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.

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.

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.

An Efficient Medium Access Control Mechanism for Flying Ad-hoc Networks

The Flying Ad-hoc Networks(FANETs)is characterized by the transition from a single large Unmanned Aerial Vehicle(UAV)to multiple small UAVs connected in an ad-hoc fashion.Since high mobility is the core feature of such networks,they are prone to route breaks within the links.The issue of connectivity loss can be coped with,to some extent,by making use of omnidirectional antennas.Such modification,however,curtails Quality-of-Service(QoS)requirements of networks in terms of bandwidth,media access delay,coverage and others.Alternately,directional antennas have advantages over omnidirectional antennas such as improved transmission range,spatial reuse and high throughput.Nevertheless,its introduction raises location-dependent issues to the Medium Access Control(MAC)protocol.This calls for an efficient MAC protocol that can cater to new directional antenna models and,at the same time,can counter the constraints associated with the dynamic UAVs.Therefore,in this article,we consider a UAV interconnection mechanism that lets the UAVs execute the communication tasks using the directional MAC protocol.The technique is advantageous as compared to the approach of utilizing the MAC protocol using omnidirectional antennas.The scheme is being implemented as a case study for Industry 4.0 inventory and traceability applications in the warehouse.For modeling and simulation purposes,we use the Optimized Network Engineering Tool(OPNET)and aim to seek an evaluation with respect to throughput,media access delay,retransmission attempts and data dropped.The results obtained demonstrate the effectiveness of the proposed scheme.

Direction of Arrivals Estimation for Correlated Broadband Radio Signals by MVDR Algorithm Using Wavelet

A theoretical relationship between the wavelet transform and the fast fourier transformation(FFT) methods in broadband wireless signal is proposed for solving the direction of arrivals(DOAs) estimation problem. This leads naturally to the derivation of minimum variance distortionless response(MVDR) algorithm, which combines the benefits of subspace methods with those of wavelet, and spatially smoothed versions are utilized which exhibits good performance against correlated signals. We test the method's performance by simulating and comparing the performance of proposed algorithm, FFT MVDR and MVDR with correlated signals, and an improved performance is obtained.

An ultra-wideband pattern reconflgurable antenna based on graphene coating

An ultra-wideband pattern reconfigurable antenna is proposed.The antenna is a dielectric coaxial hollow monopole with a cylindrical graphene-based impedance surface coating.It consists of a graphene sheet coated onto the inner surface of a cylindrical substrate and a set of independent polysilicon DC gating pads mounted on the outside of the cylindrical substrate.By changing the DC bias voltages to the different gating pads,the surface impedance of the graphene coating can be freely controlled.Due to the tunability of graphene＇s surface impedance,the radiation pattern of the proposed antenna can be reconfigured.A transmission line method is used to illustrate the physical mechanism of the proposed antenna.The results show that the proposed antenna can reconfigure its radiation pattern in the omnidirectional mode with the relative bandwidth of 58.5% and the directional mode over the entire azimuth plane with the relative bandwidth of 67%.

A Three-Dimensional Range-Free Localization Algorithm Based on Mobile Beacons for Wireless Sensor Networks

In wireless sensor networks （WSNs） the position information of individual nodes is a matter of vital importance because allows the implementation of necessary network functions such as routing, querying and other applications. The objective of this paper is to propose an algorithm of three-dimensional distributed range-free localization for WSNs, using a mobile beacon （MB） equipped with a rotary and tilting directional antenna. This algorithm, denominated as the three-dimensional azimuthally defined area localization algorithm （3D- ADAL）, is executed in each sensor node and is based only on the analysis of the information received from the MB, therefore is energy efficient and contributes to extend the lifetime of the sensor network. Additionally the proposed algorithm has the advantage of being simple and economical. The simulation results show that the proposed algorithm is a practical, effective and accurate method for a three-dimensional location of sensor nodes in a WSN.

Multi-Step Amplitude Quantization for Ultralow Sidelobe Phased Arrays by Direct Optimization Synthesis

In this paper, a new amplitude quantization synthesis method for ultralow sidelobe phased arrays is proposed, which is based on the constrained nonlinear optimization algorithm. By introducing a set of critical constraint conditions into the optimization model, we can directly quantize the amplitude distribution instead of replacing it with a continuous equivalent aperture antenna. The mutual coupling and the element patterns are also considered in the quantization synthesis. Finally, some array simulation results are given to show the effectiveness of the method.

PO Analysis for RCS of Nonorthogonal Dihedral Corner Reflectors Coated by RAM

The backscattering radar cross section (RCS) of nonorthogonal dihedral corner reflectors coated by RAM (radar absorbing materials) is formulated by the method of PO (physical optics), where singly, doubly, and triply reflected contributions are considered. The final expressions are analytical and allow for the incidence nonperpendicular to the fold axis of the reflector. The results are compared with ones of MoM (method of moment), which shows that the trend of backscatter pattern of the dihedral corner reflector can be well predicted by this method.

Effect of beam-pointing errors on bistatic SAR imaging

The purpose is to conduct a research in the energy variation of echo wave and the imaging effect caused by the aero bistatic SAR pointing errors. Based on the moving geometry configuration of aero bistatic SAR, a model of beam pointing errors is built. Based on this, the azimuth Doppler frequency center estimation caused by these errors and the limitation to the beam pointing synchronization error are studied, and then the imaging result of different errors are analyzed. The computer＇s simulations are provided to prove the validity of the above analysis.

