A novel DOA estimation algorithm using directional antennas in cylindrical conformal arrays

In this paper, a novel direction of arrival(DOA) estimation algorithm using directional antennas in cylindrical conformal arrays(CCAs) is proposed. To eliminate the shadow effect, we divide the CCAs into several subarrays to obtain the complete output vector. Considering the anisotropic radiation pattern of a CCA, which cannot be separated from the manifold matrix, an improved interpolation method is investigated to transform the directional subarray into omnidirectional virtual nested arrays without non-orthogonal perturbation on the noise vector. Then, the cross-correlation matrix(CCM) of the subarrays is used to generate the consecutive co-arrays without redundant elements and eliminate the noise vector. Finally, the full-rank equivalent covariance matrix is constructed using the output of co-arrays,and the unitary estimation of the signal parameters via rotational invariance techniques(ESPRIT) is performed on the equivalent covariance matrix to estimate the DOAs with low computational complexity. Numerical simulations verify the superior performance of the proposed algorithm, especially under a low signal-to-noise ratio(SNR) environment.

Capacity analysis of inhomogeneous hybrid wireless networks using directional antennas

Most of studies on network capacity are based on the assumption that all the nodes are uniformly distributed, which means that the networks are characterized by homogeneity. However, many realistic networks exhibit inhomogeneity due to natural and man-made reasons. In this work, the capacity of inhomogeneous hybrid networks with directional antennas for the first time is studied. By setting different node distribution probabilities, the whole network can be devided into dense cells and sparse cells. On this basis, an inhomogeneous hybrid network model is proposed. The network can exhibit significant inhomogeneity due to the coexistence of two types of cells. Then, we derive the network capacity and maximize the capacity under different channel allocation schemes. Finally, how the network parameters influence the network capacity is analyzed. It is found that if there are plenty of base stations, the per-node throughput can achieve constant order, and if the beamwidth of directional antenna is small enough, the network capacity can scale.

Collision Classification MAC Protocol for Underwater Acoustic Communication Networks Using Directional Antennas

Traditional underwater acoustic communication networks(UACNs)generally use omnidirectional transmission technology that causes a large number of data-packet collisions,thus resulting in low network throughput and high end-to-end delays.Compared with omnidirectional transmission technology,directional technology only sends and receives data packets in a specified direction.This can significantly reduce the probability of collisions and improve network performance.However,it also causes a deafness problem,which occurs when the sending node sends a data packet to the receiving node but the receiving node is unable to reply to the sender,because its antenna beam is closed.To resolve this issue,this study proposes a collision classification media access control(CC-MAC)protocol for UACNs.With this protocol,the underwater acoustic channel is divided into two subchannels,and the nodes transmit corresponding data types on them.The sending node can estimate the current status of the receiving node(i.e.,no collision,normal collision,deafness)according to the type of the data packet received and the sub-channel it arrived on,and it can choose correct options to improve network efficiency.Finally,we verify the performance of CC-MAC via simulations,showing that the protocol achieved higher network throughput and lower end-toend delays.

FAST CAPACITY ESTIMATION ALGORITHMS FOR MANETS USING DIRECTIONAL ANTENNAS

In this letter,capacity estimation for Mobile Ad hoc NETworks (MANETs) using direc- tional antennas are studied.Two Matrix-based Fast Calculation Algorithms (MFCAs) are proposed to estimate the network capacity in a network scenario in which there is no channel sharing among multiple sessions and traffic is sensitive to delay with an end-to-end delay constraint.The first algo- rithm MFCA-1 is used to estimate network capacity in a situation where all links have the same delay. It estimates the maximum number of k-hop sessions in a network based on the k-hop adjacency matrix of the network.The second algorithm MFCA-2 is used to estimate network capacity in a situation where different links may have different delays.It calculates the maximum number of sessions in a network with an end-to-end delay constraint based on the adjacency matrix and the link-delay matrix of the network.Numerical and simulation results show that both MFCA-1 and MFCA-2 can calculate network capacity much faster than the well-known Brute-Force Search Algorithm (BFSA) but with the same accuracy.

Better Platooning toward Autonomous Driving:Inter-Vehicle Communications with Directional Antenna

Recently,in the researches on vehicular Internet-of-Things(IoT),platooning have received lots of attentions due to its potential to improve the fuel efficiency and driving experience.Platoon is a group of vehicles that act as smart agents,they travel collaboratively by following the leading human-driven vehicle.A vehicle in the platoon utilizes radar and wireless communication to share important information to other vehicles in the same platoon such as speed and acceleration,to realize the safe and efficient driving.The quality of wireless communication is of great importance to manage and maintain the platoons.However,in a scenario that a large number of vehicles exist,communication delay and packet loss caused by channel congestion may endanger the safe intervehicle distance.In this paper,we introduce intervehicle communication with directional antenna into platooning.By extensive simulations,we evaluate the packet delay and inter-vehicle distance in both normal driving and braking scenarios,and verify the usefulness of directional antenna in platooning for vehicular IoT.

