With the rapid development of modern electronic technologies,antenna arrays typically operate in very complex electromagnetic environments.However,owing to the various errors such as systematic errors and random errors,conventional antenna arrays have relatively high sidelobes.Time modulated arrays (TMAs),also known as four-dimensional (4-D) antenna arrays,introduce time as an additional dimension for generating ultra-low sidelobes at fundamental component and realizing real-time beam scanning by harmonic components.Recently,the harmonic components can also be developed for various new applications including wireless communications and radar systems.In this review,we introduce comprehensively the fundamental methodologies and recent applications of TMAs.This aims to stimulate continuing efforts for the understanding of TMAs and explore their applications in various aspects.The methods mentioned in this review include three aspects:sideband radiation suppression,power efficiency of TMAs,and applications of harmonic components.These methods either improve the existing TMAs or promote the practical applications of TMAs.First,to suppress the sideband radiation,a method using non-uniform periodical modulation is introduced.The proposed method has an advantage of low computation and can be easily used for synthesizing a real-time radiation pattern according to the environmental need.Next,a TMA structure using reconfigurable power dividers/combiner is introduced to improve the power efficiency of feeding network.Finally,three applications of harmonic component including direction finding,calibration method,and space division multiple access are separately introduced to illustrate the development potential of TMAs.

This paper presents an overview of the recent advances in reconfigurable antennas for wireless communications at University of Technology Sydney.In particular,it reports our latest progress in this research field,including a multi-linear polarization reconfigurable antenna,a pattern reconfigurable antenna with multiple switchable beams,and a combined pattern and polarization reconfigurable antenna.

In this review,research progress on the wideband wide-angle scanning two-dimensional phased arrays is summarized.The importance of the wideband and the wide-angle scanning characteristics for satellite communication is discussed.Issues like grating lobe avoidance,active reflection coefficient suppression and gain fluctuation reduction are emphasized in this review.Besides,techniques to address these issues and methods to realize the wideband wide-angle scanning phased array are reviewed.

A dual-polarized multiple-input multipleoutput(MIMO)antenna is proposed for 5G base stations.Each antenna element consists of two orthogonally placed fan-shaped dipole elements and ±45°dual-polarized feeding structures are used to achieve broadband operation.The resonant frequency of the array element is from 3.3 to 4.2 GHz,which covers the mainstream spectrum allocations of 5G mobile networks.H-shaped coupling elements are used to improve the isolation between the neighboring antenna elements and the mutual coupling is reduced by over 4 dB.The envelope correlation of a 2 × 2 array is provided for verification.

In this paper,a multiple fan-beam antenna array is proposed for massive multiple-input multipleoutput(MIMO)applications.The proposed array is based on vertical spatial filtering to reduce radio frequency complexity in a massive MIMO system.A microstrip line feeding network is utilized to achieve a specific phase distribution for multiple fan beams.A 64-element antenna array is designed and fabricated to validate the design strategy.The proposed antenna array uses 16 ports to excite 64 antenna elements,which is more cost effective than traditional massive MIMO systems.The measured results demonstrate that the proposed antenna array can achieve two fan beams at 7 in the vertical dimension,and the measured gain of every port exceeds 10 dBi at 2.6 GHz.

The state of art pertaining to vertical handover decisions in next-generation wireless networks provides a detailed overview of vertical handover studies.This paper classifies the research initiatives under the vertical handover decision mechanism for heterogeneous wireless networks.A fair comparison of traditional and recent techniques is drafted to obtain direction of the vertical handover decision.Several issues related to seamless support on mobility management techniques have been described in the literature.The next-generation wireless network promises to offer enhanced data services compared to other networks in mobile communication.Since all next generation network (NGN) is an IP-based network,challenges drive toward providing quality of service in the handover process.The necessity of handover process is a seamless connection.The handover operations that minimize or even target the elimination of delay in new network connection establishment are most welcomed.However,frequent disconnection and inefficient seamless handovers result in handover operation failures.Most of the existing methods on handover decisions are based on mobile-controlled handovers.Here,the decisions are in-corporate in the mobile devices.Several mobile-controlled handovers take a single parameter or two or more additional parameters as a combination to evaluate the policy decision.These approaches are carefully studied and classified.