Mathematical Simulating Model of Phased-Array Antenna in Multifunction Array Radar

A mathematical simulating model of phased-array antenna in multifunction array radar has been approached in this paper, including the mathematical simulating model of plane phased-array pattern, the mathematical simulating model of directionality factor, the mathematical simulating model of array factor, the mathematical simulating model of array element factor and the mathematical simulating model of beam steering.

FFT-DMAC: a tone based DMAC protocol

This paper presents the flip-flop tone （FFT） DMAC protocol, a tone based MAC protocol using di- rectional antennas to solve the deafness problem, hidden terminal and exposed terminal problems simulta- neously. It uses two pairs of flip-flop tones. The first pair of tone is to send omni-directionally to reach every neighboring node to announce the start and the end of communication, and therefore to alleviate the deafness problem. The second pair of tone is to send directionally towards the sender. It is used to solve the hidden temlinal problem as well as the exposed terminal problem. Evaluation shows that FFT-DMAC can achieve better performance compared to the 802.11 and ToneDMAC protocol.

A 2.4 GHz Switched Beam Antenna for Indoor Applications Using Angle of Arrival Estimation

This study introduces a new design of planar antenna array for ISM band applications at 2.4 GHz. This prototype is switched beam antenna, namely planar antenna with four meandered slotted triangular elements (PAFMSTE), which is proposed for wireless indoor applications. The Base Station (BS) equipped with this planar antenna is preferred to be at the center position on the room ceiling to cover all sectors of the room. It is designed to use four directional triangular elements arranged to form a square planar antenna array. The PAFMSTE is used to obtain optimal directivity in four directions in azimuth plane with 3 dB beamwidth of 90°at a specific orientation of 30°in elevation plane. Switched parasitic technique is used to enable PAFMSTE to steer a directional beam through four locations by using four PIN diodes switches. The High Frequency Structure Simulator (HFSS) is used as an efficient simulation tool to optimize the performance of the PAFMSTE antenna. The fabrication and measurements of the PAFMSTE antenna are introduced. The proposed antenna enable radio positioning via Angle of Arrival (AOA) information collected from nearby devices. Then, the Cramér-Rao Bound (CRB) is presented for AOA estimation using identically and equally spaced antenna elements. The CRB depends on the directivity, where the maximum values of CRB are 1.35 × 10-3 and 8 × 10-3 at HPBW of 60° and 90°, respectively.

Beamforming and Angle-of-Arrival Estimation of Square Planar Antenna Array

This paper presents a dual-band planar antenna array for ISM band applications (2.4 GHz and 2.45 GHz). This antenna is proposed for indoor applications and enables adaptive beamforming and angle of arrival (AOA) estimation. An adaptive beamforming algorithm is applied for a planar antenna array, which is able to steer its main beam and nulls in azimuth and elevation planes over a wide frequency band. Planar antenna array operates as a spatial filter in 3D space, processing the received signals with weighting schemes. A planar antenna array is designed for AOA estimation in azimuth and elevation planes by using MUltiple SIgnal Classification (MUSIC) based on subspace algorithm. The Base Station (BS) equipped with this planar antenna is preferred to be at the center position on the room ceiling to cover all sectors of the room. It is designed to use four directional triangular elements arranged to form a square planar antenna array. Planar antenna with four elliptical slotted triangular elements (PAFESTE) is used to obtain optimal directivity in four directions in azimuth plane with specific orientation of 30? in elevation plane. It is characterized by half power beamwidth in elevation plane of about 60? and half power beamwidth in azimuth plane of about 90?.

Analysis of Geo Positioning System Using RF &DA

Indoor positioning systems (IPSs) have been intended to provide position information of persons and devices. Higher user percentage of handheld devices such as tablets or mobile phones had led to the development of a number of indoor positioning systems. In this research a work on a real time portable RFID indoor positioning device such as on smartphone will be performed. The personal networks will be designed to meet the users’ needs and interconnect users’ devices equipped with different communications technologies in various places to form one network for better result. Radio frequency identification (RFID) with directional antenna has proved its potential for locating objects in indoor environment. Hence, the proposed device idea will be used to exploit various unknown locations in an indoor environment such as college campus;this interpretation will rely on Wireless LAN, Received Signal Strength values from Access Points (AP) in specific mentioned arenas;these APs will be monitored constantly by RFID with directional antenna (DA) and handheld devices. For obtaining the better results from existing devices, algorithms of Range Estimation are proposed, which can be used on various handheld devices for locating indoor objects.

Geometrical statistical channel model arisen from scatterers around the mobile with an inverted-parabolic spatial distribution

In this paper, firstly presented a geometrically based statistical channel model with scatterers that are with an inverted parabolic spatial distribution around mobile station （MS） within a circle wherein the base station （BS） and MS are included. This paper proposed a technique to simply derive probability density functions （PDFs） of angle of arrival （AOA）, time of arrival （TOA） and Doppler spectra to characterize the outdoor macrocell and microcell environments by employing various distances between BS and MS, or different size of circular region. Employing this channel model, we analyze the impacts of a directional antenna at BS with the main-lobe width 2~z on the fading and the Doppler spectra.