A low-cost invasive microwave ablation antenna with a directional heating pattern

Microwave ablation(MWA) is a cancer treatment method. The tumor tissue absorbs electromagnetic energy, which heats and kills it. A microwave ablation antenna plays a critical role in this process. Its radiation field must completely cover the tumor but not the healthy tissue. At present, the radiation pattern of most invasive ablation antennas is spherical.However, in the clinic, the shape of some tumors may be asymmetrical or the antenna cannot be inserted into the center of the tumor for some other reason. In order to solve these problems, a directional heating antenna for microwave ablation is proposed in this paper. The proposed antenna, operating at 2.45 GHz, consists of a monopole and a reflector. The feed is given by a substrate integrated coaxial line(SICL) and coplanar waveguide(CPW). The omnidirectional radiation field of the monopole is reflected by a reflector that is extended from the outer conductors of the SICL to form a directional radiation field. The impedance matching network is designed on SICL to match the antenna to 50 Ω. The antenna is fabricated using a mature printed circuit board(PCB). The reflection coefficient of the antenna in porcine liver tissue measured by a vector network analyzer shows good agreement with the simulations. Then, an ablation experiment in porcine liver is conducted with power of 10 W for 10 min, and the experimental results confirm the validity of the design.

DIRECTIVITY OPTIMIZATION OF CURVED SURFACE DIPOLE ANTENNAS

Based on the calculation of the characteristic parameters by moment method, the curved surface dipoles are optimized by an optimization method, the maximum directivities of some V-curved and Gauss-curved surface dipoles are given.

A Low Profile Four-Way Directional Antenna with Dual Polarization

This paper presents a low profile dual polarized directional antenna composed of loop and dipole arrays mounted on a ground plane with each loops and dipoles being fed independently. Each loop antenna is paired with a reflector while each dipole antenna is paired with a director and a reflector. The proposed antenna is intended for an indoor base station (BS) with resonance frequency of 2.4 GHz and capable of producing four orthogonal directional pattern with downward elevation angle equals to 30°;and half power bandwidth (HPBW) less than 80°;in both vertical and horizontal polarization. The reflection characteristics of the loop and dipole arrays are less than -10 dB and the mutual coupling between the vertical and horizontal polarization elements is nearly less than -20 dB. In later progress, the dipole antenna was substituted with printed dipole antenna to achieve a better performance. Both the calculated and measured results demonstrated that the desired radiation patterns were achieved, and the measured results agreed well with the calculated ones. Consequently, a low profile antenna with a thickness of 0.16 λ (20 mm) having the expected radiation pattern is successfully designed.

A New Compact Omni-Directional Quasi-Self-Complementary Antenna for Wireless Communication Systems

This article describes a new miniaturized omni-directional antenna with quasi-self-complementary structure for wireless communication applications. A novel ground structure composed of five rectangular plates is proposed to enhance the impedance bandwidth and reduce the antenna size. The proposed antenna is comprised of two patches surrounded by the ground structure. Two metal patches of the antenna are located on two opposite sides of the dielectric substrate. The feed patch is used to excite the radiation patch. This unique design is realized by properly choosing the suitable feed patch shape, selecting similar slot shape on the radiation patch, and tuning their dimensions. The proposed antenna with an extremely small size of 6 mm × 9 mm has an operating impedance bandwidth ranging from 4.5 to 6.1 GHz for S11 < -10 dB, which also covers the two IEEE 802.11a wireless local area network bands (5.15 - 5.35 GHz and 5.725 - 5.825 GHz). In addition to be very small in size, the antenna exhibits omni-directional radiation patterns in the entire operating bandwidth and low cross polarization. The distortionless time domain performance of the antenna is confirmed by investigation of the phase response and group delay. The obtained results in both frequency and time domain show that the proposed antenna is suitable for use in wireless communication systems.

Directional neighbor discovery in mmWave wireless networks

The directional neighbor discovery problem,i.e,spatial rendezvous,is a fundamental problem in millimeter wave(mmWave)wireless networks,where directional transmissions are used to overcome the high attenuation.The challenge is how to let the transmitter and the receiver beams meet in space under deafness caused by directional transmission and reception,where no control channel,prior information,and coordination are available.In this paper,we present a Hunting based Directional Neighbor Discovery(HDND)scheme for ad hoc mmWave networks,where a node follows a unique sequence to determine its transmission or reception mode,and continuously r0-tates its directional beam to scan the neighborhood for other mmWave nodes.Through a rigorous analysis,we derive the conditions for ensured neighbor discovery,as well as a bound for the worst-case discovery time and the impact of sidelobes.We validate the analysis with extensive simulations and demonstrate the superior perfor-mance of the proposed scheme over several baseline schemes.

