathers sensing results from secondary nodes. Using the reported information, the FC optimizes the sensing period, sensing power, and sensing beams per secondary node. For optimization, we use a modified gradient descent method with numerical methods to solve the nonlinear optimization problem. The simulation results show that our directional spectrum sensing technique is well suited for the existing cognitive radio environment. The optimal scheme shows proposed here better performance in all simulation factors than the non-optimized scheme.

Game theoretic approach of eavesdropping attack in millimeter-wave-based WPANs with directional antennas

In this paper, we propose a game theoretic framework to analyze a passive eavesdropping attack in millimeter-wave-based wireless personal area networks. As the interaction between defenders and attackers in network security issues can be considered as a game, devices can be considered as players. Usually a player has insufficient information of other players such as strategies and payoffs especially in static situation. We assume that each player selects its strategy based on its belief about the information on opponents and the belief is known as a prior probability. The Bayesian game model is a relevant framework for this situation. It is assumed that each device is equipped with a directional antenna and knows the channel state. In the analysis, the exposure region (ER) that is determined by the antennas directions of players is considered and the ratio of ER for the total area of a network is calculated by using the probability density function of distance between players. The optimal strategies of two players, a transmitter and an eavesdropper, are derived in terms of Bayesian Nash equilibriums and payoffs for the players are computed for pure and mixed strategies in static situation. The analysis shows how the effects of using a directional antenna and the prior probability of transmitters belief are involved in the Nash equilibriums. Numerical results show the equilibriums and two players payoffs. Those values depend on several parameters such as beamwidth and prior probability of belief as well as its opponents strategies. It also shows the effect of directional antennas in the eavesdropping attack; the use of directional antenna seems to increase the transmitters payoff, while it seems to decrease the eavesdroppers payoff. The obtained results will provide the criteria for selecting appropriate strategy to transmitters when an eavesdropper exists in the network.

Elastic Routing in Ad Hoc Networks with Directional Antennas

Throughput scaling laws of an ad hoc network equipping directional antennas at each node are analyzed. More specifically, this paper considers a general framework in which the beam width of each node can scale at an arbitrary rate relative to the number of nodes. We introduce an elastic routing protocol, which enables to increase per-hop distance elastically according to the beam width, while maintaining an average signal-to-interference-and-noise ratio at each receiver as a constant. We then identify fundamental operating regimes characterized according to the beam width scaling and analyze throughput scaling laws for each of the regimes. The elastic routing is shown to achieve a much better throughput scaling law than that of the conventional nearest-neighbor multihop for all operating regimes. The gain comes from the fact that more source–destination pairs can be simultaneously activated as the beam width becomes narrower, which eventually leads to a linear throughput scaling law. In addition, our framework is applied to a hybrid network consisting of both wireless ad hoc nodes and infrastructure nodes. As a result, in the hybrid network, we analyze a further improved throughput scaling law and identify the operating regime where the use of directional antennas is beneficial. In addition, we perform numerical evaluation in both ad hoc and hybrid networks, which completely validates our analytical results.

Interference-Aware Wireless Network-on-Chip Architecture Using Directional Antennas

Wireless Network-on-Chip (WiNoC) has been recently introduced for addressing the scalability limitations of conventional multi-hop NoC architectures. Existing WiNoC architectures generally use millimeter-wave antennas without significant directional gains, along with token passing protocol to access the shared wireless medium. This limits the achievable performance benefits since only one wireless pair can communicate at a time. It is also not practical in the immediate future to arbitrarily scale up the number of non-overlapping channels by designing transceivers operating in disjoint frequency bands in the millimeter-wave spectrum commonly adopted for on-chip wireless interconnects. Consequently, we explore the use of directional antennas whereby multiple wireless interconnect pairs can communicate simultaneously. However, concurrent wireless communications can result in interference. This can be minimized in NoC by optimal placement of wireless interfaces (WIs) to maximize performance while minimizing interference. To address this, we propose an interference-aware WIs placement algorithm with routing strategy for WiNoC architecture by incorporating directional planar log-periodic antennas (PLPAs). This directional wireless network-on-chip (DWiNoC) architecture enables point-to-point links between transceivers and hence multiple wireless links can operate at the same time without interference.