Motion compensation based on the parameter estimation of a moving target has a strong influence on the inverse synthetic aperture radar (ISAR) imaging quality.For the target with built-in disturbance components or under an extremely low signal-to-noise ratio (SNR),conventional parameter estimation methods based on cross-correlation processing of adjacent profiles,such as the cross-correlation method and the accumulated cross-correlation method,give sizable aligned errors and subsequently produce low-quality ISAR images.The fractional Fourier transform is capable of concentrating the signal power; however,a large computational complexity is induced by searching the matched order.In view of the problems above,a time-weighting symmetric accumulated cross-correlation method is proposed herein.This method maps the spectrum of the range profile into a single-peak envelope to reduce range alignment errors,and presents a symmetric accumulated manner to offset the accumulated error.The simulation results demonstrate that the proposed method yields much better estimation precision than other methods,and yields extremely low computational complexity.

Integrated satellite and terrestrial networks can be used to solve communication problems in natural disasters,forestry monitoring and control,and military communication.Unlike traditional communication methods,integrated networks are effective solutions because of their advantages in communication,remote sensing,monitoring,navigation,and all-weather seamless coverage.Monitoring,urban management,and other aspects will also have a wide range of applications.This study first builds an integrated network overlay model,and divides the satellite network into two categories: terrestrial network end users and satellite network end users.The energy efficiency,throughput,and signal-to-noise ratio (SINR) are deduced and analyzed.In this paper,we discuss the influence of various factors,such as transmit power,number of users,size of the protected area,and terminal position,on energy efficiency and SINR.A satellite-sharing scheme with a combination of the user location and an exclusion zone with high energy efficiency and anti-jamming capability is proposed to provide better communication quality for end users in integrated satellite and terrestrial networks.

Routing in wireless sensor networks plays a crucial role in deploying and managing an efficient and adaptive network.Ensuring efficient routing entails an ever-increasing necessity for optimized energy consumption and reliable resource management of both the sensor nodes and the overall sensor network.An efficient routing solution is characterized by its ability to increase network lifetime,enhance efficiency,and ensure the appropriate quality of service.Therefore,the routing protocols need to be designed with an ultimate objective by considering and efficiently managing many characteristics and requirements,such as fault tolerance,scalability,production costs,and others.Unfortunately,many of the existing solutions lead to higher power consumption and communication control overheads,which not only increase network congestion but also decrease network lifetime.In addition,most of these protocols consider a limited number of criteria,in contrast to the complexity and the evolution of WSNs.This paper presents a new adaptive and dynamic multi-criteria routing protocol.Our protocol operates in multi-constraint environments,where most of the current solutions fail to monitor successive and continuous changes in network state and user preferences.This approach provides a routing mechanism,which creates a routing tree based on the evaluation of many criteria.These criteria can cover the topological metrics of neighboring nodes (the role of the nodes in intracommunications,connections between different parts of the network,etc.),the estimated power consumption to reach each direct neighbor,the path length (number of hops to the sink),the remaining energy of individual sensor nodes,and others.These criteria are controlled and supervised dynamically through a detection scheme.In addition,a dynamic selection mechanism,based on multi-attribute decision-making methods,is implemented to build and update the routing tree.In response to changes in the network state,user preferences,and application-defined goals,the election mechanism provides the best routing neighbor between each node and the sink.

Wireless Multimedia Sensor Networks (WMSN) are designed to transmit audio and video streams,still images,and scalar data.Multimedia transmission over wireless sensor networks has many applications,such as video surveillance,object tracking,telemedicine,theft control systems,and traffic monitoring.Researchers face many challenges,such as higher data rates,lower energy consumption,reliability,signal detection and estimation,uncertainty in network topology,quality of service(QoS),and security-and privacy-related issues to accomplish various applications of WMSN.This paper presents multiple input multiple output (MIMO) along with compressive sensing(CS)properties to improve system performance in terms of energy consumption and QoS in deep fade environments.The CS theory model has been proposed to reduce energy consumption by taking fewer measurements of the original signal or information and reconstructing it with acceptable image quality at the receiver side.The transmission and processing energy can be reduced by transmitting fewer measurements from the sensor side itself.The MIMO model and CS algorithm have been simulated,and results show that CS performs well on images.