Antenna geometry strategy with prior information for direction-finding MIMO radars

The antenna geometry strategy for direction finding （DF） with multiple-input multiple-output （MIMO） radars is studied. One case, usually encountered is practical applications, is consi- dered. For a directional antenna geometry with a prior direction, the trace-optimal （TO） criterion （minimizing the trace） on the av- erage Cramer-Rao bound （CRB） matrix is employed. A qualitative explanation for antenna geometry is provided, which is a combi- natorial optimization problem. In the numerical example section, it is shown that the antenna geometries, designed by the proposed strategy, outperform the representative DF antenna geometries.

Directional Modulation Based on a Quantum Genetic Algorithm for a Multiple-Reflection Model

Directional modulation is one of the hot topics in data security researches.To fulfill the requirements of communication security in wireless environment with multiple paths,this study takes into account the factors of reflections and antenna radiation pattern for directional modulation.Unlike other previous works,a novel multiple-reflection model,which is more realistic and complex than simplified two-ray reflection models,is proposed based on two reflectors.Another focus is a quantum genetic algorithm applied to optimize antenna excitation in a phased directional modulation antenna array.The quantum approach has strengths in convergence speed and the globe searching ability for the complicated model with the large-size antenna array and multiple paths.From this,a phased directional modulation transmission system can be optimized as regards communication safety and improve performance based on the constraint of the pattern of the antenna array.Our work can spur applications of the quantum evolutionary algorithm in directional modulation technology,which is also studied.

Directions of Arrival Optimization Method for Broadband Antenna Array Based on Filter Bank

This paper proposes an estimation method of the directions of arrival(DOA) for the broadband signals received by a uniform planar antenna array including the mutual coupling effect. The process modeling of antenna array receiving dynamic signal is obtained accurately via building the array system electromagnetic space-time model, and the mutual coupling effect is included in the synthesis procedure automatically. The broadband signal is divided into several sub-bands, and the complex weight of these sub-bands frequencies is figured out using the least mean square iteration programming. In the proposed method, the mutual coupling effect is compensated at the different frequencies. The calculation results show that the method is suitable for the uniform linear and uniform circular array pattern integration, and it is commendably satisfied with the requirement of engineering design.

GNSS array receiver faced with overloaded interferences:anti-jamming performance and the incident directions of interferences

Anti-jamming solutions based on antenna arrays enhance the anti-jamming ability and the robustness of global navigation satellite system(GNSS)receiver remarkably.However,the performance of the receiver will deteriorate significantly in the overloaded interferences scenario.We define the overloaded interferences scenario as where the number of interferences is more than or equal to the number of antenna arrays elements.In this paper,the effect mechanism of interferences with different incident directions is found by studying the anti-jamming performance of the adaptive space filter.The theoretical analysis and conclusions,which are first validated through numerical examples,reveal the relationships between the optimal weight vector and the eigenvectors of the input signal autocorrelation matrix,the relationships between the interference cancellation ratio(ICR),the signal to interference and noise power ratio(SINR)of the adaptive space filter output and the number of interferences,the eigenvalues of the input signal autocorrelation matrix.In addition,two simulation experiments are utilized to further corroborate the theoretical findings through soft anti-jamming receiver.The simulation results match well with the theoretical analysis results,thus validating the effect mechanism of overloaded interferences.The simulation results show that,for a four elements circular array,the performance difference is up to 19 dB with different incident directions of interferences.Anti-jamming performance evaluation and jamming deployment optimization can obtain more accurate and efficient results by using the conclusions.

The research of high-directive anisotropic magnetic metamaterial antenna loaded with frequency-selective surface

This paper uses a Computer Simulation Technology microwave studio to simulate the performance of a new highdirectivity anisotropic magnetic metamaterial antenna loaded with a frequency-selective surface. Frequency-selective surface with cross-dipole element has a great effect on the directivity, radiation pattern, and gain of such an antenna. The experimental results show that frequency-selective surface （FSS） significantly improve the radiation performance of anisotropic magnetic metamaterial antenna. For example, as a single anisotropic magnetic metamaterial antenna, half power beam width is 4 degrees in the H planes, and the gain of this antenna is 19.5dBi at 10CHz, achieving a 2.1 degree increment in half power beam width, and a 7.3 dB gain increment by loading with the FSS reflector. The simulating results are consistent with our experimental results.

Antenna selection in MIMO radar with collocated antennas

An antenna adjustment strategy is developed for the target tracking problem in the collocated multiple-input multipleoutput(MIMO)radar.The basic technique of this strategy is to optimally allocate antennas by the prior information in the tracking recursive period,with the objective of enhancing the worst-case estimate precision of multiple targets.On account of the posterior Cramer-Rao lower bound(PCRLB)offering a quantitative measure for target tracking accuracy,the PCRLB of joint direction-of-arrival(DOA)and Doppler is derived and utilized as the optimization criterion.It is shown that the dynamic antenna selection problem is NP-hard,and an efficient technique which combines convex relaxation with local search is put forward as the solution.Simulation results demonstrate the outperformance of the proposed strategy to the fixed antenna configuration and heuristic search algorithm.Moreover,it is able to offer close-to performance of the exhaustive search method.

Collision-Tolerant Transmission with Narrow-beam Antennas

The application of directional antennas in wireless ad hoc networks brings numerous benefits, such as increased spatial reuse and mitigated interference. Most MAC protocols with directional antennas are based on the RTS/CTS mechanism which works well in wireless ad hoc networks using omni-directional antennas. However, RTS/CTS frames cannot mitigate the interference completely. Besides, they also contribute a lot to the performance overhead. This paper studies the problem from a new perspective. We have found that the transmission success probability under directional transmission and directional reception is quite high when the antenna beamwidth is quite narrow. Motivated by the analytical results, we design a lightweight MAC protocol without RTS/CTS frames. The evaluation results demonstrate that this new protocol performs better than MAC protocols based on the RTS/CTS mechanism. The results also show that a collision-tolerant transmission is feasible under the narrow beam configuration.

Ambiguity Resolution in Direction of Arrival Estimation with Linear Antenna Arrays Using Differential Geometry

Linear antenna arrays(LAs)can be used to accurately predict the direction of arrival(DOAs)of various targets of interest in a given area.However,under certain conditions,LA suffers from the problem of ambiguities among the angles of targets,which may result inmisinterpretation of such targets.In order to cope up with such ambiguities,various techniques have been proposed.Unfortunately,none of them fully resolved such a problem because of rank deficiency and high computational cost.We aimed to resolve such a problem by proposing an algorithm using differential geometry.The proposed algorithm uses a specially designed doublet antenna array,which is made up of two individual linear arrays.Two angle observation models,ambiguous observation model(AOM)and estimated observation model(EOM),are derived for each individual array.The ambiguous set of angles is contained in the AOM,which is obtained from the corresponding array elements using differential geometry.The EOM for each array,on the other hand,contains estimated angles of all sources impinging signals on each array,as calculated by a direction-finding algorithm such as the genetic algorithm.The algorithm then contrasts the EOM of each array with its AOM,selecting the output of that array whose EOM has the minimum correlation with its corresponding AOM.In comparison to existing techniques,the proposed algorithm improves estimation accuracy and has greater precision in antenna aperture selection,resulting in improved resolution capabilities and the potential to be used more widely in practical scenarios.The simulation results using MATLAB authenticates the effectiveness of the proposed algorithm.

Simulation &Performance Evaluation of QoS Routing Protocol for Adhoc Networks Using Directional Communication

A wireless ad-hoc network is a self-organized wireless network without fixed or backbone infrastructure. All nodes have routing capability and use peer-to-peer packet transmission or forward packets to other node using multi hop communication. Now days mobile ad-hoc networks are being used for different applications and traffics, so it require quality of service (QoS) support in routing protocol. In this paper, a modified QoS routing protocol using directional antenna has been proposed. High and normal priority can be assigned based on type of traffic. All the nodes in the path used by high priority flow are reserved as high priority flow for that flow and normal priority flow will avoid the paths used by high priority flows. If no disjoint paths are available, there may be two possibilities: Normal priority flows are blocked and other is, normal priority flows are allow using the coupled path with high priority flow. Blocking the normal priority flow, QoS routing protocol improves the performance of high priority flow. This concept may be use in emergency communication. Simulation results show that by assigning the priorities to flows, performance of high priority flows are improved and it will further improved by blocking the normal priority flow.

Investigations and prospects of Fabry-Perot antennas:a review

Fabry-Perot(FP)antennas have characteristics of planar structures combined with high gain,and they have been widely used in wireless communications.With the progress of ongoing research,FP antennas have achieved various capabilities,but many of them are still under development,such as lowprofile,wideband,circular polarization,multi-band,low-radar cross section(RCS)and reconfigurable features.This paper discusses the theoretical analysis methods and research progress of FP antennas,and explains the realization methods of different features of FP antennas.In order to indicate different technologies for realizing various capabilities,the key technologies and features of some of the latest designs are described.Finally,the research situation and prospects of FP antennas are summarized to guide their research directions in the future.